Factors controlling the heterogeneity of shale pore structure and shale gas production of the Wufeng–Longmaxi shales in the Dingshan plunging anticline of the Sichuan Basin, China

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
Yijun Zheng , Yuhong Liao , Jie Wang , Yongqiang Xiong , Yunpeng Wang , Ping’an Peng
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Abstract

Shale gas exploration in the Dingshan plunging anticline of the Sichuan Basin, China, has uncovered substantial Wufeng–Longmaxi shale reserves. However, substantial variations exist in shale gas content and production among the wells in this region. We investigated the geological factors and mechanisms influencing shale pore structure heterogeneity and shale gas content and production in the area. We conducted comprehensive analyses of mineralogy, geochemical characteristics, and petrophysical properties on the Late Ordovician Wufeng Formation–Early Silurian Longmaxi Formation shales. Shale samples were collected from a shallow well, Anwen-1, located in proximity to the Qiyueshan thrust fault within the Dingshan plunging anticline. Additionally, samples from Dingye (DY) 1 and DY 3 wells, located at varying distances from the thrust fault, were examined. We also integrated previously published data from two correlative sections in the southeastern margin of the Sichuan Basin, each at different distances from the thrust fault. The pore volume, specific surface area, and porosity of the shales were positively correlated with their total organic content (TOC). However, strong lateral compressive stress, often occurring near the regional thrust fault, attenuated the linear relationship between TOC and pore volume/porosity. Lateral compressive stress did not significant affect shale porosity and pore structure when the distance from the regional thrust fault exceeded approximately 15 km. The specific surface area of the shale was less affected by compressive stress. Moreover, carbonate cementation reduced porosity by sealing shale matrix pores and natural microfractures, reducing nanopore connectivity. Consequently, shale gas production is not solely influenced by shale gas content but is also significantly affected by carbonate cementation. Therefore, shale reservoirs located at relatively long tectonic distances from regional thrust faults (approximately 15 km) within the Dingshan plunging anticline exhibit high pore volume, porosity, and shale gas content, rendering them favorable for shale gas exploration.

控制中国四川盆地鼎山垂向反斜五峰-龙马溪页岩孔隙结构异质性和页岩气产量的因素
中国四川盆地鼎山急降反斜的页岩气勘探发现了大量五峰-龙马溪页岩储量。然而,该地区各井的页岩气含量和产量存在很大差异。我们研究了影响该地区页岩孔隙结构异质性、页岩气含量和产量的地质因素和机制。我们对晚奥陶世五峰组-早志留纪龙马溪组页岩进行了矿物学、地球化学特征和岩石物性的综合分析。页岩样本采集自一口浅井--安文-1 号,该井位于丁山暴跌反斜线内的齐岳山推断断层附近。此外,我们还考察了距该推断断层不同距离的定业 1 井和定业 3 井的样本。我们还整合了四川盆地东南缘两个相关剖面的数据,这两个剖面与推断断层的距离各不相同。页岩的孔隙体积、比表面积和孔隙度与其总有机质含量(TOC)呈正相关。然而,区域推断断层附近经常出现的强大侧向压应力削弱了总有机碳与孔隙体积/孔隙度之间的线性关系。当与区域性推力断层的距离超过约 15 千米时,侧向压应力对页岩孔隙度和孔隙结构的影响并不明显。页岩的比表面积受压应力的影响较小。此外,碳酸盐胶结封住了页岩基质孔隙和天然微裂缝,减少了纳米孔隙的连通性,从而降低了孔隙率。因此,页岩气产量不仅受页岩气含量的影响,还受到碳酸盐胶结的显著影响。因此,位于鼎山垂向反斜线内、与区域推断断层构造距离相对较远(约 15 千米)的页岩储层具有较高的孔隙体积、孔隙度和页岩气含量,有利于页岩气勘探。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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