Geochemistry and origin of formation waters in the western Canada sedimentary basin—I. Stable isotopes of hydrogen and oxygen

Geochimicaet Cosmochimica Acta,1969,vol. 33,pp. 1321to 1349. Pergamon Press. Printedin Northern Ireland

Geochemistry and origin of formation waters in the western Canada sedimentary basin-I. Stable isotopes of hydrogen and oxygen* BRIAN HITCHON Research Council of Alberta, Edmonton,

Canada

and IRVINQ FRIEDMAN U.S. Geological Survey, Denver, Colorado (Received

10 December

1968; accepted in revisedform

28 May

1969)

Ah&a&-Stable isotopes of hydrogen and oxygen, together with chemical analyses, were determined for 20 surface waters, 8 shallow potable formation waters, and 79 formation waters from oil fields and gas fields. The observed isotope ratios can be explained by mixing of surface water and diagenetically modified 8ea water, accompanied by a process which enriches the heavy oxygen isotope. Ma88 balance8 for deuterium and total dissolved solids in the western Canada sedimentary basin demonstrate that the present distribution of deuterium in formation waters of the basin can be derived through mixing of the diagenetically modified sea water with not more than 2.9 time8 as much fresh water at the same latitude, and that the movement of fresh water through the basin ha8 redistributed the dissolved solids of the modified sea water into the observed salinity variations. Statistical analysis of the isotope data indicates that although exchange of deuterium between water and hydrogen sulphide take8 place within the basin, the effect is minimized because of an insignificant mass of hydrogen sulphide compared to the mass of formation water. Conversely, exchange of oxygen isotopes between water and carbonate minerals causes a major oxygen-18 enrichment of formation waters, depending on the relative masse8 of water and carbonate. Qualitative evidence confirms the isotopic fractionation of deuterium on passage of water through micropores in shales.

waters are an important part of the hydrologic cycle because they are the medium within which crude oil and natural gas are found, and because diagenesis, cementation, and ore deposits within the sedimentary rocks are all features for which clues to their history may be sought by study of formation waters, Indeed, formation waters may be economic minerals in their own right, for example, as sources of bromine, iodine and calcium chloride. It is the intention of this series of papers to present the significant geochemical features of formation waters from the western Canada sedimentary basin based on a wide variety of parameters obtained from a suite of nearly ninety samples. Particular attention will be directed to those features which may be of value in elucidating the history of formation waters. The western Canada sedimentary basin is structurally simple and stratigraphically well known. For a definitive detailed geological history the interested FORMATION

* Joint publication of the Research Council of Alberta U.S. Geological Survey. 1321 1

(Contribution

No. 451), and the

1322

13. HITCIWX ;wI 1. FRIEUM~N

reader is referred to MCCROSSANand GLAISTER (1964). Rock volume and yore volume data for the plains region of the basin have been compiled by HITCI~~N (1968b). Abundant modern reliable data on the formation fluids are available, and their regional variations and geochemistry have been described (HITCHOX et al., 1961; HITCHON, 1963a, b, c, 1964, 1968a). The fluid flow within this basin has been elucidated (HITCHON, 1963d, 1969a, b). Thus considerable information is available concerning the contained fluids and the rock matrix within which the)] move. It is against this background that the stable isotopes of hydrogen and oxygen in formation waters from Alberta, Canada, will be considered. PREVIOUS STUDIES Most early determinations and some current investigations of stable isotopes of hydrogen in formation waters have been made by very precise measurements of the density of the salt-free water. However, hydrogen isotopes may be fractionated during purification procedures, and furthermore, variations in the oxygen isotopes Users of the density method have all ratio also affect the density of the water. observed a more or less regular increase in deuterium content of formation waters with depth a,nd have variously associated this increase with concomitant increases of the total dissolved solids content of the formation waters, the age of the rocks, and other factors. Anomalies have been ascribed to deep circulation of surface waters or to deuterium exchange with hydrocarbons. None of the users of the density method was able to measure differences in the oxygen isotopes, and since this omission may have seriously affected their results only data determined by mass-spectrometric methods will be discussed in detail. GRAF et al. (1965) and CLAYTON et al. (1966) have provided the only comprehensive studies of stable isotopes of both hydrogen and oxygen in formation waters. BAERTSCHI (1953), DE~ENS (1962) and DEGENS et aE. (1964) have considered only oxygen isotopes, and ROTH (1956) only hydrogen isotopes. A small fractionation of hydrogen isotopes resulting from passage of water through micropores in shales was postulated by GRAF et al. ( 1965) and a major fractionation of the oxygen isotopes through exchange with carbonates of the reservoir rocks observed on the same samples by CLAYTON et al. (1966). CLAYTON and his co-workers also concluded that the water of formation waters is predominantly of local meteoric origin. This view differs from that of DEQ-ENSet aZ. (1964), who attributed the changes of the oxygen isotope ratios to mixing of meteoric waters with original marine interstitial solutions. Other processes that might alter the ratio of the stable hydrogen isotopes, such as exchange with hydrogen sulphide which takes place easily and which is used in most commercial heavy water plants, were not considered in detail. The suite of samples studied in this paper offer an opportunity to examine statistically the effects of many variables which may cause fractionation of the stable isotopes of hydrogen and oxygen. SAMPLE COLLECTION The collection and analysis of formation wat,ers (and other fluids) at reservoir temperatures and pressures would minimize physical and chemical changes that may occur when sampling and analysis are undertaken at temperatures and pressures close to those at the wellhead. Since collection is difficult, and analysis often impossible at reservoir temperatures and pressures,

Origin of formation waters in the western Canada sedimentary basin-I

1323

extreme care must be exercised to ensure that the sample is at least representative of formation water collected at normal wellhead temper&ure and pressure. The formation waters used in this study were collected at the wellhead, or at a non-operating treater or separator, thus prior heat treatment or chemical reactions were avoided. In two samples (79 and 80) about 30 ppm of corrosion inhibitor was added to the fluid deep in the well bore due to high hydrogen sulphide contents of the associated natural gas. Where free water was available, the samples for isotope analysis were collected in 4-ounce glass bottles with polyethylene inserts, direct from the wellhead, filled “heaping full” and the tops sealed with wax in the laboratory as soon as possible to minimize exchange with the air. In some instances only oil-water emulsions were recovered and these were removed to the laboratory and broken down by centrifugation or, in a few instances, by freezing at liquid nitrogen temperatures (samples 8, 9, 33, 40, 42, 43, 47 and 55). Separate portions of all samples were chemically analysed for major and minor components and this information compared with known representative chemical analyses. Only representative samples are included in this study. The formation waters from oil and gas fields come from strata ranging in age from Late Cretaceous to pre-Late Devonian (Granite Wash), and in depth to nearly 11,600 ft (Table 4). In addition to the formation waters, 20 surface waters and 8 shallow potable waters were sampled, details of which may be found in Tables 2 and 3, respectively. EXPERIMENTAL The deuterium concentrations were determined by converting samples of 0.01 ml to hydrogen gas by reaction with hot uranium metal (FRIEDMANand WOODCOCK,1957). The deuteriumhydrogen ratio in this gas was compared to the ratio in a standard gas, using a specially constructed mass spectrometer (FRIEDMAN,1953). All samples were processed and analysed in replicate, the replicates agreeing to within ho.1 per cent in 95 per cent of the samples analysed. The analyses are expressed as deuterium enrichments (plus S values) or depletions (negative 6) relative to SMOW (Standard Mean Ocean Water, having 8 D/H ratio of about 158 x 10e6, CRAIQ, 1961b). Thus a sample having a 6 value of -4 has 4 per cent less deuterium than does Standard Mean Ocean Water. The comparative study of isotope ratios of deuterium and oxygen-18 in natural waters by the International Atomic Energy Agency (I%.LEVY and PAYNE, 1967) indicates that the deuterium values reported in this paper will be about 1 per cent lighter than the mean lines for surface waters reported by CRAIG (1961b) and DANSGAARD(1954, 1960). The oxygen-18 analysis on water samples w&s carried out by the method described by EPSTEINand MAYEDA (1953). A sample of 10 ml of water was equilibrated with carbon dioxide at 25% end an aliquot of the CO, was analysed for 0 l* . Some of the very saline waters were distilled to dryness before carrying out the equilibration. The carbonates were reacted with 100 per cent phosphoric acid to liberate CO, by the method described by MCCREA (1950).

Corrections to the mass spectrometric results were carried out as described by CRAIG (1957). In addition, dolomites were corrected for the difference in isotopic fractionation factor associated with the phosphoric acid reaction, as suggested by SRARMA and CLAYTON (1965). All 01* analyses are given relative to SMOW, as suggested by CRAIG (1961a, b). For the water and carbonate samples the 0 ls data are precise to *O.l per mille. THEORETICAL

CONSIDERATIONS

Within the surface regime of the hydrologic cycle, fractionation of the stable isotopes of hydrogen and oxygen in water takes place mainly through changes of state. The processes which fractionate the isotopes of hydrogen affect the isotopes of oxygen in a similar way. For surface waters there is a close relation between 6D and 601s when both are referred to Standard Mean Ocean Water (FRIEDMAN, 1953; CRAIG, 1961a). FRIEDMAN et al. (1964) have shown that for surface water, the temperature at which precipitation takes place, and which may be correlated with altitude and latitude, is the chief variable controlling fractionation of the isotopes of hydrogen and corresponding fractionation has been observed for the isotopes of oxygen (DANS~AARD, 1954, 1960, 1961).

