Abstract
An asphaltene threat has been identified in production wells located in a Gulf of Mexico (GOM) deepwater field. After production started from different reservoirs and the operating conditions for some of the wells reached the asphaltene precipitation onset, solid deposits were detected at different points in the production system, which caused production deferrals, disturbed the operating strategy of the field, and increased the operational expenditure. To remediate asphaltene deposition in deepwater subsea wells, a rig-less remediation costs up to $0.12 million (MM); a well intervention that requires a rig costs approximately $20 MM, and a vessel-based pumping remediation costs about $5 MM. These costs do not include the impact of production deferrals.
A plan was developed to acquire and interpret the required information to properly understand and manage the asphaltene threat. The methodology includes:
Acquisition of suitable downhole reservoir fluid samples for asphaltene and wax studies
Characterization of the reservoir fluids in the laboratory using the latest asphaltene and wax technologies.
Observation of the effect of chemicals on solids builds up during field trials
Surveillance of damage near wellbore using Pressure Transient Analysis (PTA) and Multi-Rate Test (MRT)
Real time monitoring of normalized nodal analysis based on frictional pressure losses.
During the characterization of the reservoir fluids, asphaltenes were identified as key risk factor for successful field development. The laboratory tests showed the propensity for solids formation and confirmed that the variety of reservoir fluids had an asphaltene deposition envelope that extended from the reservoir rock to the topsides facilities. Solids collected from pigging returns, surface equipment, and failed downhole equipment confirmed the reservoir fluid's asphaltene deposition tendency. In some cases, field trials showed that increasing the concentration of asphaltene inhibitor injection resulted in increased build-up of organic deposits. PTA and MRT enable the identification of flow restrictions from the reservoir to the permanent downhole gauge location and real-time monitoring of normalized nodal analysis help to identify where the impediment to flow is located in the production system.
This paper presents an integrated approach to evaluate the key elements of asphaltene risk for deepwater projects, the strategy to manage the issues during production implementation, and lay out the aspects to be considered in the mitigation of the negative impact of asphaltene thread in the field development plan.
