Unlocking Well Start-Up Uncertainties with Transient Well Flow Modeling

Abstract The Absheron field is located offshore Azerbaijan in the Caspian Sea about 100km south-east of Baku and 25km north-east of Shah Deniz field, with a water depth of approximately 500m. After a successful exploration well in 2011 and several development studies, production started in July 2023 through an Early Production Scheme (EPS). This EPS consists of a single subsea well, drilled in 2019, and a 35 km insulated production line going to the existing Oil Rocks facilities. To anticipate the start-up behavior of the Absheron well, Transient Well Flow Modeling simulations integrating the well and the flowline were performed. As such simulations include hydrodynamics (conservation laws for mass, momentum and energy), thermodynamics (fluid description) and thermal exchanges with surroundings (architecture, annulus fluid, rocks…), they enabled the evolution of rates, pressures and temperatures to be predicted for the well ramp-up, in particular to establish the hydrates management procedure. Sensitivities were performed to account for uncertainty on well productivity (from the initial testing and logging data), the wellbore content, chemical injection rates and network pressure. This paper describes the successful work achieved for unlocking challenging uncertainties of Absheron offshore high-pressure gas condensate well start-up. The various sensitivities performed allowed to properly anticipate well behavior. The simulation of several well start-up sequences based on in-house experience, as well as discussions with local offshore teams in charge of operations, helped in establishing operating guidelines grounded on shared understanding and highlighted the main risks linked to the start-up phases. This therefore facilitated the confirmation of the well ramp-up strategy including the expected pressure evolution both at wellhead and at reservoir wellbore interface, as no rate monitoring was available subsea. This ensured well integrity and effective well production. The criticality of hydrates prevention for this high-pressure gas system was handled by optimizing hydrate inhibitor injection rates and flowline pressure. The work performed for this well highlights the benefits of integrated and transverse work and modeling through the integration of both well and flowline to establish optimal and flexible start-up guidelines.