Evaluation of Geological-Engineering Sweet Spots in Deep Shale Gas Reservoirs in of the North Luzhou Block

The geological conditions of shale gas in the deep layers (burial depth of 3500-4000m) of the northern area of Luzhou block are superior, but the shale gas wells in the work area have frequent casing deformation and poor gas well performance. How to scientifically divide the geological-engineering sweet spots of shale gas reservoirs in the work area determines the effective development of the gas field. Starting from the geological-engineering conditions of shale reservoir, this article conducts an analysis of the factors affecting the geological-engineering sweet spots in shale matrix. The research shows that the geological-engineering conditions in the work area are complex, with fault develop showing characteristics of multiple stages, levels, and types. The lower layer of Type I reservoirs has a large continuous thickness (7-18m), excellent reservoir quality, and developed unidirectional and network fractures; The reservoir has high brittleness content, high Young's modulus (3.685~5.004 × 104MPa), low Poisson's ratio (0.195~0.315), and good compressibility of shale; However, the reservoir stress demonstrates complex characteristics such as large differences in horizontal stress, rapid changes in direction, and a strike-slip stress state, which makes faults prone to slippage. Based on a comprehensive analysis of geological conditions, “continuous thickness of type I reservoirs, fault scale, and natural fracture type characteristics” are selected as evaluation indicators, and the work area is divided into three types of geological-engineering sweet spots of the shale matrix: “Zone A of Type I, Zone B of Type I, and Type II”; Based on a comprehensive analysis of fault slip distribution are chosen as the main indicators for evaluating engineering risks, which are divided into high, medium, and low categories; Coupling geological sweet spots of shale matrix geological-engineering sweet spots with engineering risk areas, the geological-engineering sweet spots of shale gas reservoirs in the work area are divided into four categories: I, II, III, and IV.