New insights into the evaluation criteria for high-quality deep marine shale gas reservoirs in the Longmaxi formation: Evidence from organic matter pore development characteristics

Abstract

Porosity, total organic carbon content, brittle mineral content, and gas content are now the primary references for classifying and evaluating marine shale gas reservoirs in China. Is there a more effective and appropriate reservoir classification scheme for deep marine shale? The Longmaxi Formation in Luzhou, southern Sichuan Basin, China, is the main object of study. Quantitative analysis and modeling using data from field emission scanning electron microscopy, nitrogen adsorption, and logging were used to characterize organic matter (OM) pore multi-scale development and reveal the relationship between OM pore and the high-quality reservoirs. Microscopic and macroscopic indications from OM pores show that a large number of OM pores were developed in high-quality reservoirs. OM surface porosity occupancy of the high-quality reservoir in the Luzhou area was more than 60%. OM porosity occupancy was more than 50%. The nitrogen adsorption–desorption hysteresis loops demonstrate the development of bottleneck and wedge-shaped OM pores. Characterization of multi-scale pore structure by box dimension, pore volume and specific surface area. It is found that the key to the formation of high-quality reservoirs was the massive development of OM mesopores in siliceous shale and the relatively homogeneity structure, which was conducive to the enrichment and migration of shale gas. Furthermore, the improved model decreased the relative error in predicting the OM porosity by about 32.5%. The use of OM porosity occupancy for high-quality reservoir classification was better, and the results were consistent with geological understanding. OM porosity occupancy showed that the area from Lunanxi to Luzhou to Rongchang to Jiangjin was the key exploration area for high-quality reservoirs in southern Sichuan. This study is expected to provide a new idea for OM pore modeling analysis and deep marine shale gas reservoir classification.

Deciphering the formation period and geological implications of shale tectonic fractures: a mini review and forward-looking perspectives

“…and Luzhou (Fan et al, 2020a;Xu et al, 2020a;He et al, 2022a;He et al, 2022b). The marine shale sequences in the Sichuan Basin have been subjected to myriad tectonic episodes, culminating in the genesis of intricate fracture network systems spanning various scales-tectonic fractures being particularly prevalent (Li J. et al, 2022;2023;Zhu et al, 2023). The evolution and architecture of these fractures and faults are pivotal in shaping the efficacy of shale gas reservoirs (Fan et al, 2020b).…”

“…The evolution and architecture of these fractures and faults are pivotal in shaping the efficacy of shale gas reservoirs (Fan et al, 2020b). Serving dual roles, they act as reservoir spaces and enhance reservoir connectivity by bridging pores and microfractures, thereby ameliorating pore-permeability dynamics (Hou et al, 2020;Fan et al, 2022;Zhu et al, 2023).…”

Differentiated Interval Structural Characteristics of Wufeng−Longmaxi Formation Deep Shale Gas Reservoirs in Western Chongqing Area, China: Experimental Investigation Based on Low-Field Nuclear Magnetic Resonance (NMR) and Fractal Modeling

“…The saturation of the movable fluid is much higher than that of samples from other layers (Figure 4). Previous studies have revealed that the shale in the research area exhibits a maximum maturity index (R o ) of less than 3.5% [39], indicating that the reservoir is currently in a favorable stage for the development of organic pores. The observation results of FE-SEM also confirmed that the main type of nanopores in the bottom S 1 l 1-1 sub-layer of shale reservoirs is organic matter pores (Figure 13a).…”

“…The optimization of engineering transformation layers as fracturing and mining targets in gas-bearing strata requires an understanding of the unique characteristics (particularities) of high-quality reservoirs [37][38][39]. The results of NMR testing, fractal modeling, and comparison of representative samples from different layers of the S 1 l 1-1 sub-layer suggest that the pore system of gas-rich layers is developed with particularities, compared with other layers.…”

Advancing “Carbon Peak” and “Carbon Neutrality” in China: A Comprehensive Review of Current Global Research on Carbon Capture, Utilization, and Storage Technology and Its Implications

“…We can draw from the experiences of countries such as the United States and Canada to provide CCUS technology with policy support equivalent to that of renewable energy and other low-carbon clean energy technologies. Therefore, we should learn from China’s experiences in exploring and developing shale gas, shale oil, and coalbed methane and expedite the formulation of tailored financial and tax incentive policies for the domestic CCUS industry. − These measures will help reduce the costs of carbon capture and storage, attracting more enterprises to participate in technological innovation and development along the CCUS industry chain.…”