Optimization of Shallow Shale Gas Reservoir in Mountainous Area Development Strategy and Well Type - A Case Study of Zhaotong Shale Gas Demonstration Area in Southern China

Abstract Shallow shale gas reservoirs in mountainous terrains are influenced by "low formation pressure, significant variations in burial depth, steep formation dips, and the presence of fractures and microstructures", posing challenges in aligning well types and development strategies with geological characteristics. This research introduces an innovative "tectonics-driven, multifaceted integration" approach to development and well optimization techniques. Utilizing the Petrel platform, this study constructed a detailed 3D geomechanical model for a geologically complex body, incorporating various stress patterns. The model delineates the area based on gas enrichment status, tectonic styles, stress regimes, and fracture development. Comparative analyses of stress distribution around the wells in different drilling orientations were conducted using near-wellbore geomechanical models. Additionally, production capacity evaluations and numerical simulations were employed to analyze the effectiveness of different development strategies and well types. The near-wellbore geomechanical model indicates that well placement along tectonic contours (at certain angles to the minimum horizontal principal stress) enhances wellbore stability and ensures a more uniform stress distribution conducive to homogenous modifications. Simulations reveal minimal differences in production capacity under identical fracturing processes, advantageous for efficient "water drainage and gas production". This well distribution method suits the extensively developed steep zones within the study area. Addressing the challenges in strike-slip to thrust transition zones and thrust areas, where bedding planes and low-angle fractures are prone to activation and horizontal wells face difficulties in vertical layer penetration, a pilot test for a comprehensive three-dimensional development strategy using clustered directional wells from a controlled platform was conducted. The feasibility of deploying directional wells in reverse fault stress regime zones was validated through simulations. Ultimately, considering the life-cycle benefit goals and maximized reserve utilization, the study advocates for a "tectonics-driven, multifaceted integration" concept, leading to the creation of a decision-making framework for a capacity-focused, integrated development model. Based on the mechanistic understanding that complex structure and strong non-homogeneity are essential in forming complex fracture networks, this study challenges the traditional practice of orienting wells along the direction of minimum horizontal principal stress. It innovatively proposes the method of well placement along the direction of tectonic contours or principal controlling faults, offering valuable insights for the production of other unconventional resources.