Methane Contents of Oil Shale from the Piceance Basin, CO

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Bureau of Mines Report of lnvestigations/l987

Methane Contents of Oil Shale From the Piceance Basin, CO

By S. J. Schatzel, D. M. Hyman, A. Sainato, and J. C. LaScola

UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9063

Methane Contents of Oil Shale From the Piceance Basin, CO

By S. J. Schatzel, D. M. Hyman, A. Sainato, and J. C. LaScola

UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary

BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data:

Methane contents of oil shale from the Piceance Basin, CO

(Report of investigations ; 9063)

Bibliography: p. 26 - 27.

Supt. of Docs. no.: 128.23: 9063.

1. Gas, Natural-Colorado-Piceance Creek Watershed. 2. Methane-Colorado- Piceance Creek Watershed. 3. Oil-shales-Colorado-Piceance Creek Watershed. I. Schatzel, Steven J. 11. Series: Report of investigations (United States. Bureau of Mines); 9063.

TN23.U43 [TN881.C6] 622 s [622'.81 86-600128 CONTENTS Page

Abstract ...... Introduction ...... Acknowledgements ...... Regional geolom ...... Geologic and depositional history ...... Stratigraphy...... Structure...... Drill equipment and drill-hole configuration^...... ^^...... ^^.^..^.^^^^^^.. Site geology and core lithology ...... Site geology ...... Vertical hole core lithology ...... UV1 ......

UV6 ...... 10 Results of modified direct method testing...... 10 In situ permeability ...... 15 Discussion ...... 19 Conclusions ...... 24 References ...... 26 Appendix.--Modified direct method procedure ...... 28

ILLUSTRATIONS

Outline of Green River Formation within margin of Piceance Basin. CO ...... 2 Cross section of Horse Draw Nine ...... 3 Green River stratigraphy and location of mine workings at Horse Draw Mine and Cathedral Bluffs Mine site^...... ^^...... ^^...... ^ 6 Location of holes drilled in Cathedral Bluffs Upper Void Level. with an enlarged view of the horizontal holes site...... 7 Map view of Cathedral Bluffs Upper Void Level showing locations of tuff dikes ...... 8 Compilation of vertical corehole data from Upper Void Level. Cathedral Bluffs Mine ...... e.mme( in pocket) Gases measured within container for sample UV208 ...... 11 Volumes of gases measgred within container for sample UV310 ...... 12 Gases measured within container for sample UV102 ...... 12 Amount of methane desorbed from sample UV102 between each gas sampling. divided by the amount of time elapsed between each gas sampling ...... 12 Sample UV303: gases measured within container; linear regression fit to desorbed methane data...... 13 Sample UH109: gases measured within container; second-degree polynomial fit to desorbed methane data...... 13 Sample UH210: gases measured within container; second-degree polynomial fit to desorbed methane data...... 14 Sample UH223: gases measured within container; linear regression fit to desorbed methane data...... 15 Hole UH2: variation of average equivalent fracture aperture and permeability with fluid pressure as measured by constant head ...... 18 ILLIJSTRATIONS--Cont inued Page

Actual Lneasured assay values for vertical holes before samples were eight-averaged to match the desorption sample interval...... Correlation between methane content at 40 days of desorption and oil yield for holes UV1 and UV2...... Nethane contents of samples at 3 days of desorption...... Methane contents oE samples at 40 days of desorption ...... Methane contents of samples at 125 days of desorption...... Mean and range of methane contents released from assorted rock samples ... Generalized apparatus...... b...... b.bbbbbbbb...... b...... Sample data-collection form......

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT bbl barrel h hour " C degree Celsius hp horsepower c m3 cubic centimeter in inch cm3 lg cubic centimeter K kelvin per gram lb/f t pound per cubic foot ~rn~/(~*h)cubic centimeter per gram per hour lbf (s/f t ) pound (force) seconds per square foot cP centipoise mD millidarcy D darcy mi2 square mile f t foot min minute ~t'ld cubic foot per day mm I-Ig millimeter of mercury f t/mi foot per mile (pressure)

f t/min foot per minute Pet percent ft3/st cubic foot per psi pound per square inch short ton ~sig pound per square inch, g gram gauge gal/rnin gallon per minute wt pct weight percent gallst gallon per short ton Yr year METHANE CONTENTS OF OIL SHALE FROM THE PICEANCE BASIN, CO

By S. J. Schatzel,l D. M. Hyman,l A. Sainato,* and J. C. LaScola3

ABSTRACT

The Bureau of Mines determined the gas contents of 135 oil shale samples obtained frorn approximately 630 ft of core drilling. Drilling was done within a projected mining zone of the Cathedral Sluffs Mine, located in the Piceance Basin of western Colorado. Methane contents were determined by the modified direct method, which can measure the volumes of several gases released frorn or reacted with mine rock without destructive sample treatment. Over the duration of the test, nitrogen was largely unreactive, C02 increased slightly, oxygen decreased markedly, and methane increased more than the total increase of all contained gases. The gas volumes were normalized per unit sample mass and are given in cubic centimeters per gram. Common time irzdices for test duration of 3, 40, and 125 days were used to compare methane desorption among samples. The means of the sample populations for these indices were 0.0316, 0.114, and 0.195 ~rn~/~,respectively. These quantities are lower than those reported in a Bureau emissions study at the Horse Draw Mine in the Piceance Basin. Oil shale samples that were gas enriched beyond the mean methane contents frequently contained bitumens and pyrite.

Geologist. 2~4iningengineering technician. 3~hysicalscientist. Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION

Oil shale in the Mahogany Zone of the The Bureau collected gas emissions data Green River Formation is a significant during development of mine workings at potential fuel source. In the Piceance the Horse Draw Mine, which indicated an Basin, the Mahogany Zone organic content average of 42 ft3/st (1.3 crn3lg) CH4. averages about 16 wt pct (ge4The re- The emissions data were obtained by re- maining material in oil shale is mostly lating the amount of rock mined in a mineral matter. The composition of the blast to the volume of methane released. mineral matter varies, but major constit- The volume of gas emitted was quantified uents include dolomite, calcite, quartz, by measuring concentrations usi-ng chroma- illite, sodium and potassium feldspars, tography. Tube bundles extended from the pyrite, and analcite (1). Approximately gas chromatography instruments on the 80 billion bbl of shale oil was thought surface to underground sampling loca- to be recoverable using technology avail- tions. Ventilation measurement probes able in 1976, and the total reserves of located in mine level exhaust ducts and the Green River Formation were estimated the shaft exhaust provided volumetric as 4 trillion bbl. data for the calculation of gas emissions The release of methane gas during the (4) mining of fossil fuels is a concern of the mining industry and Federal regula- tory bodies. New Federal regulations for metal and nonmetal mines are presently under review, and oil shale mines would be subject to these regulations if ap- proved. The portion of the proposed regulations that directly affects oil shale mining was established in accordance with available documentation of methane emissions from oil shale mine production. Some of this information is the result of work done at the Horse Draw Mine site (fig. 1). The Horse Draw Mine was developed by the Bureau of Mines in 1978 as an experimental mine. Between the middle of 1979 and the end of 1981, the Horse Draw Mine was operated for the Bureau by the Multi Minerals Corp. Four mining levels were driven at the Horse Draw Mine, between 1,840 and 2,230 ft below the surface (fig. 2). All of these depths are below the dissolution surface, which is the horizon where leaching of soluble minerals terminates and ground water sinks no deeper into the Green River Forma- t ion. The minerals halite, dawsonite, and nahcolite, in addition to oil shale, were preserved and were planned mining coproducts. Approx area underlain 4~nderlinednumbers in parentheses re- I' by Green River Formation fer to items in the list of references FIGURE 1.-Outline of Green River Formation within margin preceding the appendix at the end of this of Piceance Basin, CO. (Adapted from Russell (2).) report. The relationship between methane and oil shale is supportable on a theoretical as well as an empirical basis. It is generally accepted that the preservation, degradation, and thermal alteration of 1,840-ft leve organic matter in sediments can lead to the formation of methane in fossil fuels. Methane is known to be an inherent by- product of the coalification process. Methane associated with petroleum is usually considered the result of thermal cracking, the breaking down of complex hydrocarbon chains under intense heat and pressure conditions into lighter and sim- pler compounds. Genetically, oil shale is related to certain unusual coals containing abundant spore and/or algal material. These coals have historical sig- nificance, but little current economic importance. Petrologic studies can be very useful in identifying the specific progenitors of solid organically derived fuels. The petrographic identification of organic matter in Green River oil shale is usually difficult owing to interactions with the mineral matrix, the fine-grained nature of the organic and mineral matter, and the disseminated state of the organic material. However, there is gen- 2,080-ft level eral agreement that the organic matter in the Green River oil shale is chiefly formed from algae. Partially because of Raise the relationship between oil shales and algal coals, some of the same controls on 2,130-ft level gas content in coals (depth of burial, temperature, age, geologic structure, etc.) have been suggested for oil shale. The decomposition of algae may also play Raise and stope an important role in petroleum genesis from oil source rocks (5). The Bureau recently undertook field Greeno sublevel experiments at the Cathedral Bluffs Mine Raise (fig. 1) to determine the amount of gas contained in oil shale and the behav- 2,230-ft level ior of the gas within the oil shale and in the mine atmosphere. Two holes were Ramp core-drilled horizontally from the Upper Void Level, each hole being about 200 ft Sublevel deep. These holes were drilled into the face of an exploration drift. They were oriented parallel to each other and sepa- rated by about 25 ft at the hole col- FIGURE 2.-Cross section of Horse Draw Mine. (Adapted from Cole (3).) lars. In addition, six vertical holes were core-drilled from the Upper Void Level to betu~een 30 and 40 ft below the the amount of gas as that emitted by a nine floor. coal sample of equal size. 5naller cltlan- The drilling of each hole was inte- tit ies of gas can lead to ercaneous r~- grated with experimental tasks. The mail ~111-tswhen the amount4 of gas released tasks were (I) to quantify the amount and approach the sensitivity of meas:ire~nent. conposition of gas cnitted frorn both the 3ecaiise oil shale call generally be ex- core and the hole, (2) to count and lo- pected to contain less nethane than coal, cate fract~iresintersecting the core, and the sensitivity of direct neth hod testing (3) to record detailed core lithology. would pose a greater problem. A second Following rernoval of an interval of rock problem results Erorn the chemical compo- sample, the sample lengtll was mea:;;lred, sition of desorbing gas. Surcau experi- depths and orientation indicators Idere ence with U.S. coalbed gas has identified marked on the core, core loss intervals its cornposition as generally at least 90 were assigned if necessary, and core pct CH4 and as high as 99 pct CH4. The E ractures were logged. Fracture orienta- direct method test incorporates no gas t ion data were mer-lningful only relat ive analysis in the technique and ass:lmes all to other fractures within a single re- gas to be methane. Without sabstant ia- constructed core interval 5ecause the tion of similar oil shale gas composition core did not have an absolute orientation or tile incorporation of gas composition when drilled. Lithologic data were re- analytical techniques, oil shale gas de- corded next. All core logging was done terminations by the direct method would in accordance ~ithHartley and Beard (6), be inadequate. standard procedure for the cathedral A modified direct method test has been Bluffs Pline. Once the descriptive litho- designed to measure an amount of gas logic logging was complete, the cored which is siailar to that emitted from intervals were inserted into polyvinyl mined rock into the nine environment. chloride (PVC) or steel containers. The This gas is normally diluted by ventila- containers were then sealed so that gases tion air flow. The modified direct meth- desorbing from the core would remain od can produce methane content data under within the container. field or laboratory conditions with an At the time of the planning of this accuracy superior to that of the direct study, there was no acceptable test to method. Reactions between gases emitted determine quantities of gas desorbing from the ore or within the mine atmos- f rorn oil shale. The direct method test, phere can be observed by compositionally designed to quantify methane in coal sam- analyzing and quantifying cllanging vol- ples, has been used by the Bureau and umes of gas compounds. Quantifying stan- other investigators on coal (7). Howev- dard temperature and pressure (STP) gas er, adaptations of direct method testing volumes at each point in time produces to potential methane-emitting rock sam- information on rates of gas released and ples other than coal can produce less reactions, which is considered essential than sat isfactory results. One problem in understanding methane emissions in oil is that preliminary data indicate that an shale mines. oil shale sample may emit only one-tenth

