Light-Oils Transformation to Heavy Oils and Asphalts-Assessment of the Amounts of

Hydrocarbons Removed and the Hydrological-Geological Control of the Process

E. Tannenbaum1 A. Starinsky z. Aizenshtat Hebrew University Jerusa lem, Israel

Heavy oils frequently represent a residue left after removal of saturated and aromatic hydrocarbons by var-ious alteration processes. They are characterized by a high content of asphaltenes and polar compounds and by higher sulfur content than the light oils from which they were derived.

In the Dead Sea area (Israel), light oils contain 20% asphaltenes plus polar compounds and approximately 2.5% sulfur. Asphalts, which were shown to be genetically related to the above oils, but have been altered, contain 80% asphaltenes plus polar compounds and approximately 10% sulfur.

The present study attempts to explain: (1) the quantities and types of oil constituents that were removed via the alteration processes, and (2) the geological-hydrological control of these processes.

We have applied material balance calculations in which we assume that saturated and aromatic hydrocar-bons are preferentially removed from the oils at different rates, while the polar compounds and the asphal-tenes remain behind as inert components. The different removal rates are explained by contrasting intensities of water washing and biodegradation. These processes seem to be affected by the extent of mixing between brines that are in contact with the oils and meteoric water.

According to these calculations, more than 75% of the light oil constituents have been removed by the alter-tion processes, and the asphalts represent a residue of 10-20% of the original oils. The calculations also imply

that there is no reason to assume secondary enrichment of sulfur (by addition), and concentration of sulfur-ch compounds can account for the high sulfur content of these heavy oils.

INTRODUCTION

In the course of low-temperature oil alteration pro-cess~s (biodegradation and water washing), low and medium molecular weight hydrocarbons are removed fro~ the oils. Consequently, heavy oils and asphalts, wfhich are difficult to exploit, are formed. Many aspects b these processes are still unresolved; for example, iodegradation and water washing are processes that

are usually active simultaneously and are believed to ~huse. approximately the same long-term changes in

~ ~i ls (Bailey et al., 1973a; Milner et al., 1977). The re ative contribution of each of these processes to the

1Present . . L~nd TX address. Anadnll/Schlumberger, 200 Macco Blvd., Sugar

77478.

221

oil alteration is unclear. Another difficulty is in deter-mining the quantities of the original oil constituents that have been removed during heavy-oil asphalt for-mation. This question has not been investigated in detail (Tissot and Welte, 1978), although it is generally accepted that removal of tens of percents from the original oil is conceivable (Bailey et al. , 1973a; Orr, 1978; Price, 1980).

A major portion of the world's petroleum resources are in the form of tar sands and other heavy oil depos-its (Demaison, 1977; Mossop, 1980) . For example, the Cretaceous oil sands of Alberta (Canada) are now estimated to contain 1350 billion barrels of oil (Mos-sop, 1980), and it is believed that these heavy oils have been formed by water washing and biodegradation of conventional oils (Deroo et al., 1977; Rubinstein et al., 1977). This may mean that amounts of oil constituents

222 Tannenbaum, Starinsky, Aizenshtat

similar to, or perhaps even larger than the proven quantities, have been removed by the alteration pro-cesses. Hence, for better understanding of the pro-cesses that lead to formation of heavy-oil deposits, it is important to estimate the quantities that have been removed. Also these quantities should be taken into account while calculating the petroleum potential of a sedimentary basin.

The present study investigates various oil shows (light and heavy oils and asphalts) in the Dead Sea area (Israel), and by material balance considerations we explain the following :

1. The quantities of the original oil constituents that have been removed via the alteration process .

2. The changes in the gross composition of the oils, namely, the relative extent of removal of saturated versus aromatic hydrocarbons and the fate of polar compounds and asphaltenes .

3. The relative contribution of biodegradation and water washing to the alteration of the oils, and the hydrological-geological control of these processes .

All the reservoir temperatures of the oils from the present study are less than 60C, and hence, matura-tion processes in the reservoir will not be considered here.

