Study On The Mechanism And Improving Method Of Water Channeling In Hydraulic Fractured Low Permeability Reservoirs

Tight reservoirs are widely distributed in our country, which accounts for about 30% of the total amount of petroleum resources all over the nation, and the unused reserves of low permeability reservoirs takes up more than the half of the country’s total unused reserves.Due to the extreme low permeability and big flow resistance, oil wells in these reservoirs are of low production, which is why hydraulic fracturing is commonly adopted to increase the capability of wells. But cases show that this kind of exploiting method could bring out serious problem like fracture water channeling, where the breakthrough comes much earlier and the water cut roars up. Once water breaks through, the production of oil wells drops down to almost zero, which severely inhibited the development of this kind of oil reserves.This paper uses numerical simulation to do the research and development on water channeling in hydraulic fractured reservoirs. Results of the simulation are analyzed to show how different direction, length and conductivity of fractures effect on the development. Then the possible methods to decrease water cut such as fracture blocking and multiple fracturing are also analyzed through numerical simulation. Simulation results show that longer fractures and bigger fracture conductivity lead to shorter breakthrough time and more abrupt water cut uprising as well as larger residual oil saturation, which reduces the final oil recovery. Bigger blocking ratio and earlier blocking are better to increase the productivity of oil wells and to keep water cut in control. Blocking the fractures near the borehole is better than the end to decrease water cut and slow down the water channeling. Multiple fractures vertical to the original ones are most helpful to control water cut within a small scale, while the length and conductivity of multiple fractures makes little difference to general water cut.At last, models with fractures are designed and experiments are practiced to verify the two main factors affecting the water channeling in fractures. Experimental results show that the longer the simulated fractures are, the sooner the water breakthrough occurs and the bigger the residual oil saturation is. The same situation happens when the conductivity of the simulated fractures increases. And according to the results of the experiments, both of the two circumstances lead to lower oil recovery, which is consistent with the results of numerical simulation.