Prediction of fractures in tight carbonate gas reservoirs and analysis of main controlling factors: a case study on Dengying formation reservoir of Gaoshiti block in the Sichuan Basin

Natural fractures are important storage spaces and seepage channels in tight carbonate reservoirs. It is therefore of practical significance to quantitatively predicting their development and distribution patterns and revealing the dominant geological factors that control the development of gas reservoirs. This study looks at the fractures in the tight carbonate reservoir of Dengying Formation in Gaoshiti block of Leshan-Longnusi ancient uplift in the central Sichuan Basin. Based on the characterization of fracture parameters, we established a calculation model of stress field-energy-fracture parameters, and carried out quantitative prediction of fracture development and distribution patterns by combining multi-phase fracture superimposition algorithms. We then analyzed the influence of lithology, faults, and structural morphology on fracture development. The results show that: (1)The fractures in Dengying Formation of Gaoshiti block are mainly tension-shear fractures, high-angle fractures, and semi-filled fractures. The preferential fracture strike is NW-SE and near N-S directions. The fracture density is between 0 and 2 fractures per meter, and the high-value areas are mainly distributed in the fault zones and central regions; (2)There is a negative exponential power relationship between the length and density of natural fractures in the Gaoshiti block. Fracture development exhibits interlayer differences: The limestone reservoir has a high degree of fracture development, and mudstone has a blocking effect on fracture propagation; (3)Fracture development scale and occurrence are significantly affected by faults and folds: fracture around faults shows high density, large aperture and short length. Shear fractures are nearly parallel or at a low angle to strike-slip faults, and tensile fractures are at a high angle to the main strike-slip faults; folds mainly affect fracture aperture through structural curvature, with larger fracture apertures in high-degree deformation structural positions, and smaller values in the wings. The results could provide references for efficient exploration and profitable development of gas reservoirs in the study area and other regions with similar geological conditions.