Study on characteristics of oil and gas occurrence and reservoir space of medium-high maturity continental shale—A case study of middle jurassic lianggaoshan formation in fuling block, southeast of sichuan basin, south China

Abstract

Possessed of easy access to development and fair economic benefits, medium-high maturity continental shale oil and gas have become the focus of shale oil and gas study in the future. Shale oil and gas mainly occur in pores, but studies on the pore characteristics of shale oil and gas occurrence are by no means sufficient. Focused on shale from the Middle Jurassic Lianggaoshan Formation in Well TYX, Fuling block, southeast of Sichuan Basin where a breakthrough in shale oil and gas exploration was recently achieved, this study selects core samples and conducts a series of analyses, including vitrinite reflectance analysis, kerogen microscopic examination experiment, total organic carbon (TOC) content analysis, mineral composition analysis, gas content measurement, isothermal adsorption experiment, S1 content analysis, and others. The analyses are to identify the pore characteristics of the continental medium and high maturity shale oil and gas by virtue of scanning electron microscope (SEM) with Ar-ion milling and the image processing software ImageJ. The conclusions are drawn as follows: in terms of lithofacies, medium-high maturity continental shale oil and gas mainly occur in organic-rich clay shale and organic-rich mixed shale; with regard to material composition, shale oil and gas mainly occur in organic matter, illite-smectite mixed layers and illite. Shale adsorbed gas content accounts for at most 40% of the total shale gas content and shale free gas content takes up at least 60% of the total shale gas content. Pores of solid bitumen, solid bitumen-clay mineral complex mass, clay minerals, structured vitrinite, and funginite are mostly developed in shale. Among them, the first three types of pores are the main reservoir space in shale considering their large number, good roundness, medium pore diameter, fairly good roundness of pore edges, and the complex shapes which altogether contribute to the large surface porosity.

Hydrocarbon Geological Characteristics and Factors Controlling Hydrocarbon Accumulation of Jurassic Da’anzhai Continental Shale

“…From 2011 to 2018, the exploration focus shifted to the tight sandstones of the Shaximiao Formation. With the increased focus on Jurassic shale oil, the exploration targets have shifted from sandstone and limestone to lacustrine shale, and a series of breakthroughs have been made [11][12][13].…”

Paleoenvironmental Conditions and Shale Oil Potential of the Carboniferous Ha’erjiawu Formation in the Santanghu Basin, NW China

“…Inspired by the successful development of shale oil in the United States, China has conducted extensive exploration and research on shale oil over the past decade [3,7,8]. Currently, several commercially exploitable shale oil plays have been found in several basins in China [8], such as the Cretaceous Qingshankou Formation in the Songliao Basin [9,10], the Paleogene Shahejie Formation in the Bohai Bay Basin [11,12], the Paleogene Qianjiang Formation in the Jianghan Basin [13,14], the Triassic Yanchang Formation in the Ordos Basin [15,16], the Jurassic System in the Sichuan Basin [17,18], the Permian Fengcheng and Lucaogou Formations in the Junggar Basin [19,20] and the Permian Lucaogou Formation in the Santanghu Basin [21][22][23]. It is noteworthy that China's shale oil resources are primarily situated in lacustrine basins, which typically exhibit greater heterogeneity than North American marine shale [6].…”