GeocheJtnieal Studies of Nai1:ural Gas
Part 1. HYDROCARBONS IN WESTERN CANADIAN NATURAL GASES'
By BRIAN HITCHONt
ABSTRACT mechanisms inducing modification vapour. Of the common "gases" of the regional variations include available for examination within Natural gases in Western Canada undersaturation of the formation are found in sediments ranging in water with natural gas at present the accessable portions of the age from Cambrian to Tertiary. reservoir temperatures and pres Earth, hydrocarbons heavier than The hydrocarbons in these gases sures, and variations in the solubil propane will be in the form of va Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 are described and evaluated in ities of the hydrocarbons due to pours, Depending upon the actual terms of their geochemistry, origin, changes in flow direction and move migration and accumulation. ment into regions with formation conditions pertaining, so also may be the acid "gases" hydrogen sul Hydrocarbons are the chief com waters of different salinites. ponents in the majority of the phide and carbon dioxide, and the nearly 3,000 analyses of natural INTRODUcrION hydrocarbons ethane and propane. gases from Western Canada. Most Throughout these papers both va gases contain more than 90 per HIS paper is the first of a ser pours and true gases will be desig cent hydrocarbons, but as little as T ies concerned with the geo 0.26 per cent is present in some. nated as gases for ease of descrip The preferred order of abundance chemistry of natural gas in West tion. of the individual hydrocarbons is ern Canada. It discusses the bulk methane :> ethane:> propane > composition of natural gas, with Gases are minerals of a unique" n-butane:> isobutane:> isopentane particular reference to the hydro type (:1). In nature they are form :> n-pentane :> hexanes :> hep tanes. A decreasing n-butane:iso carbon components. Other papers ed as the result of a variety of pro butane ratio is accompanied by an will cover the geochemistry of hy cesses, including the actIon of high approach to unity of the isopentane drogen sulphide, carbon dioxide, temperatures, chemical reactions, :n-pentane ratio. Study of the C4 nitrogen and helium. biochemical transformations and :md Cs isomers indicates that no reservoirs are in thermodynamic radioactivity. Some gases, inclUd In each paper an attempt has ing components of the atmosphere, ::quilibrium. Variations in the C-t been made to establish the origin 3.nd Cs isomer ratios are attributed are of primordial paragenesis, and :0 catalysis by the sediments. of the components being studied formed an integral portion of the and to note important relationships 'Methane probably originates due early Earth. Others are of more to direct synthesis by bacteria, al between the components. Maps recent origin. There is a large though it is also a by-product of have been used to illustrate varia number of individual components, biochemical reactions that are able tions in the content of the compon both true gases and vapours, com to generate hydrocarbons with from ents from one region of Western two to ten carbon atoms. These re prising terrestrial gases, although actions include low-temperature de Canada to another, within a series only a few of these are considered carboxylation and reductive deam of stratigraphic units ranging in sufficiently common to warrant dis ination of amino acids and decar age from Middle Devonian to Late cussion here. boxylation of fatty acids. The part Cretaceous. The geochemical in played by bacteria in these reactions is probably important, although the formation and the maps of regional The habitat of terrestrial gases mechanism is not known with any variations have been used to relate ranges from large accumulations degree of certainty. the composition of the natural gas such as the atmosphere and natur Natural gases with relatively low es to the environment of deposition al gas deposits, comprised essential contents of methane and high con of the sediments, to the present en ly of a few major components, tents of heavy hydrocarbons are vironment within the Western Can through gases dissolved in the sea found in sediments deposited in ada Sedimentary Basin and to the and in formation waters, to those basinal environments. In sediments deposited in shelf environments the present flow regime of the forma associated with hot springs, vol natural gases have higher con tion fluids. canoes, and present as minute in tents of methane and lower con clusions in minerals. This series of tents of the heavy hydrocarbons. It is hoped that the results of papers will be concerned chiefly For pre-Cretaceous strata in West this study will be of interest and ern Canada, the depositional basins with natural gas deposits, but approximately coincide with the benefit to those whose task is the where pertinent, attention will be present structural basin, and fluid exploration for natural gas. directed to other habitats of gases. flow is updip. For Cretaceous strata, sediments in the structural basin Definition of natural gas contain natural gases with relative Gases in nature ly low contents of methane except Examination of the literature where modification due to downdip The attenuated state of matter concerning the composition of crude fluid-flow has occurred. Possible above its critical temperature (Tc) oil and natural gas shows some is termed _a gas, and below it a discrepancies in the definitions used by various authors. Implicit in the :t:Research Geologist, Research definitions of Rice (2) and Howell Council of Alberta, Edmonton, Al "'Contribution No. 208, Research berta, Canada. Council of Alberta. (3) is the unnecessarily restrictive 60 Journal of Canadian Petroleum ':'\ assumption that natural gases con sulted in reports by McLennan et Gross composition of natural gas ,'.~, sist solely of gaseous hydrocarbons. al. (11), Elworthy (12)&(13), and ,-,j Examination of the analyses in " Therefore the term natural gas has Rosewarne and Offord (14)' Com~ ;.1 been redefined, paraphrasing the pilations of analyses were publish dicates that the major components "j defiirition of crude oil quoted by ed by Stansfield and Nicolls (15), are hydrocarbons, nitrogen, carbon ,1 Howell: and Rosewarne and Offord (16) & dioxide, and hydrogen sulphide These components make up over ...., ,,' (17), Although all these papers Crude oil-A liquid in its natural were consulted for comparative 99,5 per cent by volume of the maj state and environment, com data, recent developments in analy ority of gases. Only in very rare posed principally of hydrocar tical techniques have rendered most instances do other components such bons, usually with sulphur, nit of them of historic interest only. as helium and hydrogen total more rogen and oxygen as elements than one half of one per cent by or compounds or both, and More recent sources of published volume. A tetrahedral composition traces of other elements and analytical data used in this study diagram (Figure l)-with hydro c9mpounds. comprise the reports of the Fuel carbons, nitrogen, carbon dioxide Research Laboratories of the De and hydrogen sulphide as the end 'Natural gas-A gas in its natural members-thus essentially describes state and environment, com partment of Mines and Technical the compositions of all gases exam monly composed principally of Surveys (Offord and Goodspeed, ined. In more than 75 per cent·of hydrocarbons, usually with hy (18); Offord (19); Offord and Yates Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 the gases the content of hydrocar drogen sulphide, nitrogen and (20); Offord et aI, (21»), the Al bons is more than 90 per cent by carbon dioxide, and traces of berta Oil and Gas Conservation volume. The non-hydrocarbon end other gases. Board (22), and the Saskatchewan Department of Mineral Resources member compositions are approach Implicit in these definitions is a (23), Special compilations of sel ed in only 0,3 per cent of the gases. genetic relationship between crude ected components in Alberta nat The block diagram in Figure i in oil and natural gas. This genetic ural gases have been prepared by dicates the composition of the non implication is important, because Shaw (24)&(25>. In addition to hydrocarbon components in over 90 all physical variations exist in na these published data, the acknowl per cent of the analyses examined. I, A major portion of the gases con ,,- .... :. ture, and under conditions of ex edgments at the end of this paper '.'