Abstract :
Slope Factor (SF), based on the concept of Kissin, specifies the rate of decrease in concentration with increasing carbon number in the exponential distribution of n-alkanes in reservoir fluids and pyrolysates. Two exponential series occur. SF(C2-n-C5) is invariably steeper than SF(n-C6+), reflecting stabilities and cracking mechanism. The break in slope occurs at n-C6. Pseudo-components (Pn), representing the total composition subdivided by carbon number, also decrease in concentration exponentially beyond C10, facilitating the measurement of SF(P10+). In asphaltene pyrolysates, in the C10+ range, SF(P10+) and SF(n-C10+) exhibit significant correlation, suggesting a communality of an as yet uncertain nature in generative processes. At conversion levels within the oil window, asphaltene pyrolysis yields values of SF(C2-n-C5) between 1.32 and 1.55, and values of SF(n-C10+) between 1.07 and 1.24. Reservoir fluids (oils) from the Western Canada Basin exhibit closely similar ranges and associations of values. Pyrolysates of kerogen concentrates containing pyrite yield SF values which are higher than those of both asphaltene pyrolysates and normal oils, possibly due to pyrite-induced catalysis. Migration-depletion, operating by way of exsolution due to pressure and temperature decrease, is recognized in both oils (fluids which exhibit a bubble point) and gas-condensates (which exhibit a dew point). Oils exsolve gases and light hydrocarbons, while gas-condensates exhibit preferential loss of their heavier solutes with attendant, dominant, control of their fundamental properties.
