Available lab and drilling data reveal that the effect of pressure upon the evolution of organic matter could not be fully described with a general model.In formations under normal pressure

organic chemical reactions follow the first-order reaction kinetics.In contrast

formations under overpressure act as semi-closed systems

in which the hydrocarbons generated from organic matter could not be expulsed in time and a chemical equilibrium is eventually reached when the amount of reaction product increases to a critical state.The pressure exerts its influence upon the evolution of organic matter through affecting the shifting of chemical equilibrium instead of changing the frequency factor of the chemical reaction.Therefore

organic matter evolution under overpressure is the result of temperature and pressure affecting the shift of chemical equilibrium.What can be derived from this observation is that it is pressure itself that does the works not the overpressure.What the overpressure does is to provide a semi-closed system for chemical reactions.Formation pressure controls the shift of chemical equilibrium to manipulate the thermal evolution of organic matters.The new model then was applied to actual petroliferous basins to simulate the evolution pattern of organic matter in a single well.A comparison of the modeled results with the real maturity data reveals that the model matches well with the real evolution of organic matter

confirming the effectiveness of the model.