GEOLOGICAL SETTING AND SAMPLES

Figure 1 is a location map of the oil shows and the drillholes around the Dead Sea basin . This is a pull-apart basin that was formed as a consequence of strike-slip movement along the Dead Sea rift (Freund and Garfunkel, 1976; Garfunkel, 1978). Oil shows in the area are found in the western margin of the graben (Fig. 1) in the form of asphaltic oil seeps along the graben faults and in the form of heavy and light oils in shallow and deep drillholes. Table 1 gives the description, location, and depth of various oil shows that were studied. The shows are described by their relative viscosity: asphalt is a solid, heavy asphaltic oil that is solid at room temperature and melts at higher temperatures, and heavy and light oils are liquids with high and low viscosity, respectively. The surface sam-ples are asphaltic oils and asphalts that appear in rocks from various ages. Their exposure altitudes (the values for surface samples are below mean sea level because they are located at the Dead Sea depression) are con-trolled by the regional water table (Langotsky, 1963). The drillhole samples are mostly heavy-oil impregna-tions in different reservoir rocks ranging in age from Cretaceous to Paleozoic. In two drillholes (Massada-1 and Zuk-Tamrur-1), light oil was found in Triassic formation (Table 1).

All the above oils and asphalts are concentrated in a small area and are believed to belong to one geochemi-cal family (Amit and Bein, 1979; Nissenbaum and Goldberg, 1980; Tannenbaum, 1983). The source rock for these oils is the Senonian bituminous rocks ("oil

shale") that have been buried in the Dead Sea graben to great depths (up to 10 km [6.2 mi]) (Tannenbaum 1983; Tannenbaum and Aizenshtat, 1985). This sou;c rock is composed mainly of carbonates, and it was de-e posited in marine environments with hypersaline water and reducing conditions, with bacterial rework-ing of the organic matter (Spiro et al., 1983). These conditions gave rise to the special characteristics of the kerogen in these rocks and hence also to the oils that formed from it; namely, predominance of even carbon numbers for n-alkanes in the high range ( >C20), pre-dominance of phytane over pristane, high asphaltic materials ( >20%), and high sulfur content ( >2.6%; Nissenbaum and Goldberg, 1980; Tannenbaum, 1983).

EXPERIMENTAL

Rocks impregnated by oils and asphalts were washed by benzene to avoid any contamination, crushed, and extracted with benzene:methanol (7:3). The solvents were evaporated, and the residues were treated as oils recovered by drill tests . They were dissolved in toluene, and the asphaltenes were precipitated by adding n-pentane (X50) followed by centrifugation, washing, and drying. The pentane-soluble fraction was further separated on a FlorasilR column. The saturates were eluted by hexane, the aromatics by benzene, and the polar compounds (resins) by methanol.

Gas chromatography was performed on a Packard 417 GC equipped with flame ionization detector and inorganic salts eutectic column (Snowdon and Peake, 1978). The operating conditions were 105-295, 8/min.

Evidence for Oil Alteration Table 2 gives the relative amounts of the oil frac-

tions, and these amounts are plotted in a gross compo-sition diagram (Fig. 2). There is an obvious enrichment in asphaltic materials (resins+ asphaltenes) from the light oil to the asphalts and a depletion of saturated hydrocarbons from 60% in the light oil, to 30-40% in the heavy oils and to 10-30% in the surface asphalts. These trends are now widely accepted as indicating alteration processes such as biodegradation and water washing, which result in removal of saturated and aromatic hydrocarbons from the oils (Winters and Wil Iiams, 1969; Evans et al., 1971; Bailey et al., 1973a, 1973b; Deroo et al., 1977; Connan et al., 1980). The same interpretation was suggested for the Dead Sea oils (Amit and Bein, 1979; Nissenbaum and Goldberg, 1980); Tannenbaum, 1983).