1324

13. HITCHC~N

arid .I.FRIEDMAN

Once surface water has penetrated into the subsurface, changes in the ratios of the stable isotopes of hydrogen and oxygen may t,ake place through a variety of The surface water may mix with waters of differing isotope ratios, as processes. suggested by DEGENS et al. (1964) and the isotopic composition may also change because of exchange with other fluids (ROTH, 1956), or with the rock matrix (CLAYTON et al., 1966j. In addition, the act of moving through shale microporcs et uk. (1964) have ol&may affect the isotope ratio (GRAP eb al., 1965). FRIEDMAN served that water from shallow wells is probably one of the best sources of samples Waters in the underrepresentative of the regional surface isotopic characteristics. ground environment may be separated, rather artifically, into shallow, mainly potable, formation waters, representative of the regional surface isotopic charactcristics, and deeper, variably saline formation waters. It is in the latter group that we must seek clues to the history of formation waters in sedime~ltary basins. CLAYTON et al. (1966) observed that the variation in the deuterium content of formation waters among four sedimentary basins they studied was much greater than that within each basin. They also noted that the oxygen isotopic composition showed a large range within each basin. They considered several processes in order to account for the variation they observed, and concluded that the original water from the depositional basin had been lost during compaction and subsequent flushing and that the present formatiol~ water originated as precipitation over land, under climatic conditions not greatly different from those prevailing today. They thus rejected the thesis of DECENS elt al. (1964) that formation waters result from the mixing of marine and fresh water, noting that oxygen isotope ratios alone are insufficient to merit the conclusions reached by DEGENS et al. (1964). CLAYTON that extensive oxygen isotopic et al. (1966) presented convincing evidence exchange has taken place between the water and the rock matrix, and that the deuterium content of the formation waters has not been greatly altered by exchaxlge or fractionation processes. The present authors believe that the data presented by both DEC*EWSet a,l. (1964) and CLAYTON et al. (1966) are equivocal and that, in fact, formation waters may also originate by mixing of surface waters, at the present latitude of the basin, with the modified marine (or non-marine) water present in the rocks, and that this mixing, together with extensive exchange of oxygen isotopes between the water and the rock matrix, results in the distinctive trends observed from basin to basin, The term “mixing” is used because it is the most pertinent to describe a process which is envisioned as a slow percolation of water through the basin, carrying with it the dissolved salts, and simultaneously changing both the composition of the inflowing water and the water in the basin. Neither diffusion nor flushing is an appropriate term because the former, strictly, implies only movement on a molecular scale, and the latter may be interpreted as a mass movement of water, sweeping all fluids before it. CLAYTON et al. (1966) placed considerable emphasis on the trends of 6D against SOI8 for the basins they studied in their case for rejection of the mixing hypothesis of DECENS et al. (1964). Figure 1 is based upon their graph of 6D against &OX8and shows the interpretation that must be placed upon trends which fall within specific regions of the diagram, based on our assumption that mixing of surface water and sea water (SMOW) takes place. If mixing is unaccompanied by other processes

Origin of formation waters in the western Canada sedimentary bsain-1

1325

causing differential isotope fractionation all &rmation waters would lie on the line If mixing is accompanied by a fractionation process differSurface water-SMOW. entially affecting only the hydrogen isotopes all formation waters will plot in the region above the proportional mixing line and with 6018 values less than SMOW. Similarly, if mixing is accompanied by a fractionation process which differentially affects the oxygen isotopes, all formation waters will plot in the region below the proportional mixing line and with QD values less than SMOW. It follows that if formation waters plot in the blank region of the diagram then even on the extension of the proportional mixing line, at least one process, other than mixing, must have occurred that altered isotopic compositions. At least two processes, other than mixing, are required if the two chemical species are differentially affected. A

2‘ s

t

*

0’

REGION OF MIXING ACCOMPANIED BY A PROCESS ENRICHING DIFFERENTIALLY IN DEUTERIUM

6 018( %.

SMOW)

Fig. 1. Schematic plot of 6D and 601* indicatingthe effects of various mixing and fractionating processesfor any specificsedimentary basin.

None of the Alberta samples analysed in this study fall in the blank region and only a few of those analysed by CLAYTON et al. (1966) are found there. They were predominantly from the Gulf Coast, where surface waters have hydrogen isotopic ratios fairly close to Standard Mean Ocean Water (FRIEDMAN et al., 1964). Thus, within the limits of sampling and experimental errors, and allowing for the possibility of a small fractionation of stable hydrogen isotopes by one of several processes noted by CLAYTON et al. (1966) which could place some of the Gulf Coast samples in the blank region, all formation waters examined so far lie within the region in which mixing of surface water with SMOW is accompanied by a process which differentially fractionates the oxygen isotopes. It follows that determination of the mass balance of deuterium in a sedimentary basin may indicate the degree of mixing to which the formation waters have been subjected. During the past ten years much evidence has been accumulated to indicate that shales act as membrane ultrafilters (BERRY, 1958, 1967; BERRY and HANSHAW, 1960; BREDEHOEFT et a.!., 1963; GRAF et al., 1965; HANSHAW, 1962, 1964; HANSHAW and ZEN, 1965; WHITE, 1965). Water passes freely through the micropores

but the dissolved salts are differentially removed. The deuterium concentration of a formation water is not necessarily related to the concentration of total dissolved

solids. Nevertheless, in any sedimentary basin in which mixing has taken plact~., the mass balauce of deuterium and the mass balance of dissolved solids obviousl> will be related. The Alberta basin will be used as a model to consider the processes that hrtvc: been described so far in terms of an actual sedimentary basin. In simplified terms the Alberta basin comprises a wedge of unfolded sedimentary rocks resting on buried Precambrian (Fig. 2). The thickness varies from zero at the exposed Precambrian Shield to over 16,000 feet adjacent to the folded strata of the foothills belt, which forms the eastern subdivision of the Canadian Cordillera. Most of the sediments were deposited in marine environments, with the various marine incursions separated by periods of uplift, during some of which the hydrodynamic situation allowed influx of fresh water into the rocks as evidenced by structural studies of post-diddle Devonian strata whirl1 show several periods of

Fig. 2. Model of mixing and shale ultrafiltrationm~hanisms for the Alberta basin,

solution of the Middle Devonian halite (GORRELL and ALDERMAN, 1968).However, at no time prior to the culmination of the Laramide orogeny is it likely that there existed a hydraulic head greater than that generated by the present Canadian Cordillers. Paleogeographic studies indicate regional land elevations, and hence hydraulic head, decreasing westward (the opposite situation to the present) in preLaramide time, although regional land elevations were considerably lower. In addition, the sediments deposited in pre-Laramide time would have higher porosities and permeabilities then, than they have now, thus allowing more ease of fluid movement, but at the same time shale membrane efficiency would be lower. These various aspects of the complex history of the western Canada sedimentary basin suggest that the present salinity distribution of the formation waters is largely a post-Laramide feature. Paleolatitude studies indicate essentially the same latitude situation for western Canada during the post-Laramide period, and this suggests that the deu~~urn content of precipitation in western Canada has probably not been very much different from the present content since Laramide time (except possibly during Pleistocene glaciation). Whatever the paleolatitude position of western Canada there is no conclusive evidence which suggests that the composition

Origin of formation waters in the western Canada sedimentary basin-1

1327

of ocean water has changed significantly in fhe past 150 million years, although in pre-Jurassic time the composition may have been different. A few samples show sea waters along Canadian coasts have about 156 ppm deuterium (relative to SMOW = 157.6 f 0.3 ppm absolute determination); the paucity of samples makes it difficult to determine the effect of dilution by continental run-off, but suggests that deuterium contents slightly lower than SMOW may also be reasonable (A. R. BANCROFT,personal communication, 1968). However, the water in the western Canada sedimentary basin immediately prior to the Laramide uplift was certainly isotopically no heavier than SMOW and chemically probably only slightly modified from sea water. During the period (post-Laramide) of effective mixing and shale ultrafiltration the fresh water recharge to the basin probably had a deuterium content similar to that at present. The main recharge region is the foothills belt with discharge in the low lying areas adjacent to the Precambrian Shield (HITCHON,1969a). Fluid flow is dominantly downward from the surface through much of the Cenozoic and Mesozoic strata and over much of this region salinities are less than 35,000 mg/l. Fluid flow in the deep strata is upward, out of the basin, and the result of this movement is an extensive cascade of increasingly saline waters differentially removed from the flowing formation water behind shale ultrafilter barriers, shown diagrammatically in Fig. 2. We shall present evidence later to suggest that the cascade effect results in very efficient removal of the dissolved materials. Thus, if we are able to calculate the volumes of formation waters of different salinities we are in a position to estimate the amount of water passing through the shale ultrafilters. For example, if we have a portion of a sedimentary basin containing 1000 cubic miles of formation water with a salinity of 175,000 mg/l, or five times the concentration of sea water, we may estimate that with effective complete removal of the dissolved solids, 4000 cubic miles of sea water have passed through the space now occupied by the 1000 cubic miles of formation water. If we complete a calculation of this nature for formation waters of different salinities for an entire basin and we can be confident that most of the dissolved solids in the diagenetically modified sea water are still in the basin, by doing a mass balance on the dissolved solids in the formation waters and comparing this to the salinity of the sea water, then any excess volume of water over that of the total pore space of the basin should be equal to the volume of fresh water required to rearrange the dissolved solids. Formation waters with salinities less than sea water are included in the calculations by computing the volumes of fresh water and sea water required to produce the observed salinity. The deuterium balance calculated for the basin based on the measured relation of deuterium to total dissolved solids and weighted for volumes of fluids of differing salinities should be equal to that obtained by mixing fresh water and sea water in the proportions just calculated. We can use the deuterium and total dissolved solids mass balances to estimate the membrane efficiency of the shales and the amount of water required to be passed through the basin in order to rearrange the total dissolved solids to give the variable concentration found at the time of sampling.

