Impact of Flow Assurance in the Development of a Deepwater Prospect

Abstract

Abstract In deepwater production systems, extreme pressure and temperature conditions, multipart sub-sea networks, complex reservoir characteristics, and various fluid phases flowing from the reservoir rock to the surface could promote production interruption due to the formation and deposition of hydrocarbon solids such as asphaltene, wax and hydrates anywhere in the production system. These are flow assurance key risk factors that create significant impact on field development planning, especially, when dealing with marginal deposits having varying fluid characteristics. To reduce the risk, we have adopted a systematic approach to evaluate the potential impact of asphaltene and wax precipitation and deposition. In this field case, two distinct layers of hydrocarbon deposits are considered marginal from reserves point of view; the upper deposit is a gas condensate layer and the lower is a black oil layer. Because of marginal reserves, mono-bore commingle production was thought to be an option. Also, in-situ gas lifting is considered to be a favorable option. Commingling of live crude oil with a gas stream may lead to precipitation of asphaltenes resulting from changes in composition. Changes in pressure and temperature can also take the system across the boundaries of asphaltene and wax. Being able to predict the formation of solid deposits along the whole production system from downhole to production facilities becomes progressively more important as water depths increase. This paper describes the impact of flow assurance considerations in a deepwater Gulf of Mexico development project. This study is based on experimental measurements of asphaltene and wax precipitation of a hydrocarbon fluid when contacted with gas condensate from another zone. The evaluation is performed using multiphase thermal-hydraulic behavior in an Integrated Production Model (IPM) that provides system deliverability predictions through the lifetime of the project coupled with asphaltene and wax thermodynamic models. The Perturbed Chain - Statistical Associating Fluid Theory (PC-SAFT) equation-of-state (EOS) model1,2 is the thermodynamic tool used to predict asphaltene precipitation. Wax deposition is predicted using a solid solution model. The results of experimental and theoretical flow assurance assessment indicated that the black oil has the propensity for asphaltene precipitation caused by pressure depletion during primary production. Simulation results revealed that the downhole commingling with gas condensate is expected to significantly intensify the asphaltene precipitation condition. Results also indicate that wax precipitation will not be an issue during the life of the project.