Development Characteristics and Quantitative Prediction of Multiperiod Fractures in Superdeep Thrust-Fold Belt

For a superdeep imbricated thrust-fold belt in the Kuqa depression of Tarim Basin, NW China, the structural fractures have a great impact on the tight gas reservoir productivity. In this research, structural fractures were characterized from core data and imaging logging data. Numerically, the finite element (FE) method was applied to simulate the 3-D paleotectonic stress field of the key fracture-generating period as well as the present-day stress field in the Keshen gas field. Based on previously developed geomechanical models, we further derived the models of fracture aperture and porosity under the palaeostress field. A fracture permeability model considering fracture filling degree and stress was developed based on the Fracture Seepage Theory. Finally, we obtained a series of calculation models for the present-day fracture aperture and permeability. The predictions based on these models agreed well with actual measurement results, with most of the relative errors less than 20%. The developed 3-D FE geomechanical model and fracture parameter prediction method hold great promise for characterizing fractures in other deep low-permeability reservoirs.