Pore structure and reservoir physical properties for effective development of tight sandstone gas: A case study from the Central Sichuan Basin, China

Abstract

Several large gas fields have been found in the Central Sichuan Basin in recent years, with proven reserves of more than 100 × 10 9 m3. Among these, the tight sandstone gas in the Late Triassic Xujiahe Formation is a key target in the Sichuan Basin. The key to the discovery of high‐yield areas rich in tight sandstone gas is to determine the pore structures and the lower limits of effective physical properties of reservoirs that control natural gas accumulation. In this study, we investigate the Late Triassic second Member of the Xujiahe Formation (hereinafter referred to as the Xu2 Member) in the Central Sichuan Basin as an example. We analyse the distribution characteristics of pores and throats in the reservoirs and identify that the reservoir in the study area is mainly characterized by small pores and narrow throats. The physical properties of reservoirs in the area are mainly controlled by pore‐throat radius and the permeability–porosity ratio. Nuclear magnetic resonance analysis indicates that the irreducible water saturation is mostly more than 50% and is inversely correlated with the physical properties of reservoirs in the study area. Meanwhile, with an increase in the physical properties of reservoirs, the proportion of large pores increases and the irreducible water saturation rapidly decreases. According to the gas–water two‐phase seepage experiment, for reservoirs with good physical properties, the gas relative permeability significantly increases with an increase in gas saturation and the reservoir permeability has more significant effects. Where the reservoir permeability is less than 0.4 mD, the permeability of both gas phase and water phases is only less than 0.1, and the mobility of both gas and water is poor. Only when the reservoir permeability is more than 0.4 mD, can the gas relative permeability reach more than 0.3, and the water mobility is significantly inhibited. In this case, favourable results can be achieved from the natural gas development. As verified by the development of the tight sandstone reservoirs in the Xu2 Member in Central Sichuan Basin, the lower limits of physical properties allowing for effective natural gas development include the reservoir permeability of more than 0.1 mD (preferably more than 0.2 mD) and the reservoir porosity of greater than 6%–7%.

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

“…Therefore, deepening the understanding of deep shale reservoir characteristics is a fundamental basis for the evaluation of potential reserves and the effectiveness of shale gas exploration. Pore structure parameters are critical indicators of reservoir quality, performing an essential role in the evaluation and prediction of shale gas resources [9,10]. Shale gas reservoirs are characterized by complex nanoscale pore systems, and a comprehensive understanding of the pore system's structural characteristics is key to estimating gas content and assessing the productivity of the reservoir.…”

Pore‐throat structure characteristics and fluid mobility analysis of tight sandstone reservoirs in Shaximiao Formation, Central Sichuan

“…The method of mathematical statistics cannot effectively describe the pore‐throat structure of the reservoir. It is necessary to calculate the fractal dimension with the help of fractal theory, so as to describe the complexity of pore‐throat structure, the roughness of pore surface and the heterogeneity of the reservoir (Dong et al, 2022; Guo et al, 2019; H. Li, Zhou, et al, 2022; X. M. Li, Wang, et al, 2022; Qu et al, 2020; E. Z. Wang et al, 2022; Zang et al, 2022; K. X. Zhang et al, 2019).…”

Wettability alteration and reducing water blockage in tight gas sandstone reservoirs using mixed cationic Gemini/nonionic fluorosurfactant mixtures

“…The unrecovered fluid will invade the matrix and induce water blockage due to the multiphase flow, which will lead to the formation damage and hinder the oil or gas production rate (Lyu et al, 2022). As unconventional petroleum resources, tight gas sandstone reservoirs have low permeability, strong water wettability, and narrow pore throats (Dong et al, 2022; Li, Wang, et al, 2022). Meanwhile, the water blockage damage is related to the high capillary pressure, which is affected by the surface tension of the working liquid, the radius and structure of the pore, and the wettability of the sandstone surface (Madadizadeh et al, 2022).…”