Impact of formation dilation-recompaction on cyclic steam stimulation in reservoirs with bottom water: Application of an integrated coupled reservoir-geomechanical modeling workflow

Abstract

To optimize Cyclic Steam Stimulation (CSS) in areas with thicker bottom water, it is crucial to examine the correlation of the bottom-water encroachment to changes in pay-zone pressure due to dilation-recompaction cycles and intermittent sequences of stress and fluid transfers. This study outlines an integrated workflow for the modeling and uncertainty assessment of CSS in heterogeneous reservoirs through coupled geomechanical-flow simulation, Latin hypercube design, and response surface methodology to probe into dilation-recompaction effects in presence of bottom water, by incorporating the oil-viscosity variation due to biodegradation and compositional variation, presence of water pockets due to compartmentalization, dilation-recompaction, and relative permeability hysteresis. The results suggest that the CSS performance is most sensitive to dilation pressure and the interaction of recompaction pressure-water pockets. While increase in dilation pressure and compressibility improves CSS, the recompaction pressure is negatively correlated with its performance. This is related to the underlying water pockets compression due to reservoir dilation during injection and water encroachment as a result of the rise of bottom water level. Higher dilation pressure and lower recompaction pressure delay the compression of the underlying water pockets. On the contrary, in the absence of bottom water, CSS is improved with lower dilation pressure and higher recompaction pressure. Clearly, the presence of bottom water reverses the favorable geomechanical envelope during the injection and production cycles.