VARIATION OF DEUTEEIUM DUE TO MIXING Th.e availability of reliable estima~tes of the pore volume in the western Canada sedimentary basin (HITCHOX, 1968b), together with maps showing regional variations in salinity of the formation waters (HITCHON, 1964), allows determination t,i the volume of formation waters of differing salinities. A mass balance ~al~ulatio~l using salinity variations weighted for their respective volumes indicates an average salinity of 46,400 “g/l for the entire western Canada sedimentary basin. The distribution of the individual major components indicates sea water modified by exchange of calcium and magnesium during diagenesis and by bacterial reduction of sulphate to yield H,S and bicarbonate. -However, the salinity suggests that essentially neither the remaining dissolved salts of the original sea water nor t,he products of diagenesis and bacterial action have been lost from the basin, and, in fact, some components (principally sodium and chloride) have been picked up from the rocks as a result of water movement through the basin, The total pore volume of the western Canada sedimentary basin is 63,600 cubic miles, which represents, approximately, the volume of original modified sea water with a deuterium content of no less than 158 ppm (SMOW), and a total dissolved solids content of 35,000 “g/l. This has been redistributed within the basin by fresh water, which has a local mean deuterium content of 136 ppm, to yield an average weighted deuterium content of 142 ppm for the formation waters in the basin. Forty-five thousand nine hundred cubic miles of water would be required to account for the 15,300”cubic-mile volume of formation waters with salinites greater than sea water, assuming perfect efficiency of the shale ultrafilters. The 15,300 cubic miles of formation waters contain 75 per cent of the total dissolved solids in the basin. This means essentially that the major portion of the dissolved solids in the sea water have been concentrated in a quarter of the pore space by the action of 45,900 cubic miles of fresh water. The remaining 25 per cent of the total dissolved solids have been extensively dispersed in the 48,300 cubic miles of pore space with formation waters whose total dissolved solids are less than 35,000 mg/l. Based on these figures the weighted average content of deuterium in the basin due to mixing should be 149 ppm. This is 7 ppm higher than the measured average for the basin. The measured average content of deuterium for the basin requires the mixing of about 184,000 cubic miles of fresh water. This could be interpreted to mean that the shales have at least 25 per cent membrane efficiency. The mass balance of deuterium and total dissolved solids demonstrates that the formation waters in the western Canada sedimentary basin can be derived by mixing of the diagenetioally modified sea water present in the basin prior to uplift with about 24 times as much fresh water which passes through shale ultrafilters with at least 25 per cent membrane efficiency. If the deuterium content of the diagentically modified sea water present prior to the Laramide revolution was less than 158 ppm (SMOW) due to mixing with fresh water, the effect will be to reduce the volume of fresh water mixed in post-Laramide times that is required to produce the present salinity distribution and deuterium mass balance. Thus not more than 29 times as much fresh water will The possibility exists that some sedimentary produce the observed situation. basins may have been completely flushed by fresh water, as suggested by CLAYTON et al. (1966); indeed all variations in degree of flushing and mixing probably exist.

Origin of formation waters in the western Canada sedimentary basin-I FRACTIONATION

1329

OF ISOTOPES

In addition to changes in concentration of deuterium and oxygen-18 brought about by mixing of fresh water and diagenetically modified sea water, oxygen isotopes are known to be extensively fractionated and fractionation of the hydrogen isotopes is possible. Isotopic exchange of oxygen between water and carbonates is temperature dependent and a well known reaction. CLAYTON et al. (1966) have demonstrated exchange between formation waters and carbonates of the rocks. Because temperature and pressure increase rather uniformly with depth, formation waters at greater depths should contain more O” than those at shallower depths, provided sufficient carbonate rocks are available to allow isotopic exchange. In the Alberta basin extensive volumes of carbonate rocks are found only at depth (Table 1) and so any enrichment of 018 in the shallower formation waters is most probably due to exchange with carbonate cements or, less likely because of smaller relative masses, to Table 1. Some physical and geochemical parameters of the Alberta basin in relation to the 79 sets of data on formation waters from oil fields and gas fields of Alberta, Canada

Stratigraphicunit Tertiaryand Cretaceous Jura&c and Tries&. Permian and Carboniferous Upper Devonian-Wabamm and Winterburn Groups Upper Devonian-Woodbend Group and Beaverhill Lake Formation Granite Wash

Average depth of Number of samples samples (ft)

Per cent of samples with H,S in associated Reservoir lithology natural gas

Volume of shales in Alberta basin (cu. miles)

Volume of carbonates in Alberta basin (cu. miles) -

28 5 10

3400 4200 5200

sandstone sandstone carbonate

15 20 30

110,000 4600 8900

240 15,000

13

6700

carbonate

100

230

21,000

21 2

7100 6300

carbonate sandstone

76 0

26,000 -

22,000 -

exchange with carbon dioxide, COa2- or HCOS2- in the water. Most natural gases contain some carbon dioxide with a tendency to increased partial pressure of carbon dioxide in the deeper strata (HITCHON, 1963b) and so the possibility of exchange between the oxygens of water and carbon dioxide cannot be ruled out. Fractionation of the stable hydrogen isotopes may take place between hydrogen sulphide and water, a reaction which is both pressure and temperature dependent and which takes place sufficiently readily to be of use in commercial heavy water plants. CLAYTONet al. (1966) have indicated other processes, such as exchange with the water of hydration in sedimentary minerals or between water and hydrocarbons, which may cause hydrogen isotope fractionation but reliable reaction rates are not available nor are the directions of fractionation known. Increased depth is accompanied by both increased temperature and partial pressure of hydrogen sulphide (HITCHON, 1963b). This component is absent from most of the shallower natural gases in Tertiary and Mesozoic strata and so any enrichment of deuterium in shallow formation waters must be due to factors other than exchange with hydrogen sulphide. In addition to these processes, water from shallow groundwater wells is representative of regional surface isotope characteristics, which vary with altitude and

latitude (FRIEDMANet al., 1964; DANS~AARD; 1954, 1960, 1961) and therefi~rr: isotope fractionation will relate directly to latitude and altitude. Finally, sinc:cd fluid potential is the main driving force isotopic fractionation through shale micro-. pores will vary with fluid potential. No one parameter is likely to control the total fractionation of hydrogen and oxygen isotopes. In order to evaluate each process the nine parameters discussed above were examined by multiple regression analysis. MULTIPLERE~MWXON ANALYSIS Comprehensive evaluation of the physical and geochemical data was carried out by examining the data in two separate groups for surface and near-surface fresh waters, and saline formation waters from oil fields a.nd gas fields. Table 2.

Stable isotopns of hydrogen and oxygen in surface waters from Alberta, Canada

124 133 134

Athabasca River and Paaoa River drainage basins Pembina River -.- 14.9 Peace River -- 15.9 Lake Athabescs .- 15.9

119 120 125 132 131

North SwskstchewrsnRiver drainage basin Lower Waterfowl Lake -- 16.2 North Swkatchewtm River -16.3 North Saskatchewan River -- IF.1 North Saskatctbewan River - 15.6 Battle River -- 13.4

I17 106 103 98

South Saskatchewan River drainage basin Bow River OIdman River OIdman River South S~katoha~an River

--15.6 - ii.7 -l&3 -14.9

-19.3

_. 17.3 -

212 182 249 650

104

Mississippi River drainage basin Milk River

- 14.1

-- 16.8

190

130 100

Basins of internal drainage Cooking Lake Pakowki Lake

-9.2 -9.5

--

1200 1450

123 118 122 75 74

Hot springs, sulphur springs and saline springs Miette Hot Spring, Jasper - 17*0 Upper Hot Spring, Banff - 16.4 Cold Sulphur Spring, Jasper -17.1 La Saline -20.7 --It+3 Mission Sminp

-

204 252 so

-19.9 - 19.9

-19.1 - 14.6

-

-20.6 - le.9 -20.6 -24.8 -20.8

155

146 262 261 845

1730 1040 661 73,300 329.000

Not determined.

Surface and near-szcrfacefresh waters The results of the determination of hydrogen and oxygen isotopes in 20 surface waters are shown in Table 2, and their regional distribution in Fig. 3. Comparable formation for 8 near-surface, potable formation waters is given in Table 3. Those fresh waters for which both 6D and 601* were determined are plotted in Fig. 4 and may be compared with similar data for formation waters from oil fields and gas fields. There is a very high degree of correlation between 6D and 6010 for the fresh

Origin of formation waters in the western Canada sedimentary basin-1 Table 3.

Sample NO.

