Interventions in High Cross-Flow / Auto Gas Lift Well in Chirag Field, Caspian Region

Abstract

This paper presents the intervention activities performed under high crossflow conditions in Chirag Auto Gas Lift (In-situ GL/Natural GL) completion design where crossflow between the reservoir zones posed a major challenge. Auto Gas Lift design was installed on a few selected wells of the Chirag field due to a lack of conventional gas-lift equipment, compressors, and pipelines. When Auto gas lift wells are shut in, crossflow occurs between the high-pressure gas-bearing zone used to lift the oil and the lower- pressured oil-bearing reservoir zone. The amount of crossflow is controlled by installing a choke (gas lift valve) across the gas bearing zone. On well A completed in August 2020, an oversize Gas Lift Valve was installed which created suboptimal flowing conditions, production deferrals and severe crossflow during shut-in. An intervention activity was carried out to replace the oversized valve in this severe crossflow condition. Installation of a plug was necessary to stop the cross-flow during the valve change-out operation but proved to be very challenging because the force from the crossflow - a rushing mixture of gas/sand - would be pushing against the cross-sectional area of any tool that is to be RIH. This paper describes the multiple options that can be worked out via modelling to define the optimal approach for successful intervention operations in high crossflow environments. The rate of cross-flow in the well can limit well intervention options. Due to piston force created by cross- flow, conventional methods of reservoir isolation are not always feasible, hence deployment method needs to be thoroughly analyzed during job planning. Several ways of reservoir isolation methods – utilizing slickline or e-line methodology have been cross-checked through rigorous modelling and collaboration with the contractors. This modelling revealed that well A crossflow conditions exceeded the safe operating limits of the Slickline wire and would introduce significant damages to the e-line wire due to the build-up piston force on the plug as it expands. After a few iterations, the optimized solution was identified as having an anchor that would be set before the plug and allow the passage of the gas flow through it. This intervention activity was carried out successfully on Well A as a result of the mutual efforts of all partners. The article also discusses the option of killing the well as a last resort to proceed with a required intervention job.