ACKNOWLEDGMENTS

'The authors thank the following for method test procedure; John A. Hartley, contributing technical expertise in the president, Ammeralda Resources, Inc., for co~npletionof this publication: N. Stel- description of the oil shale cor? and lavato, senior geologist, Cathedral assistance in underground activities; and Bluffs Shale Oil Mine, for assisting in William E. Bruce, supervisory mining en- the design and operation of the study; gineer, U.S. Mine Safety and Health J. Townsend, principal mining engineer, Administration, for his technical input Cathedral Bluffs Shale Oil Mine, for and for sharing his experience in other technically reviewing the modified direct types of mines. REGIONAL GEOLOGY

GEOLOGIC AND UEPOS L'r t0NAL HIS'rORY ai nerals arz preserved belo4 the dissolution s;irface and are leached oat above The Green Xiver Formation, located in the surface. Leaching of salines leaves t?le States of IJyorning, Colorado, and vuggy porr>siyy, which is ell developed Utah, contains one of the world's largest above the dissolut ion s:lrf ace. kno~ndeposits of oil shales. Deposition v-cvaporite mi neral-s are associated with of these units took place ill response to oil shales in many areas of Colorado o rogenic act ivity and subsequent down- and IJyoming. The most abundant of these iJarping or1 the western slope of what are minerals are nahcolit P_ (NaHC03), ha1 i te now tlle Rocky M0untai.n~. Two large in- (NaCl), dawsonite [NaAl(OH)2C03], and termontane lakes were formed. Take Uinta trona (Ya2CO3*YaHCO3*2H2O). Nahcolite occupied the region known as t1ne Piceance beds are common in the oil shales of Col- Basin and parts of Utah, and persisted orado's Piceance Basin as interbedded de- for 5 to 8 million yr (1).- The combined posits showing growth structclres that maximurl areal extent of the two lakes was deforined surrounding oil shale bedding. about 20,000 mi2 (1). Evidence may exist Evaporation and recession of the lake for the initiation of mountain building shoreline may have been important in dep- in the Precambrian, although corltrol of osition of the evaporites. Another mech- sediment distribution did not begin until anism for formation of these minerals is the development of the structural units possible because of the production of C02 in the Pennsylvanian, as described by during the decay of organic matter (10).-- Murray and IIaun (8).- The Grzen River Formation was formed during the Eocene epoch. The depocenter for the major oil shale units is located about 25 miles The oldest unit of the Eocene Green southwest of Meeker, CO. Several tuffa- River Formation is the Douglas Creek Yen- ceous layers found in Green River oil her which is made up of light-colored shales are frequently used as marker beds sandstone and shales, as well as some and were produced during volcanic epi- limestone. In the northern portion of sodes concurrent dith orogenic activity. the Piceance Basin, the Douglas Creek The deposltion of Green Xiver oil grades into the overlying Garden Gulch shales resulted from a combillation of Yember, which consists of gray marlstone, conditions that led to preservation of gray and brown shale, and some thin the organic material. The intermontane beds of oil shale. In the vicinity of lakes were quite saline, and conditions the Cathedral Sluffs tract, the two units of surface waters were such that a food have a combined thickness of approxi- supply was available for micro-organisms mately 500 f t. The Parachute Creek Hem- to flourish (9). The lakes were suffi- ber lies above the Garden Gulch. The ciently saline near the bottom so that Parachute Creek Yember is a gray, brown, the water was stratified, preventing mix- and black marlstone with the persistent ing of the dense saline water with the dark, rich oil shale beds such as those more oxygenated surface water. Organic in the Nahogany Zone. Near the mine lo- material flowing to the lake bottom was cation, the total thickness of the Para- preserved under reducing conditions. The chute Creek Xember is about 1,500 ft. Hahogany beds make up a persistently rich The Uinta Formation rests on the Para- layer of oil shale ranging from 50 to 200 chute Creeic Yenber and is composed of €-t thick in the Piceance Basin. During gray or brovn sandstone interbedded with the deposition of the Nahogany beds, the marlstone and some thin oil shale beds formation of Piceance Basin saline miner- 0-1 als was most abundant near the basin's The Parachute Creek Yember of the Green center. Throughout the basin, saline River Formation contains the principal oil shale units. Stratigraphic units in General stratigraphy, General stratigraphy, the Parachute Creek are frequently dif- Horse Draw Mine site Cathedral Bluffs Mine site ferentiated in terms of oil yield due to II--~our Senators the vertical lithologic consistency of the oil shales. The richness or leanness It --Ignition Level, 1,182 ft of the oil shale unit is signified by R -Groove or L, respectively, as in figure 3. (R7 --LUpper Void Level, 1,342 ft is commonly known as the Mahogany Zone.) Mahogany Zone Figure 3 shows a generalized stratigraph- B-Groove B- Groove ic column for the Horse Draw Mine and Cathedral Bluffs Mine sites. The loca- ff6 1 Level, ,620 fi tions of the mine workings are super- imposed on the rock units. Although the Dissolution surface x- elevations of the two mine sites are very ZiK different, the columns are matched at- the ff5 top of the A-Groove unit, showing the FDissoIution surface differing mining horizons.

STRUCTURE

Within the Piceance Basin Eocene units, structural trends are quite gentle. In Rio Blanco County, there is a series of synclines and anticlines with axes generally ranging from east to west and from northeast to southwest (8). Dips are limited to no more than a couple of degrees. On the Cathedral Bluffs tract, beds strike east-west and dip northward about 150 ft/mi (approximately FIGURE 3.-Green River stratigraphy and location of mine 1.5") (11). workings at Horse Draw Mine and Cathedral Bluffs Mine sites. underground mapping at Cathedral Bluffs revealed a few small-scale folds. The largest fold in the Lower Void Level was at richer units. At the service and pro- about 10 ft in amplitude and disrupted a duction shafts in the Upper Void Level, vertical section about 50 to 75 ft in other joints had strikes of N 76" W, height. The fold axis had a strike of N 57" E, N 60" E, N 78" E, and east-west. N 40" E, and the axial plane of the fold Tuff dikes are frequently encountered dipped 55" NU. Folds of this magnitude in the Cathedral Bluffs Mine workings. can be considered local features. They generally follow established joint Joint patterns on the mine tract have patterns, especially the northeast-trend- been noted by previous investigations. ing joints. Numerous tuff dikes were en- Stellavato recorded joint orientations countered on the Upper Void Level, rang- at the surface and at all five subsur- ing from 3 to about 12 in thick (11). face levels in the mine (11). One set of The contact between the dike and the oil joints was oriented at ~75"W with dips shale beds ranges from sharp and abrupt increasing from 66" on the surface to 90" to very irregular. The source of the at the Upper Void Level. Joint dips were dikes may be a curly bedded tuff, which found to increase with depth. In partic- shows characteristic thinning and thick- ular, pronounced joint steepening was ening and achieves a maximum thickness of measured just below the A-Groove. Also, 18 in (11). This tuff is located just joints were found to be persistent in above the B-Groove (fig. 3). lean oil shale units and to end abruptly DRILL EQUIPMENT AND DRILL-HOLE CONFIGURATIONS

