Summary
Objective
An assessment study is being finalized which considers the special challenges of subsea production. This assessment has identified several technical and operational gaps associated with subsea production and well systems. One of the most striking findings is the low ultimate recoveries anticipated from many subsea wells. The same long, multiphase flowlines that enable development of these resources act to reduce ultimate recoveries. This study proposes an examination of the factors affecting recovery in subsea wells. The study will also consider what role subsea processing and/or multiphase pumping can play in improve ultimate recoveries.
Subsea completed wells are a technology which enable development of both deepwater resources and marginal fields in normal water depths. Subsea technology allows oil and gas discoveries to be turned into “booked reserves.” However, wells developed without some form of subsea processing are expected to experience poor ultimate recoveries due to the high backpressures imposed on the subsea-completed well. For example, conventional production operations routinely drawdown wellhead pressures to 100-200 psig. A subsea completed well, however, may have abandonment wellhead pressures of 1,000-2,000 psig due to the backpressure added by the long multiphase flowline. In addition, these wells operate with a continual high backpressure. For gas wells, this has been shown to have a direct impact on production decline behavior, acting to reduce ultimate recovery. Maintaining a high backpressure can be viewed as a production practice that wastes reservoir energy. Energy that could be used to move reservoir fluids to the wellbore and out of the well is instead lost to flow through a choke or a long flowline. It is anticipated that some form of subsea processing of produced fluids will be necessary to improve efficiencies, allowing longer-term production from these wells and better recovery of this natural resource. Subsea processing can take several forms. These include a myriad of subsea separation and boosting scenarios. This project will compare and contrast subsea separation and pumping with seafloor multiphase pumping and wellbore based artificial lift. The project will also consider the use of new concepts such as floating support structures that can provide an effective alternative to long power cables and chemical treating and control umbilical.
The Petroleum Engineering Department at Texas A&M University is well positioned to perform the proposed study. The PI leads projects on both multiphase pumping and compact separation and processing. The Multiphase Team at Texas A&M has direct experience with operating the equipment proposed for subsea application. The Team operates a large-scale experimental facility that features both a full-size multiphase pump and a high-pressure compact separator. The team is also well trained in modeling the many various development strategies being commonly considering in industry and use of commercial multiphase simulator software.
Approach
This project will utilize classical reservoir engineering techniques combined with numerical multiphase simulation to investigate the factors influencing ultimate recovery. The project will develop new analytical techniques that tie together reservoir performance with backpressure. In addition the project will utilize state-of-the-art multiphase models such as PIPESIM and OLGA to predict multiphase flow behavior in various subsea development strategies. The project will involve direct meetings with oil & gas producers and engineering contractors to insure the most current subsea production systems are investigated. The project will involve several Texas A&M Undergraduate Students and a few select Graduate Students to perform this investigation. The goal is to provide decision makers with the information necessary to assess the conservation impact associated with various subsea production strategies; strategies that may or may not consider subsea processing or subsea multiphase pumping.
Deployment of Results
Following this work the MMS and industry will have a documented survey and a detailed assessment of the successes and failures of rig tie-down systems for Floating production Systems when subjected to environmental conditions such as those found near the path of hurricane Ivan. This information will be useful to the industry and the MMS in reviewing existing criteria and practices, and assessing if revisions are needed.
Deployment of Results
This project will provide decision makers and producers with vital information regarding the reserves impact of various subsea development strategies. This is expected to improve the long-term efficiency of subsea production systems by increasing awareness of the effects of various development strategies on ultimate recovery. Workshops and technical papers will be utilized to transfer the findings of this study to industry and raise overall awareness.
Related Publications
Martin, A.M. and S.L. Scott: “Modeling Reservoir/Tubing/Pump Interaction Identifies Best Candidates for Multiphase Pumping,” SPE paper 77500 presented at the SPE Annual Technical Meeting & Exhibition, San Antonio (Sept. 29 – Oct. 2, 2002).
Shippen, M.E. and S.L. Scott: “Multiphase Pumping as an Alternative to Conventional Separation, Pumping and Compression,” paper presented at the PSIG Conference, Portland (Oct. 2002).
Devegowda D. and S.L. Scott: “An Assessment of Subsea Well and Production Systems,” SPE paper 84045 accepted for presentation at the 2003 SPE Annual Technical Meeting & Exhibition, Denver, Colorado, Oct. 3-6.
