Demonstrating the Value of Transient Well Flow Modeling in Achieving Successful Well Start-Up

Abstract The Absheron field, situated offshore Azerbaijan in the Caspian Sea, lies approximately 100 kilometers south-east of Baku and 25 kilometers north-east of the Shah Deniz field, with a water depth of around 500 meters. An Early Production system was started in 2023, consisting of a single high-pressure, gas-condensate well, drilled and completed in 2019, and a 35-kilometer insulated production line connecting to the existing facilities at Oil Rocks. This paper illustrates how transient well and flowline simulations helped with a smooth start-up, and how a batch of sensitivity cases could cover the risks and allowed to design proper operating procedures for start-up. Due to the unique development configuration leading to a substantial buffer effect in the flowline, the very high reservoir pressure and significant uncertainties in productivity hypotheses (due to the well having been suspended for 4 years) and initial well content, well start-up was facing quite a variety of challenges, most notably, the potential for very low temperatures across chokes, leading to hydrate risks and temperatures below equipment ratings. A commercially available software for Transient Flow Modeling was used to model different start-up scenarios for the entire well and pipeline system, allowing start-up procedures to be developed in conjunction with the offshore teams who provided practical insights, and including hydrate inhibitor injection. Furthermore, the modeling allowed for better follow-up during the ramp up and adjustments to the procedures as data became available. In the context of the Absheron offshore high-pressure gas condensate well, this paper outlines how it was started smoothly and flowed successfully, reaching the desired target rate. Remarkably, the actual performance and behavior of the full system mirrored closely the predictions from simulations thanks to the various sensitivities performed. While minor discrepancies were found, they were subsequently clarified. Findings from simulations played a major role in fine-tuning initial flowline conditions as well as optimizing the injection rates of hydrate inhibitor. This global and transverse approach not only allowed better knowledge of well behavior, but also granted good anticipation and monitoring of fluid arrival at topsides facilities. Our integrated approach, combining well and flowline considerations, yielded an optimal well start-up. Managing uncertainties was deftly executed. The successful start-up of the Absheron well stands as a testimony to transverse preparation, operational experience, and shared understanding.