An electrohydraulic drill and powerpack had a tendency to become lodged in the unit was used for drilling all coreholes inner core barrel. A split aluminum for the Bureau study at the Cathedral barrel that fit inside the inner barrel Bluffs shale oil mine site. The drill was used on the second horizontal hole unit had a 30-in feed and independently drilled (UH1). This provided a much im- variable thrust and rotational controls. proved method of removing the core from All of the holes were drilled with NQ the barrel. Fractures frequently almost (2.75-in OD) drill rod and a wire-line paralleled the axes of the holes, which core-retrieval system. Horizontal coring created a tendency for pieces of the core was done with 10-ft rods and a 10-ft core to lodge in the core barrel. The split barrel. Because of height limitations at barrel reduced the time required to re- the drill sites, the six vertical holes move the core from the barrel. A split were drilled with a 5-ft core barrel and inner barrel is also recommended if any 5-ft drill rods. Roof heights had a wide detailed and/or quantitative analysis of range: less,than 13 ft for holes UV3 and the core is planned. The fractured por- UV4 and over 30 ft for holes UV5 and UV6. tion of UH2 was penetrated by rotary The width of the Upper Void Level work- drilling with a 3-in steel drag bit and ings, as measured near the horizontal reamed (the core drill string was larger hole collars, was slightly over 30 ft. in diameter than a 3-in hole) with a 6-in An assortment of NQ core bits of dif- pilot and reamer drag bit. fering configurations were used. The The spacing of the six vertical holes best core-drilling results were achieved ranged from approximately 55 to 165 ft by using a surface-set diamond bit with a (fig. 4). The terminal depth of each of semiround crown and internal discharge. these holes was planned to be 40 ft below In bit designs with conventional water- the Upper Void Level mine floor. The ways, drill water pressure below about 180 psig was not sufficient to keep drill cuttings from becoming lodged between the inner barrel bit and the inside annulus of the drill bit. A platform was constructed on which to mount the drill for drilling the ver- UV6 /- tical holes. It was constructed of 1/8- ./- in steel plate and H-beams, and it situated the drill about 50 in above the drill floor. Scaffolding was assembled to reach the required locations for drill string assembly, disassembly, and \ UVI Vertical hole maintenance. A UV4 -A D ' The face drilled for the collars of Air door b \, horizontal holes UH1 and UH2 was stepped UV5 A \, in shape (fig. 4). The added thickness -uv3 of oil shale at the UH2 hole collar was -0 "7 ', highly fractured, probably as a result 1 \ of blasting. Core drilling through this u12 \, zone was highly inefficient since the drill tools had to be pulled from the ', hole many times, as the result of loss of drill fluid through unusually large frac- FIGURE 4.-Location of holes drilled in Cathedral Bluffs Up- tures. The highly fractured rock also per Void Level, with an enlarged view of the horizontal holes site. depth at which core drilling began i.n attempted on hole UV1, but the influx each hole varied because of drill site of rubble necessitated reaning the hole conditions. Ideally, core drilling would with a drag bit. Holes IJV4 and UV6 were begin at the mine floor so that the en- rotary-drilled to depths of 4.1 and 1.7 tire drilled interval could be recovered. ft, respectively, where core drilling was However, only holes UV2 and UV5 were begun. 4 hole was dug through the muck cored entirely, starting from the Upper to establish the collar of hole UV3. A Void Level :nine floor. At all other ver- short section of 8-in steel pipe was ce- tical hole locations, the presence of mented in place at a depth of 4.2 ft, and muck accumulations of varying thicknesses coring was initiated through the pipe. deterred core drilling the mine floor. Bedrock was encountered 4.5 ft deep in Core drilling froin the mine floor was the hole. SITE GEOLOGY AND CORE LITHOLOGY SITE GEOLOGY

in projects of this nature, drilling Tuff dike mapped activities frequently consuae so much during Bureau time that little is left for detailed geologic investigations. The most time available for observation in this study was at the site of the horizontal holes. Continuous laminations in the oil shale were easily traced across a rib, the face, and the adjacent rib, although col- or changes and sometimes thickness vari- ations occurred within the confines of this site. Fracture or joint orientations were measured on a few locations and were found to be striking very near true north, roughly east-west, and also LEGEND about N 45" E. All were steeply dipping. -Tuff dike This is in general agreement with far more detailed data reported by Stellavato at the same locations (11). .- A bed of nahco~ite~ersistedabout N85OE --- 9 ft above the mine floor, which showed boudinage-like growth structures throughout. The bed ranged in thickness from a Production couple of inches to about 2 ft. A tuff dike striking N 39" E was intercepted by UH2 and was readily visible in the rib adjacent to UH1. Holes UV3 and UV4 were situated near several identifiable dikes, corresponding to the area where Stella- vat0 had mapped four tuff dikes on the Upper Void Level (fig. 5). Most of the roof on this mining level is shotcreted water dr ippage a the FIGURE 5.-Map view of Cathedral Bluffs Upper Void Level openings , making geologic observations showing locations of tuff dikes. (Adapted from Stellavao (1I).) impossible in these localities. VEK'TICAL HOLE COKE I,ITHOI,OGY Selod 36.2 ft, a core 1-oss interval, and just below 41 Et in an area of oblique Detailed lithologic descriptions of the and longitudinal fractilres. Yethane-rich cores were made before the cores were in- gas also emanated from the bottom tj~o serted into desorpt ion cannisters. Fol- f ract~ired-brecciated zones. The first lowing completion of desorption testing, and third of these gas-producing horizons the cores were removed froin the airtight also ejected water from UVl. Tuffaceous containers, and each of the six vertical layers were located at 8.4 to 8.7 ft and holes were reconstructed and situated at 25.5 to 26.4 ft, pyritic layers Erorn next to the nearest adjacent core in ac- 20.2 to 21.8 ft, and 26.5 to 30.6 ft. A cordance with the drill hole sequence marl-rich interval was intercepted he- (fig. 4). No reliable marker bed Mas tween 4 and 5.9 ft, and calcite and observed ~ithinthe vertically drilled kaolinite mineralization frequently ac- sequence to facilitate a lithologic cor- companied f ractclred and vuggy horizons. relation bet~een holes. Apparent rich Bitumen appeared only sporadically in and lean oil shale zones could not be cf- UV1. f ectively used for correlation probably uv2 because of laminae thickening and thinning and lateral changes in laminae col- Two zones of core loss were located in or. The top of each hole, the Upper Void UV2; from 4.4 to 5 ft and frorn 31.3 to Level mine floor, was used for strati- 32.3 ft. Other vuggy and/or highly frac- graphic correlation. tured zones were located at depths oE Core lithologies described below can be 34.7 to 36.8 ft and 39.2 to 40 ft. Marl- observed in figure 6 (in pocket). Frac- lime-rich horizons were found near the tured zones and mlgs partially filled top of the hole from 1.7 to 3.5 ft and with clay were encountered between about from 5.2 to 8.4 f t. Bitumen is abundant 32 and 40 ft in four of the six vertical in the upper two thirds of the hole, oc- holes. These were zones of variable curring with kaolinite and pyrite between thickness. The holes with the greatest O and 3 ft. Another bitumen-rich layer lateral distance to adjacent holes were occurs between 15.5 and 17.5 ft, with as- the two holes at the end of the vertical sociated marly streaks. Below this zone, sequence, hole UV5 (about 110 f t) and pyrite, kaolinite, and calcite, are found hole UV6 (about 165 ft). Holes UV5 and in zones of fractured vuggy oil shale. UV6 are characterized by harder, denser oil shale with fewer Eractures than the inside four holes have. The core from UV5 and UV6 was rernoved from the gale UV3 penetrated densely fractured core barrel in fewer pieces. Occasional- and vug-prone zones from 27.4 to 28 ft, ly, core from these holes was removed from 33.2 to 35.5 ft, and from 36 to frorn the 5-ft inner barrel completely 39.2 ft. Core loss intervals occurred unbroken. just below the First and last of these lJv1 zones, and the methane-producing horizons in UV3 were located just above the upper- Zones of core loss in UVl occurred be- most zone and in the middle zone. Bitu- tween footages 5.9 and 8.4, 17.6 and men and pyrite were abundant, with the 20.2, 36.2 and 36.8, and 44.7 and 45. greatest combined concentrations found Solution fractured and brecciated zones between 13.5 and 28 f t and between 31 and were located bet~ecn 34.2 and 37.6 ft, 34.5 ft. Calcite, kaolinite, and some 43and 43.7 ft, and 44.5and 44.7 ft. pyrite were associated with the upper two Gas flowed frorn the hole upon penetration fractured zones. the cored intervals were mostly unbroken and without core loss zones. Kaolinite Three core loss zones were penetrated mineralization was generally associated in hole UV4--between 13.4 and 14.8 ft, with fractures between 1.7 and 3 ft, 17 between 20.9 and 21.9 ft, and between and 20 ft, and 21 and 29 ft. Two zones 37.7 and 39.2 ft. Water and methane-rich of solution fractures were encountered, gas were discharged from the middle zone fron 23.5 to 27.5 ft and from 35.5 to and also from a thin kaolinitic and 37.5 ft. Limy zones with associated tuff bitumen-rich zone from 12.3 to 13.7 ft. stringers were intercepted between 9.5 Additional zones of dense fracturing and and 12 ft and 30 and 31 ft. Bitumen was dissolution were found from 15.3 to 17.5 found between 17 and 20 ft. Finely dis- ft, 33.1 to 36.3 ft, and 36.9 to 37.6 seminated pyrite crystals were located ft. The lithologies below 29.5 ft were between 34.5 and 37 ft. Two zones of highly tuffaceous; a tuff dike occupied small vugs (usually less than 0.5 in about a third of the cross section of the across their longest axis) were logged core from 29.5 to 32 ft, and the lower from 21 to 30 ft and 31.5 to 37 ft. two vuggy zones were very tuff rich. The top of a 0.6-ft tuff layer was located at 26.3 ft. Kaolinite and pyrite were found in fractured and water-producing zones; The most frequent material identi- bitumen and pyrite were found from 4.1 to fied in the UV6 core was bitumen. The about 7 ft. bitumen-rich intervals were located between 9 and 10.6 ft, 15.6 and 18.5 ft, and 25.5 and 29 ft. Infrequent calcite and kaolinite mineralizations were found Core from hole UV5 was characterized by on fracture planes. Methane gas was en- "poker chips" (closely spaced, regularly countered in hole UV6 at 16.5 f t; gas occurring partings) from 1.6 to 7.2 ft flow was greatly reduced after 5 min. and 18 to 22 ft. Outside these portions, RESULTS OF MODIFIED DIRECT METHOD TESTING The modified direct method test (MDM) work station. The duration of gas de- was conducted on essentially all cored sorption monitoring was nonuniform be- oil shale samples drilled during the cause measurements began as soon as the course of this study. A total of 631.1 core sample was removed from the hole and Et of oil shale was core-drilled, al- placed in the airtight container. As a though all core was not recovered. The result, the position of the sample in the recovered shale was divided into 76 hori- hole and ' in the drill hole sequence de- zontally cored desorption samples and termined the duration of desorption 59 vertically cored desorption samples. monitoring. Sample lengths were usually determined by The concentration of gases at each Sam- the length of core recovered in a single pling was multiplied by the STP total core barrel run. contained gas volume. After the comple- The 135 oil shale core samples sealed tion of gas sampling, the gas volumes can in airtight containers were gas-sampled be totaled to find the amount of gas lib- repeatedly during the study. Each Sam- erated (or consumed) over a known period pling included recording the date and of time. Some deviations to this proce- time of sampling, measuring the dif f eren- dure did occur, and the MDM test is dis- tial pressure between the container at- cussed in greater detail in the appendix. mosphere and the mine atmosphere, re- To compare gas desorption and/or reac- trieving a gas sample of the container tions between samples, it was necessary atmosphere, bleeding the container gas to eliminate inconsistencies in test dur- pressure to mine atmospheric pressure, ation and sample size. Time indices were and recording the temperature and chosen to facilitate sample compari- atmospheric pressure at the underground son. The longest common duration of NDM testing for a group of core samples, ver- the MDM test in the latter portion of tical or horizontal, was chosen for the this study. Error analysis of the MDM index: a 40-day (960-h) index for the technique showed an additive effect of vertically cored samples and a 125-day inaccuracies in volume measurenents. (3,000-h) index for the horizontally Relatively infrequent gas sampling was cored samples. The horizontal core Sam- important to maintain optimum accuracy in ple gases were also indexed at 40 days so gas content determination. Cored inter- they could be compared with the vertical vals removed fron drill holes early in samples. In addition, a 3-day (72-11) de- the study were gas-sampled as many as 13 sorption time index was determined, to times. Oil shale core produced later in simulate that period of time gas would be the study was gas-sampled three to six released from a muckpile before being re- times, and the duration of MDM testing moved f rorn the mine environnent. All gas was much shorter. totals were divided by the sample mass, For sample UV208 (fig. 7 the volume providing weight-normalized gas quanti- of nitrogen was quite high at the begin- ties for interpretation. Although there ning since the mine atmosphere was en- is precedence for metal and nonmetal gas closed in the sealed container at the normalization on a basis of cubic centi- start of the test. The volume of nitro- meters per 100 g, gas normalization on a gen decreased slightly. Oxygen decreased basis of cubic centimeters per gram was steadily in volume during the test inter- chosen to be more easily related to the val. The slope of the oxygen curve is convention of existing coal desorption much steeper than the slopes of other data. Multiplying these numbers by 32 atmosphere-contained gases, such as ni- converts the data to cubic feet per short trogen, which were not emitted in measur- ton. able volumes from the oil shale sample. Previous investigations on coal and oil Presently, it is not clear whether oxygen shale gas desorption have shown a linear is lost because of sorption onto surface relationship for cumulative methane when sites on the oil shale or whether oxygen graphed in terms of the square root of is consumed by low-level oxidation reac- time (1).Figure 7 shows a graph of tions. The decrease in oxygen was not square root of time in hours against cu- accompanied by a significant increase in mulative gas volume per unit weight. The CO or C02, as was noted in some trona and sample shown is labeled UV208, indicating coal mines where self-heating reactions oil shale removed from the eighth coring were found to occur (12).- C02 increased run on the second vertical hole drilled in volume with time. However, the total from the Upper Void Level during this volumetric increase was small compared study. This sample is an example of with that of the more abundant and more typical behavior of the gases as shown by reactive gases. The volume of methane increased markedly over the course of this test. The 40-day indexed value for

