Search

Steam injection in naturally fractured reservoirs provides an extremely challenging problem as well as a potentially effective and efficient improved oil recovery method. Coupling of the two distinct and contrasting matrix and fracture systems results in a highly non-linear problem, and it gets even more complicated as a result of steep changes in fluid properties due to the thermal effects of steam injection. Modeling and designing an optimum steam injection operation in such systems requires an accurate characterization and representation of a naturally fractured reservoir and steam injection operation parameters and dynamics. In this research effort, a thermal dual-permeability/dual-porosity numerical model is developed for the problem. The multi-phase fully implicit model is three dimensional and compositional, accounting for viscous, capillary and gravitational forces. The model incorporates detailed anisotropic and heterogeneous reservoir property description, and formulates all reservoir and operational parameters as functions of all the primary variables, (2nHC+10), where nHC is the number of hydrocarbon components. The multi-layer production and injection wells are coupled to the reservoir fully implicitly. Both an iterative and a direct solver are employed in the solution of the resulting system of linear equations. The present model is verified and benchmarked against two SPE Projects. A comprehensive and comparative study is conducted in order to understand the relative effects of naturally fractured system and injection operation properties on the oil recovery performance. This comparative sensitivity analysis is performed using the dual-permeability, the dual-porosity and the approximate conventional single-porosity model. In search of some practical guidelines, each reservoir system and operational property is studied in a range of naturally fractured reservoirs such as with different matrix block sizes, fracture/matrix permeability ratios and capillary pressures. The present study should help us better understand fluid flow dynamics, design optimum recovery operations and determine range of confidence for an oil recovery operation in naturally fractured reservoirs undergoing steam injection.