Investigation of Multiple Hydraulic Fracture Propagation for Low-Pressure Tight Sandstone Reservoirs in Northern Ordos Basin of Changqing Oilfield, China

Abstract Giant Ordos basin, located in the northern China, consists of Palaeozoic lacustrine stacked sandstone and shale deposits characterized by low-pressure, low-porosity, low permeability matrix rock and a poorly developed natural fractures (NFs) system. Recognizing the successful exploration of shale gas reservoirs in United States, Changqing oilfield primarily uses three fracturing technologies, hydraulic sandblasting technology, open-hole packer technology and drillable bridge plugging technology, to create multiple straight hydraulic fractures (HFs) in tight sandstone zones with large differential horizontal stress. For this study we consider multiple perforation clusters per stage using the drillable bridge plugging technology, which offers benefits of large injection rate and high treatment efficiency. This paper describes a hydraulic fracture propagation model (HFPM) that couples fracture deformation and fluid flow to simulate the growth of multiple HFs in the horizontal wellbore. We then integrated an embedded discrete fracture model (EDFM) and commercial reservoir simulator to analyze production prediction based on the provided data from Changqing oilfield. We calibrated the fracture propagation model with the reservoir performance data and demonstrated how to optimize the fracture treatment. The low formation pressure gradient in the Changqing oilfield impairs the production performance. To reduce the rapid decline rate in reservoir pressure, the fracturing fluid is not only used for creating fractures, but also enhancing the pore pressure by leaking off into the formation. Adjusting the pumping rate and fluid volume enables our model to increase the formation pressure gradient. Moreover, the tight sandstone deposits in the Changqing oilfield have a relatively high brittleness index (BI) and large differential horizontal stress. This is the reason why reservoir with sparse NFs in the Ordos basin has less opportunity of generating complex fracture networks. Large-scale physical simulation experiments were also conducted to validate the possibility of fracture networks generation. Our model accouts for the stress heterogeneity and offers the capability to address HF propagation in the presence of sparsely distributed NFs and adjusts the dimensions and spacing of the NFs to achieve a history match with production data. This paper emphasizes the extensive application of a fracture propagation model for lacustrine tight sandstone deposits. Considering features of Ordos basin, such as low-pressure gradient and relatively high BI, our model can provide a guideline for HF treatment design and optimization of well performance.