合水南地区长7段夹层型页岩油储层孔隙结构特征及主控因素

Pore structure characteristics and main controlling factors of interbedded shale oil reservoirs of Chang 7 Member in South Heshui Area

摘要

以鄂尔多斯盆地合水南地区长7段夹层型页岩油储层为例，利用铸体薄片、扫描电镜、XRD 分析、高压压汞、恒速压汞及氮气吸附实验，分析合水南地区长 7 段夹层型页岩油储层孔隙结构特征，探讨沉积、成岩作用对孔隙结构的控制作用。结果表明：合水南地区长 7 段页岩油储层孔隙度平均为 8.47% ，渗透率平均为 0.74 \times {10}^{-3} \mu {\mathrm{m}}^2 ，属于典型的超低孔、超低渗储层；孔隙类型以残余粒间孔和长石溶孔为主，孔喉半径集中分布在 0.02 \sim 200.00 \mu \mathrm{m} 之间，孔隙形态主要为板状平行狭缝孔和半封闭楔形孔；孔隙结构受沉积、成岩作用演化共同控制。沉积作用奠定页岩油储层的物质基础，沉积物粒度细，杂基体积分数高，原始孔渗低；储层在强压实阶段损失大量的粒间孔隙，胶结作用进一步降低储层物性；后期溶蚀作用的改造促使优势储层形成。砂质碎屑流砂体受胶结作用减孔大，浊流砂体受压实作用减孔大。砂质碎屑流砂体经历中等压实、强胶结及中等溶蚀，是研究区优势储层的主要成因。该结果对夹层型页岩油高效开发具有指导意义。

Abstract

In order to efficient development of interbedded shale oil. This study focuses on the Chang 7 Member of the Triassic Yanchang Formation in the South Heshui Area of the Ordos Basin. The pore structure characteristics of the Chang 7 interbedded shale oil reservoir were analyzed using cast thin sections, scanning electron microscopy(SEM), XRD analysis, high-pressure mercury injection, and lowtemperature nitrogen adsorption. The impact of sedimentation and dominant diagenetic processes on pore structure was also examined. The results indicate that the interbedded shale oil reservoirs of the Triassic Chang 7 Member in South Heshui Area. With an average porosity of 8.47% and an average permeability of 0.74 \times {10}^{-3} \mu {\mathrm{m}}^2, it as a typical ultra-low porosity and ultra-low permeability reservoir. The reservoir pores are predominantly feldspar dissolution pores and residual intergranular pores. The pore throat radius range from 0.02 to 200.00 \mu \mathrm{m}, with pore throats primarily consisting of plate-like parallel slit pores and semi-closed wedge-shaped pores. Sedimentation, compaction, cementation, dissolution, and diagenetic sequences collectively control the pore structure. Sedimentation provides the material basis for the shale reservoir, characterized by fine grain size, high clay content, and low initial porosity and permeability. Strong compaction significantly reduces the number of intergranular pores, while cementation further degrades reservoir properties. However, subsequent dissolution partially enhances the reservoir's porosity and permeability. The sandy debris flow reduction pore is greatly affected by cementation, and the turbid current reduction pore is greatly affected by compaction. The main causes of advantageous reservoirs are the sand debris flow undergose medium compaction, strong cementation, and medium dissolution in the research area. This result has guiding significance for the efficient development of interbedded shale oil.

关键词

陆相湖盆 / 夹层型页岩油 / 孔隙结构 / 砂质碎屑流 / 优势储层 / 长 7 段 / 合水南地区

Key words

lacustrine basin / interbedded shale oil / pore structure / sand debris flow / advantage reservoir / Chang 7 Member / South Heshui Area

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基金资助

中国石油科技创新基金项目(2021DQ02-0106)

国家自然科学基金项目(42172172)

甘肃省油气资源研究重点实验室开放基金项目(20221227)