川西北地区茅口组上部黑色岩系的层位、沉积环境及生烃潜力评价

Sedimentary environment, hydrocarbon potential and development of black rocks in upper Maokou Formation, northwestern Sichuan

胡朝伟 胡广 张玺华 陈聪 彭翰霖 高兆龙 廖志伟 庞谦 游杰

HU Chaowei HU Guang ZHANG Xihua CHEN Cong PENG Hanlin Gao Zhaolong LIAO Zhiwei PANG Qian YOU Jie

西南石油大学 油气藏地质及开发工程国家重点实验室, 成都 610500 西南石油大学 中国石油碳酸盐岩储层重点实验室 沉积与成藏分室, 成都 610500 中国石油 西南油气田公司 勘探开发研究院, 成都 610041 重庆大学 资源与安全工程学院 煤矿灾害动态与控制国家重点实验室, 重庆 400044

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China Research Division of Sediment and Reservoir, Key Laboratory of Carbonate Reservoirs of CNPC, Southwest Petroleum University, Chengdu, Sichuan 610500, China Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610041, China State Key Laboratory of Coal Mine Disaster Dynamics and Control, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China

上扬子台地北缘川西北地区西北乡剖面在茅口组碳酸盐岩与吴家坪组碳酸盐岩之间出露一套厚23.8 m的黑色岩系，岩性主要为薄层硅质岩、页岩及泥质灰岩。针对西北乡剖面开展详细的牙形石地层学、有机岩石学以及有机地球化学研究。结果表明这套黑色岩系中发现的牙形石为Jinogondolella prexuanhanensis、J.xuanhanensis和Clarkina postbitteri hongshuiensis，均为二叠纪瓜德鲁普世末期分子，确定该段黑色岩系沉积于茅口晚期，表明上扬子台地川西北地区在瓜德鲁普世末期开始发育拉张槽。详细的有机岩石学研究发现该套黑色岩系成烃生物以底栖宏观藻类为主，见少量大型浮游藻类，有机质类型主要为Ⅱ型。有机地球化学分析表明，该套黑色岩系有机碳含量（TOC）为1.04%~32.58%，氯仿沥青“A”含量为0.03%~1.05%，整体上达到好的烃源岩标准。镜质体反射率Ro范围为1.0%~1.4%，Tmax值为440℃~460℃，牙形石色变指数CAI为1.5~2.5，Ts/Tm比值为0.35~1.43，莫烷/藿烷比值范围为0.05~0.39，C2920S/（20S+20R）值为0.39~0.65，C29αββ/（αββ+ααα）为0.26~0.58，表明有机质成熟度高，为成熟—高成熟。岩性特征、牙形石生态、成烃生物和生物标志化合物综合研究表明，黑色岩系形成于较为深水的还原环境，水体具有较高的盐度。

A set of organic-rich black rocks (23.8 m), mainly consisting of siliceous rocks, shale and limestones, outcrops between carbonate rocks of the Maokou and Wujiaping formations in the Xibeixiang section, northwestern Sichuan Basin, at the margin of the Upper Yangtze Platform. Detailed conodont stratigraphy, organic petrology and organic geochemistry studies were performed on samples from the Xibeixiang section. The conodonts found in the study area were Jinogondolella prexuanhanensis, J. xuanhanensis and Clarkina posbitteri hongshuiensis. All of them lived at the end of Guadalupian, confirming that the black rocks in the section were deposited during the late period of the Maokou Formation indicating that the Guangyuan-Wangchang Marine Trough began to develop in the late Guadalupian stage on the Upper Yangtze Platform. The detailed study of organic petrology reveals that benthic algae is the main contributor for hydrocarbon in the black rock series, with a small amount of macroplanktonic algae, and the organic matter is type Ⅱ. The organic geochemical analyses of the black rocks show that the TOC content ranges 1.04% to 32.58% and the chloroform bitumen "A" content ranges 0.03% to 1.05%, indicating favorable source rocks. Thermal parameters, such as the vitrinite reflectance (Ro) value ranges 1.0% to 1.4%, the Tmax value ranges 440 to 460℃, the conodont color index (CAI) ranges 1.5 to 2.5, the Ts/Tm ratio ranges 0.35 to 1.43, the moretane/hopane ratio ranges 0.05 to 0.39, the C2920S/(20S+20R) ranges 0.39 to 0.65, and the C29αββ/(αββ+ααα) ranges 0.26 to 0.58, which indicate that these black rocks are mature to highly mature. The integrated study of lithology, hydrocarbon-forming organisms, conodonts and biomarkers indicate that these black rocks were deposited in a relatively reductive deep-water environment with a high salinity.

国家自然科学基金项目“Toarcian期大洋缺氧事件（T-OAE）的陆相响应及油气地质意义：以四川盆地下侏罗统大安寨段为例” 41872155

https://doi.org/10.11781/sysydz202002202