Case History: First Diverless Subsea Slickline Well Intervention Perfornied in Offshore Vietnam
Authors: Larimore David , Ravlich Mike , Headworth Colin , Ming Yeou Lei 
Published: October 2008

Subsea completions have been on the rise in recent years due to the economics, extreme environments, and migration to water in depths in excess of 1300-feet. In this paper, subsea slickline operations are performed on three cluster wells situated beneath the operator's semi-submersible floating production unit in Vietnam's offshore Dai Hung field. The services were needed for reservoir management, including installation and retrieval of memory gauges, performance of logging surveys, and to manipulate sliding sleeves that had been installed with the ultimate purpose of optimizing hydrocarbon recovery. A subsea wireline unit was chosen to provide the services because of its cost efficiency and capability to perform a fishing job without impacting platform space and weight restrictions on the floating production unit as would have been imposed by use of a drilling riser. This paper will provide the case history of these services, which were unique in that these were the first diverless subsea wireline jobs performed solely with ROV support for manipulation or assistance. The case history will present in-depth information on the developmental methodology used for the program, the team that was made up of operating company and service contractor personnel, special ROV personnel, and safety personnel who developed the "best practice" operational procedures and in-depth procedure manuals and checklists. Information will also be presented on the toolstrings used, the problems encountered and their solutions. The operations were completed successfully in 42 days with no incidents. As a result of the success of this operation, further subsea slickline services are being planned to provide similar services. Slickline provided an effective solution for the operator's service requirement within the specified criteria. Because of the versatility of newly developed advanced systems, slickline equipment was able to meet the restrictions of weight and size on platforms to provide a more efficient alternative for services normally requiring rig mobilization.

Introduction

Traditional methods for subsea well intervention with slickline have involved a drilling rig and hard riser. In the case history presented in this paper, a more flexible approach to slickline intervention that eliminates the need for a hard riser was used.1 The operator wished to install and retrieve memory gauges, conduct memory-production logging (MPLT) surveys, and manipulate sliding sleeves. The location of job was the Dai Hung Field, Offshore Vietnam, 270 km Southeast of Vung Tau in water depths of approximately 110 m. One well was vertical with the other two being deviated up to 55 degrees. All had been completed as single-string, multi-zone selective completions, utilizing 4-112-in tubing for the upper completion and 3- 1/2-in tubing through the production interval. A team composed of specialists in all phases of the proposed operation was to review the job needs, choose the method of intervention, plan the programs, and oversee their execution. Job solutions had to address the problems of minimal platform space and weight restrictions on the floating production unit as well as the inaccessibility of the wells. Cost efficiency was also important. After reviewing the possible service options, the team decided to use a specially designed subsea wireline service system because of its flexibility and the need to perform a diverless operation.