Figure 3 shows the changes in asphaltenes (left) and sulfur contents (right), with increasing depths of the II various samples. These two properties are usually we correlated with API gravity and are good indicators of oil alteration (Orr, 1978; Tissot and Welte, 1978). The change from 10% asphaltenes and 2.6% sulfur for light oils, at a depth of 2000 m (6560 ft) below m.s.1., to approximately 60% asphaltenes and 10% sulfur in thd surface samples, depicts very well the more advance stage of oil alteration at shallower depths.

SECTION II. Characterization, Maturation, and Degradation

160

33

080

./'" ... \

170 180 190

~ Ein Gedi - 1 J 32 55 - i ~ ,r/ ,%J";;lem

31 , I Hakanaim-fr

\ \Massada -I

070

060 -

0 50

040 -

Studied/ : area( 0

i ..

a: 0 "")

~idod - 3 8

:-Zohar 6 -0:

'Gurim - 3

Halamish -fr

\ -

224 Tannenbaum, Starinsky, Aizenshtat

Table 1-List of samples and general data.

Sample Description

Surface and shallow drillholes: E-50 Asphalt, impregnated in sandstone E-518 Heavy asphaltic oil dripping from

Cretaceous limestone E-51 Asphalt, impregnated in Recent

conglomerate; more altered than 518

E-54 Asphalt, impregnated in Cretaceous limestone and chert

E-55 Heavy asphaltic oil dripping from Cretaceous limestone

E-55A Asphalt, as 55 but more altered E-57 Asphalt, impregnated in Cretaceous

and Recent rocks E-57A As 57 but more altered SH-5 Heavy asphaltic oil, impregnated

in sandstone

Deee drillholes: EG-67A Heavy oil, impregnated in Jurassic

sandstone EK-58A Heavy oil, recovered from Jurassic

rock (drillstem test) EL-83A Heavy oil (9 API) recovered from

Triassic rock (drillstem test) EM-35 Heavy asphaltic oil impregnated in

Cretaceous dolomite EM-37 As 35 EM-86A Heavy oil, impregnated in Triassic

dolomite EM-888 Light oil (33 API) recovered from

Triassic rock (drillstem test) ET-84A Light oil (27 API) recovered from

Triassic rock (swab test) EX-94 Heavy oil (19 API), impregnated in

Paleozoic sandstone EZ-63A Heavy oil, impregnated in Jurassic

sandstone EZ-66A Heavy oil, impregnated in Jurassic

sandstone

Figure 4 shows gas chromatograms of the saturated hydrocarbons of five oils and asphalts taken from var-ious depths . The saturated hydrocarbon distribution of sample BBB (Fig. 4) is characteristic of light oil. Sample B6A is depleted in n-alkanes, especially in the lower carbon number range, relative to sample BBB, and a more prominent unresolved hump, which is attributed to acyclic and branched hydrocarbons, is observed. At shallower depths, the above changes are even more pronounced (sample 67 A); the near-surface sample (37) is completely devoid of n-alkanes. In the surface

Location/ Depth, m ---.. drillhole ) below m.s.I.

--

Tar Sand Valley Surface (-260) Nahal Heimar Surface (-320) Nahal Heimar Surface (-320)

Nahal Beer Surface (70) Nahal Massada Surface (-150) Nahal Massada Surface (-150) IPRG-1 30 (- 245) IPRG-1 30 (- 245) Sdom SH-5 150 (-390)

Gurim-3 1560 (-1260) Kidod-3 1260 (-650) Lot-1 1278 (-1600) Massada-1 28 (- 280) Massada-1 224 (-470) Massada-1 1940 (-2190) Massada-1 2100 (-2350) Zuk Tamrur-1 1865 (-1770)

Zohar-8 3127 (-2490) Zohar-6 1350 (-760) Zohar-6 1550 (-960)

asphalt (SS), only an unresolved hump and some poly cyclic compounds are present. These trends were shown in field studies and in laboratory experiments to be a result of degradation of oils by bacteria (Winters and Williams, 1969; Bailey et al., 1973a, 1973b).