Stable isotopes of hydrogen and oxygen in shallow, potable waters of Alberta, Canada 6D ( % SHOW)

Description

T~tia~-~&sk5poo Formation 94 Olds well No. 98 95 Olds town well 96 Three Hills well No. 141 97 Three Hills well No. 163

-14.3 -13.5 - 14.4 -18.8

Upper Cretaoeous-Milk River Formation 105 Mel&font farm well 09 Etzikom town well 101 skiff town well Wrentham town well 102

-16.3 -15.1 - 12.5 -9.8

-

1331

- 10.5

Depth (ft)

Total dissolved solids (c&ulated) (m&l)

25 329 shallow 107

2040 1000 3020 1690

225 600 710 800

2910 1670 1980 2440

Not determined.

1.25 .

SAMPLING AND

LOCALITY

NUMBER

u.

5.

A.

Fig. 3. Location of surface waters from Alberta examined in this study.

1332

Fig. 4. Scatter diagram showing relation of 6D ( % SMOW) to SO”* (x0 SMOW) in 13 surface and near-surface fresh waters and 79 oil field and gas field formation waters from Alberta, Canada.

waters (R = &98), and both regression lines are shown in Fig. 4 because there is no reason to expect one variable to be more dependent than another. Both regression lines for the fresh waters have slopes close to 8, similar to that found by CRAIG (1961a) for terrestrial fresh waters without significance evaporation. That nearsurface formation waters are reliable indicators of regional isotopic ratios of surface waters (FRIEDMAN et al., 1964) would probably be confirmed with additional determinations of 6018 on more near-surface potable formation waters. The stable isotope data for several hot springs, sulphur springs and saline springs from Alberta are included in Table 2 and indicate that the water is of meteoric origin. Fluid flow within cells has been suggested for the water within the Canadian Cordillera (HITCHON,1969a), and the isotope data on the hot springs support this contention. The saline spring (No. 74, Table 2) with 329,000 mg/l totaldissolved solids is predominantly sodium and chloride (323,000 me/l). The stable isotope data, the chemical composition and the hydrologic situation all support the thesis that the dissolved salts in this saline spring resuIt from the sodium of halite by meteoric waters (HITCHONet aZ., 1969). Sample 75 is probably the result of solution of halite and gypsum by meteoric waters, and determination of sulphur isotopes in the sulphate from this spring by SA~AKIet al. (1968), KROUSEand SASAKI(1968), and HITCHONet al. (1969) confirm its ancient marine origin. Multiple regression analysis of the surface and near-surfaoe waters was carried out with 6D and 8018 as the two dependent variables. FRIEDMANet al. (1964) and DANSGAARD(1954, 1960, 1961) have shown that temperature, which may be correlated with altitude and latitude, is the chief variable controlling fractionation of the isotopes of hydrogen and oxygen in the surface and near-surface regime of the hydrologic cycle. Altitude, in feet, and latitude, as township, were the two independent variables used in the analysis. Within Alberta the townships range from 1 at the U.S. border to 126 at latitude 60°N., or about 11 townships per degree of

Origin of

formationwatersin the westernCanadasedimentarybasin-1

1333

latitude. The regression equations are: Sli = -10.71 -0.00077 Altitude (in feet) -0*053 Latitude (township) Standard partial regression coefficients: Latitude -0.18 Altitude -0.16 R = 0.58 Multiple regression coefficient: 8% = -12.21 -O*OOll Altitude (in feet) -0.078 Latitude (township) Standard partial regression coefficients: Altitude -0.20 Latitude -0.19 R = 0.70. M~tiple regression coe~cient : These equations indicate that present-day altitude and latitude, which are almost equally important variables, account for less than half the variation in the isotopic ratios for the Alberta surface and near-surface waters; nevertheless, it is a sufficiently large portion of the variation to justify the inclusion of present-day altitude and latitude as independent variables when considering the deeper saline formation waters from oil fields and gas fields. The negative signs in the equations indicate that increased altitude and latitude are associated with lower values of 6D and Sol* as observed by FRIEDMAXet GE,(1964) and DAXHAARD (1954, 1960, 1961). Formation waters Determinations of 6D and 601* for 79 formation waters from oil fields and gas fields in Alberta are shown in Table 4 together with the nine independent variables considered in the multiple regression study. The matrix of correlation coefficients between these nine independent variables and the two dependent variables (Table B) indicates that the degree of inter-correlation among the temperature, pressure, and depth is sufficiently high that only one of these independent variables need be considered. Temperature was selected for inclusion in this study. Multiple regression equations were determined with total dissolved solids, temperature, present latitude, fluid potential and present altitude as independent variables in both equations. The partial pressure of hydrogen sulphide was included as an independent variable in the equation with 6D, and the partial pressure of carbon dioxide in the equation with 8018. The oxygen isotope ratio is governed by equilibrium exchange with carbonates. The functional relationship between fractionation and temperature is essentially linear in the range with which we are concerned (0-lOO”C), although non-linear over wider ranges. The standard partial regression coefficients were calculated and are ranked and listed below: Dependentvariable6D Multipleregressioncoefficient: Standard partial regressioncoefficients:

O-86

0431

Temperature Total dissolved solids P F?id potential Altitude Latitude

Dependentvariable601*

+0*32 $0.19

+0.048 -0.034 -0.026 -0.024

Temperature Total dissolved solids Fluid potential Latitude Pco, Altitude

+1*20 fO*BB -0.54 -0.18 -0.067 + 0.041

1334

H.

ant1 1.

HIT~H~X

Tablo

4.

FkiEn3x.kr

St,able isotopes

of hydrogen

and oxygen

&I

SEampI* Field

No.

Production

Pool

(% SMOW)

b0’” (&

SMOW)

Upper Cretaceous 81 82 83 28 52

Pembina Pembina Pembina Pouce Coupe South Crossfield

Lower G~etaceaus--Lower 27 85 D 80 E 66 68 11 29 36

Colorado

Oil Oil Oil Gnu Oil

-11.4 -- IO.4 -.. 12.1 --I 1.0 - 12.9

-9.3 -12.7

Gas Gas GR9 Gas Gas 011 Gas Oil Oil Oil

---Il.5 --9.8 -- 12.0 ---8.4 - 8.0 -- 9.4 -9.1 -- 10.9 - 9.7 !).7

- 8.9 - 8.9 - 12.8 -5.8 -4.4 -7.1 -7.4 -7.6 -6.4 -5.6

Bantry Mannville A Mannville Mannville A Blairmore Blairmore A

Gras GM f )il Oil Oil Gas Oil Oil Oil Oil Oil Oil Oil

- 12.2 -13.1 -8.1 -9.2 - 9.8 --11.8 -13.0 -- 13.1 -9.8 ~- 3.0 - IO.9 -- Il.0 -8.5

- 10.8 - 14.4 -0.8 -4.0 -5,s - 12.8 - 14.4 - 13.8 -5.2 -5.9 - 8.8 -8.9 -3.0

Jurassic F Swift Ellis

Oil Gas Oil

-1.7 -- 12.6 - 13.0

-0.9 ~ 15.2 --14.6

Triassic A Triassic A

Oil Oil

-8.1 -8-2

-1.7 +o.s

Rundle Banff Rundle Pekisko Rundlo Rundle Rundle Elkton Pekisko Pekisko

Oil Oil

-7.7 - 9.4 -8.0 .- 10.5 -9.3 -13.2 -12.4 -10~3 -8.9 -9.2

-+ 1.7 -7.4 +0*4 -0.5 -2.8 -15.9 -11.2 -5.1 -4.6 - 6.6

-5.7 -8.6

q-3.0 -3.7

Peace River Bow Island Bow Island Bow Isiacnd A Bow Island A Basal Colorado Viking C Viking Viking Viking l3

countess Cessford Cessford Legal JOarCEIZl Chigwell

Gordondale Cold Lake Gilby Glen Park Campbell-Nanmo Pendant D’Oreille Horsefly Lake Wildcat (Southland Bantry Aerial Chauvin B&shill Lake IMaIm

M

-9.4 _..

g*2 -- 10.0

Group

Gordondala Comrey Pendant D’Oreille countess

Lower ~r~t~eous-~annvill~ 26 35 58 1 10 89 71 70 C 55 34 33 30

Keystone Belly River Belly River I Belly River G Doe Creek A Cardium A

A

Group Gething A Colony A Basal Mannvilla B Glauconitio A Namao Blairmore D Mennville A Mannville Roy.Hays

#8-8)

Jurassic 48 88 93

Gilby Aden Conrad

Triassic 24 20

Worsley Sturgeon

Lake South

C5rboniferous 6

8 51 49 43 87 72 69 64 67

Paddle River Glen&s Harmattan Elkton Medicine River Twining North Aden Del Bonita Enchant Jenner Cessford

Upper Devonian-Wabamun 17 4

A I A A A A

GSJ3

Oil Oil GW Oil G&S Oil Oil

Group

Wildcat (Shell Simonette St. Albert-Big Lake

#12-28) D.lB

Oil Oil

111

Origin of formation waters in the western Canada sedimentary basin--I

1335

formation waters from oil fields and gas fields of Alberta, Canada Formation Depth

OrigiZlal p*W+¶We

temperaturs

Total dissolved solids (cEloulated)

Ihid potental (ft above

PH*S

PCO*

sefh level)

W)

W)

Altitude (ft)

Latitude (to~~p)

