Pressure transient analysis in fractured reservoirs with poorly connected fractures

Abstract

Pressure transient analysis in the fractured reservoirs is of great significance, as it provides useful information for the production performance forecasting of the fractured reservoirs. In the past decades, the conventional Warren and Root model (CWRM) (1963) is the popular tool for pressure transient analysis in the fractured reservoirs. However, many borehole image logs data strongly show that many fractured reservoirs are partially fractured, and these partially fractured reservoirs have poorly connected natural fractures (Ozkaya, 2018). The CWRM are not applicable in the partially fractured reservoirs any more, owing to the discretely natural fractures. Thus, more work needs to be done to address this issue. In this work, we introduce a discrete fracture model to build a dual-porosity model for the fractured reservoirs with poorly connected natural fractures. After verifying this model, the pressure transient behaviors of those fractured reservoirs are investigated in details.Results from the discrete fracture model show that flow regimes in reservoirs with poorly connected natural fractures is different from that in reservoirs without natural fractures. For vertically fractured wells with discrete fractures, the bilinear flow, linear flow, impacts of natural fractures, and pseudo-radial flow may progressively occur. Once these effects caused by natural fractures appear, the pressure derivatives show a “V-shape” dip, namely a transient flow.The main improvements in this manuscript include: (1) developing a method to determine the transmissibility factors of grids for natural fractures and hydraulic fractures, (2) presenting a numerical well model, and (3) studying the pressure map of various flow regimes in reservoirs with poorly connected natural fractures. This meaningful work provides a new angle on estimation of the influence of poorly connected natural fractures on pressure transient behaviors, which is beneficial to exploitation the naturally fractured reservoirs.