Comprehensive Evaluation of Geological and Engineering Sweet Spots of Shale Gas Reservoir: A Case Study of the Luzhou Block, Sichuan Basin

Abstract

There is a huge amount of marine shale gas resources in the southern Sichuan Basin in China, and most of the resources are at the buried depth of 3500 - 4500 meters. At present, deep shale gas is in the early stage of exploration and development. In order to achieve large-scale efficient development, in addition to optimizing favorable blocks, it is also to identify the optimal target in the vertical direction combine geology, drilling, and fracturing. Therefore, Taking the Longmaxi formation shale in the Luzhou block as the research object, based on drilling, logging, and core experiment data, through single well and 3D geomechanical modeling methods, analyze the characteristics of organic matter abundance, porosity, pore pressure, collapse pressure, mineral composition and in-situ stress of different layers of shale in Longmaxi formation. Systematically summarized the main controlling factors of the “sweet spot” of deep shale gas and establish the comprehensive evaluation system of deep shale gas “sweet spots”, to clarify the optimal “sweet spots” of geology, drilling, and fracturing in the Longmaxi reservoir. Results show that the total organic carbon content, porosity, and gas saturation of the long111 layer are higher than other layers. The Long111 layer has a low collapse pressure and a high compressive strength, the risk of wellbore instability is relatively low. The stress difference coefficient of All layers is less than 0.3, and the brittleness index of the Long111 layer is 62.35%. A complex fracture network is easier to form after fracturing. The conclusion shows that the Long111 layer is the optimal reservoir section of the Longmaxi Formation. Ensure the drilled rate of the Long111 layer and maximize the length of the horizontal section can obtain higher production.