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An introduction to the relationship between temperature and hydrocarbon phases
Org. Geochem.Vol. 17, No. 2, pp. 263-264, 1991 Printed in Great Britain. All rights reserved
0146-6380/91 $3.00+ 0.00 Copyright© 1991PergamonPress plc
An introduction to the relationship between temperature and hydrocarbon phases JOHN A. CLENDENING Amoco Production Co., P.O. Box 3092, Houston, TX 77253, U.S.A.
(Received 24 January 1990; accepted 15 July 1990)
The relationship between temperature and the various hydrocarbon phases has been understood for over a century. Specific limitations are placed on the occurrence of oil by the intolerance of petroleum in the earth's crust to elevated temperatures. Increasing temperatures create a "twilight zone" where oil and gas give way, through natural cracking, to gas only. H. D. Rogers (1843), 16 years prior to the drilling of the Drake well in 1859, unequivocally demonstrated the existence of a progressive depth of burial-related regional change from high-volatile bituminous coals in western Pennsylvania to anthracite coals in eastern Pennsylvania. In 1860, before the Philosophical Society of Glasgow, Rogers described the correlation between metamorphism, coal composition and oil and gas occurrence (Thom, 1934). An even more comprehensive presentation of the subject was published in an article on "Coal and petroleum" in Harper's New Monthly Magazine (Rogers, 1863). Rogers described the geography of oil occurrence in the U.S.A. and noted that deeper wells tended to produce lighter oils (higher Baume gravity) at progressively greater depths within a given area. Rogers' views conform in almost every respect with modern opinions regarding the vertical and horizontal variations in the thermal influences which have affected oil-yielding and coal-bearing formations since their deposition. D. White (1915) rediscovered and reenunciated the basics of Rogers' theories and observations which he named the "carbon-ratio theory". White, an eminent paleobotanist and quite familiar with the organic materials composing both coals and oil shales, described the organic substances from which coal and petroleum had been derived and the biochemical and dynamo-chemical processes inducing alteration of organic substances after deposition. He further described the degree of correspondence between the geographic limits of known commercial oil and gas occurrence and the intensity and regional variation of rock metamorphism, as indicated by the percentage of "fixed-carbon" shown by proximate analyses of coals calculated on the ash-free basis. The fundamental observations reported by White remain valid today. Very simply, the "carbon-ratio theory" states that where the progressive devolatilization of organic deposits, in any formation, has passed about 70% of fixed-carbon (pure coal basis), commercial oil deposits will not be present in that formation nor in any other stratigraphically deeper formation. Commercial gas accumulations may, however, occur in a zone of higher carbonization. White also reported that when the alteration of carbonaceous residues passes the point of about 70% fixed-carbon (pure coal basis), the light distillates appear, in general, to be gases at reservoir temperatures. White and his predecessors did not specify a fixed-carbon value at which reservoir destruction occurs but all clearly recognized that no commercial hydrocarbon production would occur from metamorphic rocks (in this case defined by anthracite coal). There is a problem of widespread disregard for thermal risk assessment in exploration and this has been recently compounded by a rash of published papers claiming that commercial production of hydrocarbons has been, or can be, achieved from strata with vitrinite reflectance levels of 3, 4, 5 or even greater %Ro. The principal source of these recent problems appears to be N. V. Lopatin, who, in 1971, published a formula for mathematical calculations of time-temperature-coalification relationships. This technique was later published by D. W. Waples (1980). Actual measurements of organic maturation and reservoir evolution have been ignored by many in favor of computer-derived pseudo-Ro values. These articles, with computer-derived Ro values, have been published as though they were legitimate Ro values. Hallam (1981, p. 12) discussed the inherent problems in applying sophisticated mathematical techniques to sedimentologic facies analysis: "The danger with this sort of research is that it may become too technical for the great majority to understand and one sometimes tends to get the impression that these 'mathematical geologists' communicate only with each other and get seduced away from significant geological problems by the beauty of the techniques they work with." o~ ~7/2-J
263
264
JOHN A. CLENDENING
This quote aptly applies to the mathematical chaos that followed publication of Lopatin's method. Not only are these mathematicians seducing themselves away from significant geological problems, but they are publishing damaging and incorrect interpretations about thermal exposure with complete disregard for actual rock data. Uninformed geologists are readily accepting, and using, these "bogus" vitrinite data. This, and other problems, will be dealt with in detail in the present symposium on the relationship of temperature, mineralogy and reservoir quality in several basins. REFERENCES
Hallam A. (1981) Facies Interpretation and the Stratigraphic Record. Freeman, New York. Lopatin N. V. (1971) Temperature and geologic time as factors in coalification (in Russian). Akad. Nauk SSSR Izv. Ser. GeoL 3, 95-106. Rogers H. D. (1843) The Geology of Pennsylvania, 2 vols. Lippincott, Philadelphia, Pa. Rogers H. D. (1860) On the distribution and probable origin of the petroleum or rock oil of Pennsylvania, New York and Ohio. Proc. Philos. Soc. Glasgow 4, 355-359. Rogers H. D. (1863) Coal and petroleum. Harpers New Mon. Mag 27, 259-264. Thorn W. T. (I 934) Present status of the carbon-ratio theory. In Problems of Petroleum Geology (Edited by Wrather W. E. and Lahee F. H.). Sidney Powers Memorial Volume, pp. 69-95. AAPG, Tulsa, Okla. Waples W. (1980) Time and temperature in petroleum exploration: applications of Lopatin's method to petroleum exploration. Bull. Am. Assoc. Pet. Geol. 64 (6), 916-926. White D. (1915) Some relations in origin between coal and petroleum. J. Wash. Acad. Sci. 5, 189-212.
