Hydrates and waxes are the main flow assurance threats in the development of deepwater fields. Prevention of wax deposition is a key component of preferred subsea deepwater system design. This paper discusses the challenges associated during the design of a deepwater field in the Indian offshore and the means of mitigation during the entire operating envelop.
The deepwater discoveries for development lie in 400 – 800 mts of water depth, spread over 25 km with a recoverable volume of around 30 MMt of O+OE of gas and are envisaged to be tied back to a centrally located FPSO for handling and further evacuation. The fluid properties are very severe with high WAT and pour point. Limited case histories exist for deepwater fields developed with similar fluid properties. Low ambient temperature and poor fluid properties aggravate the likelihood of wax deposition and hydrate formtation. Based on the fluid characterization data for the development, issues due to wax deposition are expected. The present means of preventing flow assurance issues is through use of passive insulation, active heating or by chemically altering the thermodynamic behaviour.
Various means were analysed either alone or in combination to arrive at an effective wax management strategy to surmount the deepwater barrier and to convert resources into production. The use of dual pipe-in-pipe system with high performing insulating material, combined with cluster based development aid in fluids arriving at temperatures above WAT over major part of the profile period. During the transient conditions wax management is envisaged through flooding of the well jumpers with chemicals and displacement of flowline contents, after the no touch time. Since the fields are to be developed on a fast track basis, limited data poses challenges in design. This paper highlights the flow assurance challenges that were studied to develop suitable wax and hydrate management during operational phase while maintaining the flexibility to accommodate modifications after actual fluid property data is available.
The wax and hydrate management strategy proposed in this paper would facilitate in addressing a unique challenge of handling high WAT and pour point crudes with limited fluid data specifically in deepwater environment.