Pseudo-steady state inflow performance relationship of reservoirs undergoing multiphase flow and different wellbore conditions

Abstract

This paper introduces an integrated approach for the inflow performance relationship of reservoirs that undergo multiphase flow conditions and drained by vertical wells with different wellbore conditions. The main objective is eliminating uncertainties that govern predicting reservoir performance by assuming single phase flow in the porous media. The proposed approach includes developing several models for multiphase flow conditions using PVT data and relative permeability curves. These models are assembled with the inflow performance relationship to substantially approaching the realistic reservoir pressure/flow rate trend with time.Three tasks are conducted in this study. The first is developing three models for the three reservoir fluid compressibility functions [f(Co)], [f(Cg)], and [f(w)] that consider the changes in comperssibilities with reservoir pressure. These functions are dependent on reservoir fluids properties that are in turn functions of reservoir pressure. While the second involves developing five models of reservoir fluid mobilities using relative permeability curves and the three functions of reservoir fluid comperssibilities. In this task the change in reservoir fluid saturations and the three saturations are calculated and used to calculate relative permeabilities at different reservoir pressures. Multiphase flow reservoir pressure function [f(P)mp] is estimated in third task and used to predict the inflow performance relationships for different wellbore inner boundary conditions i.e. constant Sandface flow rate and constant wellbore pressure. The models in the three tasks are obtained by multi-regression analysis of PVT data and relative permeability curves.The outcomes of this study are: 1) Developing models for reservoir fluid motilities and comperssibilities using PVT data and relative permeabilities curves by multi-regression analysis. 2) Considering the impact of multiphase flow in the porous media by generating multiphase flow pressure function [f(P)mp]. 3) Predicting inflow performance relationships for multiphase flow for different wellbore inner boundary conditions. The study has pointed out: 1) Productivity index of multiphase flow is less than the index for single phase flow. 2) There are no significant differences in the inflow performance relationships of single and multiphase flow for the two inner wellbore boundary conditions, however, constant Sandface flow rate may have better inflow performance relationship than constant wellbore pressure. 3) Most of the models generated by multi-regression analysis exhibits high accuracy (high R-squared value). 4) The proposed models may not have similar trendlines for different reservoirs.