Fracturing Fluids Flowback Model In Shale Reservoirs With Discrete Fracture Networks

In order to accelerate and optimize the shale gas development in Weiyuan block,and achieve long-term stable gas production,flowback mechanisms of fracturing fluids is urgent to be figured out as soon as possible.In addition,many research works are urgent to do in specific flowback systems and strategies and extraction technologies for shale gas.The gas water flow in fractured shale gas reservoirs is studied deeply and systematically.A two phase flow model coupled matrix and discrete fractures is built,which is solved by the Finite Element and Finite Volume method.The work provides a reliable method for predicting the flowback ratio and gas production,which is instructive to flowback measures.Three parts of the research works are done in this paper: Firstly,the mathematic model is built,considering the desorption of adsorbed gas,nonlinear flow mechanisms of free gas,differences of capillary pressure and relative permeability curves in matrix pores and hydraulic fractures.The gas water flow model can be easily transferred to the oil water flow model,which can be verified through experiment results.Then,considering the special mechanisms of shale gas accumulation,i.e.the initial water saturation in shale matrix pores is lower than the irreducible water saturation,the MATLAB program of the finite element and finite volume method is compiled.And the program is verified.Finally,an actual well model is built,and the actual production data is used to do the history match.Then,gas and water production in 1 year is forecasted.In the meanwhile,influences of geology parameters and fracturing parameters on gas and water production are investigated.Some conclusions can be drawn from the simulation results: due to the reason that the irreducible water saturation is higher than the initial water saturation,a great amount of water becomes irreducible water once it enters the shale matrix,which results in that the higher the flowback ratio,the lower the gas production.There is large difference among different wells as a result of the irreducible water saturation variation among different wells,and that makes the gas production hard to be linked with the flowback ratio.The fracture interference has a great influence on the flowback of fracturing fluids.The water saturation at the fracture junction is much higher than that at other places,which makes the gas production of complex fracture network only slightly higher than that of simple fracture network.