Material Balance Calculations: Removal of Saturates and Aromatics from the Oils

Our calculations for removal of saturated and aro matic hydrocarbons from the oils explain the changes

SECTION II. Characterization, Maturation, and Degradation 225

Table 2-Gross composition of oil and asphalts (%).

sample Sat Arom Res Asph

surface and shallow drillholes: -

50 33 21 24 22 518 28 13 19 40 51 60 54 20 12 16 52 55 23 22 20 3S SSA 13 11 20 S6 57 14 17 16 53 57A 11 13 17 59 s 15 22 25 38

Deep drillholes:

67A 40 21 19 20 58A S3 13 14 20 83A 45 17 18 20 3S 25 20 20 3S 37 30 20 20 30 86A S5 17 15 13 888 60 20 10 10 84A

94A so 15 17 18 63A 30 19 21 30 66A 42 13 20 2S

in the relative amounts of the various fractions of the ils (Table 2) and lead to estimates of the quantities of ii constituents that have been removed through the

alte ration processes. We assume that the light oil found in Massada-1 drill-

hole (sample BBB, Table 1), represents an "original" oil tha t has not been subjected to alteration processes in the reservoir. Its gross composition is used as an initial reservoir from which saturated and aromatic hydro-carbons are removed, whereas the amount of polar compounds (resins) plus asphaltenes is constant. All the ca lculations are made for the C15+ range. . Figure Sa shows the gross composition of the var-ious samples. The dashed line represents removal of only saturated hydrocarbons from the original oil (888). It is apparent that this kind of alteration cannot explain the gross compositions of the oils and asphalts hn the Dead Sea area, and removal of the aroma tic

ydrocarbons must be taken into account. .The two other lines (Fig. Sa) represent different rel-~ tave extents of removal of saturated hydrocarbons brom the saturated fractions, and aromatic hydrocar-

o~h from t~e .aromatic fraction, of sample BBB . e best fit 1s for relative extent of removal (satu-

rates:a romatics) of l :O.B3, which indicates a significant ~emoval of aromatic hydrocarbons through the altera-l~o~pro~ess . The curve in Figure Sb shows the calcu-

te residue left from the original oil for the case of

relative extent of removal of l:O.B3 (Fig. Sa) . It appears that the surface asphalts represent approximately 2S% of the original oil, the remaining 7S% representing the saturates and aromatics that have been removed.

However, there is some scatter between the differ-ent samples presented in Figure Sa, which might be due to: (1) differences in the gross composition of the "original" oils in various locations, and (2) variability of the conditions such as water salinities, nutrient con-tent, temperatures, etc., in different locations, which may lead to different alteration processes.

To avoid the above possible differences in alteration environments, we chose one drillhole (Massada-1, Fig. 1) and two asphalts from the vicinity of the drillhole (samples SS and SSA, Fig. 1, and Table 1) . We applied the above calculations to these samples .

In Figure 6, the lines between the various samples of Massada-1 drillholes represent different relative extent of removal of saturates and aromatic hydrocarbons from the original oil (BBB) . At the greatest depth (23S0-2190 m [7710-71BS ft], samples BBB and B6A, respectively), saturated hydrocarbons are removed from the saturated fraction at a slower rate than aro-matic hydrocarbons from the aromatic fraction (ratio of 1:1.3, Fig. 6) . The measured content of each fraction and the residue it represents from the original oil, cal-culated according to the above ratio, is given in Table 3 and shown on histograms in Figure 6. Sample B6A is a heavy oil that still contains SS% of saturates, part of which are n-alkanes (Fig . 4), and represents a residue of 70.S% of the original oil. At shallower depths (from 2190 to the surface, samples B6A, 37, and SS), satu-rated hydrocarbons are removed faster than aromatic hydrocarbons (ratio of 1:0.S, Fig. 6), so that the fresh surface asphalt (sample SS) represents only 3S .7% of the original oil (Table 3) . On the surface (sample SS to SSA, Fig . 6), there seems to be a ratio of unity between the relative extent of removal of saturated and aro-matic hydrocarbons. The altered asphalt (sample SSA) represents 26% of the original oil.

