Impacts Of Geomechanical Damage On Waterflood-induced Fracture Propagation In Low-permeability Reservoir Reservoirs

Waterflood-induced fractures(WIF)can enhance the production of lowpermeability oil reservoirs.However,if WIF propagate fastly,they connect injection wells to production wells earlier,inhibiting the production of low-permeability oil reservoirs.This phenomenon occurs greatly in China.In the present research,the fast propagation mechanism of waterflood-induced fractures was mainly investigate.Firstly,the damage variation of mechanical parameters of sandstone with water saturation was investigated by experiments.Secondly,Flow-geomechanics-coupled numerical simulations were performed to analyze the impacts of waterflooding on stress distribution in a low-permeability oil reservoir.Based on the fracture mechanics theory,the propagation length of the waterflood-induced fracture was calculated and the characteristics of waterflood-induced fracture propagation were analyzed.Experimental results revealed that water changed the microscopic structure of sandstones.This phenomenon decreased the Young’s modulus and compression/tensile strength of sandstones and increased the Poisson’s ratio.The changing magnitude of these properties increased with water saturation,and the maximum changing magnitude reached over 70%.The water saturation distribution is heterogeneous after waterflooding,causing a heterogeneous distribution of rock properties.The stress around the fracture tip and the fracture propagation length were significantly affected by these property changes.After the geomechanical damage,the critical injection pressure that induces fracture propagation decreased by over 19%.Moreover,the initial fracture length enhanced the propagation length of the waterflood-induced fracture.These results suggest that the propagation of waterflood-induced fractures becomes more significant during waterflooding.In order to avoid fast facture propagation,the determination of injection pressure should consider the impact of rock damage caused by water-rock interactions.