Geological Characteristics and Controlling Factors of Deep Shale Gas Enrichment of the Wufeng-Longmaxi Formation in the Southern Sichuan Basin, China

Abstract

To identify the factors controlling high-quality deep shale gas reservoirs and the exploration and development potential of the Lower Paleozoic marine shale in the Sichuan Basin, the sedimentary environment of deep shale was comprehensively analysed using core thin sections, scanning electron microscopy, gamma ray spectrometry logging, and elemental logging data. In addition, the geological conditions of deep shale gas accumulation and the effect of tectonic processes on the preservation conditions are discussed based on the experimental data of mineral composition analysis, geochemical features, and reservoir spatial characteristics. (1) The sedimentary environment changes from an anoxic water environment to an oxygen-rich oxidizing environment from bottom to top in the Wufeng-Longmaxi Formation in southern Sichuan. The deep shale gas reservoir shows overpressure and rich gas characteristics, namely, high formation pressure (2.0~2.2), high porosity (20%~55%), and high gas content (4.0~5.0 m3/t). (2) The favourable sedimentary environment has a higher hydrocarbon generation potential and deposits of rich organic matter and siliceous particles. During the hydrocarbon generation process, the rich organic matter generates a large number of organic pores and a large specific surface area, which provides the main reservoir and adsorption space for free and adsorbed shale gas. A large number of biogenic siliceous particles provide a solid rock support framework for the shale reservoir, thereby maintaining excellent reservoir physical properties. (3) Late and small stratigraphic uplifts result in a short shale gas escape time and favourable preservation conditions. Additionally, the small-scale faults and a high-angle intersection between the fracture strike and the geostress direction are conducive to the preservation of shale gas. (4) A high formation pressure coefficient, a sedimentary environment rich in organic siliceous deep-water continental shelf microfacies, and a relatively stable tectonic structure are conducive to the accumulation of deep shale gas.

Evaluation of organic geochemical characteristics and experiments of thermal pressure simulation of Jurassic coal measure source rocks in the Yanqi Basin

“…Among them, the molecular isotope of one crude oil showed a slight difference in C 30 , but the carbon isotope of the other molecules showed almost the same trend of decreasing isotopic mass with the increase of carbon number. The variation trend of the molecular carbon isotope of the crude oil further reveals a similar composition from the perspective of molecular composition (Lu et al, 2015;Wang et al, 2018;Yu et al, 2019;Li et al, 2022).…”

Densification mechanism of deep low-permeability sandstone reservoir in deltaic depositional setting and its implications for resource development: A case study of the Paleogene reservoirs in Gaoshangpu area of Nanpu sag, China

“…After strong mechanical compaction and calcareous cementation above 3000 m, a few intergranular pores with weak siliceous cementation and dissolution remain. Dissolution mostly occurs in feldspar and lithic minerals along fractures or bedding (Li et al, 2019b;Fan et al, 2020a;He et al, 2020;He et al, 2021;He et al, 2022a;Li et al, 2022a;Li et al, 2022b;Fan et al, 2022).…”

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

“…Generally, the dip angle of the stratum on the gentle wing is 20 °-30 °, and that on the steep wing is 40 °-70 °and the stratum can even be upright and inverted. (Li et al, 2017;Li et al, 2022a). The broad valleys between the arc-shaped mountains are Jurassic trapped syncline.…”