Methane Content of Gulf Coast Domal Rock Salt

Library of Congress Cataloging in Publication Data:

Schatzel, Steven J Methane content of Gulf Coast domal rock salt.

(Report of investigations; 8889) Bibliography; p. 16. Supt. of Docs. no.: I 28.23:8889. 1. Salt mines and mining-Gulf States-Safety measure s. 2. Meth ane-Safety measures. 3. Salt domes-Gulf States. I. Hyman, D. M. (David Me). II. Title. III. Series: Report of investigations (United States. Bureau of Mines) ; 8889.

TN23.U43 [TN902... All 6228 [622 .. 8] 84... 600124 CONTENTS

Abs tract .... e .... " ...... 1

Introduction .... " .. " " ...... " ...... " ...... " " .. " .. (> .. II ...... " ...... " .. II ...... " .. " ...... " " " 2

Background ...... II .. II .. It ...... " ...... 3

Acknowledgments .. ~" " " " .. " " " ...... II .. II ...... It " .... '" " " .. "It ...... "" .. ,. .... "",. .... """ .. "" .. .. 4 Experimental tests and procedures ...... " ... "...... " 4 Crushing method"" ... " ...... " ...... "" ...... 4

Dissolution method ...... , fit ••• e .... ., •••••••• ., e ••• If .... 5 Estimations of accuracy for the dissolution test ...... " ...... " ••••• " .... . 5 Application of methane content testing as part of a methane prediction strategy 6 Disctlssion of test results ••• " ...... 6 Field test of methane 11 Results and conclusions."" ...... " ...... " •• " •• 15 References 16 A&~~~u~.~~,,--Sample data base 17

ILLUSTRATIONS

1. Location of domal salt mines on Louisiana gulf coast •• " ...... 2 2. for dissolution " •••••••• " •••••• " •• " ...... 5 3. Distribution of methane contents for 80 domal salt tested. 7 4 Salt categorization and corresponding methane content of 82 samples tested ...... 8 5 .. Methane content distribution and in

each interval ...... 1>. • .... I> • I> ..... " " " .. " .. " .... " ... " ...... """ .. " .... " .. " ..... ",, .. .. 9 6 Salt for each content interval ...... 11 7 Methane contents of domal and corresponding 12 8 .. Methane contents and occurrence with for normal salt samples...... 13 9 .. Location of holes 1 and 2 and the band of anomalous salt ected to the

10 .. of methane at vent hose outlet" ...... 14

TABLE

1 " Gas of two control salt samples ... 6 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cm centimeter liter per second

cubic centimeter m meter

°c Celsius cubic meter g gram It cubic meter per metric ton

md km kilometer mm millimeter kPa Steven Schatzel 1 and Davi d

Research Center Bureau of Mines , PA" 2

INTRODUCTION

2 volumes of methane have been pressure 1 e out- into domal salt mines as a bursts appear to have accounted for the result of an outburst of salt follow- of methane hazards in these a face blast. Outbursts mines, other mechanisms do exist for blasts that release methane gas have the release of methane into the mine been known to occur in four of the Five environment Island domal salt mines of the Louisi " 1) .. The Bureau has conducted extensive re ous gas outburst data search in coal mines aimed at do not appear in the literature, a Mine methane hazards from Safety and Health Administration the coal to or Re suggests that a large outburst methane hazards in domal salt about 13,600,000 kg of salt. Gas was re leased at an estimated pressure of about 2Underlined numbers in parentheses re 8,000 kPa and expanded to a volume of fer to items in the list of references 2,800 at preceding the appendix.