v methane content equals about 31 on the square root of time axis and equals 0.116

KEY - cm3Ig. Oxygen, nitrogen, and COz were .-.-. n dV also measured by indexing. An indexed O2 - methane content value is estimated by in- -- 0.' N2 -...-... 0 terpolating a straight line between the - closest data points before and after the chosen time index. Figure 7 shows - a substantial increase in overall gas volume (dV) over time. The total in- 10 20 30 40 50 60 crease in gas volume is smaller than the TIME, h% increase in methane alone, largely because of the volumetric decrease in FIGURE 7.-Gases measured within container for sample UV208. The dashed line shows the time index value for methane Oxygen. bough le cOm~ar content at 40 days. favor normalizing gas volumes on a weight or mass basis, figure 8 shows The aforement ioncd plot of incremental the changing contained gas volumes .ig gas volumes per unit time against time cubic centimeters for sample UV310, to essent ially represents the dorivat ion of show tile scale of the nea:;:lred data from the graph of cumulative gas versus square a 5-ft core sample of oil sha1.e. root of time. Linear plots on the latter A linear increase in methane from oil graph have the form y - al"'l2+b. The shale over time as aeasared in the square first derivative with respect to time root oE hours was Eound not to be exact dould be dy/dT = a(l/~'/~). Second- in marly cases. Similar data plots of a degree polynomi,-rl curves on tile cum~lliri- number of samples show a tendency towards t ive-gas-ve rsus-t ime graph have the form curvature. The curves are generally con- y = a(~'/~)~+ ST"^ + C, where the first cave down. The curved methane plots derivative with respect to time is dy/dT have been fitted to second-degree polyno- = a + b(l/~'/~).A graph of y = (1/~'/~) mials very successfully, with tile coeffi- is very similar to the shape of the curve cient of determination (r2) values gener- shown in figure 10. The derivative of ally in excess of 0.98. Another graph the second-degree polynomial is very sim- was made to better discern whether the ilar to the derivative of the linear, second-degree polynomial was a better except that a constant is added. This description of the oil shale desorption would increase the Y-intercept of the data. A sample was chosen that was gas- plot. Since the gas desorption rate is sampled frequently and that showed a rel- high at the beginning of YDM testing atively linear increase OF culnulat ive but declines so rapidly, infrequent gas methane volume when graphed against the square root of time (fig. 9). The difference in gas volume between successive points for sample UV102 was Eound and divided by the amount of time, in hours, that passed between the two points. These gas volumes vere graphed against time in hours to show how much methane was released per unit time from the core and to illustrate how these volumes changed over time (fig. 10). The curve shows the largest amounts of gas released per unit time were at the beginning of the MDM test. The curve declines quickly TIME, hb and approaches the X-axis asymptotically. FIGURE 9.-Gases measured within container for sample UV102.

"-- "-- KEY - .-.-. dV -402 - N2 --...-... 0 c02 -- 4 CH4

10 30 40 0 1,000 2,000 3,000 20 I TIME, h TIME, h'2 FIGURE 10.-Amount of methane desorbed from sample FIGURE 8.-Volumes of gases measured within container for UV102 between each gas sampling, divided by the amount of sample UV310. time elapsed between each gas sampling. sanpling at the beginning of the test samplc in an airtight container. The ni- averages high rates of desorption with trogen ccirve in 11A ha:; three points iq- lower ones that occur shortly thereafter. stead of four ,~ossiblybecause either ni- >lore frequent sampling at the beginning trogen analysis was not done on the gas of gas monitoring reduces the av2raging sample or a gas-sampling or gas-analysis of high and lo^^ desorption rates and in- nalfl~nction occrirred. creases the Y-intercept of the graph. Figure 12A presents a graph of gas vol- This is consistent ~iththe forin of the ume per unit mass plotted against square first derivative of the second-degree root of time for sample UH109. Sample polynomial. It appears that sampling Uli109 produced a larger quantity of met11- frequency and duration of testing can af - ane than did most other Cathedral Sluffs fect the shape of the graph of cun~ll~ative samp1t.s undergoing MDM testing. The gas versus square root of time and that time-volurnet ric methane indices for this second-degree polynomial cllrve f its to sample are 0.0804 and 0.253 cn3Ig at 3 some graphs are better approxinat ions of and 40 days, respectively. Also, the du- the observed desorpt ion phenomena. ration of testing was Ear longer for this An example of a successful linear curve sample, 132 days, than for those sanples fit is given in figure 11. Sample UV303 presented thus far. The plot shown has is shown with gas volumes normalized per heen interpreted as an example of a con- unit mass in figure 11A. The methane cave-clown plot of methane per anit mass content of this sample is lower than versus square root of time. It possesses t?~atof the majority of Cathedral Bluffs all three of the qualities recognized samples. At the 40-day time i,~dex (31 as conducive to producing concave-down h'"), UV303 desorbed 0.0750 crn3Ig CH4. plots: The curve fit in figure 11B shows methane 1. The duration of testing was long, data only. The time between the Y-axis so that high early desorption rates were and the first data point represents the combined on the same graph with lower estimated lost-gas period in square root ones occurring later in the test. of hours before the sealing of the core

