Performance and recovery prediction in heterogeneous naturally fractured reservoirs under the solution gas drive process

Processes that affect recovery in solution-gas-drive reservoirs, such as vertical equilibrium, counter-current imbibition, re-saturation and gas injection, are space dependent. If spatial reservoir properties in naturally fractured reservoirs (NFRs) are not carefully mapped, then forecasts of future reservoir behavior will be uncertain.; In this study, some aspects of reservoir forecasting in NFRs are scrutinized. For short term forecasting, the inflow performance relationship (IPR) concept is re-visited with emphasis on the dual flow concept in fractured reservoirs. Additional reservoir characterization parameters are included to account for high fracture conductivities and interporosity flow. IPRs are examined for their applicability to naturally fractured reservoirs under the solution gas drive process. From numerical experimentation, it is demonstrated that new equations developed in this study more accurately represent transmissibility characteristics and interporosity properties in NFR performance forecasting.; Gas injection is shown to be a controlling factor in minimizing the re-saturation of down-structure matrix blocks. Spatial variability in matrix properties influences the overall recovery. A wide range of matrix permeabilities is considered for the case of primary and gas injection processes. Results show that there is a critical matrix permeability above which gas injection can result in recovery enhancement.; Stochastic representation of NFRs complicates the computational demands for the simulation of many recovery processes. This study shows a procedure for augmentation of the objective function to minimize the number of stochastic images. The simulated annealing method (SAM) is used for conditioning purposes with specific objective functions based on concepts examined under deterministic modeling of NFRs. Results from this study indicate that further conditioning of stochastic images is required to include spatial heterogeneity as a factor when making a recovery prediction.; An EFRP (effective fracture relative permeability) approach is proposed to represent the composite relative permeability of matrix and fracture for up-scaling purposes. The developed method reduces the dual-porosity system to a single-porosity model.