川中蓬莱—中江地区灯二段微生物白云岩储层特征、发育主控因素与勘探领域

Characteristics, controlling factors and exploration prospects of microbial dolomite reservoirs in the second member of Dengying Formation, Penglai-Zhongjiang area of central Sichuan Basin

文龙 张建勇 潘立银 马华灵 李泽奇 李文正 谢武仁 汪泽成 付小东 王永骁 黎荣

WEN Long ZHANG Jianyong PAN Liyin MA Hualing LI Zeqi LI Wenzheng XIE Wuren Wang Zecheng FU Xiaodong WANG Yongxiao LI Rong

中国石油 西南油气田分公司, 成都 610041 中国石油 杭州地质研究院, 杭州 310023 成都理工大学, 成都 610059 中国石油勘探开发研究院, 北京 100083

Southwest Oil & Gas Field Company, PetroChina, Chengdu, Sichuan 610041, China PetroChina Hangzhou Institute of Petroleum Geology, Hangzhou, Zhejiang 310023, China Chengdu University of Technology, Chengdu, Sichuan 610059, China Research Institution of Petroleum Exploration & Development, PetroChina, Beijing 100083, China

四川盆地震旦系灯影组白云岩储集层的形成与演化是近期重点关注的对象，确定其主控因素及发育规律，对天然气勘探与开发具有重要指导意义。基于四川盆地蓬莱—中江地区的钻井、地震资料，通过岩心、薄片观察与实验分析数据，对灯二段优质储集层特征及发育的主控因素进行了研究。该区灯二段储集层岩性主要为微生物白云岩、颗粒白云岩以及角砾状白云岩；储集空间以溶蚀孔洞、残余格架孔、角砾间孔为主，孔隙度主要分布在2.0%~8.0%，平均为4.39%，渗透率平均为0.53×10-3 μm2；储集层厚170~320 m。同沉积断裂造成沉积地貌分异，形成水下高垒地块，为微生物丘(礁)滩体发育提供了有利条件；且断层活动可使弱固结沉积物发生破碎形成角砾状，构成角砾状白云岩优质储层。准同生溶蚀作用是灯二段优质储集层发育的关键，纵向上集中发育在向上变浅旋回的上部。沉积微相分异导致了早期成岩作用的差异，浅埋藏胶结程度决定了孔隙保存的程度。预测川中古隆起北斜坡灯二段发育蓬莱—中江、盐亭—绵阳、苍溪—广元三大断控型台缘丘滩带，面积分别为1 600、1 870、2 280 km2，具有多阶多带特征。盐亭—绵阳、苍溪—广元地区灯二段台缘微生物丘滩体与三套优质烃源岩可形成多种有利源储配置关系，成藏条件优越，预计资源量超万亿立方米，是碳酸盐岩超深层勘探的有利区，有望成为四川盆地下一个万亿立方米气田的突破地。

The formation and evolution of dolomite reservoirs in the Sinian Dengying Formation in the Sichuan Basin have attracted much attention recently. Due to their economic significance for hosting natural gas resources, determining the key factors that govern the formation and evolution of these dolomite reservoirs are important for hydrocarbon exploration and development. Based on the drilling and seismic data in the Penglai-Zhongjiang area of the Sichuan Basin, the main controlling factors for the development of high-quality reservoirs in the second member of Dengying Formation are investigated by integrating core and thin section observation and geochemical analysis. Lithologies of the reservoirs in the second member of Dengying Formation are dominantly microbial dolomites, dolo-grainstones, and brecciaed dolomites. Moreover, reservoir spaces in these dolomites are mostly dissolution pores, residual framework pores, and breccia pores. The porosity ranges from 2.0% to 8.0% with an average of 4.39%, and the average permeability is 0.53×10-3 μm2, and the reservoir thickness is 170-320 m. Synsedimentary faulting had caused the differentiation of depositional paleo-geomorphology and led to the formation of submarine high barriers, which provided favorable conditions for the development of microbial mound (reef) and shoal complexes. Furthermore, fault activities could have broken the weakly consolidated carbonate sediments into breccias, thus resulting in the brecciaed dolomite reservoir. Penecontemporaneous dissolution is the key to the development of high-quality reservoirs in the second member of the Dengying Formation, which is consistent with their occurrence in the upper part of the shallowing-upward cycles. Differentiation in microfacies leads to distinct diagenetic pathways and porosity evolution of these microbial-dominant carbonate sediments. Overall, dolomite cementation during shallow burial had controlled thedegree of pore preservation. It is predicted that three fault-controlled, platform-margin mound regions in the study area, i.e., Penglai-Zhongjiang, Yanting-Mianyang, and Cangxi-Guangyuan, with areas of 1 600 km2, 1 870 km2 and 2 280 km2, respectively, had been developed in the second member of Dengying Formation in the north slope of the central Sichuan paleo-uplift, showing multi-stage and multi-zone characteristics. Microbial mounds in the platform margin of the second member of Dengying Formation in the Yanting-Mianyang and Cangxi-Guangyuan areas, with three sets of high-quality source rocks, may form a variety of favorable source-reservoir combinations. Additionally, the accumulation conditions may have been superior. The estimated natural gas resources in the study area, over one trillion square meters, makes it a favorable area for ultra-deep carbonate exploration and is expected to be a breakthrough site for the next one trillion square gas field in the Sichuan Basin.

国家自然科学基金 42172183;中国石油天然气集团有限公司上游领域基础性前瞻性项目 2021DJ0501

https://doi.org/10.11781/sysydz202305982