Development characteristics of natural fractures in horizontal wells for deep shale gas and their implications for enhanced development: a case study of Wufeng-Longmaxi formations in Luzhou area, southern Sichuan Basin

Abstract

The analysis of natural fracture development characteristics is crucial for evaluating deep shale gas exploration and development. It provides valuable insights for assessing reservoir quality comprehensively and designing fracturing strategies differentially. This study focused on the deep shale of the Wufeng-Longmaxi formations in Luzhou area of southern Sichuan Basin (hereinafter referred to as southern Sichuan). Using core analysis, horizontal well imaging logging and seismic data, this study systematically investigated aspects such as descriptions of core natural fractures, development characteristics of horizontal well imaging logging, and the correlation between natural fractures in horizontal wells and seismically predicted fracture zones. The results show that horizontal well imaging logging can accurately identify three types of natural fractures: high-conductivity fractures, high-resistance fractures, and micro-faults. The fracture orientations identified by horizontal wells align with the direction of the current maximum horizontal principal stress, with fracture dip distribution patterns similar to those observed in vertical evaluation wells in the same structural positions. Seismically predicted fracture zones control the development of core-scale natural fractures identified through imaging logging. The influence distances of medium-intensity curvature body fracture zones, low-intensity curvature body fracture zones, and ant-track fracture zones on core-scale fractures are 110, 80, and 30-50 m, respectively. The Luzhou area's core-scale natural fractures exhibit "double-high" characteristics (high dip angle and high degree of calcite filling). The revealed correlations between the deve-lopment characteristics of core-scale natural fractures in horizontal wells, vertical well sections and seismic fracture zones serve as valuable references for the fine characterization of natural fractures, reservoir classification evaluation and differential fracturing technology testing of marine shale in southern Sichuan.

Keywords

• horizontal well
• natural fracture
• deep shale gas
• wufeng formation
• longmaxi formation
• luzhou area
• sichuan basin