Abstract

The potential of improving surfactant-polymer flooding by using horizontalwells has been systematically investigated with a compositional chemicalflooding simulator that can model both three-dimensional heterogeneousreservoirs and realistic process behavior. This is the first time that theperformance of surfactant-polymer flooding using horizontal ells has beenreported. The potential for horizontal wells to accelerate the oil productionand thus improve the discounted cash flow may seem obvious, but the preciseimprovement depends on many complex factors such as vertical permeability andhorizontal well location and can only be estimated using realistic simulations.We model all of the process chemistry and phase behavior needed to describesurfactant flooding realistically including the effects of polymer.

The reservoir description played a central role in this study. We generatedstochastic reservoir descriptions and made multiple realizations of these tosee the impact of the spatial distribution of the heterogeneity onsurfactant-polymer flooding with both vertical and horizontal wells. This isthe first time that the performance of surfactant flooding using eostatisticalreservoir descriptions has been reported. The location of the horizontal wellis very important with respect o both the sweep efficiency and the injectivityand must be in a good location to produce the desired results. The verticalpermeability must be moderate to high for horizontal wells to give goodresults, although rising vertical drainholes off he horizontal injector canpotentially give good results even for low vertical permeability. Other factorsinvestigated include the effect of permeability-dependent residual oilsaturation which many other investigators had speculated to be an importantparameter in surfactant-polymer flooding. Under some circumstances, the use ofhorizontal surfactant injectors with vertical producers does appear to haveeconomic merit, but these circumstances are clear only after a careful studywith realistic reservoir and process descriptions.

Introduction

Due to the effectiveness of surfactant as an oil recovery agent, manysurfactant-polymer field tests have been conducted over the past three decades.One of the key findings of these tests is that effective and timely oilrecovery from surfactant-polymer field tests correlates well with maintaininggood mobility control of both the surfactant slug and the polymer buffer.Despite the successes emonstrated by some field tests that had good mobilitycontrol, surfactant-polymer flooding is still not considered a commercialprocess because of low and uncertain oil prices, high surfactant costs, concerns about performance and costs nd the relatively long time it takes torecover the targeted oil, which hurts the economics due to the high time valueof money. One of the reasons for long project life that often reventsurfactant-polymer flooding from being economic is the decreased injectivitycaused by the polymer. This problem is more acute in shallow, low permeabilityoil reservoirs.1,2

Since polymer has been found to be essential for technically successfulsurfactant floods, decreasing or removing the polymer is not the appropriatesolution to this problem. Horizontal injectors IS one possible remedy to thisproblem and the focus of this paper.

During the last decade, important technological advances ave made it possibleto drill and complete horizontal wells economically.3

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