Influence of differential structural deformation on shale reservoirs: a case study of the lower Silurian Longmaxi Shale in north Guizhou, Southern China

Abstract

Southern China is affected by multi-stage tectonic activities, with strong fold deformation, complex fault systems and poor shale gas preservation conditions. Here, we used shale samples from the lower Silurian Longmaxi shale in the complex tectonic area of Southern China, to study the relationship between differential structural deformation, and pore structure and adsorption capacity. According to the deformation mechanism of the shale, it is further divided into brittle-slip rheological deformation (BD) and ductile-slip rheological deformation (DD). The results show that all micro-fractures can be observed under scanning electron microscopy in deformed shale samples, but in shale samples with different types of rheological deformation, the micro-fractures have large differences in scale, fracture length and lateral connectivity. The micro-fractures developed in DD shales are small in scale and short in fracture length, but have strong local connectivity. In contrast, brittle minerals are more developed in BD shales, and interlayer shearing has formed micro-fractures with large fracture length and good lateral connectivity, which is beneficial for later fracturing. In these two types of deformed shales, pores in organic matter are rare, and sporadic organic pores have small pore size and poor connectivity. The total pore volume (1.8–2.4 × 10−2 cm3 g–1) of BD shale samples is higher than that of DD shale samples (0.8–1.6 × 10−2 cm3 g–1). There is a positive correlation between total pore volume and quartz content. In addition, the specific surface area (12–18 m2 g–1) of DD shale samples is larger than that of BD shale samples (6–12 m2 g–1).

The Effect of Tectonic Stress and Thermal Evolution on Shale Pores of Devonian and Carboniferous Shales in Southern China

“…A fault belt is encountered in the middle section, the core is relatively broken, and a large number of calcite veins and tectonic fractures are developed (Figures 14(e) and 14(f)). The development of calcite veins in the upper section is similar to that in the lower section, but there are more bedding fractures (Figures 14(g) and 14(h)), indicating that the tectonic activity is relatively stable during deposition [50,51].…”

“…In the lower section, core is dominated by tectonic fractures, and a small amount of calcite veins, structural deformation, and bedding fractures can also be observed locally (Figures 13(a)-13(d)). It is revealed that the tectonic activity is relatively strong during sedimentary period [50,51]. In the upper section, many bedding fractures and a few high angle tectonic fractures can be observed (Figures 13(e)-13(h)), indicating that the tectonic movement has tended to be stable and weak during sedimentation.…”

Pore Structure Heterogeneity of Deep Marine Shale in Complex Tectonic Zones and Its Implications for Shale Gas Exploration

“…The Sichuan Basin, located in the southwest China (Figure a), is known for its abundance of natural gas. , Experienced multiple period tectonic activities and surrounded by several tectonic blocks, its tectonic characteristics are quite complex. − It is usually divided into six regions, and shale gas blocks are mainly distributed in the south–southeast Sichuan Basin. Controlled by tectonic extrusion in the direction of NW-SE and NE-SW, the tectonic pattern in these shale gas fields is mainly wide-spaced anticlines (Figure b), which is called complex tectonic zones.…”

Structural deformation of shale pores in the fold-thrust belt: The Wufeng-Longmaxi shale in the Anchang Syncline of Central Yangtze Block

“…As mentioned above, the Wufeng-Longmaxi shale in the Upper Yangtze Block, which has suffered multistage tectonic compressions (Hao and Zou, 2013;Liu et al, 2019;Xu et al, 2019), recently became an ideal natural laboratory to analyze the impact of tectonic compaction (or deformation) on shale pore systems. However, relevant works have primarily focused on the anticline structures and rarely discussed syncline formations (Gu et al, 2021). In this study, an investigation of tectonic compaction was carried out on cores from the Wufeng-Longmaxi shale that were recently drilled from the Anchang Syncline (Fig.…”