Prediction of natural fractures in the Lower Jurassic Ahe Formation of the Dibei Gasfield, Kuqa Depression, Tarim Basin, NW China

Abstract

The Lower Jurassic low porosity and low permeability Ahe Formation is the major reservoir of Dibei Gasfield in the Kuqa Depression, Tarim Basin. Natural fractures are important spaces for storage of hydrocarbons in low permeability reservoirs and can significantly improve the fluid flow capability; therefore, predicting the location and intensity of natural fractures in the Ahe Formation are of extreme importance. In the present study, the Late Himalayan paleotectonic stress field, the period of time when the majority of natural fractures generated in the Dibei Gasfield, was simulated and investigated with a three dimensional finite element (3D FE) model, which serves as a starting point for the prediction. Based on the principle of energy conservation and simulated paleotectonic stress field, the relationship between fracture density and stress parameter was established, and hence, natural fractures in the Ahe Formation of Dibei Gasfield were predicted. The results indicated that the development and distribution of natural fractures were primarily fault-controlled. Regions with well-developed natural fractures were mainly located in fault zones and around faults. Tectonic activities and ultra-high pressures were the dominant factors for natural fractures in the Ahe Formation. Regions with higher development degree of natural fractures in the Ahe Formation usually have a larger gas production; therefore, regions among Well Y1, B3, X1 and B2 should be focused in the Dibei Gasfield.