1 A KEY .-.- a dV -- 02 -N2 -...-... 0 C02 ,/- ,.0.- KEY --* CH4 Od,,.O. .-.-. dV ,0<." 02 .I5 -- -7 ././. -N 2

B KEY CH4 - y= -4.695771-~x2 +0.010113~-5.691627-~

r2 = 0.999

LLI 0 10 20 40 50 60 30 1 0 5 10 15 20 25 30 35 TIME, h'2 TIME, hh FIGURE 12.-Sample UH109: A, gases measured within con- FIGURE 11 .-Sample UV303: A, gases measured within container; B, second-degree polynomial fit to desorbed methane tainer; B, linear regression fit to desorbed methane data. data. 2. Frequent gas samples were taken at UH211 was not successful in obtaining the beginning of the test to minimize representative contained-gas concentra- averaging high desorption rates with tions early in the duration of YDM lower ones that followed. testing, and no gas data are available 3. Compared with other samples in the after that time. study, this sample is relatively gas Figure 13 shows a plot of the square enriched. root of time versus cumulative gas volume Figure 12B shows only methane data per mass for sample UH210. Some devia- plotted on a graph of normalized cumu- tions from smooth predictable trends oE lative gas volume versus square root gas behavior can be seen at about the 5- of time. A second-degree polynomial was and 29-h1/2 times. These have been at- fitted to this data. For X = TI/', tributed to atmospheric contamination of y = -4.696 x ~o-~x'+ 0.0101X - 5.692 the contained gases. This phenomenon is x This equation fits the data with usually indicated by increases in the an r2 coefficient of determination equal volume of gases that are abundant in at- to 0.999. Methane-rich gas flowed from mosphere, such as nitrogen and oxygen, the hole during core drilling at a depth and a decline in those gases that are not of 45 to 47.5 ft. The UH109 desorption contained in the atmosphere, such as sample interval contains core from 41.8 methane (fig. 13A). In terms of the to 51.3 ft of hole UH1. This core sample overall sample gases, the erroneous gas is gas enriched beyond the majority of data is not extreme, and this graph is oil shale samples presented here and in- still useful in showing trends of gas cluded a gas-flow-producing zone. An as- data. The methane data is fit to a sociation between methane flows from a second-degree polynomial in figure 13R. drill hole and high methane contents from The equation is given, and the r2 the same footage interval is tentatively supported. Hole UH2 also contained examples of gas-producing zones. High-concent rat ion methane gas averaging 95.1 pct, measured

by gas chromatography on gas samples, was /' /' released from hole UH2 at a depth of KEY about 59.2 ft. Average gas concentra- .-.-.o dV ---O o2 tions of 02 + Ar, N2, C02, and C2Hh mea- N2 -. . . - . . . sured 0.45 pct, 2.8 pct, l. 65 pct, and 0 C02 0.01 pet, respectively. The first signs --4 CH4 of a free-flow gas zone were observed at about 57 ft. When the hole was sealed at I -- about 59.2 ft, no pressure buildup was observed; however, the equipment used was not sensitive enough to register a pressure buildup of less than about 10 psi. Gas flow measurements of up to 20,000 ft3/d were neasilred following coring to 63.5 ft. Manometer readings of gas flows through an orifice plate were oscillating greatly as water and gas blew out of the I I I L 1 I J 0 10 20 30 40 50 60 70 hole. The interval from 57 to 63.5 ft TIME, h1'2 was divided between two desorption sam- FIGURE 13.-Sample UH210: A, gases measured within con- ples for MDM testing, UH210 and UH211. tainer; B, second-degree polynomial fit to desorbed methane Unfortunately, gas sampling of sample data. - -- coefficient of determination is 0.995. 0.25 1 I I w A At the 40-day methane time index, sample * 20 UH210 has desorbed 0.295 ~rn~/~,one of KEY the highest gas quantities in this study. .-.-.o dV 15 In this case, methane enrichment in the -- 02 -N 2 /a -... -... desorption sample corresponds well with 10 0 C02 / /// .n -- /.A,/ gas emissions encountered while drilling -0 CH4 the interval. Me thane gas flows were observed again V) ,+.. ...-...-.,, 4.0..-... 0- ...-...-...-...-...-... 0 03 0 * in UH2 at a depth of about 115 ft and at a 5 a terminal depth of 197.9 ft. Chromatog- \ w -.050 I I I raphy on gas samples taken at the hole 5 20 40 60 80 3 collar once terminal depth had been 2 0.14 I -- reached averaged 80.47 pct CH,, 15.57 pct > KEY 'I2- CH4 N2, 3.84 pct 02 + Ar, 0.44 pct C02, and .lo- -y=2.069715-~~ about 0.02 pct C2H6. The last two desorption samples from UH2 were inter- .06 - rupted during MDM testing by experimental r 2 = 0.991 irregularities. The last two desorption samples for hole UH2 that yielded reliable experimental data measured from 0 10 20 30 40 50 60 70 172.1 it to 180.9 and from 180.9 to TIME, ht'2 182.4 f t and resulted in 40-day indices FIGURE 14.-Sample UH223: A, gases measured within con- of methane contents of 0.101 and 0.147 tainer; B, linear regression fit to desorbed methane data. cm31g, respectively. The deeper of these two samples shows a significant degree of methane enrichment. desorption curve in figure 14B. The 40- Desorption sample UH223 contains the day methane index for this sample mea- gas-producing horizon at a depth of 115 sures 0.0619 ~rn~/~,which is below the ft. Figure 14 shows the graph of the 40-day indexed value of the majority of square root of time versus cumulative Cathedral Bluffs samples. No quantita- volume divided by mass for this sample. tive gas measurements were taken from the Although an atmosphere leak appears to drill hole at a depth of 115 ft, but gas have occurred during MDM testing, it did could be seen bubbling from the returning not significantly affect the overall drilling water. IN SITU PERMEABILITY The in situ hydraulic conductivity de- One measures the steady-state fluid flow terminations were performed using a dis- from the test interval into the fissure continuum approach described by Bennett at a constant head or pressure. The and Anderson (13).- In this approach, the other, the falling-head method, is per- significant permeability is attributed formed by injecting water into a test to the fractures intercepted by the test interval and measuring the pressure drop interval (a 5.5-ft section isolated by over a period of time. The average inflatable packers); the unfractured equivalent aperture (e, in inches) for a rock matrix does not make a significant constant-head test is calculated from contribution. The average equivalent aperture of the fissure was calculated, e = [(l/n) [Q/(~~Ho)I(121Ju/Yw) and the average fracture permeability calculation was made assuming a parallel- [In (RI~O)]]"~, (1) plate model. Two test methods were used. where n = number of intercepted fractures;

Q = measured steady-state waterflow rate, gal/min;

H, = applied waterhead, ft;5

p, = dynamic viscosity of water, cP = 1147,880 lbf*(s/ft2);

Y, = unit weight of water, 62.4 lb/ft3;

R = radius of influence, which is assumed to be half the test interval length, ft; and r, = radius of borehole, ft.

When the units used in this report are inserted,

[12 (1147,880) ~bf.(s/ft~)/ 11 [In (R/r,)]

where P - Po = pressure differential.

Simplifying the above equation yields

R and ro should be measured in the same units so that R/ro becones a dimensionless quantity.

The perneability (K) of the average fissure from above is

The intrinsic permeability (k) is given by

Substituting for e and simplifying,

k = 6.041 x lo-' { [Q/(~(P- Po))] 1n (~/r,)]~/~. Converting the above equation from square feet to millidarcies and simplifying gives k = 5.686 x 10"~ [[Q/(~(P- Po))] in (~/r,)]~/~. (4)

The equivalent aperture concept is used because the surface roughness of the fracture was not known. The equivalent aperture is essentially the width of the fracture if that width is conceptualized as being wide enough such that the real surface roughness of the fracture becomes quite small. A parallel-plate model is used to approxi- mate the fracture configuration to determine its permeability.

5~ennettand Anderson (13) measured waterhead in feet.. A conversion factor of 144 (p - p,)/Y, is inserted into equation 1 to convert Ho to units of pounds per square inch to be consistent with other units in this report. For the falling-head test, the average equivalent aperture is calcul.ated by

Substituting the units used in this report, the above equation for e becomes

= {[(r02 ft2) / (2n ~t min)] [12 (1147,880 lbfo(s/ft2)

where H,, and Ho2 = test interval pressures at t 1 and t2, respectively, psi;

tl and t2 = initial and final times, respectively, corresponding to a set of permeability data; and At = t2 - tl, min.

Simplifying the above equation yields

All other variables have the same meaning and are measured in the same units as in the equation for the constant-head case.

Under pressure-drop conditions,

k (single fracture, intrinsic) = (IJ,/~~)[ro2/(2n Ate) I [In (Ho /Ho2) I

After the units used in this report are inserted, a substitution is made for e, and the equation is simplified, it is found that

This expression gives the intrinsic permeability of the average single fracture in the test zone in units oE square feet. To find k in terms of millidarcies, it is derived that

Two intervals of hole UH2 were chosen for in situ permeability testing. Both intervals had produced methane gas flows from the hole during core-drilling operations. The test interval length, the separation between the two inflatable packers, was identical for both tests: 5.5 ft. The first test zone was located between 63 and 68.5 ft. This portion of the hole was seen to be transected by fractures during logging; a total of 13 were counted. A constant-head test was conducted within this interval. Water was used as the test fluid for this and all other permeability tests conducted at the site during the study. The 63.0- to 68.5-ft section was tested at pressures of 565 to 600 psig. Graphs made from the experimental data been pressurized to the test pressure be- show how both equivalent aperture and cause test fluid was removed via fracture fracture permeability varied with in- permeability more rapidly than pressur- creasing pressure. In the shallow zone ized water was flowing in. If this con- test (fig. 15A), both the equivalent ap- dition did exist, it would eventually erture and the permeability decreased produce falling pressure at the gauge, with increasing pressure. It is diffi- but the test duration of about 68 min may cult to account for this behavior. Test not have been long enough to record a pressures were below the hydraulic frac- pressure drop at the gauge. The data do ture gradient as determined by Brieden- show that permeability and fracture aper- hoft (14). The personnel on-site indi- ture decreased with time, with the test cated that the pump used during the test pressure beginning at 560 psi and ending was functioning at maximum flow capacity at 600 psi. The unusual relationship ob- in generating the 600-psig pressure. served between fracture aperture and per- Although the gauge at the collar of the meability and fluid pressure may also be hole registered 600 psig, an unstable attributable to alteration of the in situ pressure differential within the tested stress field in the vicinity of the shaft interval could account for the perform- by shaf t-sinking operations. The capac- ance shown in figure 15A. Those portions ity of the induced fracture reservoir may of the test section at the greatest dis- have been too large for the test fluids tance from the hole collar may not have to fill.

t 1 1 I I 1 1 - - - - - . . - t - 4 A, Shallow test zone a 2GO B, Deep test zone - 7 - -a a - a

I I I I I

PRESSURE ( P - Po), psi

FIGURE 15.-Hole UH2: variation of average equivalent fracture aperture and permeability with fluid pressure as measured by constant head. The deeper test interval in hole UH2 at 900 psi and from over 0.0029 to just extended from 115 to 120.5 ft. The con- under 0.0031 in at 1,000 psi. Some of stant-head test was maintained at 900 these separations overlap those deter- and 1,000 psi. Figure 15R presents the mined in the 63.0- to 68.5-ft interval at equivalent aperture and average fracture lower pressures. Permeabilities in the permeability, graphed against absolute deeper test section of hole UH2 ranged pressure in the test interval. Although from about 280 to over 500 D. At lower only two pressures were maintained during pressures in the shallower test section this test, there does appear to be an in- of UH2, the determined permeabilities crease in equivalent aperture that ranges ranged from about 395 to 435 D. from less than 0.0023 to over 0.0025 in