., treme temperature and pressure, indicate the sources of other an tain less than :five per cent of each natural gas and crude oil become alyses used. component, with amounts over five physically indistinguishable (4, p, Per cent 3581. The above definition of nat Per cent Analyses ural gas applies throughout this Hydro. within carbons each series of papers and allows the in block elusion of those uncommon gases 50.3 composed essentially of hydrogen ::::~4~~~~~~1.95~g : 90 28.1 sulphide, nitrogen, carbon dioxide ____·90 .. "', or other gases. ~- 80 14.2 /"="' 80 GEOCHEMISTRY AND ORIGIN OF HYDROCARB NS 5,7 Low MOLECULAR WEIGHT '11> 60 ALIPHATIC HYDROCARBONS 1"';::::----,.",--_6 0 One of the most characteristic fractions of most crude oils, and '.- , commonly the chief components of __30 natural gases, are the low molecu lar weight aliphatic hydrocarbons, ranging from methane to hydrocar bons with up to ten carbon atoms. 0.3 Ethylene (4, p, 361) and cycIopen tane (5) have been found occasion ally in natural gases but as neither N, were recorded in any gases from '0 " e, of. Western Canada, they are not con~ ',' '0'l. 10 " , sidered here. 5 0 Bource of analytical data Nearly 3,000 analyses of natural 15 1.5 gases from Western Canada were examined in this study. Early pa 10 3,3 pers containing summaries of the N 0,* geology of natural gas in Western U Canada include those of Clapp et 67.3 al. (6), Elworthy (7) & (8), and 0 , Slipper (9). Further references are 10 given in McCrossan (10). Follow !V2 % 20 ing the First World War, interest Figure 1.-Gross composition of natural gas in the Western in helium resources of Canada re- Sedimentary Basin, based on nearly 3,000 analyses. Technology, Summer, 1963, Calgary 61 r per cent being preferentially nitro relationship between the relative V gen, carbon dioxide and then hydro mole fractions of the butane iso Z 100 W gen sulphide. mers and the relative mole frac :> METHANE a Although extensive comparable tions of the pentane isomers for w natural gases from 66 major oil ~ 50 data from basins elsewhere in the .... world are not so readily available, and gas fields in Alberta. The pro Z portions of normal isomers of the w those data that are available indi V cate essentially similar variations. C.l and Cs hydrocftrbons increase 234567 '"W sympathetically to one another, 0. RELATIVE ABUNDANCE Relationships among the hydro with respect to the total fraction r carbons of C.I and Cs hydrocarbons, irres- V 2100 Nearly 3.000 analyses of gases w '-0 :> ETHANE from Western Canada were exam I T I I a .. (,0' fIeld w ined to determine the preferred ,..,. c< order of abundance of the hydro , • 0.1 fIeld ~ so j] 0.9 I- - .... carbons. The results are summar z ~2 w jzed in Figwoe 2 and Tables I, II and <2 V 0...... :...... 0.8 - o III. I- . w 234567 .• '"0. 1 Z RELATIVE ABUNDANCE Methane Was the most abundant .~ Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 hydrocarbon in 99.95 per cent of , 0.7 - ,,% • . - >- r • \t . ~.. ... ~ 100 the analyses (Table n, being con J • ..... " I w siderably more abundant than eith ... ~ :> PROPANE ~ .' a er ethane or propane in the maj 0.' l- • . . • - w J . . ~. :: 50 ority of gases. Where the content ~ ...... of ethane was greater than that of I- - Z 0.' w methane, ethane was only slightly V oL--,-...Ja c< more abundant than methane. I , , ., w 1234567 Where the contents of ethane and 0-' 0. RELATIVE ABUNDANCE 0.' 0.' 0.' 0-' 0.' 0' r propane were equal, or when the r•.,"."." J V content of propane was greater Llolo' penton.. ~ 100 N-BUTANE than the content of ethane, neither Figure 3. - Relationship between :> a gas was present in appreciable butane and pentane isomers in w natural gases from major oil and quantity. These minor variations ~ gas fields in Alberta. '".... 50 probably arise because of differ Z pective of the presence of associat w ences in sampling or are due to ed. crude oil, or of the depth or V analytical errors. The relationship '" oL--,-_~- formation temperature. w 12.34567 between methane - ethane - propane The isomeric ratios between bu a. RELATIVE ABUNDANCE and the butanes is summarized in tanes and pentanes in natural gas r Table II. N-butane is preferably V es indicate that the relative con Z 100 present in greater amounts than W fSOBUTANE centrations of the isomers are not :> isobutane, no matter what the rela in thermo-dynamic equilibrium at a tionship of methane, ethane and w reservoir temperatures. Rossini ~ 50 propane. Table III contains the re '" (26, p. 161) has shown that at .... suIts of an examination of 430 gas Z about 75°C. (average reservoir w analyses reporting hexanes and V temperature), equilibrium condi heptanes-plus, or hexanes-plus. The 2 .3 4 5 6 tions would result in a proportion '"w difference in the ratios of the bu 0. RELATIVE ABUNDANCE of n-butane:isobutane of 0.4:0.6, tane and pentane isomers is quite > and of isopentane:neopentane:n v marked. With respect to the pen Z 100 pentane of 0.6:0.35:0.05. Non-equil tanes considered alone: a'5 150 PENTANE ibrium conditions are indicated in w isopentane > n-pentane (69.08%) natural gases by the facts that the '"~ so isopentane = n-pentane (19.76%) concentration of n-butane is com .... n-pentane isopentane (11.16%) z > monly more than that of isobutanc, w V Hexanes were least abundant in and that neopentane is generally o. L-'----'-----'-~_ 98.82 per cent of these analyses. absent. '"w 12.3·4567 0. RELATiVE ABUNDANCE Two relationships may be adduc Sachanen (27, PP. 17-19) discuss >- ed from these data. First, the pre ed the relationship of isomers in ~ 100 crude oils and concluded. that their w ferred order of abtUldance is me :> distribution was not consistent with a N-PENTANE thane > ethane > propane > w n-butane > iso-butane> isopen thermo-dynamic equilibrium condi :: 50 tions. He noted, however, that iso .... tane > n-pentane > hexanes z > heptanes. This preference is merization reactions may proceed w V summarized in the frequency dia in the presence of certain hetero '" oL--'------'_"-->...... J_ geneous catalysts such as alumina~ w 1234567 gram in Fig'u,re 2. Second, there is a. RELATIVE ABUNDANCE a tendency for a decreasing n-bu silicate systems. This is a problem tane:isobutane ratio to be accom that should receive more attention. Figure 2.-Preferred order of abun panied by an approach to unity of Dadashev and Salayev (28) have dance of hydrocarbons in natural gases from the Western Canada the isopentane:n-pentane ratio. demonstrated that in certain areas Sedimentary Basin. The data in Figwoe 3 indicate a of AZE'rbaidzhan the strongly char- 62 Journal of Canadian PetraJoum ·T·~~------_....._._.. ---_.. _- ."
