Influence of Multi-Period Tectonic Movement and Faults on Shale Gas Enrichment in Luzhou Area of Sichuan Basin, China

Abstract

The Luzhou area in the southern Sichuan Basin has experienced multiple tectonic movements, forming a complex fault system; the activity has an important impact on the enrichment of shale gas in this area. In order to reveal the influence of the fracture system on the differential enrichment of shale gas, this paper takes the southern Sichuan Basin as the research object. The structural evolution process and fracture development characteristics of the different tectonic units in Luzhou area of southern Sichuan were characterized by conducting a seismic profile analysis, structural recovery using a back-stripping method, and core hand specimen description. We clarified the control effect of the structural deformation and fracture on the differential enrichment of shale gas, and we established a differential enrichment model of shale gas in the Luzhou area. The results show that: (1) The Luzhou area has undergone the transformation of a multi-stage tectonic movement. There are many sets of detachment structures in the longitudinal direction, and the plane structural form is a thin-skin fold-thrust belt composed of wide and narrow anticlines in the north–south direction. (2) The faults in the study area are affected by the Himalayan tectonic movement. The high-angle reverse faults are developed, and the number of large faults is small. The second and third faults are mainly developed. The second faults are only developed at the high position of the structure, which has a significantly destructive effect on shale gas reservoirs, while the third and fourth faults have no significant destructive effect on shale gas reservoirs. (3) In the study area, the types of cracks are categorized into transformational shear cracks, bed-parallel shear cracks, intraformational open cracks, lamellation cracks, shrinkage cracks, and abnormal high-pressure cracks. The thickness of the shale rock mechanical layer, brittle mineral content, and organic matter content jointly control the crack development degree in the shale of the Wufeng–Longmaxi Formation. (4) The uplift erosion, structural deformation, and fracture development caused by the structural evolution have affected the preservation of shale gas, resulting in the differential enrichment of shale gas reservoirs in the region. Based on the enrichment factors of shale gas, we established a differential enrichment model of shale gas in typical structural units and optimized the favorable enrichment areas, which are important contributions for guiding shale gas exploration and development in the Sichuan Basin.

Mechanism of Wettability and Pore Water Occurrence State in Overmaturity Shale: A Case Study of Longmaxi Formation Shale in South Sichuan Basin, China

“…The Sichuan Basin has experienced multiple phases of tectonic movements. According to the regional geotectonic background and evolutionary process, the Sichuan basin can be divided into five primary tectonic units, including the West Sichuan Depression Belt, the North Sichuan Low Steepness Fold Belt, the Central Sichuan Low Gradient Fold Belt, the East Sichuan High Steep Structural Belt, and the South Sichuan Low Steep Structural Belt. , The samples in this study are from the Changning and Luzhou blocks in the southern Sichuan Basin, tectonically located in the South Sichuan Low Steep Structural Belt (Figure a).…”

A novel method for evaluating shale gas preservation conditions in an area on a regional scale

“…Currently, Chinese recoverable resources of shallow shale gas (below the burial depth of 4,500 meters) are about 22 trillion cubic meters, making China one of the leading regions in the world to achieve large-scale shale gas development (Wang et al, 2019;Qiu et al, 2020), of which the proven shale gas reserves are 560,559 million cubic meters, mainly located in the southwestern region (Yi et al, 2019;Xi et al, 2022). The southwestern region is characterized by complex geological conditions and diverse stratigraphic structures, resulting in uneven distribution of shale gas resources (Yi et al, 2019;Shi et al, 2022). Meanwhile, due to mountainous and other geomorphologic conditions, shale gas drilling is di cult, time-consuming and costly (Nie et al, 2020;Ma et al, 2021).…”