DISCUSSION

Figure 6 presents geologic data for specific gravity. Specific gravities each of the vertical holes. The hori- were calculated using Smith's empirical zontal distance between hole collars is relationship between oil shale density not given, but depth is shown to scale and oil yield (15). as distance in feet below the Upper The next column to the right on figure Void Level mine floor. The desorption 6 is another histogram showing the 40-day sample number in the leftmost column. index of methane content per unit mass as The next column gives lithologic informa- measured by desorption in a closed con- tion about the core. The relative litho- tainer. The column on the right gives logical abundance is given by the number the location and quantity of fractures in or density of symbols indicative of the the core. Distinctions are made between appropriate constituent. The next coll~mn fractures and bedding plane separations. is a histogram showing oil yields as de- Also, different types of core breaks are termined by modified Fischer assay by accounted for. Where fractures occur too Dickinson Laboratories, Inc. The assay close together to map accurately, a sym- sample sizes were generally 2 ft or less. bol (shown in the key) gives information The measured assays are given in figure about fracture density. 16. A high degree of lateral continuity Figure 6 allows the qualitative evalu- in grade is apparent. These data were ation of interdependence between several normalized to match the desorption sample factors. In general, gas flows emanated interval by a weighted average. Sample from fractures, vugs, fracture planes mass was determined by multiplying the coated with kaolinite, and core loss volume of the oil shale sample by its zones. The relationship between gas

-Approx location of Upper Void Level mine floor

Depth, lo[0 ft

0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 GRADE, gal /st

FIGURE 16.-Actual measured assay values for vertical holes before samples were weight-averaged to match the desorption sample interval. flows during drilling operations 'and gas 0 12 I enrichment neasured by MDM gas desorption II - testing was tentatively upheld. It may lo - be that methane flows are better cotre- 09 - a lated with the form or structure oE the 08 - methane-2nitting zone than with its de- 07 - sorption gas content or chemical conposi- - tion. This is a somewhat appealing pren- F 06 I()E 05- a ise because methane that readily f lo~s 04- from a drill hole is probably mobile and 20 2 5 exists in a free gas state or dissolved 6 2 0.18 I T I I ! I in water before penetration by drilling x KEY uv2 W - Normalized difference operations. It woul-d not be necessary ,, 6 5 in CH4 at 40days for this gas to remain near its source. However, reservoirs that produce gas appear to have been very limited in volume as they bled ofE within the duration of a single shift. Although the permeability data represent only an initial step to- 08I I 1 ward understanding the reservoir charac- 25 30 35 40 45 50 55 60 teristics of oil shale ore bodies, they OIL YIELD, gallst do indicate high permeability, hundreds FIGURE 17.-Correlation between methane content at 40 days of darcies, within the fracture network of desorption and oil yield for holes UV1 and UV2. of gas-producing zones. Although data fron this study on the permeability of unfractured oil shale are not yet available, previous workers have found the un- Oxygen can also be problematic in terms fractured rock to have a permeability on of additive experimental error because the order oE microdarcies. its volume decreases over time. Graphs It has been postulated that an asso- of oxygen per unit mass agaigst oil yield ciation might exist between the amount did not show them to be correlative. of methane enrichment and the oil yield The parameter shown in figure 6 that richness of oil shale fron the same Sam- directly and most consistently varies ple upon retorting. Predictions of oil with methane content appears to be the shale specific gravity based on oil yield occurrence of asphalts or bitumen and imply a relationship between assays and sometimes pyrite. Asphalts in the con- the actual amount of organic matter con- text of this study refer to streaks or tained in a sample. The histograms in small, rounded inclusions of bituminous figure 6 do not qualitatively support an material found in the core. The fine- association bet~een methane content and grained, dispersed nature of this mate- oil yield. A quantitative approach was rial suggests that the organic materials attempted by graphically representing in the oil shale have been the source of methane desorbed per unit mass in terms the bitumen formation. The exact mech- of oil yields, in figures 17A and 17B. anisms for this formation are not totally An association is not supported by either understood; however, associations between of these plots. Similar graphs were pre- bitumen and oil shale are common in the pared for other gases with similar re- Uinta Basin. sults. Nitrogen was quite unreactive. Three primary factors are recognized as C02 generally increased slightly in vol- influencing the type or chemical composi- ume but was not highly reactive, and the tion of bitumen produced in environments calculated quantities of C02 are less of oil shale genesis. The first factor reliable with increasing test time as is suggested by petrologic investiga- additive experimental errors increase. tions of coal. It has been shown that the specific botanical conposition of and nethane contents penetrated by the coal proge~litors is an inportant Factor vertical holes. These postal-ntes are not in the physical and cl~emical makeup of substantiated. the coal formed. The pr~genitors of l7rigur~ 19 presents methane contents of Green River oil shale and rare algal the sample population on a 40-day time coals are similar, so it is arlticipated index. The mean of the group is 0.114 that both oil shale and coal share this cm3/g, with a standard deviation of primary control. Oil shale does contain 0.0505 c~n~/~.A bimodal distribution for far more mineral matter than conventional the vertical hole samples and a slightly coal. The other recognized primary fac- higher degree of methane enrichment €or tors of bitumen Formation are related to horizontally derived samples is apparent. the chemical environment of the ancient Figure 20 shows the 50 horizoiltal hole lake oE oil shale deposition. It has samples indexed to 125 days of methane been inferred that the lake waters varied desorption. Similar to data shown in the chemically through time, and differing previous two figures, the overall distri- bitumens are preferred on the basis of bution is skewed to the left, toward the the salinity of the environment where loder end of the scale. The data of fig- they form (16).- The third primary con- ure 20 have a mean of 0.195 cm3/g and a trol of bitunen formation is the avall- standard deviation of 0.071 ~m'/~. ability or depletion of oxygen during The composition oE gas released from deposition and burial of the bitumens' oil shale samples can be estimated from precursors. The degree of reduction in this study. The gases rvutinely analyzed the lake waters favors the chemistry oE by gas chromatography included Ar, N2, certain bitumens (16).- 02, C02, CH4 and, less frequently, CO and A secondary control might result from C2Hs. Of the seven oil shale samples differences in the chemical and physical discussed in the section "Results of Mod- stabilities of the bitumens and/or their ified Direct Yethod Testing," five pro- precursors. These stabilities could de- duced smooth and regular gas evolution termine the presence or absence of the and/or reaction curves indicative of re- substances now found in the rock. The liable experimental execution. CH4, C02, pyrite sometimes associated with these and C2H6 were the only gases showing pre- bitumens probably resulted from reduction dictable increases in volume. Vitrogen of sulfate to sulfide, which combined showed an increase in some instances and with iron from mineral matter, similar to a decrease in others. Nitrogen volume pyrite formation in coal-forming swamps. did not increase in a regular trend be- Figure 18 shows the frequency distribu- tween sample points. Overall changes tions of methane contents indexed to 72 h generally accounted for less than 10 pct of desorptions for the total sample popu- of the N2 starting volume. When CH4, lation (n) in this study. The mean (X) C02, and C2H6 were normalized to 100 pct, of the samples is 0.0316 cm3/g, with a the five samples averaged 91.56 pct CH4, standard deviation (S) of 0.0169 cm31g. 8.43 pct C02, and 0.01 pct C2H6. Experimental malfunctions reduced the to- Comparisons can he made between the tal sample population from 134 to 119 at gas contents of oil shale samples and 72 h and to 100 at 40 days. The bimodal the gas contents of a variety of other distribution of the vertical holes has rock samples. The methane content means not been accounted or The slightly and ranges of all oil shale samples are higher degree oE methane enrichment of given for the tine indices of 3, 40, and the horizontal hole samples might be 125 days in figure 21. The units of gas attributable to shorter lost-gas tines content are cubic centimeters per gram. or to gas enrichment OF the horizon(s) All three time indices for oil shale sam- drilled by the horizontal holes as op- ples overlap with high-volatile bitu- posed to the diversity of oil shale beds minous coal (e.g., Pittsburgh Coalbed). KEY I Samples taken from horizontal coreholes 3I Samples taken from vertical coreholes n- =I19 X = 0.0316 crn3Ig S = 0.0169 cm3Ig

METHANE CONTENT, cm3/g

FIGURE 18.-Methane contents of samples at 3 days of desorption showing vertical corehole sample distribution and total sample distribution.

However, the logarithmic horizontal scale volume of gas released from the gassiest shows the mean of high-volatile bitumi- domal salt type categorized by the Bureau nous coal to be an order of magnitude and the amount released in the shortest higher than the mean gas content of oil time duration of oil shale gas-content shales reported for 40- and 125-day time testing reported here. There is overlap indices and two orders of magnitude high- shown between the ranges of the 3- and er than the mean gas content of oil shale 40-day time indices of oil shale gas con- samples at the 3-day time index. Gas tents and the ranges of the other two contents of Cathedral Bluffs oil shale salt types. samples at the 3-day time index are quite It is not possible to account for the similar to outburst-type domal salt in differing gas-content test methods for both mean and range. This does not indi- salt, coal, and oil shale. The MDM cate outbursting tendencies in oil shale. technique used on the oil shale samples It does show a resemblence between the METHANE CONTENT, 10-2cm3/g FIGURE 19.-Methane contents of samples at 40 days of desorption showing vertical corehole sample distribution and total sample distribution.

- 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 METHANE CONTENT, 10-~cm~/g

FIGURE 20.-Methane contents of samples at 125 days of desorption showing horizontal hole sample distribution.

involves no destructive sample treatment treatment. The direct method data re- and measures gas released from the Sam- ported for coal samples in figure 21 are ple under essentially atmospheric con- obtained generally by a few months of de- ditions after the rock is removed from sorption testing until the process has in situ conditions. Dissolution gas- greatly declined, after which the coal content testing for evaporites measures samples are crushed and the gas released gas released only by destructive sample is measured and added to the total. I I I I 1 I I I I I 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 lo1 102 TOTAL GAS CONTENT, cm3/g

KEY CL Lignite OA 3 days of desorption SB Subbituminous Formation test lng HB High-volatile bituminous oil shale, 06 40 days of desorption Piceance Basin testing MB Medium-volatile bituminous OC 125 days of desorption LB Low-volatile bituminous testing SA Semianthracite SN Gulf Coast domal rock CA Anthracite salt, normal AC Average SG Gulf Coast domal rock salt, anomalous, Impure, gassy SO Outburst salt

FIGURE 21 .-Mean and range of methane contents released from assorted rock samples.