DISCUSSION

So far, we have shown that gross composition of oil, in various stages of alteration, may be explained by assuming different relative extents of removal of satu-rated and aromatic hydrocarbons. However, the changes in the ratios of removal with depth, depicted in Figure 6, should be explained by the conditions in the subsurface.

The phenomenon of more extensive stages of degra-dation of oils at shallower depths has been explained by invasion of oxygenated meteoric water into these depths, which resulted in biodegradation and water washing of the oils (Winters and Williams, 1969; Bailey et al., 1973a, 1973b; Milner et al., 1977). Invasion of meteoric water into the subsurface in the western margins of the Dead Sea graben was shown by Sta-rinsky (1974) and Fleischer et al. (1977), and their data are illustrated in Figure 7. In drillholes located near the

226 Tannenbaum, Starinsky, Aizenshtat

SATURATES

o light oils

90 .

o heavy oils

,' heavy ospholl1c oils 80 D. asphalts

Jr altered asphal t s 70

888 ~ 60 86A 0 58A 0

0 Jr

50 94A 0 83A o

~ 66A e 0 67A 40

63A . so

'' 30 5166 37 35

54 .. "ss '"' 20

55A _.. D.57 5 R 10 .. 57A

RESINS + ASPHALTENES

"b "b -' ""

'b 'O 'b

228

b

Tannenbaum, Starinsky, Aizenshtat

RELATIVE EXTENT OF REMOVAL

RESIDUE(%) OF ORIGINAL OIL

SAT AROM

0

0.83

a

0 20 40 60 80 100 60

50

0 40-~ en w

~ 30 0:: ::::> t-

~ 20

10

'88B

30

0 L____!. _ ____ ~ RESINS+ ..90

ASPHALTENES

50

40

SATURATES

90

80

70

60

/ .

0 . 0 ./, o/ /

o ./

/ 0

888

AROMATICS

Figures-A. Calculated curves showing changes in gross composition of the original oil (_888) at different levels of r~moval of saturated and aromatic hydrocarbons (for legend see Fig. 2). 8. ~~lcula~ed curve showing the saturated hydrocar on content of oils and asphalts vs. the residue they represent of the original 011.

Table 3-Removal of saturates and aromatics from oils and asphalts in Massada-1 dri llhole.

86A 37 55 55A

Fraction 888 a1 b2 a b a b a b

Sat 60 (55) 39 (30) 11.8 (23) Arom 20 (17) 11.5 (20) 7.8 (22) Res 10 (15) 10.5 (20) 7.8 (20) Asph 10 (13) 9.5 (30) 11.8 (35)

8.2 (13) 3.4 7.9 ( 11) 2.8 7.1 (20) 5.2

12.5 (56) 14.6 -

Residue of 888 (%) 70.5 39.2 35.7 26.0 --

1a measured content of each fraction (%). 2b', calculated residue of each fraction of the corresponding fraction in the original oil (BBB).

SECTION II. Characterization, Maturation, and Degradation 229

SATURATES

RELATIVE EXTENT OF REMOVAL:

SAT: AROM= 1:1.3

SAT: AROM 1 :0.5

60

SAT : AROM I : 1 40

30

20

10

RESINS + ASPHAL TEN ES ~ ~

90

80

70

~ Asphaltenes Q] Saturates ~Resins rn Aromat ics

RESIDUE OF ORIGINAL OIL(%) 0 20 40 60 80 100

K>OWi===i~ttililil!l: SURFACE SURFACE

1' DEPTH(m)

Figure &-Changes in gross composition of oils and asphalts from Massada-1 drillhole, explained by different levels of removal of saturated and aromatic hydrocarbons. The histograms indicate the residues (heavy oils and asphalts) of the original oil (888).

CONCLUSIONS

We have applied material balance calculations to explain the changes in the gross composition of oils in the Dead Sea area, through alteration processes. The calculations assume removal of saturated and aromatic hydrocarbons at differing degrees, whereas the polar compounds plus asphaltenes constitute an inert phase.

