Types and Distribution of Lower Silurian Gas-Bearing Shales in Pengshui Area of Southeast Sichuan Basin, China

Abstract

Marine shale is one of the main reservoirs of shale gas. A large number of marine shales were developed in the Lower Silurian in Pengshui area of southeast Sichuan Basin. Types and spatial distribution of gas-bearing shale are key factors to the exploration and development of shale gas. Based on the results of TOC and total rock analysis of samples from cored well and outcrop sections, a quantitative classification standard for shale is established for gas-bearing shales in the area of Pengshui. TOC, quartz and clay minerals content which reflecting shale sedimentary characteristics and environment are selected as three evaluation parameters in this standard. According to this standard, Longmaxi Formation gas-bearing shales in Pengshui area are divided into five types: quartz-rich clay-bearing organic shale, quartz-rich clay organic shale, quartz clay organic, quartz clay-bearing organic shale and quartz clay organic-bearing shale. The intersection diagram of TOC and gas content of different shale in typical well shows that quartz-rich clay-bearing organic shale and quartz clay-bearing organic shale have high gas content and are the most favorable shale types for shale gas exploration, followed by quartz clay organic shale. The planar distribution of various shales is obtained by synthesizing the planar TOC content equivalent map, quartz content equivalent map and clay minerals equivalent map. The results show that quartz-rich clay-bearing organic shale is developed in southwest of Daozhen County and an area from Zouma Town to Zhufo Town in Pengshui, which is the most favorable shale gas exploration area. Quartz clay organic shale is developed in the periphery of the above regions, which is the second favorable shale gas exploration area. The method to determine the types of gas-bearing shale and favorable shale distribution area is of great significance to the selection of shale gas exploration in similar areas.KeywordsPengshui areaShale typesQuartzClay mineralsFavorable area