川东南奥陶—志留纪之交全频斑脱岩特征及页岩气指示意义

Characteristics of Full-frequency Bentonite of Ordovician–Silurian Transition in Southeastern Sichuan and Its Significance Indicator of Shale Gas

李博硕 单长安 梁兴 顾小敏 何方雨 石海龙

LIBoshuo SHANChang'an LIANGXing GUXiaomin HEFangyu SHIHailong

西安石油大学地球科学与工程学院, 陕西 西安 710065 西安石油大学陕西省油气成藏地质学重点实验室, 陕西 西安 710065 中国石油浙江油田公司, 浙江 杭州 311100

School of Earth Sciences and Engineering, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China Shaanxi Key Laboratory of Petroleum Accumulation Geology, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China Zhejiang Oilfield Company, PetroChina, Hangzhou, Zhejiang 311100, China

川东南地区五峰组—龙马溪组页岩中发育多套斑脱岩层，记录着诸多地质历史事件的关键信息。为明确斑脱岩发育特征及其对页岩气的指示意义，针对川东南地区多口页岩气井岩芯及邻区典型剖面开展了斑脱岩特征系统观察与统计，并进行了薄片鉴定、扫描电镜观察、全岩黏土X射线衍射分析等实验测试，得到以下成果： 1）川东南地区标准井共识别出斑脱岩59层，进一步划分为6套斑脱岩发育段； 2）火山灰沉积过程中碱性水体环境对笔石硬质蛋白质结构有化学性破坏，造成了斑脱岩上下围岩均不发育笔石的现象； 3）斑脱岩存在蚀变现象，产物多为黄铁矿； 4）斑脱岩低频率高强度发育往往指示着优质页岩，高频率高强度和高频率低强度发育指示着次优质页岩，低频率低强度发育则认为是普通有机质页岩。

In the shale of the Wufeng-Longmaxi Formation in the southeastern Sichuan Basin, there are several sets of bentonite beds, which keeps records of key information about numerous geological events. In order to clarify the characteristics of bentonite development and its significance for shale gas, core observation, thin section identification, SEM observation, whole rock X-ray diffraction have been carried out for the core of several shale gas evaluation exploration wells and typical sections in neighboring areas in southeastern Sichuan, and the following results have been obtained. 1) In the standard well of bentonite in southeastern Sichuan Province, 59 bentonite layers are identified, and were further divided into 6 sets of bentonite development segments. 2) In the process of volcanic ash deposition, the alkaline water environment chemically destroys the hard protein structure of graptolite, resulting in the phenomenon that graptolite does not develop in the surrounding rocks above and below the bentonite. 3) There are alteration phenomena in the bentonite, and the products are mostly pyrite. 4) Low-frequency and high-intensity development of bentonite often indicate high-quality shale, and high-frequency and high-intensity, highfrequency and low-intensity development of bentonite often indicate subprime-quality shale, while low frequency and low intensity development of bentonite is regarded as ordinary organic shale.

10.11885/j.issn.1674-5086.2024.01.11.02