A field in western offshore India proved to be a major hydrocarbon-bearing structure, but wells in the field gradually declined in reservoir pressure and production when they were self-flowing. To improve recovery, water injection was performed, which almost doubled the field production. However, water cut eventually increased drastically, thereby reducing oil production. To curtail increasing water cut and improve oil recovery, a tertiary recovery method was sought.

After closely studying various recovery methods, simultaneous water and gas (SWAG) injection was proposed in which a predefined mixture of produced gas and water was injected to improve oil sweep and reduce residual oil saturation by oil swelling, ultimately increasing oil recovery. However, to practically observe field suitability and feasibility of the SWAG method, a pilot project that included four injectors and one producer was launched.

Efficiency of SWAG injection increases as a result of the consistent gas and water fine bubble flow regime developed in the wellbore, depending on casing size, tubing-shoe distance from perforation, and deviation. To evaluate this efficiency, production logging with optical probes to detect gas holdup was proposed in three injectors with different casing sizes and deviations. The existing wellbore flow regime from results of production logging were observed and compared with respect to favorable flow behavior to understand the effect of these factors on SWAG injection effectiveness. We found and suggested the deviation and casing-size configuration that was deemed optimal.

This was the first time production logging was used in India to evaluate the SWAG injection wellbore flow regime, and the method proved effective. The results are to be used for full-field SWAG injection implementation to improve overall field recovery.

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