A New Approach to Embed Complex Fracture Network in Tight Oil Reservoir and Well Productivity Analysis

Accurate modeling of the distribution of induced fractures and pre-existing natural ones in unconventional reservoirs is essential for the analysis of the productivity of horizontal wells after fracturing. A novel approach is proposed here to establish a three-dimensional geological model of induced fractures, natural fractures and the horizontal well using a discrete random distribution method, based on micro-seismic data and natural fracture properties from the S oilfield. Taking the stress sensitivity into consideration, a coupled model calculating the fluid flow in the horizontal wellbore, the reservoir matrix and fractures were established to simulate the productivity of the S oilfield. This model was calibrated by the production data in the S oilfield, and the productivity of horizontal well under different natural fracture intensities, hydraulic fracture spacing and lengths was analyzed. The results show that the area without stimulation in the tight oil reservoir can rarely be exploited. The fluid pressure in the horizontal wellbore cannot be treated as uniform, especially when the production pressure keeps decreasing; otherwise, the cumulative production will be larger than the actual one. Increasing the hydraulic fracture length and natural fracture intensity and decreasing the fracture spacing are all beneficial to the daily and cumulative oil production. However, these methods accelerate the decline of the daily production. The production decline rate with higher natural fracture intensity was about 4 times that of lower natural fracture intensity. The natural fracture intensity and the fracture spacing are factors that are more influential to the productivity compared to the fracture length.