Hydrocarbon Generation Kinetics of the Gas-Prone Kerogens in the Central Uplift of the South Yellow Sea Basin

摘要

A kinetic hydrocarbon generation model is critical to the evaluation of hydrocarbon prospects, which can promote offshore oil-gas exploration in the South Yellow Sea Basin (SYSB). To ascertain the hydrocarbon generation kinetic parameters of the gas-prone kerogens in the Central Uplift of the South Yellow Sea Basin (CUSYSB), open-system pyrolysis gas chromatography (PY-GC) simulation experiments were performed on two silty mudstones containing type II2 kerogens from borehole CSDP-2, which were supplemented by a literature investigation of the kinetic models for type III kerogens. The hydrocarbon products of type II2 kerogens are mainly gas, accounting for 54.56%-57.31% of all products, and oil, accounting for 42.69%- 45.44% of all products. In the parallel first-order reaction model with multiple frequency (pre-exponential) factors and a discrete activation energy distribution (the MFF model), the activation energy of gas generation primarily ranges from 43.0 to 52.6 kcal/mol (average: 46.8 kcal/mol), which is slightly lower than the oil generation activation energy ranging from 45.4 to 54.9 kcal/mol (average: 49.9 kcal/mol). Geological extrapolation results reveal that the three sets of source rocks, i.e., the Lower Triassic Qinglong Formation (T(1)q), Permian, and Lower Silurian Gaojiabian Formation (S(1)g) source rocks, are characterized by sequential multistage hydrocarbon generation, with average hydrocarbon transformation ratios of 18.51%, 51.14%, and 95.58%, respectively. However, under the action of anomalous heat flows, the highest hydrocarbon transformation ratio of the Lower Permian source rocks reaches 92.81%. Moreover, on the basis of previous knowledge on the effective Upper Permian sandstone reservoirs and the suitable accumulation conditions, the Permian rocks with favorable hydrocarbon prospects have been identified in the CUSYSB, which are characterized by high-intensity hydrocarbon generation and expulsion.