Gemini Subsea System Design

Abstract

Field development planning and execution is influenced by a number of different factors, but ultimately must be based on a project's ability to deliver the maximum economic benefit to the project partners while maintaining safety and environmental goals. The Gemini development was executed as a fast track project with simultaneous appraisal and implementation tasks. This approach brings with it an inherent reduced scope definition which must be accommodated by the system design while still remaining focused on the project drivers. The Gemini development reflects a sound project execution plan that accommodated significant unknowns while still delivering production ahead of schedule and improving on the capital cost expectations for the development. Introduction The Gemini prospect was discovered by Texaco with the drilling and testing of the Mississippi Canyon Block 292 Well No. 1 in the third quarter of 1995. Following the discovery, Texaco (60% GWI) and their partner Chevron (40% GWI) continued their appraisal process with two additional wells with sidetracks to investigate the original discovery and other deeper potential areas. Concurrent with the appraisal process, Texaco began preparations for a phased development of Gemini with an early gas development in the Allison reservoir. In January 1998, both project partners received board approval to proceed with the early Allison gas development with a subsea tie back to a shallow water host facility. The facility selected based on location and expansion potential was VK-900 which is jointly owned by Texaco (25% GWI) and Chevron (GWI 75%, operator). An integrated project team was formed to implement the project and a subsea equipment contracting strategy already established by Texaco was extended into the Gemini development. The subsea trees and control system under fabrication for Texaco's inventory program was adopted for Gemini to reduce the project cycle time with the goal of improving project NPV. Project Drivers The project team identified the following drivers for the development:The development wells could be clustered around the MC-292 Well No. 1 location to provide a single drilling center.Due to schedule requirements, the rig would be on location prior to the subsea equipment being ready for installation.A first production target date of July 1, 1999 was committed to by the project team.The system should consider the potential for future expansion in the area. This included sizing flowlines to meet the corridor development needs.The Ocean Star semi-submersible rig would be used due to long term contract commitments by Texaco. This would also be the primary installation vessel for the subsea equipment.System operability would be critical since an overall production uptime target of 90% was a development goal. Field Layout The subsurface team determined that the reservoir take points could all be accessed from the single drilling center at the MC-292 Well No. 1 location. Fig. 1 is an illustration of the local seafloor layout.

Gas Condensate Subsea Systems, Transient Modeling: A Necessity for Flow Assurance and Operability

“…The Gemini subsea development 1,2,3,4 was brought on stream in June 1999, sixteen months after project sanction. Suites of dynamic simulation runs were made at various conditions before and after the field went on production.…”