Single Point Gas Lift (SPGL) is preferred in subsea wells due to its certain advantages over conventional completion with unloading valves in meeting the aim for no intervention, pressure barrier requirements etc. Current paper presents a flow assurance study of an SPGL system in a deepwater field in India. The development strategy envisages clustered subsea wells with common flowlines connected to an FPSO about 12 km away.
Requirement of gas lift is envisaged from mid-life due to expected depletion in reservoir pressures and increase in water cut. Subsea gas lift in deepwater environment typically requires higher injection pressure to lift from desired injection depth. The gas lift, flowline and riser system is expected to operate over a wide range of conditions in terms of fluid composition, pressure and flow rates. Optimum design and operation of an SPGL system under such conditions is a challenge. Integrated dynamic modelling from down hole to host facility at the pre-FEED stage can provide valuable inputs for system design and operability.
The impact of various gas lift parameters like orifice size, setting depth, kick off pressure and operating injection pressure on the system has been studied. The field is having waxy crude with high pour point of 36°C with gelation propensity during long shut downs. The paper also brings out the operability windows during start up, turndown, shutdown, restart etc. and their impact on topside design. Transient modelling has been used to invetigate threats to system integrity due to high velocities of fluid through orifice, low temperature limits due to JT cooling, pressure surges into the production line resulting in large slugs arriving at FPSO. Slugging in riser may lead to process shut downs due to the pressure and rate variations resulting in loss of production. Design and optimization of the SPGL system is also aimed at increasing total production by avoiding process shut downs due to well instability and pipeline slugging.