Three main stages of oil alteration were recorded in reservoirs in the sedimentary column of one drillhole (Massada-1): (1) faster removal of aromatics relative to saturates (at depths of 2000 m [6560 ft]) as a result of wt ater washing by brines (200 g/l TDS) that are in con-act h h b wit t e oils; (2) fast removal of saturated hydro-

car ons, with complete elimination of n-alkanes at

depths of 1500 m to the surface, due to bacterial activ-ity that was initiated after invasion of meteoric water into the subsurface; and (3) surface weathering of asphalts by processes such as biodegradation, water washing, evaporation, and oxidation. In the last two stages, formation of additional asphaltenes was appar-ent, presumably due to condensation reactions of polar molecules and perhaps, also, high molecular weight aromatics.

The calculations indicate that 75% of the original oil constituents in the C15+ range were removed via the alteration processes. If we take into account the lower carbon number range, we estimate that the surface asphalts represent residues of only 10-20% of the orig-inal oils.

230

00 Dept h

m

Tannenbaum, Starinsky, Aizenshtat

TDS g/ { 20 40 60 80 100 120 140 160 180 200 220 240

Zahar-6 Zahar- 8

i

I

Figure 7-Salinities (total dissolved solids) of water from the Dead Sea area vs. depth of occurrence.

A similar type of material balance calculation applied to large deposits of heavy oil such as that of Athabasca (Alberta) and the Orinoco Belt (Venezuela) may reveal that the quantities of light constituents of the original oils that have been removed are even greater than the proven deposits.

ACKNOWLEDGMENTS

We would like to thank Oil Exploration (investment) for supplying the oil samples and Ors. I. R. Kaplan and S. M. Steinberg for reviewing the manuscript .

This study was supported by a grant from KFA Julich (West Germany) through NCRD (Israel).

REFERENCES CITED

Amit, 0., and A. Bein, 1979, The genesis of the asphalt in the Dead Sea area: Journal of Geochemical Exploration, v. 11, p. 211-215.

Bailey, N. J. L., A. M. Jobson, and M.A. Rogers, 1973a, Bacte-rial degradation of crude oil: Comparison of field and experimental data: Chemical Geology, v. 11, p. 203-221 .

Bailey, N. J. L., H. H. Krouse, C. R. Evans, and M. A. Rogers, 1973b, Alteration of crude oil by waters and bacteria-evidence from geochemical and isotope studies: Bulletin of the American Association of Petroleum Geologists, v. 57, p. 1276-1290.

Chapman, R. E., 1982, Effects of oil and gas accumulation on water movement: Bulletin of the American Association of Petroleum Geologists, v. 66, p. 368-378.

Connan, J., A. Restle, and P. Albrecht, 1980, Biodegradation of crude oil in the Aquitaine basin, in A. G. Douglas, and J. R. Maxwell, eds., Advances in Organic Geochemistry, 1979: Oxford, Pergamon Press, p. 1-17.

Demaison, G. J., 1977, Tar sands and supergiant oil fields: Bulletin of the American Association of Petroleum G 1 ogists, v . 61, p. 1950-1961. eo -

Deroo, G., T. G . Powell, B. Tissot, and R. G . McCrossan 1977, The origin and migration of petroleum in the ' Western Canadian Sedimentary Basin, Alberta: Geolo i-cal Survey of Canada Bulletin, v. 262. g

Evans, C.R., M.A. Rogers, and N. J. L. Bailey, 1971, Evolu-tion and alteration of petroleum in Western Canada: Chemical Geology, v. 8, p. 147-170.

Fleischer, E., M. Goldberg, J. R. Gat, and M. Margaritz, 1977 Isotopic composition of formation water from deep drill '. ings in southern Israel: Geochimica et Cosmochimica Acta, v. 41, p. 511-525.

Freund, R. , and Z. Garfunkel, 1976, Guidebook to excursion along the Dead Sea Rift: Department of Geology, Hebrew University, Jerusalem.