TABLE I. position of the natural gas with Relationships Among the Hydrocarbons emphasis on the n~n-hydrocarbon METHANE ETHANE PROPANE components. Order of Magnitude Frequency Per Cent Origin of methane ethane propane 97.28 Methane > > Methane occurs freely in natur-e. Abwtdant evidence is available to ethane = PJ;opane 0.27 Methane > indicate that certain species of bac teria are able to synthesize hydro-: propane ethane 2.17 ""J- Methane > > carbons directly, and the bacterial production of methane by a variety Methane > ethane some other> propane > hydrocarbon 0.23 of processes during the anaerobic ", decomposition of organic matter is well established. Processes ob propane 0.05 Ethane > methane> served include production from ,: .~-~ ..' carbon dioxide derived from the in 100.00 complete oxidation of fatty acids (30)&(31), from almost any organ Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 ic material 'except· hydrocarbons, TABLE II. ethers and lignin (32), from var Relationships Among the Hydrocarbons ious acids but not cellulose (33), METHANE ETHANE PROPANE BUTANES and by reactions involving carbon When- monoxide and hydrogen (34) or carbon dioxide and hydrogen (35). .!§.Qpentane > n-pentane (70.75) The production of methane by the ~-butane > isobutane(89.65)--- then isopentane = j!'"pentane (17.83) catalytic cracking of organic maw g-pentnne > isopentane (lL42) terial in sediments during matura tion, and an origin from amino acids or fatty acids are discussed 1!Qpentane > .n-pentme (66.67) elsewhere in this paper. n-butane isobutane (2.55)--- wen .!§Qpentane = .n-pentane (20.83) n-pentane > .!§.Qpentane (12.50) Several authors (36),(37)&(38) have studied methane- produ~g bacteria obtained from core samples. ~ntane > n-pentane (57.45) isobutane- > n-butane (7.80) --- then i§.Qpentane n-pentane (34.04) They concluded that the methane .. !:-pentane > isopentane (8.51) is produced in biOChemical reactions involving carbon dioXide and hydro gen. Evdokimov (38) suggested TABLE III. that the hydrogen may be' derived Relationships Among the Hydrocarbons partly from hydrocarbons and part .. BUTANES PENTANES , (Frequency per cent in parentheses) ly from the decomposition of water .,i by natural radioactivity. It seems Order of Magnitude Frequency Per Cent generally established, therefore, that the bulk, If not all of the Methane ethane > propane n-butane > isobutane 85.01 methane found in the sediments 'r," > propane > 'fsobutane n-butane 7.20 :<~< ~~.:;~ Methane > ethane > > > owes its origin to biochemical re .. Methane > ethane > propane > ;ll-butane TsobutaDe 2.47 actions of various types. Indeed, 94.68 Nechaeva (37) has suggested that the production of methane in an· Methane ethane px:opane n-butane > isobutane 0.08 cient sediments of the Second BakU > isoburane g-butane 0.08 Methane > etlJane ~ propane > is a current process. Methane > ewane > propane .a-butane isobutane 0.08 0.24 The hydrocarbons present in small amounts in gases associated Methane > ethane = propane > ~utane > B.-butane 0.30 with volcanoes, post-volcanic pro Methane > propane> ethane > a-butane > isobutane 3.81 c~sses, metamorphic and magmatic Methane > propane> ethane isobutane > a-butane 0.07 rocks may have originated from Methane > ethane > n-butane > W'0pane > isobutane 0.75 Methane ethane isobutane> propane .> a-butane 0.15 the combination of carbon from > > carbonaceous rocks with dissociated 5.08 water vapour caused by tlie intru 100.00 sion of molton rocks (39)&(60). acteristic n~butane:isobutane and Western Canada Sedimentar.y Ba n-pentane:isopentane ratios may be sin indicate no significant variation Origin of heavier hydrocarbons used to distinguish natural gases of the n-butane:isobutane and n from different stratigraphic units pentane:isopentane ratios, in differ It has been stated above that within the Tertiary sediments. Sim ent areas, in different stratigraphic methane, the first member of the ~'. :' ilar variations were found in asso wtits, with the presence or absence aliphatic hydrocarbons, occurs free ciated volcanic muds (29). The of associated crude oil, by the type ly in nature and probably owes its large number of analyses from the of crude oil, or with the gross com- origin to biochemical reactions of Technology, Summer, 1963, Calgary 63 ------
various types. Ethane, propane, component in dissolved gases in vironmental control of the deposi the two butanes and the three pen formation waters (49)&(50) may be tion of organic matter in the sedi tanes have not been reported as significant. ments. Thus basinal sediments forming constituents of living or 'Decarboxylation mechanisms may contain small quantities of organic ganisms or as metabolic products also result in the production of matter, enriched in paraffinic hy (40), Indeed, n-heptane is the low hydrocarbons from fatty acids. drocarbons as compared to sedi est molecular weight member of Thus acetic acid may give rise to ments deposited on the shelf area this series known to be a constitu methane, propionic acid to ethane, which have greater amounts of or ent of living organisms; it is a n-butyric and isobutyric acids to ganic matter with more nonpar component of turpentine in certain propane and so on. Fatty acids are affinic hydrocarbons. With respect species of the genus Pinu,s (41) & abundant in nature but occur in to natural gases, the generally re (42), However, ethane, propane ancient sediments in very small ducing basinal environment con and butane are reported as meta quantities. Although possibly not tains abundant hydrogen sulphide bolic products of the bacterial an the major source of the hydrocar (and associated carbon dioxide), aerobic decomposition of organic bons, they are at least a potential whereas there are higher contents substances (43) and as exudates source. Cooper and Bray (51) have of nitrogen in the shelf regions. from some plants (44), and ethane postulated a mechanism by which The situation with respect to de and propane have been detected in decarboxylation of fatty acids in veloping hydrocarbons in natural microbially-produced gases from recent sediments will yield increas_ gases is not at all clear, although Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 the decomposition of sludge (45L ing quantities of low molecular there is circumstantial evidence to Evidence concerning the direct weight n-paraffins having a carbon support the idea of control of me bacterial generation of hydrocar preference distribution similar to thane composition by basin-shelf bons heavier than methane is thus that of crude oil. The Kolbe Syn position of the sediments. These inconclusive and it appears that in thesis, with accompanying loss of environmentally controlled varia direct bacterial synthesis must be carbon dioxide from the fatty acid, tions give rise to small quantities sought for the production of the is probably the most reasonable re of paraffinic crude oils associated bulk of the heavier hydrocarbons. action. Competent biochemical de with natural gases rich in hydro However. heavy hydrocarbons can carboxylation mechanisms are not gen sulphide and carbon dioxide in be attacked and broken down by known with any degree of certainty. the original basinal regions. On the hydrocarbon - oxidizing bacteria, original shelf areas, large quanti which act preferentially upon the In summary, it can be stated that ties of asphaltic crude oils are asso heavier hydrocarbons to yield methane probably originates due ciated with natural gases rich in simpler hydrocarbons and carbon to direct synthesis by bacteria, al nitrogen and methane. dioxide, and theoretically could pos though it is also a by-product of sibly generate all the low molecu (biochemical) reactions that are Several factors have interfered lar weight aliphatic hydrocarbons. able to generate hydrocarbons with with the pattern of regional varia tions developed by