\ , ) I •

1. .. Location of domal salt mines on Louisiana gulf coast. 3 mines very different of included sediments is ect to de from coal because of different gas occur bate.. Problematic methane emissions have rence, retention, and release proper been associated with certain unusual ties Salt domes are not with or anomalous features .. g .. , included a natural fracture network nonsalt bands, interconnected void zones, outbursts) 3 .. to coal cleat, the Some of salt dome mining meth- is consid- ods are suited to with ered many authori- methane hazards.. intake and ties values from return air is difficult in many areas of zero to about 600 md have domal salt mines because of their rela In coal mines, which have much smaller

domes .. of air strata outside the salt continue to serve their purpose in into the dome but the most severe crisis situations is the result of

BACKGROUND

to their unusual structure and internal The authors the association with that hazard rences salt domes ous methane occurrences are distributed been the ect of scientific and eco- nomic interest .. of salt domes are evidence exists distribution of on in domestic and methane in the dome to be nonuniform .. However methane occurrences volumes of source mate salt dome seem to be a rial that methane and and utilization formation are not in the halite concern .. methane occurrences rich Gulf Coast The same are not in detail in the methane resist uniform distri- but ion escape of any gases literature does document some in a salt dome@ structure work in content in and its associated gas content variabil domal salt rock. some methane must be addressed when contents have been , related geo the methane content of domal information has not been limits the usefulness and zones brines

not of methane released into the mine However such a still be enriched in methane of salts

TESTS A..ND

METHOD

The first in lem of methane in domal salt of a new determine the amount of gas volume of salt@ Two tests were the Bureau and are described 8 " any gas reactions and reduces the interference to release methane upon gases the first method in of salt results of gas determina in a ball mill was tions the modified appara continuous or conventional tus exhibited a considerable scatter of Some of the data Re is used for determi the nations of coal gas Certain ball mille dis- modifications were necessary solution method tation to salt The the 5

DISSOLUTION METHOD of the The conducted at a Dissolution in a controlled than has been cited as a means of gas content side contamination atmos determination in literature and the near at tests had been conducted pressure also decreases errors the Bureau The noncor in chamber gauge and decreases rosive construction of the dissolution errors in Standard chamber allows for easier maintenance and ature and Pressure ( ( C, 760 rom time between tests. conditions.

ESTIMATIONS OF ACCURACY FOR Whatever THE DISSOLUTION TEST chamber space to is much smaller in An indication of the dissolution test the dissolution as low-end resolution was in with the The result its Chemical reagent sodium is higher concentrations of released ) was obtained as an exper- gases within the dissolution control. The reagent is chamber, which decreases the effect of .98 pure NaCI. The reagent error factors over the course is in a controlled environment, which precludes the of methane Two samples of out at near the for the dissolution chamber. to be the poor est operating condition for the experi ment. Gas volumes were then a data established for all The procedure gas samples before and after dissolution of a salt sample to be drawn from the chamber The shows 0.0002 of the three gas sam of one of the I) .. The oth no detectable methane.

For a conservative estimate of the gas detection limit, .. conditions Instead of aver- from

methane content was the methane con- of was calcu- worst case conditions as to the methane limit Data reduction indicated 0 0003 /100 g to be is considered an estimate disso resolution exceeded to be as 6

TABLE 1. - Gas of two

Before dissolution •• eee 0 .. 57 1.78 0.015 ND .. 53 1,,72 .014 1<2 After dissolution." .... " 1.13 023 .. 0002 .47 1 .. 17 .022 ND 1 .. 15 .. 022 ND 2: Before dissolution ••••• 1 .. 24 4 .. 30 .. 016 ND 1 .. 47 5 .. 10 .012 ND

After dissolution.e e• e • 1,,61 4 .. 68 e020 ND 1 62 4.70 ,,021 ND 1,,63 4 .. 71 ,,021 ND ND Not detected. lparts per million"

NOTE .. --Carbon monoxide and were not detected ..

Errors from measurements Mine emission rates for methane from all phases of the experiment and combined normal salt and the same band of anomal in data reduction have ous argillaceous salt were measured below been found to methane this level while a devel content error of about 5 decline. Normal salt emitted less than 0,,16 Measurements of mine APPLICATION OF METHANE CONTENT TESTING emissions of methane in the anomalous AS PART OF A METHANE PREDICTION STRATEGY salt ranged from 0.47 to 2.18 Average gas contents of of A field test of methane hazard evalua two types of salt from the two Belle Isle tion procedure was planned. In a Louisi core holes were 0.0046 and 0.021 CH4 / ana domal salt mine, plans were made for 100 g NaCI, two holes to be core drilled at nearly from within mine work Both holes were to be monitored for ings. The first hole was to be drilled emissions during drilling. gas flows in an area that was from a zone encountered would be measured and that had emitted very small amounts of for gas composition The cores methane during The second hole were to be tested for gas content and was oriented to intercept a continuous compared to determine the of zone of anomalous argillaceous salt known potential methane hazard prediction to have been related to increased methane gas content .. emissions .. DISCUSSION OF TEST RESULTS

