中深层致密砂岩储集层成岩特征与孔隙演化定量研究:以沧东凹陷南皮斜坡孔店组二段为例

Quantitative study on diagenetic characteristics and pore evolution of middle-deep tight sandstone reservoirs:a case study of the Second Member of Kongdian Formation in Nanpi slope,Cangdong sag

渤海湾盆地沧东凹陷古近系孔店组孔二段埋深普遍大于3000 m,埋藏史较长、致密化严重,而成岩特征和孔隙演化问题是该区进行油气勘探与开发的关键。本研究基于沉积岩石学、储集层地质学以及基本的岩石矿物学理论和相关分析测试的基本资料,对渤海湾盆地沧东凹陷南皮斜坡孔二段储集层特征和成岩作用进行了系统研究,明确了成岩作用的类型及特征;结合成岩矿物流体包裹体均一温度及地温埋藏史,建立了针对研究区中深层储集层成岩演化的序列;建立了定量模型,利用“回剥法”在充分考虑沉积及不同成岩作用对孔隙演化影响的基础上,分析了各个成岩阶段的孔隙演化特征和孔隙演化过程。结果表明:研究区孔二段储集层目前处于中成岩阶段A2-B期,储集层先后经历了压实作用、早期胶结作用、溶蚀作用及晚期胶结作用,其中压实作用是主要的储集层减孔因素并贯穿成岩过程始终。

Diagenesis plays a crucial role in shaping the evolution of reservoir physical properties and ultimately governs reservoir quality.Understanding the relative sequence of diagenesis is of utmost importance for oil and gas exploration.The diagenetic evolution of the Jurassic Yan'an Formation palaeochannel sandstone in the Jiyuan area of the Ordos Basin and its main sources of cements were studied based on core observation,common thin sections,cast(stained)thin sections,scanning electron microscopy(SEM),cathodoluminescence(CL),X-ray diffraction,fluid inclusion and carbon&oxygen isotopes.In addition,the impact of cements and compaction on the loss of intergranular pores was quantitatively analyzed.The results show that paleochannel sandstone reservoir of the Yan'an Formation is mainly composed of arkoses and lithic arkoses,with an average porosity of 15.1%and average permeability of 19.5×10^(-3)μm^(2),classifying it as a medium-porosity and low-permeability reservoir.The diagenetic process has experienced compaction,early cementation,medium dissolution,late cementation and late replacement.Among the cements,ferrocalcite exhibits the highest content,while kaolinite is the most widely distributed cement.Cements are the main contributor to the reduction of original intergranular pore volume,accounting for an average contribution of 37.5%,while compaction was the minor contributor with an average contribution of 29.4%.In addition,calcites directly derived from diagenetic fluid related to atmospheric water,whereas dolomite originated from early calcite,coal and mudstone thermal evolution products.Ferrocalcite,on the other hand,primarily originated from thermal evolution of coal and mudstone interlayers.This study establishes a diagenetic sequence for the Jurassic Yan'an Formation palaeochannel sandstone reservoirs in the Jiyuan area,which serves as a fundamental basis for reservoir assessment and provides valuable insights for future exploration and development.