environmental The work of several authors (46), from two to ten carbon atoms. control. In Western Canada study (471&(48) has confirmed the pau These reactions include low tem perature (below 200°C. and possib of the trends is complicated to city of Cz to C10 hydrocarbons in some extent by the fact that up to both' recent sediments and recent ly below 100°C.) decarboxylation Cretaceous time the major basinal sediment gases, as compared to and reductive deamination of am ino acids, and decarboxylation of facies lay to the northwest or west, their abundance in ancient sedi approximately coincident with the ments and natural gases. It is im fatty acids. The part played by bacteria in these reactions is not present structurally deeper parts portant to note, however, that these of the basin and the Roc]i;:y Moun hydrocarbons are volatile and that known, but it probably is import ant. tains. It is thus difficult to sep sampling is difficult. Nevertheless, arate effects due to basin-shelf con these findings strongly suggest REGIONAL VARIATIONS trol from effects due to increased that they are formed over a maturation accompanying increased The composition of natural gases long period of time. Erdman pressure and temperature with from the Western Canada Sedimen~ (40) has suggested that decar depth. Only in Cretaceous time boxylation and reductive deam tary Basin varies vertically and was the marine connnection with ination of amino acids in sedi areally. The vertical trends do the Pacific Ocean finally severed. ments will yield all the aliphatic exist, although there can be little The major depositional basins then hydrocarbon isomers with the ex vertical exchange of fluids due to lay to the north and south, with ception of neopentane, which is a the very low vertical as compared practically the entire area of Al rare constituent of natural gases. to the horizontal permeability. On berta forming a shelf environment It is of some interest to note that a regional scale within each strati during the deposition of sediments of the four major amino acids pres graphic unit, there is a relationship of the Ellerslie Formation and the ent in recent sediments, only three between the composition of crude are of major importance in ancient oils, and natural gases, and the en Mannville Group. sediments. Glycine, which shows vironment of deposition of the sed In order to relate regional varia the greatest relative decrease, gives iments. This basin-shelf control tions in composition to the migra rise on decarboxylation and reduc concept has been outlined by the tion path of the natural gas, poten tive deamination to methane. The author (52) and considered more tiometric surface maps were con facts that it is the only amino acid completely elsewhere (53L It may structed for all pertinent strati to give rise to methane, that it be summarized briefly as follows. graphic units. These maps indi shows the greatest relative de Study of the volume and type of cate the elevation, relative to sea crease, and that methane is by far hydrocarbons in recent sediments level, of the surface to which fresh the most abundant hydrocarbon in from several depositional basins water would rise in wells drilled to both natural gases and the major lends support to the concept of en- any particular aquifer. The direc- 64 Journal of Canadian Petroleum __ ~.'--,--~_~ ·.~ '_.o __ . --.-,
non of fluid flow may be indicated at higher formation pressures than in natural gases from Devonian conveniently by arrows drawn at in shallower sediments updip to the strata and the contents of methane ./. right angles to the potentiometric east. The regions of high forma in natural gases from post-Devo surface contours in the direction of tion pressure have lower contents of nian strata have been chosen for the lowest elevation. These arrows methane and higher contents of illustrative purposes, and for ease
are contained in the hydrocarbon ethane-plus in their natural gases of contouring, because of the vari _0" " regional variations maps used to than those in the areas of lower able range in total hydrocarbon illustrate this paper. pressure. These regional trends content throughout the stratigraph are consistent for all stratigraphic ic column. Variations in the fluid flow pat units, even though the direction of tern para)lel those for natural gas flow of the formation fluids is Effect of gas-oil ratio and separator composition, suggesting migration downdip in certain areas of the pressure on gas composition under a pressure gradient. How Cretaceous stratigraphic units con Quite apart from environmental ever, the direction of flow in most sidered here. characteristics and alteration dur Cretaceous strata differs from that ing migration, the composition of in pre-Cretaceous strata. This These facts suggest the control natural gas may be affected by phenomenon will be discussed more of the non-methane hydrocarbon man-controlled processes used dur fully elsewhere In this paper. It variations, not by basin-shelf en ing the production of the gas. These should be noted that the control of vironment, but by maturation. They include: rate of production, which Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 both the salinity trends of the for support the indirect biogenic matur affects the produced gas-oil ratio; mation water and the fluid flow ation concept for the origin of the sampling point with respect to the pattern is governed primarily by heavy hydrocarbons. Some authors, hydrocarbon-water contact in the the degree of compaction of the for instance Dobryansky (55), sup reservoir; and the physical operat sediments (54). The degree of com port the concept of the total gen ing' condition of the separators. paction is related to the lithology. eration of crude oil and natural gas Other phenomena may also be oper Thus the lithology controls the by a maturation process, with the ative, but lack of reliable correla trends of the high-permeability natural gas originating as a by tions between these factors and channels along which formation product of the crude oil. It is diffi produced gas composition preclude fluids migrate from regions with cult to accept this theory in its pertinent discussion. high potentiometric surfaces to re entirety. gions with lower potentiometric In this series of papers, selected A study* of some oil and gas surfaces. This explains the close maps have been used to illustrate pools In Alberta Indicates that the relationship of the pattern of iso regional variations in the composi effect of varying produced gas-oil concentration contours of natural tion of natural gases in Western ratio and separator pressure upon gas composition with the fluid flow Canada. The above comments wpl the composition of the natural gas pattern. The maps illustrating this serve to introduce these maps and may be generalized, as in Figure 4. paper show consistent regional var to indicate features of the maps It will be seen that the volume per cent of nitrogen, carbon dioxide and iations in the content of total hy consistent with the basin-shelf con ;- ./. " drocarbons and methane, and sim trol concept and the maturation hydrogen sulphide is only slightly ilar maps may be constructed for theory. Both processes have doubt *The writer is indebted to D. R. ethane-plus, for all stratigraphic less been operative and their rela Shaw, Ohief Ohemist, Oil and Gas ...... units. In every unit the fluids in tive importance will be discussed Oonservation Board, Edmonton, Al~ the structurally deeper sediments following presentation of the maps. berta, for this timely study and for permission to reproduce the two adjacent to the "Disturbed Belt" arE? The contents of total hydrocarbons graphs.
'00 100
METHANE
I I Z Z w w U U a: a: w w a. a. w w :E ::;; => => -' --' o ETHANE o ETHANE > PROPANE > PROPANE N-BUTANE N-BUTANE :'." . .' " . 150BUTANE ISOBUTANE ~1~,~? .,~ .. . ' .-.
