鄂尔多斯盆地南缘奥陶系平凉组微生物碳酸盐岩储层特征与演化过程

Characteristics and evolution of microbial carbonate reservoirs in the Pingliang Formation on the southern margin of Ordos Basin

张军涛 金晓辉 孙冬胜 杨佳奇 丁茜

ZHANG Juntao JIN Xiaohui SUN Dongsheng YANG Jiaqi DING Qian

中国石化 深部地质与资源重点实验室, 北京 102206 中国石化 石油勘探开发研究院, 北京 102206 中国地质大学 能源学院, 北京 100083

Key Laboratory of Deep Geology and Resources, SINOPEC, Beijing 102206, China Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 102206, China College of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, China

微生物碳酸盐岩储层作为一种重要的油气储层，蕴含大量油气资源。近期在鄂尔多斯盆地中东部马家沟组发现有工业气流，证实这类储层在鄂尔多斯盆地也具有十分广泛的勘探前景。在盆地南缘同样发现类似储层，通过岩石学和地球化学手段，研究了该区奥陶系平凉组微生物碳酸盐岩储层发育特征及演化过程。盆地南缘发育有较盆地内更大规模的微生物丘滩复合体，厚度可达100 m以上；微生物岩类型主要为凝块石灰岩，以溶蚀孔为主。平凉组微生物岩储层经历了准同生期和表生期两期岩溶作用，埋藏期存在油气充注。准同生期经历了短暂暴露，形成大量不规则状溶孔，放射纤维状方解石孔隙充填在早期孔隙之中，具有与基质方解石相似的碳氧同位素和Sr、Mg等微量元素含量，说明其来源于同期海水。表生期，早期溶孔发生扩大，形成了大量的裂缝和溶洞，同时伴有粗晶方解石和泥质的充填，部分粗晶方解石显示出大气降水的特征。埋藏期存在油气充注，现今溶孔和裂缝中存在有沥青残余，埋藏期充填方解石中也能见到大量液态烃包裹体。鄂尔多斯盆地南缘平凉组微生物碳酸盐岩发育优质储集空间，存在油气充注过程，是潜在的油气勘探领域。

As an important type of hydrocarbon reservoir, microbial carbonate contains great amount of hydrocarbon resources. The recent discovery of industrial gas in the Majiagou Formation in the east-central part of the Ordos Basin indicates that this type of reservoir also has very extensive exploration prospects in the Ordos Basin. Similar reservoirs were also found on the southern margin of the basin, but no systematic research has been achieved. In this paper, petrological and geochemical anatomy of microbial carbonate reservoirs of the Pingliang Formation on the southern margin of the Ordos Basin were carried out. Results show that the study area developed a larger-scale microbial mound and beach complex than that in the basin, and the thickness can be more than 100 m. The microbial rock is mainly agglomerate limestone with dissolution pores. The microbial rock reservoir of the Pingliang Formation has experienced two stages of karsting, quasi-syngenesis and epigenesis, which are the key for the formation of reservoir, and there is oil and gas charging during the burial period. Among them, the quasi-syngenetic stage experienced a brief exposure, forming a large amount of irregular-shaped solution pores, and radial fibrous calcite pores filled in the early pores, with similar oxygen/carbon isotope and trace element contents such as Sr and Mg as the matrix calcite, it is then indicated that they were originated from seawater in the same period. During the epigenetic stage, the early solution pores expanded, forming a large number of fractures and cavities, accompanied by the filling of coarse-crystal calcite and mud, and some of the coarse crystalline calcite shows the characteristics of atmospheric precipitation. There is oil and gas charging during the burial period. There are bituminous residues in the present-day solution holes and fractures, and a large amount of liquid hydrocarbon-bearing inclusions can be observed in the calcite filling during the burial period. In summary, the microbial carbonate of the Pingliang Formation at the southern edge of the Ordos Basin, where both reservoir formation and hydrocarbon filling processes exist, is a potential exploration field.

国家自然科学基金企业创新发展联合基金项目 U19B6003;国家自然科学面上基金 42072177;中国科学院A类战略性先导项目 XDA14010201

https://doi.org/10.11781/sysydz202203385