The Oil Generation Maturity Limits for a Type I Kerogen as Determined by Hydrous Pyrolysis

Abstract

Changes in the physical properties (measured in terms of vitrinite reflectance, elemental analysis, and C-13 nuclear magnetic resonance) of an immature coal (0.46% R{sub o}) from Craig County, Colorado, that was thermally altered using hydrous pyrolysis were used to establish a correspondence between hydrous pyrolysis time/temperature reaction conditions and relative maturity (expressed in terms of vitrinite reflectance). This correspondence was used to determine the oil generation maturity limits for an immature hydrogen-rich (Type I fluorescing amorphous oil-prone kerogen) source rock from an offshore Congo well that was thermally altered using the same reaction conditions as applied to the immature coal. The resulting changes in the physical properties of the altered source rock, measured in terms of decreasing reactive carbon content (from Rock-Eval pyrolysis), were used to construct a hydrocarbon yield curve from which the relative maturity associated with the onset, main phase, and peak of oil generation was determined. Results, substantiated by anhydrous pyrolysis techniques, indicate that the source rock from Congo has a late onset of appreciable ({gt}10% transformation) oil generation (0.9% R{sub o} {plus minus} 0.1%), generates maximum quantities of oil from about 1.1 to 1.3% R{sub o}, and reaches the end (or peak) of the primary oilmore » generating window at approximately 1.4% R{sub o} ({plus minus}0.1%) when secondary cracking reactions become important. However, the bottom of the oil window can be extended to about 1.6% R{sub o} because the heavy molecular weight degradation by-products (asphaltenes) that are not efficiently expelled from source rocks continue to degrade into progressively lower molecular weight hydrocarbons.« less