数值模拟揭示深层泄压圈闭差异成藏机制OA

It is widely acknowledged that pressure relief within deep hydrocarbon traps is usually accompanied by hydrocarbon leakage.The CFD-A and CFD-B traps in the CFD6-4 Structure of the Bozhong Sag,Bohai Bay Basin possess analogous reservoir-forming conditions and both belong to pressure relief traps,yet they exhibit striking disparities in hydrocarbon enrichment.Revealing the differential accumulation mechanisms of the two traps can provide theoretical guidance for deciphering the coupling relationship between deep formation pressure relief and hydrocarbon accumulation,as well as for predicting similar favorable traps.In this study,we first compare the reservoir-forming elements of the two traps from four dimensions,namely hydrocarbon source rocks,reservoir properties,hydrocarbon migration pathways and preservation conditions.On this basis,we propose a hypothesis that differences in fault activity rates constitute the primary factor controlling differential hydrocarbon accumula-tion.Taking the CFD-A and CFD-B traps of the CFD6-4 Structure as research targets,we carry out numerical simulations of fault-triggered pressure relief and fault-controlled hydrocarbon accumulation based on a heterogeneous geological model,so as to quantitatively validate the hypothesis.The simulation results are summarized as follows.(i)The reservoirs of the 3rd member of the Dongying Formation(Ed3)initiated pressure relief at 5.1 Ma.Over-pressure decreased rapidly from 5.1 Ma to 5.0 Ma,followed by a slow decline from 5.0 Ma to the present.(ii)When trap-controlling faults feature low activity rates(25-30 m/Ma),the pressure release rate ranges from 23.1 MPa/Ma to 25.0 MPa/Ma,with a hydrocarbon leakage rate of 2 272-3 472 t/Ma,and both pressure relief and hydrocarbon leakage proceed relatively slowly.Once fault activity rates exceed 30 m/Ma,the pressure relief rate surges to 36.6-75.0 MPa/Ma,and the hydrocarbon leakage rate rises synchronously to 5 208-5 952 t/Ma.The differential accumulation mechanisms of deep pressure-release traps in the CFD6-4 structure are clarified as follows.During the hydrocarbon charging stage,the migration intervals(1st member of the Shahejie Formation,Es1)and charging intervals(Ed3)of the trap-controlling Fault F1 and Fault F2 show comparable activity rates for the CFD-A and CFD-B traps,respectively,and their activity rates are higher than those of the leakage intervals(2nd member of the Dongying Formation,Ed2).The hydrocarbon charging volume exceeds the leakage volume,enabling dynamic hydrocarbon accumulation in both traps.During the hydrocarbon adjustment stage,the leakage interval(spanning Ed3 and Ed2)of Fault F2 presents a higher activity rate than that of Fault F1.As a result,the hydrocarbon leakage volume surpasses the charging volume within the CFD-B trap,leading to complete hydrocar-bon dissipation inside the trap and secondary accumulation in the shallow Guantao Formation.In contrast,the CFD-A trap maintains a larger charging volume than leakage volume,preserving its dynamic hydrocarbon accu-mulation state.Two key exploration insights are summarized as follows:(i)In regions with superior hydrocarbon supply,fault-block traps should be preferentially selected as drilling targets where trap-controlling faults have high activity rates in migration and charging intervals during the reservoir-forming stage,while their leakage intervals record activity rates lower than 30 m/Ma during the adjustment stage.(ii)Numerical simulation tech-nology can be adopted to realize quantitative pre-drilling evaluation of the accumulation potential for such pres-sure relief traps.