@if

PC)

f%m

3216 3663 3656 1438 6776

976 1170 1000 440 3670

35 36 42 20 65

12,200 17,200 4500 10,300 6970

1981 1901 1508 2305 6373

0 0 0 0 0

0 2 1 I 0

2896 2762 2880 2727 3877

47 48 47 78 28

2831 2452 2113 2914 2974 2981 3232 2802 3323 4693

626 776 724 1070 1070 1245 1240 860 865 1135

32 26 26 35 36 27

22,900 4780 9110 23,200 26,000 27,200 19,600 64,100 57,100 28,900

1244 260% 2587 2122 2122 2440 2478 1492 1249 865

0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 7 2 0

2624 3282 2979 2490 2490 2362 2706 2326 2546 2828

79 1 3 20 20 24 27 57 48 41

4196 896 7078 4629 3762 2767 3186 3136 3263 4192 2029 2987 4723

1758 226 2300 1920

64 15 6% 68 47

1186 1480 1170 1675 1440 700 940 1475

:l 36 33 47 24 33 65

18,200 31,300 46,500 101,000 103,000 10,900 7170 7600 26,800 19,800 87,000 81,500 154,060

2308 1366 1380 2303 1346 3189 3107 3000 2868 1849 1641 1473 1408

0 0 0 0 0 0 7 0 3 0 0 22 140

8 0 97 27 24 0 100 0 23 1 6 42 28

2493 1743 312% 2469 226% 2950 2862 2604 2471 2702 2046 2282 2707

7% 63 40 40 54 3 8 13 18 2% 43 41 44

7166 2658 3081

2840 920 1300

36 31 34

47,300 2770 6610

1411 2975 3200

0 0 1

140 1 44

3118 3668 3082

40 1 5

3298 481%

1230 2100

43 69

119,000 162,000

1899 2061

0 0

96 66

2345 2121

87 6%

63 43 97 71 64 34 ff 33 43

116,000 81,200 78,100 40,600 48,900 2340 11,000 28,600 24,700 17,300

1416 1664 3004 1470 1232 3168 1905 3244 2500

75 0 2 0 0 1 0 0 0 0

44 Q 140 0 6 11 71 0 37 14

2397 2420 3811 3047 2836 3763 4298 2598 2530 2993

56 65 31 38 33 1 1 x3 20 27

110 63

278,000 119,000

3300 1332

480 11

120 64

2928 2151

63 53

(ft)

6112 4306 9128 8725 6467 2860 6163 3346 3314 4202

10,860 4066

1636 3640 2430

:: 39 46

a

-

1336

Sample No. ~-

Field

Upper Devonian--Winterblrm 2 14 12 44 H 56 37 41 42 48 73

Zipper Devonirtn 25 90 16 19 80 79 50 3 9 13 A 45 38 32 31 H 40 54 47

-Woodbend

I-2A I)-2 D-2B 1%2A D-2 D-2 IX2A J)-2A I)-% D-2-A Arcs

Oil Oil Oil Oil Oil Oil Oif Oil Oil Oil Oil

D-3G I>-3B 11.3 I)-3 D-3 1)-3X 11-3 I)-3A D-3A Cooking Lake 1).3A I)-3A 1).3A Ii-&on A 11.3A 3).3B I)-3A Fenn D-3E D-3A

G&S Oil Oil Oil CA! Gas OiI Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil Oil

.-_(j.* __g.5 __g.‘i - 4.8

n.3 .._ Q.4 3.8

-

___;.I

-8.9 -

8.4

-~I::.4

-+.3.5 - 4.2 ._ 5.2 -1. 7.7 $- 3.6 - j.; 1 7.1 1-0.2 ~~-3.8 -4.6 ~- 14.1

Group

Worslev Norma~dvillo Simon&to Little Smoky Pine Creek Windfall Homeglen-~irn~~~y Bonnie Glen Aoheson Skaro Wimborne Wimborne Cliva Bashaw Malmo Duhamd stott1er Fenn-Big Vallay West Drumheller

Upper Davonian-3eawrhill 92

Group

Wizard Lake Excelsior Fairydell-Bon Accord Wimborne J&i% Alix Chigwoll St&t& Fenn-Big Valley West Drumheller Youngstown

--3.7 -- 5.3 -4.1 ._ 5.0

- 3.4 _ 4.2 - 8.2 -- 6-8 --%I --9.6 -4.9 1.8

- I.2 _._0.3 $3.1 -+ 3.1 __ 7.2 ,6.2

--8.7 -- 8-8

j-5,4 +3.0 +0,4 ---4.0 +7+3 +I.8 +7.6 +7.6 +3?2 j-2.4 -3.2 -4.2 -4.0

Oil Oil

- 5.4 -5.6

-4-2.7 +3.7

Oil Oil

-- 6.4 -4.6

-2.7 -2.6

--6.1 _--5.8

-6.7 5.0 -- 8.5

Lake Formation

Snipe Lako

Beaverhill Lake IVest Beaverhill

Lake

Granite Wash 23 91

Wildcat (Triad Iroquois #l&16) I&d Earth

Granite

Wash A

The multiple regression coefkients are high and indicate that most of the variation found in 6D and 601s (65 and 74 per cent, respectively) is explained by the interactions of the six variables used in the regression equation. The effect of regional variations in the isotope ratio of the initial fresh water entering the regional flow system in Alberta upon the isotope ratios of the deeper saline formation waters is negligible as indicated by the very low standard partial regression coefficients for altitude and latitude. It is also apparent that for both 6D and 60f*, the major portion of the variation can be correlated with temperature and total dissolved solids. The matrix of correlation coefficients in Table 5 shows that for both 6D and 601* the independent

Origin of formation

waters in the western Canada sedimen&ry

basin-4

(oantinued)

194,000 116,000 106,OQO 220,000 183,000 217,000 250,000 161,000 118,000 124,ooo 32,700

1287 1266 2607 1754 2464 2067 1642 167% 1717 1722

10 26 59 800 42 430 170 57 56 2 92

TtY 40 81 81 66 69 68 68 66 5s 56

209,000 256,000 284,000 286,000 199,000 1OQ,OQO 239,000 258$QQ 213,000 161,QOO 204,000 212.000 216,000 206,000 198,000 21O.OOQ 134OOQ 121,QQQ 127,QQO

2621 2449 3225 2806 3446 3107 K69Q 1626 1294 1239 2788 2788 2828 2605 24QQ 2029 1694 1648 1735

0 0 860 270 1140 580 160 If 0 34 480 480 470 280 80 9 49 14 8

3820 3600

87 96

228,000 186,000

27BO

3130 2320

81 42

209,000 2Q7,OOQ

2800

5710 3001 3lb8 7433 7004 5977 Bow 6198 5319 5530 3696

2000 1265 1186 2970 2640 2410 2300 1740 1810 2000 f270

7246 6793 11673 871Q 11179 8469 7809 7084 6122 3678 7664 7487 6296 6610 6267 4812 6386 5216 6637

3330 3166 5166

8902 9112

7826 4763

4700 3810 2835 2480 1730 1230 3070 3070 2640 2200 2166 1876 1360 1850 2040

*II 48 46 79 76 60 69 63 68 56 42

76 1:: 81 118 9% 82

1477

2437

8

2638 2296 2303 3175 2800 2886 2794 2698 2800 2604 2489

48 66 61 33 39 40 41 38 36 29 31

2248 1876 2860 2206 3730 2671 3086 2837 2354 2078 3243 3243 2941

2481 2774 27QQ 2653

87 7% 63 67 67 60 43 47 52 67 34 34 40 42 44 45 38 36 30

68 bl

2838 3638

10 63

13 6

2081 1796

76 87

79 310 160 82 120 41 4 210 210 18Q

0 29 40 44 200 220 43 16 19 14 59 it 67 48 3% 260 230 96

Notes: 1. Origind pressaad fbrmatio~ te~~per&me d&a abtaimd mainly from report OGGl3-65-9, Oil snd Gas Conservation Bomd, Calgsry, Alberte. 2. Total dissolved solida obtained from D. R. SILAW, Chief Chemist, Oil and Caa Consanration Board, Edmonton, Alberte. 3, Fluid potential calcuIEuted using origins1 pressure, euba@a elevation of sampling paint and freshwater density

(p = 1.0). 4. Partial pressures of H,S and CO, obtained using original pressure snd data from SHAW (1968).

variable with the highest correlation coefficient is total dissolved s&ids. There is also a ~eas~nably high degree of correlation among depth, pressure, temperature and t&af dissolved solids. The multiple regression equation confirms the dominance of these variables in controlling the variation of 8D and 6CP and demonstrates that exohsnge of deuterium between water and hydrogen sulphide or of oxygen between water and carbon dioxids is of much less importance. 2

As was anticipated by our model. the effect of increasing depth, total dis;solved solids and partial pressure of hydrogen sulphide is to cause enrichmcint of the water in the heavier isotope, as evidenced by the signs of the standard partial The rather large negative effect of fluid potential in tltcb regression coefficients. 6018 equation may result from the fact that exchange of oxygen between the water and carbonate rocks can mainly take place only in the regime of the low fluid potential drain which lies within the thick sequence of Carboniferous and Upper Devonian carbonate rocks in the dlberta basin (HITCHOX, l!N%). i4 decrease in fluid potential accompanies an increase in depth; when only temperature and total dissolved solids are the independent variables the multiple regression coefficient is 0.84, which implies that these two variables alone are sufficient, to account8 for 70

6D I.000 g,

Depth i)O’8 _..--_-..