PRESSURE (p.s.i.) GAS - OIL RATIO ~igure 4.-Schematic diagrams showing the effect of produced gas-oil ratio (left) and separator pressure (right> upon the composition of natural gas. Technology, Summer, 1963, Calgary 65 Lower Palaeozoic strata in the Wil Corresponding contents of hydro liston Basin, analytical data were carbons heavier than butane range not available. In the potentially from generally less than 0.1 per commercial, helium-rich natural cent in northeastern British Colum gases in the Upper Cambrian sedi bia to over 5 per cent at the Red ments of southern Saskatchewan, Earth field. To a certain extent hydrocarbons range from 0.26 to these trends of heavy hydrocarbon 2.87 per cent (56). contents are a reflection of the con~ trast in relative formation pres Natural gases in Middle Devonian sures between the deeper, low-pres strata sure gas fields in northeastern Major gas fields have been found British Columbia and the shallow in northeastern British Columbia er, high pressure occurrences in with combined original in-place re northern Alberta. Thus the eleva serves of nearly 1,900 billion cubic tion of the potentiometric surface feet, although some minor oCCur at the Clarke Lake-Fort Nelson rences are also known from north field in northeastern British Colum ern Alberta. Total hydrocarbons in bia is about 1,600 feet above sea these gases range from 75 to 95 per level, and 2,450 feet at the Red Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 cent, with methane from 50 to 90 Earth field. per cent. The content of ethane plus is characteristically very low Natural gases in Upper Devonian (generally less than 0.5 per cent) Beaverhill Lake Gronp stl'ata in natural gases from northeastern Analyses are available for natur 'CA« " ~"" "-----=--.-'0 • .. British Columbia, increasing to be- al gases from carbonates immc tween 4 and 20 per cent in north- diately below the predominantly ar LEGEND western Alberta. About 30 per gillaceous beds of the Beaverhill ·_~·:·JS"b"cP cent ethane-plUS is found in the Lake Group in northwestern Alber ~ D'.do-d',"Jr~,o'o~ C' 'i"ol ," pTo' ~ q '·IC~- hi, natural gas associated with the ta, from carbonates near the depo : ,,,,,, <_,'o'~o' <'C<~ bel, light (38.20 A.P.I.) crude oil at the sitional edge of the Beaverhill Lal Figw"e 0 f~~)-----=--r 5. - Regional variations in 55 { +- :;[,------.-\550 the content of total hydrocarbons in natural gases from the Leduc Formation, Woodbend Group, in central Alberta. ~.s.: ~ i :y /' I J i affected by changes in either gas /~ w ! I. ?t" 1-. NatW'al gases in Lower Palaeozoic SCALE 1'J MILE:> strata 32 0 .)2 64 96 ~__ ---'oj _ ~ _b--':-::--::-:- :=:::J Although natural gas undoubtedly FigU/t'e 6.-Regional variations in the content of total hydrocarbons in occurs associated with crude oil in natural gases from Winterburn Group strata in central Alberta. 66 Journal of Canadian Petroleum .. ;: Peace River Arch, from the car TABLE IV Hydrocarbons in Beaverhill Lake Group Natllra! Gas bonates of the Swan Hills Forma (All values in volume per cent) , , tion reefal development, and from Northwestern Peace River Arch Swan Hills Southern Alberta. and the shelf region of southern Alber Alberta. Formation southwestern ta and sOl.lthwestern Sa'skatchewan. Saskatchewan These areas are widely separated Nonassociated Nonassociated Associated Nonassociated and the analytical data are best presented in tabular form. The 57.3 - 90.9 59.2 63.4 - 76.2 1.9 - 13.3 data (Table IV) indicate total hy drocarbon contents commonly over 4.1 - 10.5 20.9 18.2 - 41.9 0.7-4.0 , ;- .:. 80 per cent, with the exception of 0.9 - 6.5 0.0 - 1.3 much lower amounts in southern Alberta and southwestern Saskat chewan. Corresponding relative Total hydrocarbons 67.8 - 95.0 80.1 SS.S - 96.9 ·2.6 - 14.9 . .. ~, contents of methane, ethane-plus and butanes-plus are indicated. than 0.2 per cent) and butanes-plus tions in the hydrocarbon content of There is no obvious relationship to (7.8 to less than 0.1 per cent). Gas Wabamun Group natural gases the fluid flow pattern due to the occurrences in the subcrop region (Figllre 7) and the potentiometric scattered nature of the gas occur are composed essentially of meth surface map exhibit three similar Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 rences. ane with very low contents of characteristics, implying a relation heavier hydrocarbons. ship between these two attributes Natural gases in Upper Devonian of the formation fluid. In northern Woodbend Group strata Natural gases in Upper Devonian Alberta there is a characteristic Of the nearly 9,700 billion cubic Wabamun Grou,p strata north-eastward bulge in the con. feet of initial in-place natural gas Major hydrocarbon occurrences tours which otherwise trend ap discovered in Woodbend Group sed essentially comprise the large gas proximately parallel to the eastern iments, over half is not associated fields in southern Alberta near the limit of the "Disturbed Belt." Near with crude oil. The natural gases "Disturbed Belt," with original in the major gas fields in southwest show a remarkable range in the place gas contents totalling three ern Alberta both the isoconcentra contents of all the major compon and one eighth billion cubic feet. tion and potentiometric surface ents, with quantities of zero to 86 Both the map of regional varia- contours change rapidly in a short per cent hydrogen sulphide and car bon dioxide and up to 85 per cent 57 120· US" lJ6" 114" 112" 1l0~7' nitrogen. There is a close rela f ~. --T----~--,---,rr_--'T--I. tionship between the pattern of the '\1"2''r ~! ! .. fluid flow and the pattern of the \ ~;!~ i total hydrocarbons, methane, o!~ to! '22·.... Wo u,·w 95 -9.~ . ethane-plUS and butanes-plus con \:. '-...!.~ 0.... 1(; tents of the natural gas. The iso ..... :rl~ ::E lated nature of the Leduc Forma «~~ "''-- .':!,:~ --- - ...... •• 0". 1-,·0 tion reef masses has resulted in ~.,' \-~~'----'81":J7F7<""-:ot--_-".-\.j:...,~h_-_r---~0:: Natural gases in Upper Devonian "\".\ i Winterburn Group strata \ \ Two thirds of the discovered in Sub"op ·~·,4--~--1I1l_---+__ itial in-place natural gas (770 bil W -I\Sl. lion cubic feet) are associated with E::::J Predommon!ly argillaceous sediments \.~.I --" \ .., crude oil. Regional variations in --- - Direction of flUid mIgrat,on"' I the content of hydrocarbons in nat \ ~~ o Origmalln.place 011<[0 mm.bbls. \ I ural gases from Winterburn Group ... Original m-place 90s>60 b.c.f.' " strata are illustrated in FigU1'e 6. i., The available data indicate a very 6. Original in-place gas <60 b.d. \. close relationship to the fluid flow ...... ""\ l . _70 - Volume per cent isoconcenrrahon contour'll 49.~._ ..-l.•. _ .