Characteristics of shallow coal measure gas reservoir and key technologies of exploration and development in Yaojie mining area

The exploration and development of coal measures gas can not only effectively improve the single well production of coalbed methane in coal mining areas, reduce the waste of resources, but also alleviate the energy crisis in China, reduce coal mine gas accidents, protect the atmospheric environment, and contribute to the realization of carbon peak and carbon neutralization. Based on the shallow coal measure gas development demonstration project in the third mining area of Haishiwan mine field, the characteristics of coal measure gas reservoirs in Yaojie mining area are analyzed, and the key technologies for coal-measure gas exploration and development are discussed. The research showed that coal measure gas in the mine field is mainly present in the oil shale and oil sandstone of the fourth rock group(J₂yj⁴) of the Jurassic Yaojie Formation coal system, and the oil A layer and the second coal layer of the second group(J₂yj²). The gas content of oil layer A and second coal layer increases with the increase of burial depth; The CO₂ concentration in oil layer A and second coal layer is higher, and decreases with the increase of burial depth; The second coal layer has a strong adsorption capacity, and the oil layer A is easier to desorb; Oil sandstone permeability > oil layer A permeability > second coal layer permeability > oil shale permeability; Compressive strength, tensile strength, elastic modulus, Poisson's ratio and brittleness index show that the difficulty of reformation of them in descending order is oil sandstone, oil layer A, oil shale, and coal second layer; The organic matter abundance of oil shale is 4.06%, and kerogen type is Ⅱ₂-Ⅲ. The abundance of organic matter in the oil layer A is 43.27%, and the degree of metamorphism is polarized. The saprolite vitrinite reflectance is 0.48%-0.53%, and the humic coal vitrinite reflectance is 0.89%-0.97%. The abundance of organic matter in the second layer of coal is 92.87%, including vitrinite 67.90%, inertinite 29.10%, exinite 3.5%, the degree of metamorphism is mainly fat coal with a small amount of gas fat coal; Compared with most low pressured formations in China, the reservoir pressure of each producing layer is normal and the gas production potential is great; The second coal layer o, the oil layer A and the oil shale should be optimized in the development of coal measure gas. The fracturing technology of multiple clusters, flow-limiting perforating technology and fine sand filtration loss, ball drop temporary plugging, two large and one low(large displacement, large sand volume, low sand ratio) fracturing technology are suitable for the reservoir transformation of the ultra-thick and tight formation in this area, and the pump hanging position is lower than the two-layer perforating section of coal and the gravity spiral gas anchor drainage process can reduce the effect of CO₂ and improve the drainage efficiency. The application of these key technologies has significantly improved the gas production effect of the mine field demonstration project. The daily gas production of a single well exceeds 2 000 m³