Abstract
In a Gulf of Mexico ultra-Deepwater field (with a water depth of 10,000 ft), high-boost single-phase centrifugal subsea pumps operation under gas conditions were used to optimize overall field production by lowering the pump suction pressure below the bubblepoint to safely operate the pumps under two-phase liquid and gas production. The subsea single-phase pump (SPP) system used in Stones Field comprises multistage centrifugal pumps for high-rate (30,000 B/D) and high-boost applications. In pump applications, multiphase flow can cause problems such as performance degradation, system inefficiency, and failures that must be considered to safely operate pumps under free gas flow.
Stones pressure/volume/temperature (PVT) fluids have a range of uncertainties, leading to bubblepoints from 900–1,200 psia. Subsea Single-phase pump has been in operation in Stones since 2019, with a minimum suction pressure operating limit of 1,200 psi. The primary objective in further decreasing the suction pressure to operate below the bubblepoint was to increase the overall production through a process that integrated risk assessment, pump performance and flowline dynamic modeling, topside considerations, operating procedures, and a management of change process to approve opportunity and move to execution.
Risk assessment and operator in-house pump expertise were key enablers to assess the feasibility of the opportunity and define the primary risks to the artificial lift system while operating below the bubblepoint. A risk/value tradeoff was performed to understand value over pump failure for the Stones overall production.
Following implementation, a detailed surveillance strategy was put in place to mitigate the primary risks associated with the pump operating with allowed free gas. Up to today a total net gain of approximately 10% is being increase in the overall Stone production operating subsea pump below bubble point at 875 psia suction pressure.
The primary technical contributions of this work are the detailed technical approach and the use of analysis and data with field operation to predict pump performance and safely operate the pumps in two-phase flow in the SPP.
