冀中坳陷霸县凹陷古近系中深层古地层压力演化及对储层成岩作用的影响

综合运用测录井、试油和实验分析测试资料及盆地模拟方法，在霸县凹陷古近系中深层今地层压力分析的基础上，恢复了古地层压力的演化过程，探讨了古地层压力对储层成岩作用的影响。分析结果表明，古近系中深层地层压力存在超压原始积累-超压降低2个阶段，其演化表现出“低-高-低”变化特征。沉积初期地层压力以常压为主，在距今约40 Ma开始发育超压，约25~20 Ma期间超压达到最高值，表现为强超压，随后地层压力持续降低，至今演化为常压、弱超压，局部地区发育中超压。早期快速埋藏导致的欠压实作用是地层超压形成的主要原因，而后期生烃增压作用不明显。古地层超压抑制了储层的成岩作用，具体表现为：①抑制压实作用的进行，从而保护储层的原生孔隙；②抑制黏土矿物的转化，减少Ca²⁺等的来源，从而减弱胶结作用发生，保护储层的孔隙；③抑制有机酸的生成，阻碍流体渗流与物质交换，从而不利于长石溶蚀作用的发生。

Paleopressure evolution and its effects on diagenesis of reservoirs in middle-deep Paleogene strata in Baxian sag,Jizhong depression

This study reconstructed the process of paleopressure evolution and investigated its effects on diagenesis of reservoirs in middle-deep Paleogene strata in Baxian sag, on the basis of present-day pressure analysis through a combination of detection logging, oil testing, experimental analysis of test data, and basin modeling. Results showed that the pressure in middle-deep Paleogene strata experienced two stages, primary accumulation and reduction of overpressure, showing low-high-low evolutionary characteristics. Formation pressure was generally normal during initial deposition, whereas overpressure began to develop around 40 Ma ago and peaked during 25-20 Ma as strong overpressure. Formation pressure continuously declined thereafter and evolved to the present-day normal pressure and low overpressure, with moderate overpressure developed in localized regions. Uncompaction caused by rapid burial in the early stage was the primary cause of abnormal overpressure while hydrocarbon generation in the late stage had no significant effect on formation pressure. Paleopressure inhibited diagenesis of reservoirs in middle-deep Paleogene strata from the following aspects: (1) It inhibited compaction and thus protected primary pores of the reservoir; (2) It inhibited transformation of clay minerals and reduced ion sources such as Ca²⁺, delaying cementation and thus protecting pores of the reservoir; and (3) It restrained organic acid generation and hindered fluid seepage as well as material exchange, unfavorable for feldspar dissolution.