Characteristics of microscopic pore heterogeneity and development model of Wufeng–Longmaxi Shales in the Pengshui area of south-east Chongqing

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Frontiers of Earth Science Pub Date : 2023-12-28 DOI:10.1007/s11707-023-1087-5
Lu Sun, Zhigang Wen, Guisong He, Peixian Zhang, Chenjun Wu, Liwen Zhang, Yingyang Xi, Bo Li
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Abstract

Normal-pressure shale gas reservoirs are widely distributed in south-eastern Chongqing and show good potential for resource exploration. This paper reports the organic matter (OM), physical, and pore characteristics, mineral composition, and gas content of representative shale samples from the Upper Ordovician Wufeng Formation and Member 1 of the Lower Silurian Longmaxi Formation (Long 1 Member). Microscopic pores within different shale layers of the Long 1 Member were classified, quantitatively evaluated, and their development mechanisms were systematically studied. We found that OM characteristics, mineral composition, and pore type were the main factors affecting the enrichment and preservation of shale gas. The characteristics of the Long 1 Member are mainly controlled by changes in the sedimentary environment. There are evident differences in total organic carbon content and mineral composition vertically, leading to a variable distribution of pores across different layers. Organic matter abundance controls the degree of OM pore development, while clay minerals abundance control the development of clay mineral-related pores. Total organic carbon content generally controls the porosity of the Long 1 Member, but clay minerals also play a role in OM-poor layers. Pore connectivity and permeability are influenced by the development of pores associated with brittle minerals. We propose a microscopic pore development model for the different layers. Combining geochemical data and this pore development model, layers 1–4 are considered to be excellent shale gas preservation and enrichment reservoirs. Poor preservation conditions in layers 5–7 result in high levels of shale gas escape. Layers 8–9 possess a better sealing condition compared with layers 5`-7 and are conducive to the enrichment and preservation of shale gas, and can thus be used as future potential target strata. This research provides a theoretical basis for exploring and evaluating shale gas potential in the studied region or other complex normal-pressure shale blocks.

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重庆东南部彭水地区五峰-龙马溪页岩的微观孔隙异质性特征及发育模式
常压页岩气藏广泛分布于重庆东南部地区,具有良好的资源勘探潜力。本文研究了上奥陶统五峰组和下志留统龙马溪组 1 号层(龙 1 组)代表性页岩样品的有机质、物性、孔隙特征、矿物组成和含气量。对龙一系不同页岩层中的微观孔隙进行了分类和定量评价,并对其发育机制进行了系统研究。研究发现,OM 特征、矿物组成和孔隙类型是影响页岩气富集和保存的主要因素。长 1 号成员的特征主要受沉积环境变化的控制。总有机碳含量和矿物成分在垂直方向上存在明显差异,导致孔隙在不同地层的分布各不相同。有机质丰度控制着有机质孔隙的发育程度,而粘土矿物丰度则控制着与粘土矿物有关的孔隙的发育。总有机碳含量通常控制着长 1 号成员的孔隙度,但粘土矿物在有机碳贫乏的地层中也发挥着作用。孔隙连通性和渗透性受到与脆性矿物相关的孔隙发育的影响。我们为不同地层提出了一个微观孔隙发育模型。结合地球化学数据和孔隙发育模型,1-4层被认为是极佳的页岩气保存和富集储层。5-7 层的保存条件较差,导致页岩气逸散程度较高。8-9 层与 5-7 层相比具有更好的密封条件,有利于页岩气的富集和保存,因此可作为未来潜在的目标地层。该研究为勘探和评价研究区域或其他复杂常压页岩区块的页岩气潜力提供了理论依据。
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来源期刊
Frontiers of Earth Science
Frontiers of Earth Science GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.50
自引率
5.00%
发文量
627
期刊介绍: Frontiers of Earth Science publishes original, peer-reviewed, theoretical and experimental frontier research papers as well as significant review articles of more general interest to earth scientists. The journal features articles dealing with observations, patterns, processes, and modeling of both innerspheres (including deep crust, mantle, and core) and outerspheres (including atmosphere, hydrosphere, and biosphere) of the earth. Its aim is to promote communication and share knowledge among the international earth science communities
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