0.8i3 1.000

Depth P.WSSWW Temperature Total dissolved solids Fluid potential

0.691 0.732 1.000

Total Temprbr- dissolved Fluid Pressure tlwe solids potentml PQA ________-._-__-_--I-_-_-I

0.698 0.686

o.i20 0.778

0.768 0.08i O.B2!) I).:!% -0.012 O-844

0.956 l-000

0.968 0.927 I-000

0.702 0.705 0,754 I.000

PHeS

Pco,

I’CO,

Altit udo

0.19; --0~06’3 0.247 0.012

0.298 0.496 0.260 0.062

0.608 0.628 0.615 0.501

0.338 0.301 0‘369 0.229

0.327 0.259 0.270 -0~185

1.000

0.346 1.000

--0.039 0.348

0.430 0.261 0.127 I.000

I.000

Altitude Latitude

Letituril? -. O-410

0.383 0,305 0.316 0.354 0.524

-.0.224 0.121 0.038 - 0.513 1.000

per cent of the variation in the oxygen isotope ratios. Similarly, for 6D, these same two variables yield a multiple regression coeflicient of @SO. The major part of the variations in isotope ratio of the stable isotopes of hydrogen and oxygen in formrttion waters of Alberta may be expressed by the following regression equations: Sfi = -12.57 &?I16= -13.90

+0*040

Temperature

$-O-12 Temperature

(“C) +O~OOOOlS Total dissolved

solids (mg/l)

(“C) +0*000035

solids (mg/l).

Total dissolved

The limited importance of isotopic exchange between water and hydrogen sulphide may be indicated more precisely by treating the data as two groups, one with hydrogen sulphide and the other in which this component was absent in the associated natural gas. E’or the 40 samples without hydrogen sulphide, the multiple regression coefficient was 0.7 1 with temperature and total dissolved solids as the dominant independent variables. Thirty-nine samples were associated with natural gases containing hydrogen sulphide at partial pressures up to 1140 psi. Multiple regression analysis of these samples was carried out against the same independent variables as were used in the samples without hydrogen sulphide, and the resulting multiple regression coe%oient was O-88. Temperature and total dissolved solids The inclusion of partial pressure of hydrogen were again the dominant variables. sulphide as an independent variable in the regression analysis of the samples with hydrogen sulphide resulted in a multiple regression coefficient of O-89. Apparently

1339

Origin of formation waters in the western Canada sedimentary basin-1

isotopic exchange between water and hydrogen sulphide in the Alberta basin is not an important factor controlling the deuterium content of the formation waters. IXPORTANCE

OF RELATIVE

MASSES

OF M~TERLALS

IN ISOTOPIC

EXCHANGE

The relative masses of the materials undergoing the exchange reaction is an important parameter in any study of isotopic exchange. The predominant fluid in the underground environment is formation water. The effect of the temperature dependent isotopic exchange between water and hydrogen sulphide will be insignificant simply because of the insignificant amount of hydrogen sulphide relative to that of the formation water. Thus variations in isotopic ratio of hydrogen (and oxygen} in formation waters will reflect exchange mechanisms which have affected the major mass of the formation water throughout the basin. Table 6.

Smple No.

Parameters

used in the study of water samples rejected on the basis of their chemical composition

Cm Production (% SMOW)

SO’S (x0 SMOW)

PH*8 (psi)

RI5

Oil

-6.2

R18 R21 R52 R63

Oil Oil Oil GM

-5.7 - 10.7 -6.3 - 15.2

+4.3 -8.6 - 17.0 -6.1

128,000 21,600 1920 680

175,000 221,000 7000 62,000

0 0 0 20

R67 R59 R61 R62 R63

Oil GaS G&W GN Gas

-6.2 -j-11*9 -+8.8 -/-6.5 -104

+7*4 -0.2 -2.3 - 8.8 -8.1

89,600 1610 40,200 6420 1010

214,000 76,000 69,000 24,000 7000

0 1000 940 100 0

R65 R77 R84

Oil Oil GaS

6110 1590 2630

23,000 70,000 77,000

3 36 34

-9.6 -2.7 -4.4

+ I.8

Total dissolvedsolids As (rug/l) (calculsted) RepresenttLtive sampled V&e

-1l.O -4.3 -2.8

62,200

133,000

0

The importance of the relative masses of the materials undergoing isotopic exchange may be illustrated by examining the isotopic ratios in formation waters collected during the course of this study, but which, on the basis of chemical analyses, were rejected as non-representative. The pertinent data for these samples are given in Table 6. The samples contain very low total dissolved solids relative to representative formation waters from their respective oil fields or gas fields, and in some cases the proportions of the individual ions fail to agree with the best analysis available. In oil fields contamination with waterflood water is the most likely explanation for the low total dissolved solids content. The water collected from the gas fields is probably condensed water vapor which has been brought up with the natural gas and mixed with a minor amount of formation water. As might be anticipated, graphs of SD and 601a against measured total dissolved solids (middle diagrams, Figs. 5 and 6, respectively) show that many of these rejected samples fall far outside the trends obtained by plotting these same variables using the 79 representative formation waters in Table 4 (top diagrams, Figs. 5 and 6, respectively). When 6D and 6018 of these rejected samples are plotted against the respective representative total dissolved solids for each sample (bottom diagrams, Figs. 5 and

1340

Fig. 5. Scatter diagrams showing relations of 6D( % SMOW) to total dissolved solids for 79 representative formation waters used in this study (top diagram); to measured total dissolved solids of 13 non-representative formation waters (middle diagram) ; and to the representative value for total dissolved solids in the same 13 rejected samples (bottom diagram). 6, respectively), the adjustment to the correct salinity places all points on the Sol* graph within the trend obtained for the data in Table 4, but this is not true for the SD graph. This is interpreted to mean that the 60x8 value an the rejected samples is correct, and that it is the BD values which are in error. The most sensitive graph on which to check this assumption is that of BD against 6018, for which the 79 representative samples had a correlation coefficient of 0.87. When plotted on this graph (Fig. 7) five of the samples fall within the trend for the rep~sentative data, one on the deute~um-de~cient side and the remaining

Origin

of formt&xi

waters in t&3 w0stern

Canada gedimantary bcasin-4

1381

1342

13.

HITCHOX

and I.

FPJEDMAN

oil fields are subjected to water flooding and because the surface waters lie at the deuterium-poor and oxygen-l&poor end of the trend for the representative data the effect of mixing formation water and fresh water used for water flooding in fields without hydrogen sulphide will be to move the data points down the trend for the representative data towards the region of the graph in which the surface and nearsurface water data are found. The effect of water flooding would be exactly the same for samples associated with natural gases with high partial pressures of hydrogen sulphide. The reason that samples associated with high partial pressures of

+ 10 ‘0 R61

+5

Fig.

7.

I-

-10

-

-15

r

= R62

o R 53

i

Scatter diagram showing relation of dD( % SMOW) to 6016 (zO SMOW) in 13 non-representative formation waters.

hydrogen sulphide and non-representative total dissolved solids fall outside the trend for the representative data is not because of incorrect 601* values, but because the water sample has been subjected to exchange of deuterium with hydrogen sulphide consequent upon dilution of the formation water. The amount of condensed water vapor found with natural gases when they are sampled at the surface is insignificant in relation to the amount of formation water with which the natural gas is associated in the reservoir. High partial pressures of hydrogen sulphide result in extreme enrichment of the small amount of condensed water in deuterium but not in O18. The fact that one sample (R53) falls on the deuterium-deficient side is possibly an indication that the proportions of formation water, condensed water vapor and natural gas may be altered under differing temperature and pressure gradients during the passage of the fluids from

Origin of formation w&ers in the western Canada,sedimentary besin-1

1343

the reservoir to the sampling point to yield either enriched or depleted samples, The separation factor between depending upon the exact physical conditions. H%O/H,S favors enrichment of the H,O as the temperature decreases (BANCROFT, 1968), and this is undoubtedly an important feature in explaining some of the deuterium enrichment in the non-representative samples. This study of thirteen rejected samples demonstrates the importance of considering the relative amounts of materials involved in all isotopic exchange reactions. It also indicates the care which is required in sampling formation waters and suggests that two parameters should be measured to ensure confidence in samples to be used for isotope studies. These parameters are : (1) a chemical composition consistent with the water in the formation, and (2) 6D and 601* data which fall within a fairly narrow trend for that geographical region. With the data available the isotope fractionation between water and carbonate rocks cannot be treated statistically as comprehensively as that between water and hydrogen sulphide. If the 79 sets of data in Table 4 are divided into two groups, samples from sandstone reservoirs and samples from carbonate reservoirs, a more precise indication of the relative importance of mixing and of exchange of the oxygen isotopes between water and the carbonate rocks can be obtained. Multiple regression analysis of the 35 waters from sandstone reservoirs indicates a multiple regression coefficient of O-79, with temperature and fluid potential almost equally weighted-but with opposite signs in the regression equation. A similar analysis of the 44 waters from carbonate reservoirs showed temperature the dominant independent variable, but a multiple regression coefficient of 0.82. This suggests that oxygen isotopic exchange between water and carbonates is effective in all reservoirs because sufficient carbonate is present as either cement or host rock to allow equilibration. To evaluate further the oxygen isotopic exchange between carbonate and water, oxygen isotopes were determined for a selected suite of rocks representing reservoirs from which the formation waters had been sampled. The measured 601* of the carbonates, and subsequent calculations based on these values, are shown in Table 7. In making these calculations, we have assumed that the water and the reservoir carbonate were in equilibrium and the relative amount of sea water and fresh water in the strata can be found by consideration of the deuterium content of the formation water. The fourth and fifth columns show the measured 6018 of the formation water in contact with the carbonate at reservoir temperatures (taken from Table 4), and the calculated 601* of the water that should be in equilibrium with the measured oxygen isotopic composition of the carbonate at the same reservoir temperature using the equilibrium relation 1000 In a = 2.7 (106T-2) - 2.0 (J. R. O’NEIL, personal communication, 1968). The discrepancies between the measured and calculated oxygen isotopic composition of the water are due to differences in the relative masses of carbonate and water in the various stratigraphic units. If, as a first approximation, the deuterium content of these formation waters is used as an indicator of the degree of mixing of the diagenetically modified sea water (SMOW) and the fresh water, and which has a local mean deuterium content of 136 ppm, then the proportion of fresh water in each sample can be calculated (Table 7, column 6). CRAIG (1961a) has calculated the regression relation between

$3. HITCH~K Ltnd I. FI~IIEI)MIAN

1344

Tsble 7.