• _.' "-"-;':-:-""0"49 pattern. The content of hydrocar SCAlE m '''L(S 114" U. bons ranges from 65 to over 97 per .'J?160 J<' 64 96 ==>~ cent, with corresponding ranges Figure 7.-Regional variations in the content of total hydrocarbons in for methane (53 to over 97 per natural gases from Wabamun Group strata in Alberta and British cent), ethane-plus (over 30 to less Columbia. Technology, Summer, 1963" Calgory 67 122' a d8' Figure B.-Regional variations in the content of methane in natural gases D> "-.. - NOR T HWES ,14' Ii,j' from Carboniferous strata in Western Canada. The letters in the subcrop ·_··_··_·)_··_··-r-··-.. · TT ERR'I TOR IES regions indicate the following stratigraphic units: A. Banff Formation; i . .__."1"- .. _.:'\.. _.-; B. Pekisko Formation; C, Shunda Formation; D. Turner Valley Formation . 1 and lower Debolt Formation; E. Mount Head Formation and upper Debolt Formation; F, Stoddart Formation; G. Bakken Formation and Souris Valley Beds; H. Tilston, Frobisher-Alida, Midale, Ratcliffe and Poplar Beds; I. .~ i Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 1--/ I Kibbey Formation. ., 59' I I LEGEND ! I .Oufcrop Direction of fluid m'9ro!lor\ ! I I! --~ Original in.place 011>10 mrn. bbls. o Original in-place oil <10 mm. bbls. L~ - I '98' l r---- SA'S KAT C HE W·A N \ i c, \ I \ \ L 1-<- \, j.~~' ,•-~\ -v".,.~, 1- -t .. - ~-t---. -__I __ .- !- -+ "\-\--\ t-)",,,,,,_ '"'" c.."'{-j--I---·· I l' \'" I , I \ W7~~' -\J«\ .. ."\ <9",\.~ I i - \ " .. !. 'A i \~ ~C(,. .\\ I"'('0 ('( \ U"l\\f ~ ' i ,., "i g ~ I \ . .. \ 3 "".'l. I !!. ". ··r .~'>--"". _.L .L ..,.... \ \ ~ \ n \... f((~·'"~' "B, .:J \ • ..0 • \ \"'\! I.... iI) \ .. a5 I o· I'"';r I £:, ". • i r ~ \.5, I~'l Y ...... 1 ... ..-." ... ~ ~ 1 _ ,.. ~ ./ -', !-I ) I/ _.. _... 1-.. - ... -_.- .. 3 ~)~~ ~ ""~O ~ _."A._... -' 102.' ;; '9.-\.,1 "'...... ). ...~x;r~L/..l...._._... J .. _._...u._' .. ..s. c JI';' !.tl c:i ~,j' lOS' 3 NORTHWE 1240 5 T T ERR ITO R I E 5 distance, from 42.8 to 85.6 per cent total hydrocarbons, and from 3,250 ;t-'. - ...._ .. ...!.2.'C .. _ /'20° 1180 116..0_ .. _ .. _114' ,/ "-'1-"-"-" .. _ .. _ .. to iess than 2,000 feet above sea level, respectively. Along the sub t~ ,' crop. the zone of over 95 per cent total hydrocarbons corresponds to a 5~" ~:I trough in the potentiometric sur ---L 59" face map, with elevations below "" 1,250 feet above sea level. Maps of ;;: ! variations in the content of meth "i--'. ane, ethane-plUS and butanes-plus " are essentially similar to that for " °1 the total hydrocarbons. The con U~ tent of methane ranges from 38 to ;0: 98 per cent, ethane-plUS from' 14 tp Iw 0.1 per cent. and 'butanes-plus from 4.4 to less than 0.1 per cent. In the ,,--~lJ!: subcrop region to the north of the ?~. \.~ 7~ :,';. : ~: 5 map area, two wildcat wells yield ~r' ed natural gases from Wabamun Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 "~.I. J..,6 ij Group strata with over 96 per cent o total hydrocarbons. ~~O '" . N atu1'al ga8es in Oarboniferous 122' ~ '" k' \ '" :6 strata 0" ; --- The facts that the major reserves .'...... "''0; I of crude oil and natural gas in 5S0~- . 55" Carboniferous strata occur in pools adjacent to the post-Carboniferous ~t~~; 0'<1 unconformity and that most of the / ","- sediments have been subjected to I "",,- severe erosion led to a decis~on to '. , c. '< treat the Carboniferous strata as , l' '<. , a "- one stratigraphic unit.. The map in ~ Figure 8 shows the subcrop boun (' D" daries of the various formations ...... comprising the Carboniferous of '-.f'., Western Canada. The content of LEG END 5,,0',,-_--,--_ 53' 114~ methane in natural gases from Direction of fluid migration Carboniferous sediments is illus trated. Essentially similar trends •-- Original i~-place od>IOmm. bbls~ exist for total hydrocarbons, ethane plus and butanes-plUS. o Original in.place oil <10 mm. bbls. A Original in-place gas>60 b.c.f. Natural gases in Permian strata 6 Original in-place gas <60 b.d. Natural gas occurrences contain generally over 90 per cent total _70 -- Volume per cent isoconcentration contours hydrocarbons, though amounts as SCALE IN MILES low as 85 per cent occur in fields 32 16 0 32 64 96 near the "Disturbed Belt." The con :-. , . = tent of heavy hydrocarbons varies Figure 9.-Regional variations in the content of methane in natural gases from strata of the Daiber Group and Halfway Formation in Alberta and from less than 0.5 per cent to over 12.7 per cent in gases associated British Columbia. '. , with crude oil at the Fort St. John ':'. - TABLE V. field in northeastern British Col Hydrocarbons in Woodbend Group Natural Gases umbia. Trend patterns of hydro (AIl values in volume per cent) carbon composition are similar to Peace River Arch Swrgeon Lake • Windfall Princess Southern the fluid flow pattern. .':.' FrlngingRcef, Reef Reef Field, Alberta northern Alberta northern Alberta northern Alberta sQutJiern Alberta N at1l,ral gases in Triassic stratfL Associated No~ Associated Associated No~ Associated Non· • associated associated associated Combined associated and non-as sociated initial in-place natural gas elf, 57.6-60.1 82.4-86.6 60.9-66.2 48.8 41.4-78.8 66.3 2.4-12.3 contents are well over 1,000. under 100, and over 2,500 billion cubic C2H6+ Zl.5-38.4 8.1 8.5-23.9 25.3 0.5-18.0 11.2 0.6- 2.8 feet in the Daiber Group and Half C4 HlO + ,., 1.1' 2.1 2.5- 9.4 2.9 0.2- 9.4 10.2 0.1- 0.7 way Formation, Charlie Lake For Total Hydro~ mation. and Baldonnel Forrn.ation, =bon, 85.1-91.5 91.6-96.3 78.3-81.3 74.1 42.4-79.6 77.5 3.0·15.4 respectively. Regional variations Technology, Summer, 1963, Calgary 69 in the content of methane in natur al gases from two of these units o R I E 5 are shown in Figures 9 and 10. Both 0 show trend patterns similar to 116 11-1-' those of their respective fluid flow patterns. Table VI summarizes the concentration ranges of hydrocar bons in natural gases from Trias sic strata. -+-_._--" Natural ga:ws in Jllras,';;i(; strata Natural gas is associated with heavy crude oil in a series of fields on the flanks of the Williston Basin and in the Conrad Sand stone in southern Alberta. Major and minor gas reserves are known from the Nordegg Formation and Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 Fernie Group in western Alberta and northeastern British Columbia. Regional variations in the content of hydrocarbons (91.0 to 100.0 per cenO, methane (Figure 11), ethane plus <0.3 to 28.8 per cent) and bu~ tanes-plus <0.1 to 4.4 per cent) show trends similar to the fluid flow pattern. The numbers in par entheses are the ranges in con centration observed for the data 55" available. Natural gases in Lower G1'etaceOlls Mannville G1'OU,P strata. Initial in-place natural gas re~ serves of nearly 8,000 billion cubic feet have been discovered in Mann ville Group