Modeling and Designing Improved Oil Recovery by Steam Injection in NaturallyFractured Reservoirs

摘要

Steam injection in naturally fractured reservoirs provides anrnextremely challenging problem as well as a potentiallyrneffective and efficient improved oil recovery method.rnCoupling of the two distinct and contrasting matrix andrnfracture systems results in a highly non-linear problem, and itrngets even more complicated as a result of steep changes inrnfluid properties due to the thermal effects of steam injection.rnModeling and designing an optimum steam injection operationrnin such systems requires an accurate characterization andrnrepresentation of a naturally fractured reservoir and steamrninjection operation parameters and dynamics.rnIn this research effort, a thermal dualpermeability/rndual-porosity numerical model is developed forrnthe problem. The multi-phase fully implicit model is threerndimensional and compositional, accounting for viscous,rncapillary and gravitational forces. The model incorporatesrndetailed anisotropic and heterogeneous reservoir propertyrndescription, and formulates all reservoir and operationalrnparameters as functions of all the primary variables,rn(2nrn2nHC HC+10), where n +nHC HC is the number of hydrocarbonrncomponents. The multi-layer production and injection wellsrnare coupled to the reservoir fully implicitly. Both an iterativernand a direct solver are employed in the solution of thernresulting system of linear equations. The present model isrnverified and benchmarked against two SPE Projects.rnA comprehensive and comparative study isrnconducted in order to understand the relative effects ofrnnaturally fractured system and injection operation propertiesrnon the oil recovery performance. This comparative sensitivityrnanalysis is performed using the dual-permeability, the dualporosityrnand the approximate conventional single-porosityrnmodel.rnIn search of some practical guidelines, each reservoirrnsystem and operational property is studied in a range ofrnnaturally fractured reservoirs such as with different matrix block sizes, fracture/matrix permeability ratios and capillaryrnpressures. The present study should help us better understandrnfluid flow dynamics, design optimum recovery operations andrndetermine range of confidence for an oil recovery operation inrnnaturally fractured reservoirs undergoing steam injection