A histogram of methane contents for all The various domal salt rock lithologies samples tested is presented in figure 3. were grouped into three major classes The horizontal scale shows methane con based on geological association and meth tent on a five-cycle logarithmic axis re ane emission history during mining. The quired to accommodate all of the data types were defined as follows: points. The vertical scale shows the number of samples in each methane content 1 .. Normal salt--white to gray, trans interval. parent to translucent, very rich in 7

30 I I I II I I I I I I I" II I , , I 1'1'1' , I I

i- -

20 I- -

15 i-- -

10 i--

5 i-- - z o I I I I I I II I I I I I I I I I I I I I I I I I I I I I I

E 9 sah sodium chloride, few normal salt and anomalous salt medium in normal salt are categor the same criteria as the other 2.. Outburst white to The cored were obtained gray, sometimes holes to crystal size and in a sectionG The sometimes show salt control samples are ing curved cleavage traces continuous less methane over a few centimeters, gas bubbles some 100 g NaCI, the esti times included in the salt mass. The low-end resolution, essential criterion for all outburst are intersection of the salts is that are associ abcissa and ordinate ated with an outburst .. are considered to have essentially zero methane content .. 3 Anomalous salt--includes central and edge anomalous zones, dark and rel Some of methane contents can atively continuous, frequently with be seen between the salt types.. How brine and gas seeps, occasionally with ever, anomalous salts and outburst salts petroleum seeps, argillaceous represent the of sandy.. This also includes litholo- methane-content salts. Normal salts gies such as sandstone breccias and represent the of low-methane- vite as bands that can be con- content salts.. Some of the normal salts tinuous or may be discontinuous and indicated methane contents of the same out over distances of 30 to magnitude as the control sam- 70 m. Other non-NaCI materials are in ples. Outburst range from 0.0 cluded in this to 7 4 NaCI Anomalous salts, gypsum, salts range from to 2 6 etc .. ) 100 g NaCI. Methane contents for normal salts vary from less than 0 .. 0003 to 0.31 4 shows these cm3 /100 g NaCI. with some additional delineationsG Core 8

o 0

sets tics of domestic shared more than been noted in the related to ardous conditions that some hazardous conditions in salt mines are

