Overcoming the Challenges of Completion and Installation Operations Associated with the Gemini System from the Ocean Star
Authors: Cromb John , Summers Alan , Jefferies Andy 
Published: October 2008

The paper reviews the planning and execution of the Gemini completion activities and the subsea system installation from the Ocean Star semi submersible drilling rig. The completion philosophy and design, including wellbore preparation, perforating, gravel packing, completion string design, and well flow and clean up, are discussed. The installation operations include the manifold, trees, 12" jumpers, and 4" jumpers.

This paper describes the rig and equipment modifications implemented to provide clear access for the 4-slot manifold and trees, maximize the benefits of simultaneous operation, and optimize the completion installation. The modifications, combined with jointly developed procedures, enhanced the overall safety on the jumper installations simultaneous with drilling/completion operations.

The paper provides details of the installation of the subsea trees and the completions. This includes the deployment of the multiplexed Electro/Hydraulic Installation/Work Over Control System (E/H IWOCS) and the inaugural running of the Enhanced Direct Hydraulic (E-D-H) Schlumberger SenTree 7 subsea test tree.

The paper includes an overview of the operation scheduling issues including the identification of primary and secondary simultaneous operation windows.

Introduction

In September 1999, Texaco Gulf Of Mexico (GOM) Deepwater Drilling team successfully completed their operations on the Gemini Subsea Development with zero Lost Time Incident Rate (LTA), and 2.60 Total Recordable Incident Rate. The project consisted of installing a production manifold, drilling two wells, sidetracking one well, and completing three wells in the Mississippi Canyon Block 292 (Gemini Field) with Diamond Offshore's Ocean Star semisubmersible rig in approximately 3400 feet of water. The operation was carried out between January 1999 and September 1999. One of the development wells (Well No. 1) was previously drilled and tested, then temporarily abandoned with a packer plug in 1996.

The project's excellent safety performance is largely attributed to Texaco's safety awareness program on the rig, and the job safety analysis (JSA) conducted before all phases of the operations. The drilling team adopted the philosophy of batch operation when ever possible. The batch operation would offer efficiency gains, cost reduction, and better focus the personnel on critical activities. Lessons learned from each phase of the project were documented, communicated and applied on a continuous basis during the project which resulted in improvements in the offshore performance as the project progressed. This improvement in performance is reflected in Fig. 1.

The original offshore operations sequence is shown in Fig. 2. Due to changes in the rig availability and the flowline installation operation, the sequence was modified to coordinate the rig operations with the host facility upgrade activities. The resulting modified sequence is shown in the schedule in Fig. 3.

Planning Phase

Previous history has shown that pre-planning on deepwater projects is essential for success. The success of the Gemini project will be measured by the well system reliability along with the performance of the high-rate gas completions (60 MMCFPD) over time. In an effort to minimize installation problems, and limit the risk for future interventions, the Gemini project team expended a great deal of effort in project planning.