CONCLUSIONS

The occurrence of methane when mining beds usually of major interest to the oil shale is supportable theoretica1l.y oil shale mining industry, including the and empiricall-y. However, there is not Hahogany Zone. The geologic character a great deal of agreement on the amount of the oil shale is very different above of methane released upon mining a given the dissolution surface in the Piceance quantityof oil shale. Data frorn the Basin, where vuggy porosity and water Horse Draw Nine probably represent some movement through fractures are relatively of the best information available on this commonplace. The stratigraphic differ- subject; the average arrived at was 42 ences between the Cathedral 3luffs and ft3/st (1.3 ~m~/~).In using these data, Horse Draw Nines probably inhibits the it is useful to consider that the Horse sharing of methane data between the two Draw Mine was designed to recover daw- sites. sonite and nahcolite in addition to oil A number of geologic factors have been shale. This required mine workings to be suggested as being important in the con- developed below the dissolution surface, trol of methane enrichment in oil shale. where the saline minerals are preserved. This report has attempted to address These horizons are below many oil shale some of them. There is no evidence for a si~nificantcorrelation between oil yield tuffaceous or argillaceous material-. by modified Fischer assay and methane Use of a split inner barrel is suggested. content. The existence of certain local 1 drill with independently variable structural features s:lch as fractures and thrust and ro~ational controls imparts vugs nay provide channels for gas move- maximur? flexibility to the driller for ment in oil shale. These features are cont ~ndingwi th inhomogcnei t ies varying sometimes associated vith methane enrich- from conparat ivel;~ hard and somewhat ment in oil shale but appear to be more elastic oil shale to fractures, and to significant in controlling the movement vugs oc fractures Filled with loose or of free gas in the ore body. The featare weakly lithified material. 4 drill unit having the most persistent direct rela- powered by 25 hp or more is appropriate tionship with gas enrichment sas the oc- for all but very short hole drilling. currence of bitumen and possibly pyrite Permeability data presented here should in the rock. The bitumen occurred as be considered preliminary. The most re- streaks and small rounded inclllsions of liable data gener.3ted during this study solid material in the rock matrix. suggests that very high permeabil- The amount of methane contained in ities can exist in the fracture network, fresh oil shale samples was measured by especially in zones that produced gas a new technique knot~n as the modified flows during drilling. The permeabil- direct method (MDM). The method is de- ities given here ranged from about 300 to scribed in detail in the appendix. This 500 D. Evidence also suggests that gas test measures the STP volume of gas re- reservoirs as they exist in oil shale leased from a rock sample that is removed format ions are very limited in volume, f rorn in situ conditions to essentially perhaps because of the narrow apertures atmospheric conditions without crushing of the fracture system. or similar destructive action on the sam- rlethane contents per unit as: were ple. Quantifying STP gas volumes each calculated from MDM for three time inter- time a sample is taken during the dura- vals of gas desorption. Methane contents tion of the test produces information on were calculated at 72 h to simulate a rates of gas desorption and gas reac- typical amount of time rauckpiles would tions. It has been shown that methane is remain underground. The mean value of released relatively rapidly when a sample 119 samples was 0.0316 clo3/g. Methane is first removed from the in situ envi- contents were calculated at 40 days to ronment, but this rate quickly declines, get higher gas values without excluding probably in less than 24 h. It is recom- samples removed from drill holes com- nended that in using the test, (1) if the pleted near the termination of the study. objective is to measure total gas con- This population numbered 100 oil shale tent, infrequent gas sampling be done, samples, and the mean gas content was with samples taken most frequently at the 0.114 ~m'/~. At 125 days, the longest beginning of the test and (2) if rates of time for which gas contents were indexed, gas releases or reactions are the objec- a mean of 0.195 cm3/g was determined for tive, then samples be taken much more of- 50 samples. All sample populations devi- ten; the methane desorption rate can be ated somewhat from normal distributions, expected to change rapidly immediately with the majority of samples being skewed Following removal of the sample from the slightly toward the low end of the scale host rock. and a few samples forming a tail in the This study represents a detailed drill- more gas-enriched direction. ing program successfully completed from Comparisons can be made between the gas underground mine workings. A surface-set contents of oil shale samples and other diamond drill bit with a seniround crown rock samples. Rock sample testing has and internal discharge was the best determined that methane released from choice for core drilling in the Piceance Mahogany Zone oil shale from the Piceance Zasin, in order to maintain water pres- Basin is far less than that evolved from sure in penetrating vugs filled with U. S. high-volatile bituninous coal. Test results also indicate that oil shale min- gas released without destructive sample ing may produce slightly more methane treatment. One can only speculate on how than is generally released in domal salt much gas remains in the oil shale even mines. However, dissimilarities in gas- after 125 days of gas desorption, as content testing methodology are highly reported here. Under no circumstances significant to these comparisons. Coal would it be advisable to apply data re- and salt gas determinations attempt to ported here to oil shale occurring in neasure the total gas contained. MDM other basins or within differing strai- testing for oil shale samples measures graphic units.

REFERENCES

1. Robinson, W. E. Origin and Charac- Basin Colorado, ed. by Do KO Murray. teristics of Green River Oil Shale. Ch. Rocky Mto ASSOC. Geol., 1974, pp. 29-40. in Oil Shale, ed. by To Fo Yen and Go V. 9. Yen, To F., and Go V. Chilin- Chilingarian. Elsevier, 1976, pp. 61-79. garian. Introduction to Oil Shales. Ch. 2. Russell, P. L. History of Western in Oil Shale, ed. by To Fa Yen and Go V. Oil Shale. Cent. Prof. Adv. , East Bruns- Chilingarian. Elsevier, 1976, pp. 1-12. wick, NJ, 1980, 152 pp. 10. Eugster, He P. Origin and Deposi-

3. Cole, Re Do, Go Jo Daub, and Be Eo tion of Trona. Contrib. Geol.: Trona Weichman. Geology of the Horse Draw Nah- Issue, v. 10, NO. 1, 1971, pp. 49-56. colite and Oil-Shale Mine, Piceance Creek 11. Stellavato, No Results of the Basin, Colorado. Paper in 15th Oil Shale Geologic Mapping Program During Shaft Symposium Proceedings (Golden, CO, Apr. Sinking and Subsequent Station Develop- 28-30, 1982). CO Sch. Mines, Au~. 1982, ment at C-B Tract. Paper in 15th Oil pp. 15-28. Shale Symposium Proceedings st old en, CO,

4. Sapko, Me J., J. KO Richmond, and Apr. 28-30, 1982). CO Sch. Mines, Au~. J. P. McDonne11. Continuous Monitoring 1982, pp. 115-136. of Methane in a Deep Oil Shale Nine. Pa- 12. Kuchta, J. Me, Me Hertzberg, per in 15th Oil Shale Symposium Proceed- Re Cato, C. Do Litton, Do Burgess, and ings (Golden, CO, Apr. 28-30, 1982). CO Re W. Van Dolah. Criteria of Incipient Sch. Mines, Au~. 1982, pp. 320-340. Combustion in Coal Mines. Paper in 15th 5. Teichmuller, Me Origin of the Pet- Symposium (International) on Combustion rographic Constituents of Coal. Sec. (Tokyo, Japan, Au~. 25-31, 1974). Com- in Coal Petrology. (Engl. transl. ). bustion Inst., Pittsburgh, PA, 1974, Gebruder Borntraeger, West Berlin and pp. 127-136. Stuttgart, 3d ed., 1982, pp. 219-294. 13. Bennett, Ro Do, and Re Fo Ander- 6. Hartley, Jo A*, and To No Beard. son. New Pressure Test for Determining A Standard Technique for Handling, Mark- Coefficient of Permeability of Rock ing, and Logging Oil Shale Core. Paper Masses. U.S. Army Eng. Waterways Expo in 16th Oil Shale Symposium Proceedings Stn. , Tech. Rep. GL-82-3, July 1982, (Golden, CO, Apr. 13-15, 1983). CO Sch. 41 PP. Mines, Au~. 1983, pp. 81-98. 14. Bredehoeft, J. Do, Re Go Wolff, 7. Kissell, Fe No, C. Me McCulloch, W. S. Keys, and Eo Shuter. Hydraulic and C. He Elder. The Direct Hethod of Fracturing To Determine the Regional Determining Methane Content of Coalbeds In Situ Stress Field, Piceance Basin, COO for Ventilation Design. BuMines RI 7767, Geol. Soc. America Bull., v. 87, NO. 2, 1973, 17 pp. 1976, pp. 250-258.

