Origin of organic matter pore heterogeneity in oil mature Triassic Chang-7 mudstones, Ordos Basin, China

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
Yingzhu Wang , Jijin Yang
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引用次数: 0

Abstract

Organic matter (OM)-hosted pores play a crucial role in hydrocarbon storage and migration in unconventional shale oil and gas systems. An accurate identification of different OM compositions is critical to understanding the origin of heterogeneity in OM-hosted pore development, which remains challenging due to the lack of apparent intrinsic connection between them. This study correlates light-electron-Raman spectroscopy to investigate various OM maceral types and their molecular structures with respect to the pore characteristics in an oil mature Triassic Chang-7 lacustrine mudstone from the Ordos Basin, China. Moreover, the occurrence and distribution of soluble bitumen and its effect on OM-hosted pore development were directly characterized by comparison of a stitched large SEM image mosaic (∼1 mm2) before and after organic solvent extraction. Results show that terrestrial OM including inertinite and vitrinite fragments display well-preserved biological structure and high reflectance intensity in light microscopy. They often are nonporous under SEM, and have no change before and after solvent extraction. Solid bitumen is the predominant maceral of the examined mudstone, and shows two general populations: 1) nonporous or weakly porous solid bitumen (SB1) that often occurs in large-sized and structured accumulation; 2) porous solid bitumen (SB2) that is filled or dispersed in mineral matrix. After extraction, SB2 was completely removed and have a noticeable recovery of pores, while SB1 changed slightly. The heterogenous pore characteristics can be related to the varying OM molecular structure which shows a decreasing trend of aromaticity in the order of terrestrial macerals, SB1, and SB2 as indicated by Raman parameters. A relatively higher pore abundance in SB2 may be attributed to chromatographic fractionation which led to more mobile and compliant components of SB2.

中国鄂尔多斯盆地石油成熟三叠系长-7泥岩中有机质孔隙异质性的起源
有机质(OM)寄生孔隙在非常规页岩油气系统中的碳氢化合物储存和迁移中起着至关重要的作用。准确识别不同的有机质成分对于了解有机质寄存孔隙发育的异质性起源至关重要,但由于它们之间缺乏明显的内在联系,因此这种识别仍然具有挑战性。本研究利用光-电子-拉曼光谱法研究了中国鄂尔多斯盆地三叠系长-7湖相泥岩中的各种 OM 大体类型及其分子结构与孔隙特征的关系。此外,通过对比有机溶剂提取前后拼接的大型扫描电镜图像(∼1 mm2),直接确定了可溶性沥青的发生、分布及其对有机质孔隙发育的影响。结果表明,包括惰性石和玻璃石碎片在内的陆生有机质在光学显微镜下显示出保存完好的生物结构和较高的反射强度。它们在扫描电镜下通常是无孔的,在溶剂萃取前后没有任何变化。固体沥青是受检泥岩中最主要的大分子物质,一般有两种类型:1)无孔或弱孔固体沥青(SB1),通常呈大块结构堆积;2)多孔固体沥青(SB2),填充或分散在矿物基质中。提取后,SB2 被完全去除,孔隙明显恢复,而 SB1 则略有变化。不同的孔隙特征可能与不同的 OM 分子结构有关,从拉曼参数来看,OM 分子结构呈现出芳香度递减的趋势,依次为陆生大分子、SB1 和 SB2。SB2 中的孔隙丰度相对较高,这可能是由于色谱分馏导致 SB2 中的移动性和顺应性成分较多。
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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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