VASPS Prototype in Marimba Field - Workover and Restart

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 95039, "VASPS Prototype in Marimba Field - Workover and Restart," by G.A. Peixoto, G.A.S. Ribeiro, P.R.A. Barros, and M.A. Meira, Petrobras, and T.M. Barbosa, UENF/LENEP, prepared for the 2005 SPE Latin American and Caribbean Petroleum Engineering Conference, Rio de Janeiro, 20-23 June. The vertical annular separation and pumping system (VASPS) represents an innovative concept for subsea gas/oil separation and pumping. A prototype was installed in 2001 in the Marimba field in the Campos basin. The full-length paper presents the second operational phase of the prototype after a successful rig intervention to change a damaged electrical submersible pump (ESP). Introduction The VASPS is a gas/liquid-separation system associated with an ESP. After the gas/liquid mixture is separated by passing through a helical channel, the liquid phase is pumped by the ESP, and the gas is vented to the platform. This subsea phase separation reduces the bottomhole pressure required for a given production rate, thus increasing production from an individual well. A joint-industry project (JIP) involving AGIP, ExxonMobil, and Petrobras developed the VASPS prototype installed inside dummy Well MA-23 to separate the production from Well MA-01 and produce to the semisubmersible platform P-08. The VASPS prototype operated as expected from July until December 2001, when a failure occurred in the ESP system. Because the failure was related to the control system and not to any of the technology challenges of the project, the JIP partners decided that the technology was successful and ended prototype testing. After this, Petrobras assumed the technical and financial responsibilities to return the system to operation. Between the failure in December 2001 and the beginning of 2004, Well MA-01 continued production to P-08 by bypassing the VASPS unit. In January 2004, a rig intervention replaced the ESP. The VASPS prototype resumed operation in May 2004. Several changes were made in the control system to improve reliability. The full-length paper details the workover process, improvements to the control and supervisory system, and system performance after the intervention. VASPS Components Fig. 1 shows the main components of the VASPS. The supervisory and control system comprises a hydraulic-power unit, a subsea control module (SCM), a master control system, a subsea choke, and two level sensors. The electrical system includes the ESP connected to the liquid-discharge tube, downhole sensor, power cable, wet-mateable connectors, and variable-speed drive (VSD) on the P-08. Initial Operation Phase In July 2001, Well MA-01 was producing 750 m3/d of fluid with 100 000 m3/d of gas from gas lift. Wellhead pressure was 36 kg/cm2. After VASPS installation, the subsea phase separation allowed the wellhead pressure to be reduced to 11 kg/cm2. This resulted in a production increase of 1000 m3/d without gas lift. After 5 months operation, the VASPS prototype failed because the ESP control and production systems did not act as expected after a process-plant incident.