富油凹陷洼槽区古压力演化特征及影响因素——以冀中坳陷饶阳凹陷为例

Characteristics of paleopressure evolution and its influencing factors in sub-sags of hydrocarbon-bearing sag:A case study of Raoyang sag in Jizhong depression

为了明确富油凹陷洼槽区古压力演化特征,以冀中坳陷饶阳凹陷为研究对象,运用录测井、试油等资料,在现今地层压力研究的基础上,采用盆地模拟技术与流体包裹体测温技术相结合定量恢复了不同洼槽古压力演化过程,并探讨了富油凹陷洼槽区古压力演化的影响因素,认为洼槽区古压力演化经历了原始积累—释放—再积累3个阶段,不同阶段不同洼槽古压力演化特征差异明显;源岩生排烃能力控制的生烃增压作用是大规模生排烃时期(12~0 Ma)古压力明显增强的主要原因.结果表明:饶阳凹陷洼槽区发育东营组—沙一段和沙三段2套压力系统,河间、马西与留西洼槽为上弱下强型,任西洼槽为下强上弱型,其中河间洼槽超压强度最大,压力系数可达1.58.古压力恢复结果表明饶阳凹陷洼槽区成藏期普遍发育超压,最大压力系数可达1.51,相邻构造带发育弱超压,最大压力系数为1.29.洼槽区沉积充填特征决定了不同层系的岩性、厚度与沉积速率等特性,影响了欠压实增压机制对超压的贡献大小;大规模生排烃时期异常压力快速积累,洼槽区古压力变化率fVR随生排烃量差值增大而提高,马西洼槽fVR可达0.030 Ma-1.

To determine the paleopressure evolution characteristics of sub-sags in hydrocarbonbearing sags,taking Raoyang sag of Jizhong depression as the research object,based on the study of the formation pressure,basin modeling technology and thermometry of fluid inclusions were applied to reconstruct the process of paleopressure evolution in different sub-sags and investigate the influencing factors with the analysis of the detection logging and oil testing datas.The paleopressure evolution in sub-sags experienced three stages：primitive accumulation-releasing-reaccumulation and the significant difference of the paleopressure evolution characteristics in different sub-sags was observed.During the large-scale hydrocarbon generation and expulsion period（12—0 Ma）,the overpressure caused by the hydrocarbon generation and expulsionof the source rock is the main reason for the high growth rate of paleopressure in sub-sags.The results show that the double overpressure structure exists in Dongying formation-Sha-1member and Sha-3member,including the lower pressure stronger than upper in Hejian,Maxi and Liuxi sub-sag while the upper pressure stronger than lower in Renxi sub-sag.The strongest overpressure develops in Hejian sub-sag with the pressure coefficient of 1.58.The result of the paleopressure restoration shows that the overpressure in sub-sags of Raoyang sag develops with the highest pressure coefficient of 1.51 during the accumulation period,while the low overpressure in the adjacent structural belts develops with the pressure coefficient of 1.29.The lithology,thickness and deposition rate determined by the sedimentary character of different sub-sags influence the contribution of disquilibrium compaction pressurization mechanisms.The abnormal pressure accumulates rapidly during the large-scale hydrocarbon generation and expulsion period and the paleopressure variation rate which can reach 0.030 Ma-1 in Maxi sub-sag increases along with the growth of the difference between hydrocarbon generation and expulsion.