8. Murray, Do KO, and Jm Do Haun. 15. Smith, Jo W. Theoretical Rela- Introduction to the Geology of the Pice- tionship Between Density and Oil Yield ance Creek Basin and Vicinity, Northwest- for Oil Shales. BuMines RI 7248, 1969, ern Colorado. Ch. in Guidebook to the 14 PP. Energy Resources of the Piceance Creek 16. Bell, K. G., and J. M. Hunt. Na- 19. Cheng, K. C., K. K. Feng, and tive Bitumens Associated With Oil Shales. R. Augsten. Test Procedure for Methane Int. Ser. Monogr. Earth Sci., v. 16, Desorption From Coal By Direct Method. 1963, pp. 333-366. Can. Explos. Res. Lab., CANMET Kep. FRP/ 17. Darton, N. H. Occurrence of Ex- MRL 81-63 (TR), Aug. 1981, 18 pp. plosive Gases in Coal Mines. BuMines 20. McCulloch, C. M., .J. R. Levine, B 72, 1915, 248 pp. F. N. Kissell, and M. Deul. Measuring 18. Bertrard, C., B. Bruyet, and the Methane Content of Bituminous Coal- J. Gunther. Determination of Desorbable beds. BuMines RI 8043, 1975, 22 pp. Gas Concentration of Coal (Direct Meth- 21. Curl, S. J. Methane Prediction in od). Int. J. Rock Mech. and Min. Sci., Coal Mines. TEA Coal Res., London, 1975, v. 7, 1970, pp. 43-65. 77 PP* APPENDIX. --?.iODIFIED D IRECT METHOD PROCEDURE

Several procedures have been used by consideration at any point in time. The the Bureau to study the occurrence of gas main advantages of the :lDM are (1) de- in coal and oil shale. A method reported sorption or release and/or reaction rates by Darton in 1915, essentially examined of individual gas species can be accu- the gas composition of the atmosphere oE rately deter~ninedand (2) the deter~nina- a sealed can or bottle containing lump tion of these rates can be perfor~ned011 or crushed coal at various points in tine samples of snaller size or lower gas con- (1-7).' The original atmosphere of the tents than in previous direct method container was either ambient atmosphere practices. These advantages allow a more or a vacuum. The method reported by accurate and flexible characterization of Darton measured only gas released upon multiple gas source variables where the crushing the coal sample. Oxygen sorp- direct method yields information on the tion and/or reaction by coal was changing overall volume of the total also examined and in some cases was gases contained. This method can be per- considerable. formed in laboraLory, field, and under- A frequently used procedure For mea- ground settings. suring the amounts of gases released from coal uses displaced water volume PROCEDURE, CALCULATIONS, and yields the algebraic gas volume of a AND EXPERIMENTAL APPARATUS scaled co~~tainerwith a rock sample. This technique is known as the direct Procedure method and is described in references 7, 18, and 19. The gas volume can be com- The main purpose of the XDM is to ob- posed of one or more gases that have ei- tain gas volumes over a period of time to ther desorbed and thus comt ributed "posi- characterize gas desorption and reaction tive" volumes or sorbed and/or reacted, rates. Gas should be sampled more f re- contributing "negative1' volumes. Essen- quently when a rock sample is first tial, but generally not practiced, is the sealed into the container and less fre- sampling of the container atmosphere so quently at later times. Coal samples are the relative proportions of the individ- usually sampled six to eight times within ual gas species can be examined. A di- the first 2 h, a week later, and once a rect method type of test without gas com- month for each of the next 2 to 6 months. position information yields an approxima- The buildup of pressure in the sealed tion of the gas contents and desorption sample container should be minimized so rates of the rock sample, which can be that the desorption process is not inhib- erroneously small because of the negative ited. However, taking samples of small volume effects of sorption and/or reac- volume changes can introduce potentially tion of gases with the sample in the large cumulative errors. By controlling sealed container. Standard temperature pressure and atmosphere composition in and pressure (STP) corrections to these the sealed container, desorption, sorp- desorbed gas volumes are applied in gen- tion, and reaction phenomena can also be eral but not always. studied at different conditions. The method described in this report, MDM, uses the ideal gas law equation to Basic Calculation determine the STP gas volume in the sealed sample container and a gas sample The essence of this procedure is the of the container atmosphere to compute calculation of gas composition and vol- the volume of each gas species under ume (corrected to STP conditions) in the sealed sample container at a given point in time. This quantity of gas is com- Underlined numbers in parentheses re- pared with the container atmosphere at a fer to items in the list oE references prior point in time, and the gas species preceding the appendix. volume differences are accumulated. Using the ideal gas law, the volume at Differential pressure STP conditions of gas species x in a con- gauge, tainer at time interval n (V,,) is deter- miiled by 0' Selector valve, V,, = {[(~atmn+ ?ventn + dPn) Vg]

where Pat~n= atinosphere pressure, mm Hg;

Pvent = underground mine ventila- container tion pressure differential over Patm from surface if samples are sealed underground, mm Hg;

FIGURE A-1 .-Generalized apparatus. dP = differential pressure of container atmosphere with respect to (Patm + Pvent) , compositional analysis: '1 to 2 pct of mm Hg; value. 5. Sample container with at least one Tg = temperature of gas atmos- inlet and valve with volume measured: tl phere in container, K; to 2 pct of total volume (determined by weight oE water required to fill con- Vg = free space for gas atmos- tainer with and without sample to obtain phere to occupy in con- sample and free-space volumes). tainer, cm3; The Bureau's experience with gas Sam- T = standard teinperature pling of rock samples has found the de- (273 K); sign of experimental apparatus to be of paramount importance in obtaining accu- P = standard pressure (760 rate results. Hematological test tubes Inm Hg); and needles have proven very reliable as containers for sampled gas and for trans- and [x] = volume fraction of gas ference of released gas. A diaphragm- species or group x in type pressure gauge is used to measure container atmosphere, partial pressures in the oil shale sample cm3/crn3. containers. Magnahelic pressure gauges are avail- Experimental Apparatus able in a variety of ranges and are built to be accurate to within 2 pct of the A typical configuration of the appara- full scale measured. Sample containers tus is presented in figure A-1. The ex- for the oil shale core were constructed perimental apparatus used in demonstrat- of 2.5-in-diameter schedule 40 PVC pipe. ing this method was estimated to perform It is desirable for the diameter of the within the following limits: container to be somewhat larger, in this case by slightly more than 0.5 in, than 1. Barometer: +1 to 2 mm Hg. the core diameter, to facilitate inser- 2. Thermometer: f0.5 to l.OO C. tion and removal from the container. 3. Differential pressure gauge: '1 to Schedule 80 PVC caps were tapped and 2 pct full scale. fitted with quick disconnects for clos- 4. Evacuated container and gas sample ing the open end of the container under- port for gas sample or detector giving ground. The opposing ends had been closed by the gluing of schedule 40 caps A sample data collection form is pre- at the Bureau. Hansen, Swagelock, and sented as figure A-2. Milton-type quick disconnects were used on the core containers. Data Reduction

BASIC DATA COLLECTION CYCLE The first step in t,he data reduction process is to determine the atmosphere To obtain a container atmosphere data composition when the sample is first point at a given time: sealed. The ambient atmosphere is sampled for composition, and the temperature 1. Record date and time of data point and pressure are measured. The free determination. space in the container with the rock 2. Measure atmosphere pressure (Patm) sample is known, and the STP-corrected and temperature of the gas in the con- volumes of the gases sealed in the container (Tg), which can be considered to tainer with the sample are calculated by be ambient if the storage area for con- equation A-1 and represent the initial tainers does not undergo large and/or conditions. rapid temperature changes. Gas samples of the container atmos- 3. Measure barometric pressure. If phere, as well as measurements of the the test site is located underground corresponding pressures and temperature, (e.g. , coal mine) and only the surface are taken periodically, and the gas spe- atmospheric pressure is known, then the cies STP volumes are calculated by equa- ventilation pressure differential (Pvent) tion A-l for each sampling period. In with respect to surface must be measured. each sampling period, measurements are 4. Connect a differential pressure taken both before and after release of gauge to the sample container, and mea- excess gas pressure. The current initial sure an initial differential pressure gas volumes in the container are compared with respect to ambient pressure (dPi). with the final gas volumes from the pre- 5. Purge the sample circuit with con- vious sampling period: The individual gas tainer gas if dPi 2 0 or with an inert volumes before any release of excess gas gas if dPi < 0, then take a gas sample of pressure are subtracted from those calcu- the container atmosphere. This gas sam- lated at the end of the previous sampling ple is for gas composition analysis. period after release of excess pressure. 6. If assurance is required that an These differences represent the changes appropriate volume of gas from the con- in gas species volumes that have taken tainer was obtained, take an interme- place since the end of the previous sam- diate differential pressure measurement pling period. The volume changes are ap- (dpinter) after the gas sample, and applied to the cumulative gas volumes that proximate the volume (V sample): began with the initial conditions when the container was sealed. The cumulative V sample = [(dPi - d~inter)(Vg)l/(Patm) gas species volumes can then be presented graphically as a function of time. The 7. After gas sampling, if dPinter is-- STP gas volumes should be normalized to a. Positive, then bleed excess either a unit mass (cubic centimeters per differential pressure (dPf ) to atmos- gram) or volume of rock (cubic centime- pheric pressure and measure. This termi- ters per cubic centimeter) basis. nates measurements at this data point. The MDM testing discussed in this re- 3. Zero or negative, terminate port was performed underground at the data point measurement; dPf = dPinter. Cathedral Bluffs Mine, where the test If any gases are injected or air leaks environment was at a nearly constant tem- into the container, another gas composi- perature over the duration of measure- tion sample must be taken and a final dPf ments. However, core removed f ron sur- taken to terminate the measurements. face drilling in a separate study was tested and stored at a surface site, and advisable that a lost-gas technique be results were not totally satisfactory be- applied to MDM experiments in any study cause of the differing rates at which the where the rock sample is exposed to at- gas, core, and container equilibrate with mospheric conditions for more than about changing air temperatures. A constant- 1 h before being sealed in a container. temperature environment is recommended. The necessary data are available to Unaccounted for with the MDM are the perform a lost-gas correction on the gases lost between the time the rock sam- Cathedral Bluffs results, although some ple is taken and when it is sealed in the question does remain concerning the ini- container. Essential to determining the tiation of lost-gas conditions in this lost gas is determining the length of study . time that gas has been desorbing from the The one component of a rock's gas con- sample before it is sealed in the content not yet addressed is the gas remain- tainer. Previous researchers have calcu- ing in the sample after the monitoring of lated the lost-gas time for a vertical gas activity in the sealed container has drill hole filled with water or drilling been terminated. To determine this, some fluid by assuming that desorption begins form of crushing of the sample can be when the sample has traveled half the performed in a sealed container with an distance out of the drill hole (20).- In inert (nitrogen) atmosphere (1,2). The using this technique, the lost gas can be released gas volumes are determined with determined graphically by plotting the the above method. Since it takes rela- cumulative gas volumes on a graph with tively great lengths to liberate this re- the square root transformation applied to maining gas from the rock, it seems prob- the time axis and drawing a linear ex- able that this component of the total gas t rapolation to "zerov1 time. content of the rock is not significant in Lost gas was not calculated for data mine emission or gas drainage studies. presented in this report, but it is