Transient Pressure Analysisof Volume-Fractured HorizontalWells Considering Complex Fracture Networks and Stress Sensitivityin Tight Reservoirs

摘要

Tight reservoirs, as an important alternative for conventional energy resources, have been successfully exploited with the aid of hydraulic fracturing technologies. Because of the inherent ultralow permeability and porosity, tight oil reservoirs generally suffer from the effects of stress sensitivity. Both hydraulic fractures with complex geometries and a high-permeability area known as stimulated reservoir volume (SRV) may be generated by the massive hydraulic fracturing operations. All these bring huge challenges in transient pressure analysis of tight reservoirs. Up till now, although many research studies have been carried out on the transient pressure analysis of volume-fractured horizontal wells in tight reservoirs, unfortunately, there is still a lack of research studies that have taken stress sensitivity, complex fracture networks, and the SRV into consideration, simultaneously. To fill up this gap, this paper first idealizes the reservoir after hydraulic fracturing as two radial composite regions, that is, the unstimulated outer region and the inner SRV. The stress sensitivityis characterized by the variable permeability depending on the porepressure. A linear source with consideration of the stress sensitivityin the composite reservoir is obtained by the perturbation technique,Laplace transformation, and the flow coupling of two regions. Second,the complex fracture networks are discretized into segments to capturetheir geometries. A semi-analytical model is finally established andvalidated by the comparison with previous models. On the basis ofour model, six flow stages of volume-fractured horizontal well areidentified and special features of each regime are analyzed. The stresssensitivity has a great impact on the later stage of production. Themobility ratio and the SRV radius mainly affect SRV pseudo-steady-stateflow period and interporosity flow period in the outer region. Fracturenumber mainly affects the linear flow in the SRV. Fracture geometriesmainly affect linear flow and interporosity flow in the SRV. Thisstudy has some significance for well test interpretation and productionperformance analysis of tight reservoirs.