Subsea Multiphase Pumping

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 88562, "Subsea Multiphase Boosting - Maturing Technology Applied for Santos Ltd.'s Mutineer and Exeter Field," by H.J. Grimstad, SPE, Framo Engineering A/S, prepared for the 2004 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 18-20 October. The full-length paper presents the state of the art in subsea multiphase pumping, including the subsea pump, power and control systems, umbilical, and intervention tool. Benefits to the users are related to reduced investments and increased oil production. Multiphase pumps may be used in combination with gas lift or downhole pumps to provide integrated systems with premium reliability and economics. Introduction Systems for subsea pumping of unprocessed well flow were first developed 20 years ago. The initial motivation was to enable economical production rates from new, often marginal subsea fields tied back to existing production facilities. The first subsea multiphase pump was installed in the Shell-operated Draugen field in 1993. This pump successfully boosted the production from the satellite Rogn South, which was approximately 5.6 miles from the main platform. The additional 5,000 BOPD produced with the subsea pump proved the feasibility and the advantages related to this technology and indicated the robustness and high reliability that has since been reconfirmed by other installations. An increasing number of operators either have installed subsea multiphase pumps or are considering this technology seriously. The most recent project to select seabed-installed multiphase pumps are the Santos-operated Mutineer and Exeter fields. First oil from these fields is expected in mid-2005. System Description The majority of subsea multiphase pumps are electrically driven units with power and control functions supplied through a dedicated umbilical. The pumps may be integrated with existing infrastructure such as the Christmas tree or manifold. However, the most common solution is to install completely self-contained pump modules on the seabed with associated piping and valves to allow remote operation of one or two pumps from the host platform. Main system components are subsea pump module, combined power and control umbilical, power and control system, and intervention tool. Subsea Pump Module. The subsea pump module contains the multiphase pump and motor cartridge, process piping, and isolation valves as well as the control pod for valve operation. For long tieback distances, there also will be a step-down transformer included in the subsea pump module. Typically, the module will be supported on mud mats or a single pile. Fig. 1 shows installation of a typical subsea pump module for a dual-pump installation. The pump station is designed with reliability comparable to subsea trees and manifold modules. The process piping normally will allow connection to one or two flowlines upstream and downstream of the multiphase pump. There also will be a bypass line to enable pigging as well as natural production with the pump out of operation. There are isolation valves upstream and downstream of the pump for maintenance purposes. The valves may be remotely operated.