Geological Factors Controlling the Accumulation and High Yield of Marine‐Facies Shale Gas: Case Study of the Wufeng‐Longmaxi Formation in the Dingshan Area of Southeast Sichuan, China

Abstract

The main geological factors controlling the accumulation and yield of marine‐facies shale gas reservoirs are the focus of the current shale gas exploration and development research. In this study, the Wufeng‐Longmaxi Formation in the Dingshan area of southeast Sichuan was investigated. Shale cores underwent laboratory testing, which included the evaluation of total organic carbon (TOC), vitrinite reflectance (Ro), whole‐rock X‐ray diffraction (XRD), pore permeability, and imaging through field emission scanning electron microscopy (FE‐SEM). Based on the results of natural gamma ray spectrum logging, conventional logging, imaging logging, and seismic coherence properties, the exploration and development potential of shale gas in the Dingshan area have been discussed comprehensively. The results showed that (1) layer No. 4 (WF2‐LM4) of the Wufeng‐Longmaxi Formation has a Th/U ratio <2 and a Th/K ratio of 3.5‐12. Graptolites and pyrite are relatively abundant in the shale core, indicating sub‐high‐energy and low‐energy marine‐facies anoxic reducing environments. (2) The organic matter is mainly I‐type kerogen with a small amount of II1‐type kerogen. There is a good correlation among TOC, Ro, gas content, and brittle minerals; the fracturing property (brittleness) is 57.3%. Organic and inorganic pores are moderately developed. A higher pressure coefficient is correlated with the increase in porosity and the decrease in permeability. (3) The DY1 well of the shale gas reservoir was affected by natural defects and important late‐stage double destructive effects, and it is poorly preserved. The DY2 well is located far from the Qiyueshan Fault. Large faults are absent, and upward fractures in the Longmaxi Formation are poorly developed. The well is affected by low tectonic deformation intensity, and it is well preserved. (4) The Dingshan area is located at the junction of the two sedimentary centers of Jiaoshiba and Changning. The thickness of the high‐quality shale interval (WF2‐LM4) is relatively small, which may be an important reason for the unstable production of shale gas thus far. Based on the systematic analysis of the geological factors controlling high‐yield shale gas enrichment in the Dingshan area, and the comparative analysis with the surrounding typical exploration areas, the geological understanding of marine shale gas enrichment in southern China has been improved. Therefore, this study can provide a useful reference for shale gas exploration and further development.

Fine Logging Evaluation of Fractures in Continental Tight Oil Sandstone Reservoirs of Yanchang Formation in the Ordos Basin

“…Fractures always act as the migration channels and accumulation sites of underground fluids, and the migration and accumulation of fluids may lead to the precipitation of radioactive substances and then lead to radioactivity enhancement. However, the increase in the natural gamma value is generally weak, and it usually appears as a relative increase on a background of relatively low values of the natural gamma curves (Fan et al, 2020c;Fan et al, 2019).…”

Numerical modeling of complex hydraulic fracture networks based on the discontinuous deformation analysis (DDA) method

“…The Longmaxi shale is characterized by a highly-developed NF system (Shen et al., 2018a; Wang et al., 2017; Xu et al., 2020). According to outcrop observations and core measurements, the NF networks in the Longmaxi shale reservoir mainly consist of bedding planes and high-angle fractures which are approximately perpendicular to the bedding planes (Fan et al., 2019). Figure 11(a) shows a Longmaxi shale outcrop in the Sichuan Basin, in which the bedding planes and high-angle fractures are clearly visible.…”

Radial Permeability Measurements for Shale Using Variable Pressure Gradients

“…The Sichuan Basin is an area of approximately 1.8×10 5 km 2 in Southwest China, surrounded by several mountains, e.g. Micang Mountain, Dalou Mountain and Longmen Mountain (Chen et al, 2011;Chen et al, 2018, Fan et al, 2019, Huang te al., 2019, as shown in Fig. 1.…”