Kinetics of the hydrocarbon generation process of marine source rocks in South China

The kinetics of hydrocarbon generation of different types of marine source rocks and planktonic algae in South China were analyzed using the Rock-Eval 6 instrument and the Optkin kinetic software. The average activity energy of marine source rocks has the characteristics of EAI<EAII1<EAII2<EAIII, in the effective hydrocarbon generation period, with the kerogen transformation being from 10% to 90%. The variation of the hydrocarbon generation activity energy (ΔE) is ΔEIII>ΔEII2>ΔEII1>ΔEI, the hydrocarbon generation speed is VmI>VmII1>VmII2>VmIII, while the planktonic algae has a very low activation energy for hydrocarbon generation and can generate a great abundance of heavy oil during the immature –low mature period. According to the results of kinetic experiments on thermal simulation experiments and simulation residue samples, the kinetic hydrocarbon generation process of marine source rocks can be described by four stages: (1) heavy oil generation, where the vitrinite reflectance (Ro) is 0.3%–0.6%, and the average activation energy is about 220 kJ/mol; (2) normal oil generation, where the vitrinite reflectance is 0.6%–1.2%, and the average activation energy is approximately 250–270 kJ/mol; (3) condensate and gas generation, where the vitrinite reflectance is higher than 1.2% and the average activation energy is higher than 270 kJ/mol; and (4) gas “dead line” of kerogen, where the vitrinite reflectance is higher than 4.21% and the average activation energy is higher than 320 kJ/mol.