Discrete Fracture Modeling Of Fractured Reservoirs

Naturally fractured reservoirs are an important component of the world's hydrocarbon resources.Owing to the existence of natural fracture networks,the reservoirs generally exhibit a higher degree of heterogeneity when comparing to conventional reservoirs.As a result,the flow mechanisms are more complicated.Besides,in shale and tight gas(oil)reservoirs,the development of horizontal well drilling and fracturing stimulation techniques has created high permeable hydraulic fractures to enhance the communications between the shale matrix and the production well,which is responsible for the multiscale effect of fractures.At present,there is still a lack of insightful understanding of the complex flow mechanisms of fractured reservoirs.Therefore,it is of either scientific significance or engineering applied importance to strengthen the study on the flow model and numerical simulation of fractured reservoirs.Massive hydraulic fracturing creates irregular fracture networks,which requires accurate modeling methods.The Discrete Fracture Model(DFM)could overcome the insufficiency of the traditional Dual Porosity Models(DPMs)in describing large scale fractures.In this dissertation,we develop a Discrete Fracture Model(DFM)for fractured reservoir simulation.Constrained PEBI grids are generated to describe the unstructured discrete fractures.Finite volume method is used to discretize the partial differential equations,and the linearized equation system is solved iteratively in a fully implicit scheme.We also study the special mechanisms of shale gas reservoirs and provide reliable methods for the gas property calculation.Based on the proposed DFM,a series of simulations are conducted and the following conclusions are drawn from this work:1.As some micro-seismic measurements depict a dendritic-like morphology of hydraulic fractures in tight gas reservoirs,we correspondingly derive an off-center well model.The derived well model is coupled in the DFM to predict production performance of the horizontal wells.Afterward,the off-center well model is verified against ECLIPSE,and a field case of multi-stage fractured horizontal well from a shale gas reservoir is studied.Finally,the effects of some fracture geometric parameters(e.g.,fracture angle,fracture asymmetry and fracture branch number)on well production are investigated in detail.2.Geomechanical effect is an important mechanism in shale reservoirs and occurs simultaneously with gas flow during the production period.It may not only result in production variation,but also have an impact on reservoir behaviors.We develop a discrete fracture model that couples geomechanical effect to predict well production and reservoir dynamics.Numerical simulations are conducted to study the influence of geomechanical effects on a reservoir with complex fracture networks.The results show that geomechanics has an obvious impact on the gas production and the pressure distribution.The percentage of production loss increases with reservoir pressure,while decreases as matrix permeability or fracture conductivity increases.Concerning the influence of integrated geomechanics(IG),it depicts that the natural fracture geomechanics(NFG)is dominant,the hydraulic fracture geomechanics(HFG)is minor,and the matrix geomechanics(MG)is negligible.Less percentage of production loss caused by the IG is observed than the sum caused by the NFG,HFG and MG.3.We construct an immiscrible two-phase discrete fracture model,and the model is solved using the IMPES formulation.Simulation results for CO2 injection in fractured reservoirs show that the existence of fractures,the fracture orientation and the fracture conductivity have an obvious effct on the recovery efficiency.