Prediction of Water-Oil Relative Permeability through Fractured Reservoirs: Analytical Development and Numerical Investigation

摘要

One of the most challenging subjects in modeling of fractured petroleum reservoirs is quantifying fluids competition for flow in fracture network(relative permeability curves).Unfortunately,there is no standard technique for experimental measurement of relative permeabilities through fractures and the existing methods are very expensive,time consuming and erroneous.Although,several formulations were presented to calculate fracture relative permeability curves in the form of linear and power functions of flowing fluids saturation,it is still unclear what form of relative permeability curves must be used for proper modeling of flow through fractures and consequently accurate reservoir simulation.In this work, the demonstrated importance is shown by using different relative permeability functions in dual porosity reservoir simulation of one of Iranian naturally fractured reservoirs.Numerical simulation results indicate that using lower values of relative permeabilities postpones water breakthrough,decreases water-cut and consequently increases predicted oil recovery rate.After indicating the significant effects of fracture relative permeability curves in reservoir simulation,basic fluid flow equations are combined to develop a new simple analytical model for water-oil two phase flow in a single fracture.Eventually,the model gives rise to simple analytic formulations for fracture relative permeabilities.The model explicitly proves that water-oil relative permeabilities in fracture network are functions of fluids saturation,viscosity ratio, fluids density,inclination of fracture plane from horizon,pressure gradient along fracture and rock matrix wettability,however they were considered to be only functions of saturations in the classic X-type and power(Corey and Honarpour)models.Eventually,validity of the proposed formulations is checked against literature experimental data.The proposed fracture relative permeability functions have several advantages over the existing ones.Firstly,they are explicit functions of the parameters that are known for each of simulation computational cells or easy to measure in laboratory.It is also the first model that takes gravity effects and wettability of fracture walls into consideration and individually developed for water and oil-wet systems.Furthermore,the newly developed formulations are simple,efficient and accurate. Thus,they are recommended for implementation in dual and multiple continuum commercial reservoir simulators.