Heterogeneity Characteristics of Lacustrine Shale Oil Reservoir Under the Control of Lithofacies: A Case Study of the Dongyuemiao Member of Jurassic Ziliujing Formation, Sichuan Basin

Abstract

The lacustrine shale in the Dongyuemiao Member of the Fuling area, Sichuan Basin, is widely distributed and has huge shale oil resource potential. It is one of the important replacement areas for shale oil exploration in China. To investigate the key shale oil evaluation well, Well FY10, in the Fuling area, X-ray diffraction (XRD) mineral analysis, Rock-Eval, argon ion polishing-scanning electron microscope (SEM), Mercury injection capillary pressure (MICP), and low pressure nitrogen adsorption were launched to determine the heterogeneity of the pore system in the lacustrine shale of the Dongyuemiao Member. The mineral composition exhibits a high degree of heterogeneity, and the shale can be divided into two main lithofacies: argillaceous shale and mixed shale. The porosity ranges from 2.95 to 8.43%, and the permeability ranges from 0.05 to 1.07 × 10−3 μm2. The physical properties of mixed shale are obviously better than those of argillaceous shale. Inorganic mineral pores, such as linear pores between clay minerals and calcite dissolution pores, are mainly developed, while a small amount of organic pores can be observed. The average total pore volume (Vp) is 0.038 ml/g with an average specific surface area of 5.38 m2/g. Mesopores provide the main Vp (average 61.72%), and micropores provide mostly specific surface area. TOC imposes a strong controlling effect on the development of micropores. Clay minerals are the main contributors to mesopores and macropores. The organic-inorganic interaction during the process of diagenesis and hydrocarbon generation controls the formation of shale pore systems.

Evaluating Shale Gas Sweet Spots of the Jurassic Da'anzhai Member in the Yuanba Area, Sichuan Basin

“…The total PV varies from 0.006 to 0.022 ml/g with an average of 0.014 ml/g and has similar distribution characteristics with SSA. Li et al (2021) showed that for the lacustrine laminar shale samples, SSA was negatively correlated with macropore and mesopore volumes, but positively correlated with micropore volume, which indicated that micropores played a decisive role in the SSA and gas adsorption capacity. Based on the above analysis, type A has the overall greatest micro-reservoir performance for the J 1 da 2 shale.…”

A New Method for Comprehensive and Quantitative Characterization of Shale Microfractures: A Case Study of the Lacustrine Shale in the Yuanba Area, Northern Sichuan Basin

“…Analytical techniques such as RTS observations, micro-CT analysis, and SEM have their own resolution ranges. Similar to the fact that pores of different scales in shale need to be characterized through comprehensive utilization of the CO 2 adsorption, N 2 adsorption, and high-pressure mercury intrusion techniques [53][54][55], the quantitative characterization of microfractures of different scales in shale requires the combined use of different analysis techniques. Full-scale quantitative characterization of microfractures, such as a combination of nuclear magnetic resonance and micro-CT analysis to obtain the microfractures of different scales in rocks, has been reported, but only microfractures with a fracture width greater than 50 µm can be characterized using previously reported methods [56].…”

Nanoscale pore characteristics of the Jurassic Dongyuemiao member lacustrine shale, Eastern Sichuan Basin, SW China: Insights from SEM, NMR, LTNA, and MICP experiments

“…A large number of pore structure studies have been carried out on marine shale and found that nanoscale pore structure is strongly affected by mineral composition and organic matter abundance (Li et al, 2016;Jia et al, 2020). However, due to the huge difference in sediment composition, mineral composition and organic matter abundance between lacustrine shale and marine shale (Yang et al, 2019;Li et al, 2021;Wei et al, 2021), the previous results of marine shale cannot be directly applied to lacustrine shale.…”