are as precursors to conditions Because one of features can others in were used methane to aid cates that if a dissolution test methane enriched , the presence are , the mine opera- the molecular tor should be alerted to a meth- ratio is less than ,and ane enriched zone enrichment were examined for correlation with methane enrichment@ The presence of for the indi appears to be vidual salt the gas icant and it is associated with content distribution among methane contents This The in a tabular format in are also shown All normal salt contained less than 0.1 Carbon dioxide enrichment of some NaCI Of all methane content salts was observed; classified as normal, fil1""'''''--I"'''''''''' content d sa 10 contained Anomalous salt samples show a wide NaGI. No range of methane contents. These served within this interval. share the 1.0 to 10.0 100 g NaCl of the normal salt samples tested interval with outburst salts and the contained between 0.001 and 0.01 / 0.001 to 0.01 100 g NaCl interval 100 g NaGI with 23 pct of those samples with normal salts.. Most of the anomal 7 pct ous salt samples were collected in areas of the normal salt samples contained be to be associated with edge or tween 0.01 and Oel cm3 CH4/l00 g NaCI central anomalous zones which may repre with two of the four in this in sent relatively continuous and terval higher hydrocarbons. One gas paths and/or reservoirs salt sample was between 0.1 and within the dome structure. This could /100 g NaGI and it showed allow for high methane contents where gas content. Of the 54 was within the hand sample until normal salt samples tested, 17 con- released dissolution. However, tained since these zones appear to have the gases, samples The methane contents of the anomal the escape of gas before ous salts are shown in figure 5ee A dissolution tes in low ex- salt sample is in determined methane contents. cluded here because it is geological Therefore, a low gas related to the anomalous not reflect zones included in this class. The gas that zone contents of the 12 anomolous salt sam- are with three of the sam- The of each domal salt between 0.001 and 0.01 100 g making up the total salt sample popula NaCI. Of those three , one showed tion within each gas content interval is higher hydrocarbons. The next higher in 6. The interval from 3 3 methane content interval, 0.01 to 0.1 cm 0.0001 to 0.001 cm CH4/100 g NaCI con /100 g NaCI contained five of the ano tains only normal salt samples. Anomal salts. Two of these showed higher ous salts account for about a tenth of hydrocarbons. were between the between 0.001 and 0.01 cm3 0.1 and 1.0 NaGI with one /100 g NaCl with the remainder being sample higher normal salt. The area bounded 0.01 In the 1.0 to 10 cm3 CH4/100 and 0.1 cm3 100 g NaCl represents a g NaCI group were two of the samples. group of of four normal Both of the samples in this interval salt, five anomalous salt, and two out contained higher hydrocarbons. Overall, burst salt samples. Between 0.1 and 1.0 6 of the 12 anomalous salt samples con CH4/lOO g NaCI are samples of all tained higher hydrocarbons. three salt types. The samples between 3 1.0 and 10 cm CH4/100 g NaCI consist of Outburst salts accounted for 14 of the outburst salt, for one anomalous samples tested, 11 samples indicating salt sample .. the presence of higher hydrocarbons (fig. 3D). The lowest gas content interval of It was apparent from the analyses that the outburst salts was from 0.01 to 0.1 those samples with higher methane con cm3 GH4/100 g NaCl where two of these tents had a greater frequency of higher samples were present and where no samples than those with relatively were determined to have a higher hydro low methane contents. Higher carbon content. Higher were bons can be a useful methane hazard indi all four of the samples from cator in samples where methane may escape 100 g NaGl and seven before testing .. of the samples in the 1.0 to 10.0 CH4/100 g NaCI interval (fig. 5D). 1

6...

Methane content, methane emissions, and an unbiased manner with re outburst hazards in coal have Since all salt been found to increase with discussed are included in this and a of The same relation- of methane content variabil- has been suggested for domal salt the , the mines where methane related mine disas data may involve variables that have not ters and depths have increased in been accounted for. recent years. Potential energy stored in content the salt mass can be at may be more as gas pressures between methane content and gas content will increase Of the three salt o .... W!...... , Gas content pressures were not determined the normal salts were the most abundant in this study .. and could most be found in different mines at various Mine opera- A of contents of domal tors tend to in rock salt normal salt and avoid anomalous zones .. is in A of normal salt methane contents pIes taken from the shallowest versus 8. have low methane contents with No direct and generally low , a trend of in- does creasing methane content with appear to is not clear. The sample popula- creased occurrence tion in this was not and increased FIELD TEST OF METHANE PREDICTION STRATEGY Two core holes were drilled horizontal- outlet (fig.. Methane concentrations from the 427-m level in the were measured core retrieval Inc., Belle Isle Mine when the hole was flushed with brine was drilled into an area of fluid, which the gases normal salt. Hole 2 was oriented to in out of the hole and the vent tercept a ected band of anomalous ar hose.. Methane concentrations were gillaceous salt. below 0.15 and returned to zero after the hole. At no time the Hole 1 drilled in 1982 to a drilling of hole 1 were any measurable m. Methane from the hole was methane flows detected. monitored at the vent hose 2