Garfunkel, Z., 1978, The Negev-regional synthesis of sedi-mentary basins: Guidebook, 10th International Congress on Sedimentology, p. 35-110.

Hunt, J.M., 1979, Petroleum geochemistry and geology: San Francisco, Freeman & Company, 617 p.

Jobson, A. M., F. D. Cook, and D . W. S. Westlake, 1979, Interaction of aerobic and anaerobic bacteria in petro-leum biodegradation: Chemical Geology, v. 24, p. 355-365.

Langotsky, Y., 1963, Asphalt in the Dead Sea area: Report M. P./129/62, Geological Survey of Israel, p. 78 (in Hebrew).

McAuliffe, C., 1966, Solubility in water of paraffin, cyclopar-affin, olefin, acetylene, cycloolefin and aromatic hydro-carbons: Journal of Physical Chemistry, v. 70, p. 1267-1275.

Milner, C. W. 0., M. A. Rogers, and C.R. Evans, 1977, Petro-leum transformations in reservoirs: Journal of Geochem ical Exploration, v. 7, p. 101-158.

Moschopedis, S. E., and J. G . Speight, 1973, Oxidation of pet roleum fractions : Fuel, v. 52, p. 83.

Mossop, G . 0., 1980, Geology of the Athabasca oil sands: Science, v. 207, p. 145-152.

Nissenbaum, A., and M. Goldberg, 1980, Asphalts, heavy oils, ozocerite and gases in the Dead Sea basin: Organic Geochemistry, v. 2, p. 167-180.

Orr, W. L., 1978, Sulfur in heavy oils, oil sands and oil shales, in 0. P. Strausz, and E. M. Lown, eds ., Oil sand and oil shale chemistry: New York, Verlag Chemie, p. 223- 243.

Price, L. C., 1976, Aqueous solubility of petroleum as applied to its origin and primary migration: Bulletin of the American Association of Petroleum Geologists, v. 60, P 213-244 .

___ , 1980, Crude oil degradation as an explanation of the depth rule: Chemical Geology, v. 28, p. 1-30.

Rubinstein, I., 0. P. Strausz, C. Spyckerelle, R. J. Crawford, and D . W. S. Westlake, 1977, The origin of the oil sand bitumens of Alberta: A chemical and microbiological simulation study: Geochimica et Cosmochimica Acta, v. 41,p. 1341-1353. I

Snowdon, L. R., and E. Peake, 1978, Gas chromatography 0 It high molecular weight hydrocarbons with an organic sa

1 eutectic column: Analytical Chemistry, v. 50, p. ~79-3:

Spiro, B., D . Oinur, and Z. Aizenshtat, 1983, Evaluation source, environment of deposition and diagenesis of some Israeli" oil shales" n-alkanes, fatty acids, tetrapyr~ roles and kerogen: Chemical Geology, v. 39, p. 189-21

Starinsky, A., 1974, Relationship between Ca-chloride brines: and sedimentary rocks in Israel: Ph.D. Oisserta

SECTION II. Characterization, Maturation, and Degradation

tion, Hebrew University, Jerusalem, 176 p. (in Hebrew) . Tannenbaum, E., 1983, Researches in the geochemistry of

oils and asphalts m the Dead Sea area, Israel: Ph.D. Dis-sertation, Hebrew University, Jerusalem (in Hebrew, English abstract) .

Tannenbaum, E., and Z . Aizenshtat, 1985, Formation of immature asphalt from organic-rich carbonate rocks . 1. Geochemical correlation: Organic Geochemistry, v. 8, p. 181-192 ..

Tissot, B. P., and D . H . Welte, 1978, Petroleum formation and occurrence: Heidelberg, Springer-Verlag, 538 p.

Winters, J. C., and J. A. Williams, 1969, Microbiological alter-ation of crude oil in the reservoir: Symposium on Petro-leum Transformation in Geological Environments, American Chemical Society Division of Petroleum Chemistry, New York, 7112 Sept ., Preprints 14(4), E22-E31 .

231