Guidelines for Converting Steamflood to Waterflood
- K.C. Hong (Chevron Oil Field Research Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1987
- Document Type
- Journal Paper
- 67 - 76
- 1987. Society of Petroleum Engineers
- 4.2 Pipelines, Flowlines and Risers, 6.5.2 Water use, produced water discharge and disposal, 2.4.3 Sand/Solids Control, 4.1.9 Tanks and storage systems, 5.5.8 History Matching, 5.2.1 Phase Behavior and PVT Measurements, 5.4.6 Thermal Methods, 4.1.5 Processing Equipment, 5.2 Reservoir Fluid Dynamics, 5.4.1 Waterflooding, 5.1.1 Exploration, Development, Structural Geology, 4.1.2 Separation and Treating, 4.3.4 Scale
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This paper presents a set of guidelines that field engineers can use for the optimum conversion of maturing steamflood projects to waterfloods. The guidelines were developed from a simulation study of Chevron's oldest steamflood-followed-by-waterflood project, the Kern River 10-Pattern project in California. They have been validated against different reservoirs and operating conditions. The simulation study showed that by judicious conversion of a steamflood to a waterflood as the steamflood matures, the cumulative net salable oil (cumulative oil produced minus oil used as steam generator fuel) can be maximized. The optimum time of conversion has been characterized in terms of eight performance variables that can be monitored in the field. A field engineer can use these characteristics or guidelines to estimate the optimum time of conversion and use this result to maximize the net salable oil production from his project. project. The procedures used for developing the guidelines from the Kern River 10-Pattern project performance and for validating them against different reservoirs and operating conditions are presented. The recommended procedure for applying these guidelines to other fields is also discussed. procedure for applying these guidelines to other fields is also discussed. Introduction
Steam injection is the principal EOR method in use today, accounting for 78% of all oil produced in the world by EOR methods. Steam methods (cyclic steam and continuous steamdrive) have been used widely since the early 1960's to recover heavy oils in California the Kern River 10-Pattern project was one of the earliest applications of the continuous steamdrive process. The project started in 1968 and was converted to a waterflood in project started in 1968 and was converted to a waterflood in 1975. The poststeam waterflood is still continuing with an oil production rate averaging a highly economical 120 B/D [19.1 M /d] per pattern. As a steamflood matures, oil production rate decreases and the steam/oil ratio (SOR) eventually becomes uneconomical. It then becomes necessary to decide whether to continue steam injection. The high SOR generally signals that (1 ) a large amount of heat is retained in the rock and fluids in the reservoir near and away from the injection well and (2) some heat is being, cycled through the reservoir without affecting oil recovery. If steam injection is continued until the project is terminated. the heat contained in the rock and fluids would be left behind and wasted. Hence, a method must be found to use this heat for optimum operation of a steamflood project. Gas flood or waterflood could be used to scavenge this heat: however, waterflood is a better choice because water is less expensive and has a higher heat capacity than a gas. Converting from steamflood to waterflood serves the following purposes.
1. It reduces fuel consumption and frees steam generators for use in project expansion.
2. It resaturates the steam zone with liquid water to reduce subsidence and possible reverse migration of oil to the steamflooded areas after cooling.
3. It recovers oil near the bottom of the reservoir that has not been heated because steam traveled preferentially across the top of the reservoir. Injected water becomes preferentially across the top of the reservoir. Injected water becomes heated as it passes through the heated zone and moves downward because of gravity, thereby delivering heat to the unaffected zone. During the latter part of a steamflood, the produced water becomes hot. This water is a valuable source of heat; properly treated, it can be reinjected into the reservoir and possibly used to generate steam, thus reducing fuel consumption further. Determining the best time to convert a steamflood to a waterflood has been a problem for many operators. If a steamflood is converted to a waterflood too early in a flood life, the reservoir is not sufficiently heated to produce the maximum recoverable oil under produce the maximum recoverable oil under steamflooding conditions. If the conversion is made too late, a large amount of heat will be left behind and wasted. There must be a time of conversion that produces an economical optimum for a specific situation under consideration. The objective of this study is to find this optimum time of conversion for a specific project and to extend the application of this information to other steamflood projects. This paper discusses the approach used for finding the optimum time of conversion and the method for characterizing this optimum in terms of field performance and operating parameters. The guidelines for determining the optimum time of conversion for other projects are presented and discussed. presented and discussed.
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