The Shannon Reservoir at the Naval Petroleum Reserve No. 3, Natrona County, Wyoming, has some six years of Thermal Steam EOR history and has been expanded to six patterns with four 50 MMBTU/hr natural gas fired steam generators in operation.

During Pilot Steam Flood operations, scale formation at producing wellbores and tubulars became excessive. One pulling unit was employed full-time to mechanically cleanout tubulars and replace scaled pumps in 21 original Pilot producers. Acid Cleanouts and scale inhibitor squeeze jobs were expensive and short lived.

Due to planned fieldwide expansion of the Steamflood Pilot, the magnitude of costs associated with production side scale treatment would adversely impact project economics. A means to inhibit scale formation insitu from the injection to production wellbore was investigated.

Based on scale inhibitor application in steam generator tubulars in California, a successful chemical formulation was known to be available. Research determined that the product could be injected with the softened generator feed water and remain in the liquid phase of the injected steam. Sufficient residual was expected to be seen at the producing wellbore to prevent scale formation. A new analytical method had recently been developed to allow measurement of the chemical residual in the produced water. The chemical formulation had not been used in this type of application prior to use at NPR-3.

This paper details the successful application of scale inhibitor injected in the steam generator feed water, transported through the reservoir in sufficient concentration to inhibit scale and to provide measurable residual for confirmation. The economic feasibility is shown to be dramatic with long term reduction in pulling costs, elimination of ineffective acid cleanouts and scale squeezes, and minimal chemical cost to maintain residual at producing wellbores.

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