/ 9

7 ... Methane contents and ,...,....· .. ""'~n ..'nn

Hole 2 was drilled in 1982 to a held methanometer and were between 90 and total of 38 me The methane monitor of hole 1 was , these events occurred at hole 2 transition zone of ano work shift malous salt bands interca- in another area of lated in normal salt was encountered the mine@ The hole was not about 6 m before the ected location shut in any in-hole pressure of the anomalous zone and before because under similar circum the cut core was retrieved, a cemented have been odor was noticed. Checks for gas the blast, were made more often in this zones When returned to the drill site to collect the core was retrieved, well-defined for gas and check the bands of white salt and black behavior of the flow.. The methane con ous salt were observed. The presence of centration and the gas methane near the collar of the hole was flowed at 0.,33 indicated and increased in concentration the open ended drill steel circumstances unrelated to could be detected but forced one-half not Methane concentrations of additional drill site access in the hole were measured with a hand The hole was left open The 1

'J'-'--,-,-,,",-,orooo 00 0

c:cco 0 14

coincide with the dark bands in the core

methane contents of core sam from the transition zone collected Depth of mining; 427 m in hole 2 were not as enriched as some anomalous salt were enriched the of normal salt core in one instance / Hole 2 drilled in July 1982 contained Three of Methane emissions first encoun tered at 38 m, approximately 6.1 m the four were within a methane before the band of anomalous salt content interval zone of the three salt between 0 01 and Oe1 /100 g NaCI. A more continuous se quence of anomalous salt about 6 m and continues on for meters. The forced termination Intake halted the collection of more in this zone Pre- data taken at several locations this anomalous zone indicate that FIGU 9'JJ .. Location of hoi es 1 and 2 and the band methane content is the center of anomalous salt ected to the 427"m levelll of the zone than at its

FIGURE 10111 '" Continuous of methane at vent hose outl et. 15

RESULTS AND CONCLUSIONS

Gas movement in salt is not gases. Methane contents of of well defined as gas movements in anomalous salt from 0 001 to 0.01 some characteristics 100 NaCI, a methane content in- gas terval normal salt and movement, fracture from 1.0 to 100 g NaCI where network, do not occur in salt domes. the group of outburst is Methane occurrences in domal salt are found. It is unclear whether anomalous nonuniform. of five orders salts that are discontinuous and not as of in methane content indicates sociated with or central anomalous that the methane does not in zones are methane enriched. the salt and may be limited to mi localized gas and central anomalous zones will Thus, determination of gas con- emit much methane than tent can information normal salts 0.47 to methane hazards, 2.18 m3 /t) with sirable sites will for increased Normal salt methane contents have been methane emissions. found to be low. Over 90 of the normal salt tested con- indicates that normal salt tained less than 0 01 100 g NaCI does a measurable gas flow. There are wide ranges of methane en central anomalous zones have richment in normal versus outburst gas flows in some mines. The salts criteria have been initial gas flow from a 7.6-cm-diam drill forth as associated with outburst hole in a band of anomalous salts (increased size, included 0.33 with methane concentra- gas bubbles, contorted cleavage sur tions 93 faces, of a core , etc.) but these features were not The of is dent in the outburst salt common methane content salts For the purposes of this and in low methane content association with an outburst salts. They may be useful in sential criterion for the the anomalous salts where methane may es- cation. However, where a out- cape from the before burst zone is being breached testing. for the first time, sociation cannot be used and shallow domal salt mine levels features are unreliable. The dissolution had generally low methane contents, no test can information trend of methane content with to distinguish outburst salt. can be seen from the 80 salt sam- There are no other methods tested. Carbon dioxide enrichment available. The methane content of out may coincide with methane enrichment but burst salt is high. The outburst does not appear to be as variable as salt samples had a methane content methane. than nearly all of the normal salts in cluded in this paper. of an ro- core program, gas

Anomalous salt oa=V4~:O, contents from dissolution testing, and from what was identified as one mine's geologic mine could edge anomalous zone, have variable allow a mine operator to assess the po methane contents because of the tential for encountering methane gas. of these zones to

