Study on the Spontaneous Imbibition Characteristics of the Deep Longmaxi Formation Shales of the Southern Sichuan Basin, China

Abstract

Deep shale gas reservoirs are a significant alternative type of shale gas reservoir in China. The productivity of deep shale gas wells is lower than that of shallow shale, and the imbibition characteristics of deep shale have a significant effect on the retention and backflow of fracturing fluid and the productivity of shale gas wells. In this study, the pore structure characteristics of organic-rich deep shale in the Lower Silurian Longmaxi Formation of Weiyuan-Luzhou play were analyzed by low-temperature nitrogen adsorption experiments, and then the imbibition characteristics and factors influencing deep shale were extensively investigated by spontaneous imbibition and nuclear magnetic resonance experiments. The results show that mainly micropores and mesopores are growing in the deep organic-rich shale of the Longmaxi Formation. The spontaneous imbibition curve of deep shale can be divided into an initial spontaneous imbibition stage, an intermediate transition stage, and a later diffusion stage, and the imbibition capacity coefficient of deep shale is lower than that of shallow shale. The transverse relaxation time (T2) spectrum distributions suggest that clay hydration and swelling produce new pores and microcracks, but then some pores and microfractures close. Deep shale reservoirs have an optimal hydration time when their physical properties are optimal. The increasing pore volume and the decreasing TOC content can enhance the imbibition capacity of shale. An inorganic salt solution, especially a KCl solution, has an inhibitory effect on the imbibition of shale. Higher salinity will result in a stronger inhibitory effect. It is crucial to determine the optimal amount of fracturing fluid and soaking time, and fracturing fluid with a high K+ content can be injected into the Longmaxi Formation deep shale to suppress hydration. These results provide theoretical guiding significance for comprehending the spontaneous imbibition and pore structure evolution characteristics of deep shale and enhancing methane production in deep shale gas reservoirs.

Study on the Pore Structure and Fractal Characteristics of Different Lithofacies of Wufeng–Longmaxi Formation Shale in Southern Sichuan Basin, China

“…Shale gas, as a recognized clean energy source, is becoming increasingly crucial in satisfying the growing energy demand. According to the statistics, shale gas production in the United States accounts for more than half of its total natural gas production; meanwhile, shale gas production will reach 500 × 10 8 m 3 by 2030 in China. , Due to the extremely low permeability in shales, large-scale horizontal drilling and hydraulic fracturing, as well as multistage hydraulic stimulation technologies, were realized to improve the development of shale gas reservoirs in the past decades . As the reservoir space and migration channel of shale gas, the pore structure of shale affects not only the reservoir and adsorption capacity of shale gas but also the seepage characteristics of shale gas.…”

Experimental Investigation on the Spontaneous Imbibition Characteristics of Shale under the Combined Action of CO2 and Water

“…The initial imbibition stage of dodecane is shorter and the nonlinear transition stage is longer. This is due to the fact that the SI of dodecane begins to diffuse slowly in the micropores after rapidly penetrating the intermediate-wetting or oil-wetting macropores and microcracks . In contrast, the SI of brine penetrates the micropores of water-wetting before penetrating the macropores .…”

“…This is due to the fact that the SI of dodecane begins to diffuse slowly in the micropores after rapidly penetrating the intermediate-wetting or oil-wetting macropores and microcracks. 40 In contrast, the SI of brine penetrates the micropores of water-wetting before penetrating the macropores. 17 It is worth noting that, compared with Figure 4a, the imbibition volume of dodecane in Figure 4b is larger.…”

Experimental study on the influence of pore structure on spontaneous imbibition in marine black shale

“…Wang et al (2021) established that the vertical bedding direction limits imbibition, positively correlating it with calcite content but not quartz and clay minerals. Chao et al (2021) claimed that higher TOC content weakens the imbibition rate of the deep Longmaxi Formation shale, while inorganic salt solutions, especially potassium chloride solution, inhibit shale imbibition and the inhibition strength increases with salinity. Based on an NMR-based study of the imbibition process, Zhu et al (2023) concluded that micropores have the largest cumulative proportion of water absorption, followed by mesopores, and macropores make up the lowest cumulative proportion.…”