strata. Only the ma jor fields are shown in Figm'e 12. Fluid flow within the Ellerslie Formation and Mannville Group sediments is very complex and strongly influences movement of ~ Direction of fluid mlgrohon the fluids in strata immediately be Figure 10. -- Re neath the pre-Cretaceous uncon • Onglnal in-plac~ od>IOmm. bbls. gional variations formity. Although the regional in the content of variations in the content of meth Orlginol in-place oil <10 mm. bbls. methane in nat o ural gases from ane in natural gases from this Charlie Lake For stratigraphic unit have clearly £::.. Original In-place gas <60 b.c.f. mation strata in been affected by the flow regime, Alberta and Brit· _70 - Volume per cent lsoconcentratlon contours especially in central and south ish Columbia. western Alberta, the large-scale regional pattern is essentially sim 64 96 ilar to those observed for other "'== units. Total hydrocarbons are gen TABLE VI. erally over 90 per cent and com HydTocarbon-s in Triassic N atnral Gases monly over 95 per cent. Ethane (All values in volume per cent) Daiber Group and Charlie Lake naldOrntcl plus varies from nearly 0.15 per Halfway Formation Formation Formntion cent to 20 per cent in some of the deep oil fields. Associated Nonassociated Nonassociated Nonllssociatcd Natu'ral gases 'in Lower GTetaceous~ 70.2 - 89.3 68.4 - 95.2 81.6 - 92.9 62.9 - 96.5 Viking FOTmation stTata 6.2- 7.2 3.4 - 12.0 8.1 - 10.5 1.6 - 26.8 Sands of the Viking Formation are reservoirs for crude oil and 1.0 w 6.0 0.1- 3.5 1.2- 2.8 {l.O· 2.6 natural gas at many localities in central Alberta. Correlative strata include the Bow Island Formation Total Hydro in southern Alberta and the Pelican carbons 92.5 - 96.9 80.4 - 97.5 91.4 - 99.6 89.7 - 99.8 7~ Journal of Canadian Petroleum ~,,: "',":..."" , .,.... '-:iLi:~ i, '-"";';4~',~ '~';'i_~..t , ~. ~ ~ f. .. 118' 114' 110' o• RTI-IWEST TERRITORIES Ii 0" "-]"'- .. - ....,. .. - .. - .. .,. .. - "-.. ~ .. - "! I' ~a::t~ oroolQ \=~'''' a;g~ \ ""-oq1:....j:J" .... "f-Io m~ ro:J t-'" 8' t-j..... I 1-$~::SEt"'l ::S~'::lrorb ..... A9· l,' ''''... OQ~. ""0I1 §::S :Ja-~PJe.8'E. P',,','lg.~ .... '" ~. - ::rm g,~ , ": . ., '/ ,',~, .f ."', " . '. ~::~~~f~{;;fF;;;¥~~~;lf[~i!,:;!.t"),;;·;" ··-~t; , ::~;:i?":i1;l: :. ',/ .(., t~~: .' ,~.< . r· '" '" ,. , ) ------ in Figltre 14, and again the trends TERRITOR I parallel those of the fluid flow pat 114" ". 'T tern. ! i Natural gases in Upper CretacerJ//.') 1I1t--~\- Belly Ri1)er Fonltation strata Minor crude oil and natural gas I occurrences have been found in the I basal sandstones of the Belly River I Formation. Total initial in-place I natural gas is about 150 billion cubic feet. Total hydrocarbons in the natural gas range between 95 and 99 per cent. The content of methane decreases from over 95 I per cent near the outcrop to near I.' ly 80 per cent near the "Disturbed Belt" (Figure 15), with a COrTes I·' Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 ponding change of heavier hydro ~T_--_Pt-.-'~::jLo-..-__::o~~-¥--} carbons from less than 1.0 per cent . I to over 15 per cent. The pattern , i of methane isoconcentration lines i are similar to those of the fluid flow pattern, although the floW dir ection is reversed from that in tlw pre-Cretaceous strata. :-EGE"\JD Natw'al gases in Tertian; strata Mcr.n~llIe • Group oulcnl!' Only two analyses arc available ~///] Aihabo5ca 001 ~olld~ for natural gases from Tertiary strata, both for gases from wells • Paloeolo,c outcrop in central Alberta. Total hydro ~ ;)"~C" "" r>f :lu.d m'9'01>o" carbons are over 97 per cent with o -:"'9 -olm.pk:ce o.l>HJm"'.uol~. ethane-plus contents between 0.15 A '~'r'g,,,a1 ,,,_place gO$>60 b.~.f. and 0.35 per cent. DISCUSSION It has been indicated above that the contents of total hydrocarbons, ..L.~' • methane, ethane-plus and butanes '0 plus in natural gases from each of the stratigraphic units considered Figure 12.-Regional variations in the content of methane in natural gases from Mannville Group strata in Alberta and British Columbia. vary regionally. Also, it seems reasonable to conclude that metb ane probably originated due to and Paddy Sandstones of northern Natnral gases in UP1)e~' Gl'etaceous direct synthesis by bacteria, and Alberta, all of which contain nat Cardium, Fonnation strata that the heavy hydrocarbons WP!'l' ural gas reserves. Combined ini the products of decarboxylation This stratigraphic unit contains tial in-place natural gas in these and reductive deamination of amino units is about 6,000 billion cubic the largest oil field in North Amer acids or decarboxylation of fatty feet. Despite reversal of flow dir ica in addition to three other major acids. In both of these types of l'(' ection over the major portion of oil fields and several minor oil and actions methane is a by-prOdUCt. central Alberta, there is the same gas fields. Initial in-place asso and the origin of part of the meth general compositional trend in evi· ciated natural gas content is over ane from these reactions is proh dence, namely, low methane and 3,000 billion cubic feet. Total hy able. Furthermore, study of the high ethane-plus contents associat drocarbons in the natural gas basin-shelf relationship of crude ed with the deeper higher-pressure range from just less than 95 per oil and natural gas deposits, and regions, passing updip to regions cent to over 99.4 per cent. The their precursors as represented in of lower pressure with high con minor non-a:::jociated gas fields have recent-sediments, has demonstrated tents of methane and low concen methane contents of 85 per cent (53) low-methane natural gases as trations of the heavier hydrocar and over, although the content in sociated with paraffinic crude oils bons. Regional variations in the the associated gas may fall as low in the depositional basins and high content of methane are illustrated as 65 per cent. Heavy hydrocar methane natural gases associatNI in Figure 13. Total hydrocarbons bons may be up to 35 per cent, with asphaltic crude oils on tilt' are generally over 95 per cent. though those heavier than butane depositional shelf regions. Ethane-plus varies from less than seldom exceed 10 per cent. Re 0.1 per cent to over 30 per cent at gional variations in the content of Three features must be consid('r the Joffre and Gilby oilfields in methane in natural gases from the ed before relating all the above ob central Alberta. Cardium Formation are illustrated servations into a unified conc('pt. 72 Journol of Canadian Pctrolcum ...,. Throughout Western Canada in 122' 120' creasing depth of burial results in '" lie' 116' increased formation pressure, and from the maps illustrated it can be concluded that regions of high formation pressures generally co incide-with regions