APPENDIX.--SAMPLE DATA BASE PRINTOUT

SAMPLE TYPE DE CONTENT H ER NUMBER (CM3/100G) ---~~------10. W C 195 W NORMAL C 201 W NORMAL C 46.196 W C C2H6, C3H8, C4H 47 .. 195 W C 65 .. 155 Z D , C , C 12 68 .. Z D 159 Z D Z D Z B Z D Z ANOMALOUS D 0 .. 7000 C2H6, C3H8, 7 Z D 2 .. C2H6, C 80 .. 189 W OUTBURST C 1.6000 C2H6, C3H8, 80 .. W OUTBURST C 1.. 4000 C2H6, .. 255 W C C , C 2 82 .. 255 W OUTBURST C C2H6, C3H8, 83,,252 W OUTBURST C C2H6, 84 .. W C C2H6, C3H8 W C 86 .. 253 W OUTBURST C C2H6 87 .. 256 W OUTBURST C C2H6, C4H1 C 88 .. 257 W C C2H6 89 .. 274 X NORMAL B 0.. 0006 90 .. X B 91 .. 273 X B 0.. 0000 92 .. 273 X B 0 .. 0028 C2H6 93 .. X NORMAL B 0.. 0000 94 .. 272 X NORMAL B 0005 95 .. 271 X NORMAL B 0 .. 0000 X NORMAL B 0.. 0004 97 .. 356 X NORMAL B 0.. 0000 98 .. 361 X NORMAL B 0.. 0005 99 .. 361 X NORMAL B 0.. 0000 100 .. 027 X NORMAL B 0.. 0000 101 .. 362 X NORMAL B 0.. 0006 102 .. 362 X NORMAL B 0 .. 0009 103 .. 363 X NORMAL B 0,,0017 C 104 .. 363 X NORMAL B 0.. 0000 105 .. 028 X NORMAL B 0.. 0000 106 .. 364 X NORMAL B 0000 107 " X B 0.. 1 X B 0.. 1 X B 0.. 0026 C 1 X B 0000

* A < M < B < M < C < M < 0 18

SAMPLE NE SALT TYPE CH4 CONTENT HIGHER HYDROCARBONS NUMBER (CM3/100G) -~~~------111 .. 032 Y OUTBURST D 1 .. 5000 C2H6 112 .. 032 Y OUTBURST D 1 .. 1000 11 033 Y NORMAL D 0890 C2H6 114 .. 033 Y NORMAL D 0 .. 3100 C2H6 115 .. 034 Y OUTBURST D 0 .. 6200 C2H6 116 .. 035 Y ANOMALOUS D 0 .. 0350 117 .. 038 Y ANOMALOUS D 0 .. 1200 951 .. 351 X NORMAL B 0 .. 0000 1001 .. 210 Z NORMAL C 0 .. 0021 1002 .. 214 Z NORMAL C 0 .. 0020 1003 .. 214 Z NORMAL C 0 .. 0130 1004 .. 166 Z NORMAL C 0 .. 0070 1005 .. 168 Z NORMAL C 0 .. 0039 1006 .. 168 Z NORMAL C 0 .. 0053 1007 .. 168 Z NORMAL C 0 .. 0110 1008 .. 169 Z NORMAL C 0.0024 1009.175 Z NORMAL C 0 .. 0032 1010 .. 175 Z NORMAL C 0050 1 1 .. 176 Z NORMAL C 0008 1012. Z NORMAL C 0 .. 0029 1 174 Z NORMAL C 0 .. 0032 Z NORMAL C 0 .. 0027 2002 .. Z NORMAL C 0 .. 0030 2003 .. 245 Z NORMAL C 0 .. 0110 2004 .. 246 Z NORMAL C 0 .. 0066 2005 .. 250 Z NORMAL C 0 .. 0090 2006 .. 252 Z NORMAL C 0 .. 0019 2007 .. 258 Z NORMAL C 0 .. 0011 2008,,259 Z NORMAL C 0047 2009 .. 260 Z NORMAL C 0 .. 0012 263 Z NORMAL C 0 .. 0028 2 1 .. 236 Z ANOMALOUS C 0 .. 0120 1 237 Z C 2011 .. 238 Z ANOMALOUS C 0 .. 0060 2011 .. 251 Z ANOMALOUS C 0 .. 0390 C2H6 * DEPTH: A < 230 M < B < 380 M < C < M < D

<>U. S. GPO: 1984-705-020/5038 INT.-8U.OF MINES,PGH.,PA. 27683