Improve Ultimate Reservoir Recovery from Deepwater Wells in the Gulf of Mexico Using an Emerging Subsea Processing System
Authors: Torbergsen E. , Khade S. , Reimers O. , Hanea D. , Hjelmeland M. , Scarsdale K. T. 
Published: April 2016

Abstract
The emerging subsea processing system described in this work, comprises several deepwater wells equipped with electric submersible pumps (ESPs) and one or more seabed booster pumps. This system provides efficient reservoir hydrocarbon recovery by maximizing pressure drawdown at the sandface. The in-well ESPs increase the pressure drawdown to improve production throughout the life of the reservoir, while the subsea booster pump lifts the combined production from all wells to reach the processing facilities at sea surface. This system integrates several production technologies to optimize performance, lower operating costs, and support reliable and safe operation.
The Lower Tertiary trend (LTT) in the Gulf of Mexico (GOM) poses a number of documented challenges for flowing reservoir fluid from the sandface to surface facility. The key challenges are operations due to low permeability, high pressures, high temperatures, and water and well depths. The primary objective of this work was to document the feasibility of the subsea processing system and quantify its production performance for a typical LTT field. The work included development of a full field system layout and simulations of production performance for a range of reservoir and system assumptions. In addition, operational issues such as system stability, power balancing, and basic control methods were considered, including the use of transient simulations, to ensure a reliable and efficient operation of the system. These form the basis of a unified pump control methodology. To verify the impact of in-well ESP reliability on field performance, a comprehensive availability model was developed using reliability data for individual system components; ESP reliability, ESP intervention time, and rig deployment time were varied to determine their impact on overall system availability. The results of the availability model were then combined with the steady-state production results to define production availability and calculate a range of internal rate of return (IRR) values for a typical LTT field development.
Utilization of the system showed enhancement in oil recovery in the range of 20 to 50% over use of a seabed boosting pump alone and substantial improvement in total liquid and oil gain as compared to natural lift. The system resulted in very satisfactory IRR and achieved production availability targets by using alternatively deployed ESPs. Moderate improvement in in-well ESP reliability combined with shorter rig mobilization time for intervention shows significant improvement in production availability. In total, the combination of seabed boosting pumps and in-well ESPs should be considered as a viable method of enhancing recovery from challenging deepwater subsea fields such as those of the LTT in GOM.
The unified pump control methodology is the key to safe and reliable operation of the system. The current work presents an approach on how to operate ESPs safely, by minimizing transient responses and shifting total operating load as much as possible to the seabed pumps, thereby reducing stress on the ESPs. Furthermore, the development of an enhanced production availability model of the system quantifies the production performance for a variety of field scenarios and subsystem behavior.