Pressure and Rate Analysis of Fractured Low Permeability Gas Reservoirs: Numerical and Analytical Dual-Porosity Models

Abstract

Abstract Most oil and gas production comes from heterogeneous, fractured reservoirs. These fractures can be naturally induced or generated / re-activated through completion and stimulation techniques. In fractured reservoirs, the fluid flow is governed by both fracture and matrix rock-fluid characteristics. Hence, modeling of fractured reservoirs need special considerations to account for these rock-fluid interactions in the matrix and fractures. Currently used formulations of dual-porosity models give a good understanding of heterogeneous fractured reservoir systems. However, determining reservoir properties like effective permeability and estimating the pore-volume or reserves of fractured reservoirs (especially for tight formations) are some of the technical challenges related to reservoir characterization. In industry, similar reservoir properties can be estimated using prolonged rate or bottomhole pressure controlled drawdown analysis. In this study, numerical dual-porosity models have been implemented and studied for a range of parameters. Grid geometry (radial / linear), type of well (vertical / horizontal), formation tightness (matrix permeability), mode of control (constant flowing pressure / constant flowing rate), and connectivity of fractures (connected and disconnected fracture-continuum) are among the cases investigated to capture the transient behavior of fractured tight gas formations using a numerical dual-porosity model. In addition, for the linear, flow rate controlled case, numerical and analytical model results are compared with good matches. Fracture and matrix permeability, effective permeability, fracture conductivity, fracture and matrix storativity, and radius of investigation are among the reservoir parameters inferred / calculated from simulation results using the numerical model. Inferred results match the input values to an acceptable degree of accuracy. Hence, it can be concluded that numerical dual-porosity model is a very good tool to analyze transient response of tight formations.