Stable

oxygen

isotopes

in carbonat,es

._______ ._ Sample No.

Description

601R (%, mow) carbon&! (measured)

(measured)

(celouleted in quilibriurn at, reservoir temporatnrc)

upper Creetaceous Sandstone 28

+K+5

-9.3

Lower Cretaceous-Lower Colorado Grow 27 Sandstorm D Sendstonn 60 Sandstone 36 Sandstone

+2X.4 + 22.4 $19.2 $21.8

-8.9 .- 12.8 - 5.8 ._ 5.6

- 5.8 -. 6,O -7*4 -3.0

Samistone

Sandstone Sandstone

+ 16.0 + IS.4 + 20.4

-4-O .- 12*8 - 5.9

-6-7 -- 8.5 -0.4

Dolomitic sandstone

+ 26.5

-0.9

$3.2

Dolomite Secondary calcite Dolomite Limestone Limestone Limestone Secondary calcite

126.3 i 18.0 + 26-2 + 20.8 +20.6 +!a.0 + 16.9

-7.4 -7.4 __ 15.9 - 15.9 - 15*9 .__5.1 -. 5.1

0.0 -0.8 -6.0 -6.0 -5.1

Upper Devonian-Winterburn Group Dolomite 12 Dolomite 37 Dolomite (vugula;r porosity) 46 Dolomite (intestine porosity) 46A Dolomitic anhydrite 73

+25*7 + 26.8 + 26.9 + 26.8 + 24-8

-5.2 J-7.1 -4.6 -4.6 - 14-1

0.0 +5.3 +3*4 +3*4 -0.7

Upper Devonian-Woodbond Group Dolomite 90 Dolomite 16 Dolomite 19 Secondary dolomite and anbydrite 19A Dolomite 80 Dolomite 50 Secondfcrydolomite 5OA Dolomite 3 Seaondery dolomite 3A Dolomite 38 Dolomite 40

+ 26.7 +26.3 + 26.3 +21.6 $24.3 _t26,2 + 24.6 +24.?? +23.7 + 26.5 +25*9

-0.3 -t- 3.1 -j-3.1 .-+3.1 f7.2 j-5.4 + 5.4 Jr 3-O j-3.0 C7.6 .._ 3.2

+a.0 +9*0 $7.6

T1.7 + 3.9

Upper Devonian-Beeverhill Lake Formation Limestone 92 Limestone F

j-21.7 +21-7

1-2.7 +3.7

+2*6 + 3.6

Lower Cretaoeous-Mtxmville I

89 55 Jurlrssic 48

-11.0

Grow

Carboniferous 8 $A 87 87A 87B 69 69A

+8.3 15.5 14.8

Origin of formation waters in the western Canada sedimentary basin-1 from reservoir rocks, Albeti, Proportion of fresh water baaed on deuterium content

Canada,

Calculated original SO’* (“/ SMOW) of form&ion water before equilibration

Change in &Ox* ($& SMOW) from original formation water to present, due to equilibration

-

Change in 6018 (% SMOW) from original limestone to present, due to equilibration

Change in oarbonate Change in formation water

o-79

-13.4

+4*1

-11-6

2.8

0.82 0.86 0.60 0.09

-14.0 - 14.6 -10.2 -11.8

-j-6*1 f-1.8 +4*4 +a*2

-3.6 -7.6 - 10.8 -8.2

1.7 4.2 2.6 1.3

046 O-84 o-21

-11.2 -14.3 -3.6

+7*2 +l*b -2.3

- 14.0 -11.6 -9.6

1.9 7*7 4.2

04%

-9.4

j-8.6

-3.6

0.41

0.67 0.94 0.94 0.94 0.74 -

-11.4 - 16.0 - 16.0 -16.0 - 12.5 -

$4.0

-3.7 -3.8 -9.2 -9.4 --9*O -

0.69 0.41 0.60 0.60 0.96

-11.8 -7.0 - 10.2 -X0*2 -16.3

0.38 0.29 0.36 0.24 o-59 0.49 0.44 0.61

-6.4 -5.0 -6.1 -4.1 - 10.0 -8.3 -7.4 -10.3

o-39 0.40

-6.6 -6.8

t-o.1 +0*1 -j-O*1 t7.4 -

+a*6 -+-la.1 f6.6 +&6 +2+2

+9*4 -t_ 10.6

-4.3 -3.2 -3.1 -3.2 -5.2

0.93 38.0 92-o 92.0 I.2 -

0.66 0.23 0.55 0.67 2.4

- 3.3 -3.7 -3.7 -6.7 -4.8 -6.2 -3*b -4.1

0.54 0.46 0.40 0.60 0.31 0.46 0.23 0.56

-8.3 -8.3

0.68 0.79

&D and 6Ol8 for fresh waters throughout the world, and from this relation, a,ntl knowledge of the proportion of fresh meter in the sample, we can calculate then 6018 value of the original formation water before oxygen isotopic exchange with the carbonates took place, and this value is shown in column 7 of Table 7. If WV now assume that the original 601” of the limestone was +3i)%,, a value representative of modern carbonates, then the change in oxygen isotopic composition of both the formation water and the limestone from their original values to their present values under the influence of both reservoir temperature and their relative masses can be computed (Table 7, columns 8 and 9). Although the 6018 values of both modern and ancient limestones vary within fairly narrow limit#s, the range of values is sufficiently small that even if extreme vaIues were used in the calculations the conclusions would remain valid. By comparing the change in 6Ol8 in the limestone with the change in 601* in the formatio~l water, the relative proportions of calcite and water which reacted to give the measured carbonate 601* values can be calculated, and this proportional is shown in the final column of Table 7. If we consider the values in two groups, those from the Cretaceous and those from the pre-Cretaceous, which * have arenaoeous and carbonate reservoirs, rr$spectively, then among the Cretaceous samples those with the highest values and hence the largest mass of water, relative to carbonate, are from active fresh-water recharge areas (D, 60, 89, 55). Similarly, in the pre-Cretaceous samples, those from active freshwater recharge areas (87, 69, ‘73) have values greater than unity; all other samples range from 0.23 to 0.93 with an average of 0.53, indicating inverse proportions of carbonate and water. As with deuterium, the relative masses of the components undergoing isotopic exchange exerts a’ strong influence on the resulting isotopic composition.

DEUTERIU~~ FRACTIONATION

BY SHALE

~C~OPORES

GRAF et al. (1965) have postulated a small isotopic fractionation of deuterium resulting from passage of water through micropores in shales. This postulation can be qualitatively checked using the more comprehensive set of data now available from Alberta. If, on a graph similar to the top diagram in Fig. 5, there are superimposed lines joining up points on the same flow paths, as in Fig. 8, then this diagram can be used to illustrate the effect of both mixing and shale micropore fr&ctionation on the deuterium content of formation waters. In Fig. 8 the arrows point in the direction of flow, as determined from hydraulic head maps (&TCHOTU', 1969a, b). Those lines pointing, in general, from lower left to upper right are from regions where there is active freshwater recharge. In these regions the formation waters become more saline downflow and the deuterium content increases through All lines trending generally from upper right to lower left represent mixing. formation waters moving from the deeper parts of the Alberta basin, updip, out of the basin. In these formation waters the more saline waters are those on the upflow side of the shale ultrafilters and have consequently increased contents of both dissolved solids and deuterium. The formation waters that have passed through the ultrafilters are fresher and contain lower amounts of deuterium. In Part 2 of this

Origin of formation waters in the western Canada sedimentary basin-I

1347

400,000

: 300,000 m E m " G Ln 200.000 D Y d 2 0 ;

/

100,000

b t-

A ,_C.

