南华北盆地鹿邑凹陷太原组泥岩微观孔隙特征及影响因素

Microscopic pore characteristics and influencing factors of mudstone in the Taiyuan Formation, Luyi Sag, Southern North China Basin

摘要

鹿邑凹陷太原组是南华北盆地海陆过渡相页岩气勘探的重点区域。以LY1井太原组泥岩为研究对象,采用有机地球化学、X射线衍射、扫描电镜、CO₂吸附、N₂吸附和高压压汞等实验测试方法,探讨太原组泥岩微观孔隙特征及影响因素。结果表明:太原组泥岩孔隙类型主要分为黏土矿物层间缝、收缩缝、剩余粒间孔、粒间溶孔和有机质孔隙。孔径以介孔为主,微孔次之,大孔最少,其中孔径为0.40~0.80nm的微孔和孔径为2.00~6.00、10.00~40.00nm的介孔对孔体积贡献最大。孔隙形态分为3种类型:类型栺以墨水瓶状孔及一端或两端开口的楔形孔为主,孔隙发育差;类型栻和类型栿以两端开放的管状孔和四面开放的平行板状孔为主,孔隙发育较好,后者介孔发育程度更高。泥岩孔隙发育受多种因素控制,有机质是控制微孔发育的重要因素,二者呈正相关关系;石英对大孔和介孔的保存有利,黄铁矿发育晶间孔并伴生收缩缝而对大孔的保存有利;高岭石、伊利石具有特殊的晶体结构而对微孔和大孔的保存有利,碳酸盐矿物和伊/蒙混层形成的偏碱性环境及大孔的充填导致对微孔和大孔的保存不利,对介孔的保存有利;压实作用和胶结作用是导致孔隙孔径大幅缩小的主要因素,有机质热成熟作用、溶蚀作用和破裂作用对孔隙的发育具有建设性作用。该结果为鹿邑凹陷页岩气储层精细评价及研究提供依据。

Abstract

The Taiyuan Formation in Luyi Sag is a key area for marine-continental transitional shale gas exploration in Southern North China Basin. Taking the mudstone of the Taiyuan Formation in well LY1 as the research subject, this study employs experimental methods such as organic geochemistry, X-ray diffraction, scanning electron microscopy, CO₂ adsorption, N₂ adsorption, and high-pressure mercury intrusion to investigate the microscopic pore characteristics and influencing factors of the mudstone in Taiyuan Formation. The results indicate that the pore types of the mudstone in Taiyuan Formation primarily classified as interlayer fractures of clay minerals, shrinkage fractures, residual intergranular pores, intergranular dissolution pores, and organic pores. The pore size distribution is dominated by mesopores, followed by micropores, with macropores being the least developed. Micropores with pore sizes of 0.40-0.80 nm and mesopores with pore sizes of 2.00-6.00 and 10.00-40.00 nm contribute the most to pore volume. Pore morphology is divided into three types: type I is mainly composed of ink bottle-shaped pores and wedge-shaped pores with one or both ends open, showing poor pore development; types II and III are dominated by tubular pores with both ends open and parallel plate-shaped pores with four open sides, exhibiting better pore development, type III has a higher degree of mesopore development. Pore development in mudstone is controlled by multiple factors. Organic matter is a crucial factor influencing micropore development, with a positive correlation between them; quartz is beneficial for the preservation of macropores and mesopores, pyrite promotes macropore development due to intergranular pores and shrinkage fractures; kaolinite and illite are beneficial for the preservation of micropores and macropores due to their unique crystal structures. The alkaline environment during the formation of carbonate minerals and illite/montmorillonite mixed layers, as well as their filling of macropores, are unfavorable for the preservation of micropores and macropores, but favorable for the preservation of mesopores. Compaction and cementation are the primary factors causing significant pore size reduction, while organic matter thermal maturation, dissolution, and fracturing have constructive effects on pore development. These findings provide a basis for the detailed evaluation and research of shale gas reservoirs in the Luyi Sag.

关键词

泥岩 / 微观孔隙特征 / 影响因素 / 页岩气 / 太原组 / 鹿邑凹陷 / 南华北盆地

Key words

mudstone / microscopic pore characteristics / influencing factors / shale gas / Taiyuan Formation / Luyi Sag / Southern North China Basin

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基金资助

河南省财政地质勘查基金项目(豫自然资发〔2019〕22号)

河南省矿产资源总体规划项目(2026-2030年)