Well Test Interpretation And Productivity Evaluation Of Multi-fractured Horizontal Wells In Tight Oil Reservoir

Multi-fractured horizontal well is the key technology in the development of tight oil reservoirs.However,most researches about fractured horizontal well test is based on traditional Darcy flow without considering the threshold pressure gradient and stress sensitivity.Besides,there are little theoretical studies about two phase flow.So it is necessary to establish a set of well test interpretation and productivity evaluation method of multi-fractured horizontal wells in accordance with the real tight oil reservoir characteristics.The pressure and rate performance for multi-fractured horizontal well of single phase flow and oil-water two phase flow in single porosity tight oil reservoir as well as single phase flow in dual porosity reservoir is studied.The single phase flow model is solved analytically by correction point source function method: Firstly,a point source mathematical model of single phase flow in infinite formation which considers threshold pressure gradient and stress sensitivity is established in single and dual porosity reservoir;Then correction point source solution is obtained by using Laplace transformation;Finally,based on mirror image and principle of superposition,analytical bottomhole pressure and production of multi-fractured horizontal well is acquired.Two phase flow model in single porosity reservoir is solved by numerical method: hydraulic fractures is reduced dimensions by discrete fracture model,unstructured meshes are generated,the finite volume method is applied and numerical algorithm accuracy is verified by comparing with analytical solution.Besides,regimes of fractured horizontal wells are identified and parameter sensitivity to pressure performance is analyzed.Then effect factors on production are studied and finally orthogonal experiment is applied to determine the primary and secondary factors.The results demonstrate that Pressure transient curve will upturn in the late flow period after considering threshold pressure gradient and stress sensitivity and pressure derivative curve no longer shows 0.5 horizontal line during late pseudo-radial flow.Under the same circumstances,the dimensionless Pressure transient curve of two-phase flow is the same as that of single phase flow.The total mobility capacity of oil and water must be considered when studying effect factors on pressure and rate of two phase flow.The formation flow coefficient has the greatest impact on productivity in single porosity reservoir while natural fracture permeability has the greatest impact in dual porosity reservoir.Well test interpretation and productivity evaluation methods established in this paper can provide theoretical basis for characterizing tight oil reservoir comprehensively and evaluating fractured horizontal well production.