0 -20

-15

-

.-..-.-.._

___L -10

-5

0

SDIXSMOW)

Fig. 8. Relation of 6D and SO’* to flow directions in formation waters from Alberta, Canada.

series of pctpers (BILLINGS et al., 1969) evidence will be presented to show that there is ionic fractionation, as well as changes in total dissolved solids. Acknowledgme&+-Special acknowledgmentis made to Dr. J. T~TH, Research Councilof Alberta, for many constructive ideas originatingout of extensive discussionswith the senior author on a multitude of topics related to hydrodynamics. We appreciatethe cooperationof the Oil and Gas ConservationBoard of Alberta in collecting the form&ion waters and especially the able assistance of Mr. D. R. SEAW, Chief Chemist. Mr. MELVIN STROSEERof the Research Council of Alberta assisted in the field work and was responsiblefor sample preparation prior to isotope analysis and his thorough work is specially appreciated. The assistance of Dr. ROBERTRYE, Mr. JIM GLEASONand Mrs. JOY CWRCH in carrying out the isotopic analyses is most gmtefully acknowledged. Critical and constructive reviews of the manuscript were provided by Dr. H. W. HA~~OOD, Dr. R. GREEN,and Dr. A. VANDENBERU of the Researoh Council of Alberta; Dr. BRUCEB. HANSHAWand Dr. BLAIRF. JONESof the U.S. Geological Survey; Dr. DONALDL. GRAF,Department of Geology and Geophysics, University of Minnesota; Dr. H. ROY K~OUSE, Physics Department, University of Alberta; Dr. G. K. BILLINUS,Department of Geology, Louisiana State University; Dr. PETER FRITZ, Department of Geology, University of Alberta; Dr. J. E. KLOVAN, Department of Geology, University of Calgary; and Mr. A. R. BANCROFT, Chalk River Nuclear Laboratories, Ontario. To all these reviewersthe authors express their sincerethanks for their comments. REFERENCES BAERTSCHI P. (1953) tuber die relativen unterschiedeim H8’*0-gehalt n&.irhcher wiisser. He&v. Chim. Acta 86, 1352-1369. BANCROB”~ A. R. (1968) The Canadian approachto cheaperheavy water (1967). Atomic Energy of Canada Limited, Report AECL-3044. BERRYF. A. F. (1958) Hydrodynamics and geochemistryof the Jurassicand Cretaceoussystems in the San Juan basin, northwesternColorado. Ph.D. Thesis, Stanford University. BELAY F. A. F. (1967) Role of membrane hyperfiltrationin origin of thermal brines, Imperial Valley, California. Amer. ASSOC.Petrol. Ueol. Bull. 51, 454-455.

1348

1~.HHrYcrior and I. FRIEDMAN

F. A. F. and H~N~HA~ B. B. (1960) Geologic field evidence suggesting membrane properties of shales. I’ol~me. ofAbstracts, Tvi~ev~t~-~~rst Int. GeoL Congress. ~open,h~gen, p. 209. I& Berlingske Bogtrykkeri, Copenhagen. BILLINGS G. R., HITCHON B. and SHAW I). R. (1969) Geochemistry and origin of formation waters in the western Canada sedimentary basin. 2. Alkali metals. Chevn. Geol. 4,21 l-223. BREDEHOEFTJ. D., BLYTII C. It.. WAITE W. A. and MAXEY G. B. (1963) Possible mechanism for concentration of hriues in slrbsurfaoe formations. Amer. Assoc. Peb~rol.Geol. Bull. 47, 257-269. CLAYTON R. X., FRIED~UN I., GXAF D. L., MAYEDA T. K., MEE~TS W. F. and &IMP h’. F. (1966) The origin of saline formation waters, 1. Isotopic composition. J. GeopJ~~~s. Res. n, 3869-3882. CRAX3 H. (1957) Isotopic standards for oarbon and oxygen and corxection factors for msssspectrometrie analysis of carbon dioxide. Geochim. ~o~moch~~b.Acta 12,133-149. CRAIQ H. (196la) Isotopic variations in meteoric waters. Scie7ace133, 1702-1703. CRAIG H. (1961b) Standards for reporting conoentrations of deuterium and oxygen-18 in natural waters. Science 133,183331834. DANSCUD W. (1954) The Cl’*-abundance in fresh water. Geochim. Cosmochivn. Acta 6,241-260. DANSGAARDW. (1960) 01* in atmospheric waters. Summer Course on Nuclear Geology, Varenvq 1960, pp. 150-166. Comitato Xazionale per L’Energie Nucleare, Lab. di Geol. Pu’ucleare,Piss, Italy. DANSCAARD W. (1961) The isotopic composition of natural waters with special reference to the Greenland ice cap. Medd. Gr~la~~ 165, I-L20. DE~ENS E. T. (1962) Geochemische untersuohungen von wiissern aus der Agyptischen Sahara. Geol. Rundsch. 52, 625-639. DEGENS E. T., HUNT J. M., REUTER J. H. and REED W. E. (1964) Data on the distribution of amino acids and oxygen isotopes in petroleum brine waters of various geologic ages. &dimentology 3, 199-225. EPSTEIN S. and MAY~DA T. (1953) Variation of Oxa content of waters from natural sources. Geoe&m. ~osmoch~m. Acta 4, 213-224. FRIEDMAN I. (1953) Deuterium content of natural waters and other substances. Geo~~~~~. Cosmochim. Acta 4,S-103. FRIEDMAN I., REDFIELD A. C., SCHOENB. and I%ARRISJ. (1964) The variation of the deuterium content of natural waters in the hydrologic oycle. Rev. Geophys. 2, 177-224. FRIEDMAN I. and WOODCOCKA. H. (1957) Determination of deuterium-hydrogen ratios in Hawaiian waters. Tellus 9, 553-556. GORRELLH. A. and ALDER~M~NG. R. (1968) Elk Point Group saline basins of Alberta, Saskatchowan, and Manitoba, Canada. Geol. Sot. Amer. Xpec. Paper 88, 291-317. GRAF D. L., FRIEDMAN I. and DENTS W, F. (1965) The origin of saline formation waters, II. Isotopio fractionation by shale micropore systems. I~~~no~sState GeoE.Swrv.‘r.Circ. 393. HA~LEVYE. and PAYS B. R, (1967) Douterium and oxygen-18 in natural waters: analyses compared. Science 133,669. HANSHAW B. B. (1962) Membrane properties of compacted clays. Ph.D. Thesis, Harvard University. HANSHAW B. B. (1964) Cation-exchange constants for clays from electrochemical measurements. Clays, Clay Minerals 12, 397-421. HANSKAW B. B. and ZEN E. (1965) Osmotic equilibrium and overthrust faulting. Geol. Sot, Amer. B&l.. 76, 1379-1386. HITCHON B. (1963a) Geochemical studies of natural gas. Part I. Hydrocarbons in western Canadian natural gases. J. Can. Petrol. Tech. 2, 60-76. HITCHON B. (196313)Geochemical studies of natural gas. Part II. Aoid gases in western Canadian natural gases. J. Cun. PetroE. Tech. 2, 100-l 16. Inert gases in western HITCHON B. (19630) Ceochemical studies of natural gas. Part III. Canadian natural gases. J. Can. Petrol. Tech. 2, 165-174. HITCHON B. (1963d) Composition and movement of formation fluids in strata above and below the pm-Cretaoeous unconformity in relation to the Athabasca oil sands. The K. A. Clark Volume, pp. 63-74. Research Council of Alberta, Edmonton, Alberta. BERRY

Origin of formation waters in the western Canada sedimentary basin-I

1349

HITCHONB. (1964) Formation fluids. In Beological History of Western Canada, Chap. 15. Alberta Sot. Petrol. Geol., Calgary, Alberta. HITCHON B. (1968a) Geochemistry of natural gas in western Canada. Natural Bases of North America, Vol. 2, pp. 1995-2025. Amer. Assoc. Petrol. Geol., Tulsa, Oklahoma. HITCHON B. (1968b) Rock volume and pore volume data for plains region of western Canada, sedimentary basin between latitudes 49” and 60”N. Amer. Assoc. Petrol. Beol. Bull. 52, 231% 2323. HITCHON B. (1969a) Fluid flow in the western Canada sedimentary basin. 1. Effect of topography. Water Reaour. Res. 5, 186-195. HITCHONB. (1969b) Fluid flow in the western Canada sedimentary basin. 2. Effect of geology. Water Resour. Res. 5,460-469. HITCHON B., LEVINSON A. A. and REEDER S. W. (1969) Regional variations of river water composition resulting from halite solution, Mackenzie River drainage basin, Canada. Water Resour. Res. in press. HITCHONB., ROUND G. F., CHARLESM. E. and HODGSONG. W. (1961) Effect of regional variations of crude oil and reservoir characteristics on in situ combustion and miscible-phase recovery of oil in western Canada. Amer. Assoc. Petrol. Geol. Bull. 45, 281-314. KROUSE H. R. and SASAKI A. (1968) Isotopic studies of springs in western North America. Beol. Sot. Amer. Program with _&strmt8, 1968 Ann. Mtg., p. 16’7. MCCREA J. M. (1950) On the isotopic chemistry of carbonates in a paleotemperature scale. J. Chem. Phys. 18,849-857. MCCROSSANR. G. and GLAISTERR. P. (1964) CTeologicalHistoq of We&em Cunuda. Alberta Sot Petrol. Geol., Calgary, Alberta. ROTH.E. (1956) Problemes relatifs a la production d’eau lourde en France. Atti Congress Sci., Sez. Nucleare, III, Roma, 1956, p. 337. SASAEI A., tiOUSE H. R. and COOKF. D. (1968) Sulphur, carbon and oxygen isotope variations in springs of western Canada. Physics in Canuda 24, 10. SUMA T. and CLAYTONR. N. (1965) Measurement of 018/01Eratios of total oxygen of carbonates. Beochim. Cosmochim. Acta 29, 1347-1353. SEIAWD. R. (1968) Acid gas content of Alberta natural gases-to June 1, 1968. Oil and Gas Conservation Board, Calgary, Alberta. WHITE D. E. (1965) Saline waters of sedimentary rocks. In Fluids in Subsurface EnvironmentsA Symposium, pp. 342-366, Mem. 4. Amer. Assoc. Petrol. Geol.