EXPERIMENTAL SIMULATION OF THERMAL MATURATION IN SEDIMENTARY ORGANIC MATTER. (VOLUMES I AND II)

This study simulates thermal maturation of liptinitic and humic organic matter (Phosphoria shale and Rattlesnake Butte lignite) by isothermal pyrolysis at temperatures of 230(DEGREES), 275(DEGREES) and 325(DEGREES)C for heating times as long as 5000 hours, and programmed temperature pyrolysis using both Chromalytics MP-3 and Rock-Eval instruments. Comparison of artificially and naturally matured Phosphoria starting materials suggests that natural maturation is simulated best by the experiments conducted at 230(DEGREES) and 275(DEGREES)C. The character of the bitumen from experiments using kerogen with simulated maturities in the oil generation range (greater than about 0.5%R(,o), vitrinite reflectance) are quite similar to Phosphoria crude oils, especially in the saturated hydrocarbon fraction. Absence of steranes and triterpanes in the saturated fraction from experiments using previously solvent extracted Phosphoria shale suggests that these large biological marker molecules are not released from the kerogen during heating. They were apparently present only in the native bitumen, probably inherited from the original depositional environment. There does not appear to be an effect from the presence or absence of mineral matrix on the amounts and character of the degradation products. Excess water in the experiments results in larger amounts of CO(,2), hydrocarbon gases and bitumen. The experiments with added water had slightly higher relative amounts of the aromatic fraction in the bitumen. During the early stages of maturation, the liptinitic and humic organic starting materials generate hydrocarbon gases at about the same rate, though the humic material yields much more CO(,2) during the same period. Determination of pseudo-activation energies for the kerogen-to-bitumen conversion step by programmed temperature pyrolysis of artificially and naturally matured liptinitic-rich kerogen is about 26 to 30 Kcal/mole, regardless of the maturity of the kerogen. The pseudo-activation energy of the lignite is about 22 Kcal/mole, suggesting that the humic material contains more low energy bonds, probably those with oxygen such as ether bonds. Applying the relationships between the artificially matured kerogen and the products of thermal maturation seen in the laboratory simulations to geological situations will permit a better evaluation of the changes which have occurred during the natural maturation process. This should make possible more accurate assessment of source-rocks for both type and amounts of generation product and should be important for petroleum exploration in predicting where and how much oil or gas may be in a specific volume of rock