0146-6380/91 $3.00+ 0.00 Copyright© 1991PergamonPress plc
An introduction to the relationship between temperature and hydrocarbon phases JOHN A. CLENDENING Amoco Production Co., P.O. Box 3092, Houston, TX 77253, U.S.A.
(Received 24 January 1990; accepted 15 July 1990)
The relationship between temperature and the various hydrocarbon phases has been understood for over a century. Specific limitations are placed on the occurrence of oil by the intolerance of petroleum in the earth's crust to elevated temperatures. Increasing temperatures create a "twilight zone" where oil and gas give way, through natural cracking, to gas only. H. D. Rogers (1843), 16 years prior to the drilling of the Drake well in 1859, unequivocally demonstrated the existence of a progressive depth of burial-related regional change from high-volatile bituminous coals in western Pennsylvania to anthracite coals in eastern Pennsylvania. In 1860, before the Philosophical Society of Glasgow, Rogers described the correlation between metamorphism, coal composition and oil and gas occurrence (Thom, 1934). An even more comprehensive presentation of the subject was published in an article on "Coal and petroleum" in Harper's New Monthly Magazine (Rogers, 1863). Rogers described the geography of oil occurrence in the U.S.A. and noted that deeper wells tended to produce lighter oils (higher Baume gravity) at progressively greater depths within a given area. Rogers' views conform in almost every respect with modern opinions regarding the vertical and horizontal variations in the thermal influences which have affected oil-yielding and coal-bearing formations since their deposition. D. White (1915) rediscovered and reenunciated the basics of Rogers' theories and observations which he named the "carbon-ratio theory". White, an eminent paleobotanist and quite familiar with the organic materials composing both coals and oil shales, described the organic substances from which coal and petroleum had been derived and the biochemical and dynamo-chemical processes inducing alteration of organic substances after deposition. He further described the degree of correspondence between the geographic limits of known commercial oil and gas occurrence and the intensity and regional variation of rock metamorphism, as indicated by the percentage of "fixed-carbon" shown by proximate analyses of coals calculated on the ash-free basis. The fundamental observations reported by White remain valid today. Very simply, the "carbon-ratio theory" states that where the progressive devolatilization of organic deposits, in any formation, has passed about 70% of fixed-carbon (pure coal basis), commercial oil deposits will not be present in that formation nor in any other stratigraphically deeper formation. Commercial gas accumulations may, however, occur in a zone of higher carbonization. White also reported that when the alteration of carbonaceous residues passes the point of about 70% fixed-carbon (pure coal basis), the light distillates appear, in general, to be gases at reservoir temperatures. White and his predecessors did not specify a fixed-carbon value at which reservoir destruction occurs but all clearly recognized that no commercial hydrocarbon production would occur from metamorphic rocks (in this case defined by anthracite coal). There is a problem of widespread disregard for thermal risk assessment in exploration and this has been recently compounded by a rash of published papers claiming that commercial production of hydrocarbons has been, or can be, achieved from strata with vitrinite reflectance levels of 3, 4, 5 or even greater %Ro. The principal source of these recent problems appears to be N. V. Lopatin, who, in 1971, published a formula for mathematical calculations of time-temperature-coalification relationships. This technique was later published by D. W. Waples (1980). Actual measurements of organic maturation and reservoir evolution have been ignored by many in favor of computer-derived pseudo-Ro values. These articles, with computer-derived Ro values, have been published as though they were legitimate Ro values. Hallam (1981, p. 12) discussed the inherent problems in applying sophisticated mathematical techniques to sedimentologic facies analysis: "The danger with this sort of research is that it may become too technical for the great majority to understand and one sometimes tends to get the impression that these 'mathematical geologists' communicate only with each other and get seduced away from significant geological problems by the beauty of the techniques they work with." o~ ~7/2-J
263
264
JOHN A. CLENDENING
This quote aptly applies to the mathematical chaos that followed publication of Lopatin's method. Not only are these mathematicians seducing themselves away from significant geological problems, but they are publishing damaging and incorrect interpretations about thermal exposure with complete disregard for actual rock data. Uninformed geologists are readily accepting, and using, these "bogus" vitrinite data. This, and other problems, will be dealt with in detail in the present symposium on the relationship of temperature, mineralogy and reservoir quality in several basins. REFERENCES
Hallam A. (1981) Facies Interpretation and the Stratigraphic Record. Freeman, New York. Lopatin N. V. (1971) Temperature and geologic time as factors in coalification (in Russian). Akad. Nauk SSSR Izv. Ser. GeoL 3, 95-106. Rogers H. D. (1843) The Geology of Pennsylvania, 2 vols. Lippincott, Philadelphia, Pa. Rogers H. D. (1860) On the distribution and probable origin of the petroleum or rock oil of Pennsylvania, New York and Ohio. Proc. Philos. Soc. Glasgow 4, 355-359. Rogers H. D. (1863) Coal and petroleum. Harpers New Mon. Mag 27, 259-264. Thorn W. T. (I 934) Present status of the carbon-ratio theory. In Problems of Petroleum Geology (Edited by Wrather W. E. and Lahee F. H.). Sidney Powers Memorial Volume, pp. 69-95. AAPG, Tulsa, Okla. Waples W. (1980) Time and temperature in petroleum exploration: applications of Lopatin's method to petroleum exploration. Bull. Am. Assoc. Pet. Geol. 64 (6), 916-926. White D. (1915) Some relations in origin between coal and petroleum. J. Wash. Acad. Sci. 5, 189-212.