Stimulated Reservoir Volume by Hydraulic Fracturing in Naturally Fractured Shale Gas Reservoirs

摘要

The stimulated reservoir volume and permeability enhancement of tight sand and shale gas reservoirs after stimulation by hydraulic fracturing is of major interest to the petroleum and geothermal reservoirs. In this work, we build a 3D fracture model for a hydraulically induced fracture in an infinite reservoir, and investigate the response of the reservoir rock in the vicinity of the main fracture with reference to rock failure and permeability variation. In this model, the 3-dimensional fracture-induced stresses and pore pressure around the hydraulic fracture are estimated using an analytical approach: The response of the rock mass to the variations of pore pressure and in situ stress is calculated by considering the joint orientations and frictional properties, as well as a rock mass failure criterion. By considering the minimum required effective treating pressure and the pore pressure distribution due to stimulation by hydraulic fracturing, we estimate the extent of the slip zones around the main fracture. The stimulated reservoir volume can thus be calculated based on the predicted failure geometry around the injection zone. This is of interest in interpretation of micro-seismicity in hydraulic fracturing and in assessing permeability variation around a stimulation zone. The model can also be used to optimize the treating pressure for stimulation, as well as to assess the accuracy of more complex numerical models.