A commercial reservoir simulator capable of simulating operational changes in a steam flood was used to investigate the effect of steam slug size, water injection temperature, water injection rate and pattern lifting capacity in converting from steam to water injection. Inverted seven-spot and five-spot patterns were used for heavy oils and light oils reservoirs, respectively. The optimum steam slug size which is dependent on the injection, production and reservoir parameters was determined for both the heavy and light oil reservoir cases based on economic studies for realizing the maximum revenue on a project.
Steam flooding is a proven, highly successful recovery process for heavy and light oil reservoirs. Oil recoveries in excess of 50% can be expected from reservoirs undergoing steam flooding.
Since the technique of putting energy in the form of heat back into a reservoir to recover additional oil is costly, an economic limit will exist beyond which the additional gain realized from continued steam injection will not be cost effective. Current industry practice in steam flooding projects is to convert to water injection at some point during the project projects is to convert to water injection at some point during the project life. Reasons for this conversion include:
The injected water will fill the void space created by steam and prevent subsidence and oil migration into the flooded area afterabandonment.
The injected water can be used to recover residual heat from the reservoir for use in other areas of the project.
The conversion to water injection will conserve fuel and free steamgenerators for use in project expansion.
The conversion lowers the cumulative steam-oil ratio and improves the overall economics of the steam flood project.
Figures 1 and 2 show the effect that conversion has on a pattern's overall performance. Recovery and cash flaw are plotted, respectively, for a case performance. Recovery and cash flaw are plotted, respectively, for a case involving continuous steam injection compared to that for a 1.0 pore volume steam slug injection followed by water injection. In Figure 1, net recovery is defined as the cumulative oil produced less the cumulative oil required as fuel to generate the necessary steam.
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