Development of production decline curves for non-Darcy oil flow in low-permeability reservoirs

Abstract

The purpose of work is creating a new technique for result interpretation of long-term well monitoring by production decline curve analysis in low-permeability reservoirs. For these reservoirs oil flow does not obey Darcy law, in some cases threshold pressure gradient exists. Standard techniques for well test results interpretation do not allow to determine reservoir parameters reliably. Currently, most of works devoted to the interpretation of well test results for nonlinear flow use the approach of numerical modeling and the method of type-curve matching to determine reservoir parameters. Of course, these methods are powerful tool, but analytical solutions of the considered problems are also of practical interest. Obtained solutions make it possible to determine not only reservoir parameters but also flow law parameters and to diagnose characteristic regimes of non-Darcy flow. That is why, it becomes necessary to develop new approaches for reservoir parameters and flow law determination, which was implemented in the proposed paper. A one-dimensional isothermal problem of single-phase non-Darcy flow is considered in two geometries: plane parallel (flow from fracture) and plane radial (flow from single well). Well operates with constant bottomhole pressure. Flow equation is characterized by two parameters: threshold pressure gradient and coefficient describing the change in flow rate near the threshold gradient value. To obtain analytical solutions, integral equation method was applied. The behavior of flow rate at different times was investigated, the results showed good agreement with numerical simulation. Decline flow rate curves were analyzed when changing parameters of flow equation. Also, the possibility of reservoir parameters determination was investigated.