Hydrocarbon generation potential under different experimental conditions and its petroleum geology significance

Hydrocarbon generation rate and process and the geochemical characteristics of experimental products were compared between formation porosity thermocompression simulation and conventional autoclave simulation of hydrocarbon generation and expulsion. Different experimental conditions of the two methods resulted in various discrepancies of pyrolysis analysis data. At the same temperature, the oil and gas production rate of formation porosity thermocompression simulation is twice of that of the conventional autoclave simulation. Free hydrocarbon (S₁), hydrocarbon generation potential (S₂) and hydrogen index (I_H) of solid products of the thermocompression experiment are higher than those of the autoclave experiment. In a conventional autoclave experiment, high temperature not only accelerates C-C bond cleavage to form hydrocarbon, but also generates bitumen, CO₂ and H₂, which deviates from the natural evolution of source rocks. The experimental conditions (higher fluid pressure, smaller hydrocarbon generation room filled with liquid water) in the formation porosity experiment are more similar to the conditions of real geological evolution. Experimental data show that gas and oil yield is much larger than hydrocarbon potential in the thermocompression experiment, and the solid products after the experiment still have a high hydrogen index. As a result, hydrogen index and hydrocarbon yield in laboratory experiments fail to estimate the real hydrocarbon potential of source rocks. Accordingly, an Oil and Gas Index (OGI) is proposed to estimate the maximum hydrocarbon potential of source rocks.