having low con tents of total hydrocarbons and methane and high contents of the heavy hydrocarbons in the natural , gases... Conversely, natural gases " from the low-pressure regions have higher contents of total hydrocar bons and methane, and lower con tents of heavy hydrocarbons. These observations may be applied on a basin-wide basis, with but two ex ceptions. In some stratigraphic units, for instance the Wabamun Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 Group (Figure 7), the flow direc tion in the subcrop region has been affected strongly by the lIow reg imes in the Ellerslie Formation and LEGEND Mannville Group, and this has mod ified an otherwise normal pattern • Outcrop of . variations, In stratigraphic units in which the fluid flow pat Dlrechonof rluld migration tern indicates the presence of a re • Orlgmal in~ploce orl>lOmm. bbl~. gion of low elevation completely --~ Original in-place ga~> 60 b.c.f. surrounded by a region of higher _70 - Volume per cent i~oconcenlralion contours elevation (analogous to a region of internal drainage on the land sur S(.1.L( ttl MILE:> 3~.':..";2 64 .. face), as for instance in Figures 12, ',' 13, 14 and 15, the regional isocon , Figure l3.-Regional variations in the content of methane in natural centration contours - on the high gases from Viking Formation strata in Alberta and British Columbia. formation-pressure side have been ..... modified. With respect to the fluid flow pat tern, it has been demonstrated that in all of the pre-Cretaceous strati graphic units, the high surface co • 120' 56;:-- -- ~ ------r----' lie' incides with the region of high , formation pressure, and fluid flow , ' is from the region of high forma tion pressure to the region of low er formation pressure, excepting for minor modification in the sub crop region. In the case of the Cretaceous stratigraphic units studied, although increasing depth of burial is accompanied by in creasing formation pressure, the potentiometric surface maps for i I 1 these units indicate fluid flow in I I certain regions to be from the ~. "- :'. lower formation pressure to the \_..... O/'" .. 1 , ;,~ '\ "" --"J"' J-L~""-",,r::',.~+ ane may be expected in the natural Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 gases from the shelf regions. In creased depth of burial of the rela tively paraffin-rich organic matter in the basinal sediments would re sult in the opportunity of greater yields of heavy hydrocarbons with enhanced conditions for maturation. Generation solely on a maturation mechanism, such as is implied by Dobryansky (55), seems unliltcly. In the stratigraphic units in which the general increase ill 51" -'. heavy hydrocarbons and decreasp 116" in methane content with increased SCALE IN MILES depth of burial and more basin 32 16 0 32 64 96 ward position are modified, rc 1§CE§Cl§§_===-_ course must be made to other fac· tors. Chief among these arc altel'· LEGEND ation due to changes in flow direc tion, and possible undersaturatioll at the present formation tempera· __ Outcrop lures and pressures, of the forma .".,.. Direction of flUid m,grohon tion water with natural gas. Direct increased solubility of natural gas • Orl9lnolln-ploce oil>IOmm.bbls. in the formation water with in o Or'9Inollo-ploce otl 74 Journal of Canadian Petroleum ,sible mechanisms to account for es. Where modifIcation of the gen ACKNOWLEDGMENTS these modifications include under eral pattern has been observed, The writer expresses his grati~ saturation and variations _ in the there is also modification of the tude to the and Gas Oonserva· solubilization of the hydrocarbons fluid flow pattern. These features on tion Board, Oalgary, Alberta; the due to changes in flow direction suggest that changes in the solub and movement into regions with ilization of the hydrocarbons or un Department' of Mines, Victoria, British. Columbia; Imperia.l Oil formation waters of different salin dersaturation may be the indirect Limit'ed, OalgaT1.J, Alberta,' and the .:. ities. cause of the modification of the Petroleum and Natural Gas Divi hydrocarbon isoconcentration con sum, Department of Mineral Re SUMMARY AND CONCLUSIONS tours. s01brces, Regina, Saskatchewan, for There are generally systematic A close relationship exists be supplying the major portion of the regularities in the order of abund tween the depositional environ analyses used in this study. Partic ular thanks are due to D. R. Shaw, ance of the individual hydrocarbons ment and the developing crude oil in natural gases. The ratios of the Chief Chemist; A. N. Lucie-Smith, and natural gas, and these factors, Chairman, Conservatfon Commit butane and pentane isomers indi in turn, show a close relationship cate that no reservoirs are in ther tee; the late J. W. Yotmg, Manager to the environment in which mat Production Research and Technical modynamic equilibrium, and pend uration may take place and to the Service Department, and J. T. Mc· Downloaded from http://onepetro.org/jcpt/article-pdf/2/02/60/2165264/petsoc-63-02-05.pdf by guest on 30 September 2021 ing further investigation the cause J flow regime of the fluids. Explora ManusJ Senior Reservoir Engineer, of variation in isomers must be tion for natural gases with spec of these organizations, respectively. attributed to some form of cataly ific compositional ranges may thus The writer also wishes to thank sis. be conducted more expeditiously, the numerous other individuals and "'.' their respective companies for mak Regional variations in the total and from limited observations, ing available additional data. The hydrocarbons, and the contents of when all of these factors are con data on reserves were compiled methane and heavy hydrocarbons sidered. A general prediction can from information supplied by the in natural gases are consistent be made concerning the composi pertinent government department with the basin-shelf control con tion of natural gas in unexplored in each of the Western Canadian cept and with maturation process- regions. Provinces. REFERENCES (7) Elworthy, R. T.J tLNatural Gas (14) Rosewarne, P. V., and OffordJ in AlbertaJ" Canada, Dept. R. J., "Helium in Canada from (1) Kartsev, A. A., Tabasaranskii, Mines Tech. Surveys, Mines 1926 to 1931," Oanada, Dept. Z. A., SubbotaJ M. I., and Mog Branch, Rept. 616, 1924. Mines Tech. Surveys, Mines ilevskii, G. A., HGeochemical Bmnch, Rept. 7Z1, 42-54, 1932. Methods of Prospecting and (8) Elworthy, R. T·, "Natural Gas Exploration for Petroleum and and Petroleum in Northern (15) Stansfield, E., and Nicholls, J. Natural Gas," Translated by Alberta," Canada, Dept. Min H. H., "Analyses of Canadian P. A. Witherspoon and W. D. es Tech. Surveys, Mines Fuels. Part IV. 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