An Analysis of the Effect of Surfactant Flood on Residual Oil under Composition-Dependent Multi-Contact Water-Oil Miscibility in a North Sea Reservoir

摘要

Surfactant flooding has become a more common method in recent decades in which the phase behaviorrninside the reservoir can be manipulated by the injection of surfactants, leading to favorable conditions tornmobilize trapped oil. Carefully designed surfactants that are injected into the crude oil can generaternmicroemulsions at the interface between crude oil and water, thereby reducing the interfacial tension tornvery low levels, which ultimately mobilizes the residual oil. However, the adsorption of surfactant to thernrock during the injection and chromatographic separation of the surfactant in the reservoir are criticalrnphenomena in which the surfactants must be resistant to reservoir conditions, including high pressures andrntemperatures. The application of surfactant methods is usually constrained by the cost of the chemicalsrnand is adversely affected by adsorption and loss into the rock, making it crucial to understand thernsignificance of those factors that affect the performance of this enhanced oil-recovery method so that morernrobust decisions can be made. This study aims to outline the lessons learned regarding the impact thatrnthese factors had on a North Sea reservoir.rnIn this study, a reservoir simulation model is harnessed in which the injection of cold water into therninitially hot reservoir results in a reverse temperature gradient is simulated using a commercial fullphysicsrnreservoir simulator. A surfactant slug is followed by several years of water injection, where thernreservoir contains a light oil trapped between a gas cap and an aquifer.rnSurfactant effects on residual-oil detrapping and wettability are modeled by interpolating betweenrnrelative permeability sets according to a capillary number, which depends on temperature and surfactantrnconcentration, where composition-dependent K-values describe multiple-contact water-oil miscibilityrnaccording to the concentration of water-based surfactant in which the adsorption of surfactant affects itsrnavailability and propagation.rnUsing a real reservoir model coupled with a robust optimization tool to provide useful insights beyondrnthe limitations of the theoretical results, this study takes an extra step beyond experimental data andrnsimulation studies that are carried out with synthetic models. The influence of each decision andrnuncertainty parameter important in reservoir management decisions is outlined with the optimizationrnresults under different scenarios on the performance of surfactant flood, thereby illustrating the phenomenonrnwith a real reservoir model that will shed light onto similar cases.