In BSP layered reservoirs where thin oil rims are overlain by gas caps, oil production can be severely hampered by high gas/oil ratios. The negative consequences include reduced oil rates and oil recovery, early shut-in of production wells, environmental pollution resulting from excessive amounts of flared gas, loss of energy drive, downstream processing constraints and problems.

Oil production can be improved by means of a gas-blocking foam barrier in the near wellbore area.

The Gas Shut-Off (GSO) foam treatments can be applied through tubing by means of bull-heading and are therefore especially suitable where selective placement using straddle packers is not possible. A wet foam is injected non-selectively in oil as well as gas bearing sand layers. However, the wet foam will only develop into a barrier of dry foam as a result of the high shear from free gas in the gassed out layer(s). This effect allows wet foam placed in the oil layers to be back produced relatively quickly.

Key success factors for application of foam barriers are the optimum control of placement of the barrier-forming material and selection of the foams with the maximum gas-blocking ability. Selecting suitable foamer systems can only be done by means of laboratory flow tests at the prevailing reservoir conditions due to the interaction of the foam forming surfactant with its interfacial environment.

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