In Subsea production systems (SPS), choke valves can be considered to be the heart of the system and are typically set up to control the hydrocarbon production flow and injection of gas and water during both steady-state production and transient flow scenarios. The control functionality of subsea choke valves comprises several aspects: balance of the subsea manifold pressure (when fed from multiple wells with different reservoir pressures), reduction of the flowline pressures (and cost), mitigation for reservoir collapse during startup, adjustment of the flowrates to extend production life and support the functionality of the subsea gate valves to avoid high-pressure drops during startup and shutdown.
Safe and reliable operation as well as the controllability performance of the subsea choke valve depend on the effectiveness of the sizing and selection process as well as on the positioning of the choke in the SPS when designing the SPS. The optimum location of the choke valve in the SPS and the arrangement of the piping system upstream and downstream of the choke, including any intrusive probes, are crucial and can impact the operation of the choke valve itself and affect the SPS integrity. The optimized location must consider the production profiles and operation philosophy of the wells, as well as the associated flow assurance issues. Sand particle production and erosion risks, flow induced vibration, hydrates and other deposit hazards are major flow assurance challenges that can affect the choke valve performance and in turn these effects can be amplified by the choke valve and impact the SPS integrity. This mutuality should be considered when designing the SPS and positioning the choke valve in it.
This paper summarizes GE Oil & Gas experience in sizing and selection of the subsea choke and its placement in the SPS. The focus is on the integration of a subsea choke valve in the SPS to achieve safe and reliable operation and extend the life of the valve and SPS. In general, the paper provides an overview of flow assurance aspects related to sand production and erosion that should be considered when designing the SPS and optimal positioning of the choke valve. It describes methods to examine erosion issues associated with the subsea choke valve by the means of Computational Fluid Dynamics (CFD) simulations. Numerical experiments were performed on various choke and SPS arrangements to explore these issues and provide best practices.
The results show that details of the fluid composition and operating conditions strongly affect the fluid/particle flow patterns in and around the choke and trim, suggesting the necessity for erosion analysis to ensure safe and reliable operation and emphasize the benefit from using CFD tools for system optimization.