This paper summarizes the overall riser system design, analysis, and execution efforts leading to the successful installation and operation of the Holstein riser and well system equipment.
The Holstein spar includes 15 vertical dry tree risers comprising 12 dual casing production risers and 3 dual casing water injection risers. This is the first spar to use hydraulic tensioners to support these risers in place of the conventional spar buoyancy can tensioners. The risers are designed for a combination of drilling and production from the spar without needing a dedicated drilling riser. Six wells were pre-drilled to depth using a MODU.
The use of spar supported tensioners required coupled vessel and riser analysis to accurately define the vessel motion for global riser analysis. The benefit of smaller riser strokes were realized through the coupled analysis and in turn allowed the design of a fixed platform for ease of surface tree access for operation and maintenance. The integrated tensioners and their support structure were proven to provide huge benefits in terms of shortening the offshore installation, providing more than 95% onshore hook up and commissioning opportunities and an excellent safety record. The use of strakes to suppress the vortex induced vibration on risers and the innovative keel joint design and riser equipment qualification programs provided a ready and deployable system for the development of this deepwater, high-current field.
The Holstein Field is located in Green Canyon Blocks 644 and 645 in the Southern Gulf of Mexico, 190 miles south of New Orleans, Louisiana in 4,344 ft of water. BP Exploration & Production, Inc. and Shell Offshore Inc. each owns 50% working interest in the property. BP is the operator of the field.
The Holstein Development Project Team developed the field utilizing a truss spar as the central facility with dry trees and top tension risers (TTR). The development includes 15 wells, which include one well already drilled as an appraisal well, six wells pre-drilled from a MODU, and nine wells to be drilled from the platform. The spar is designed to handle up to three additional future wells.
A well systems team was organized within the Holstein project team, made up of BP's project execution staff, members from the Exploration & Production Technology Group and Technip Offshore, Inc. and Vetco Gray, the two main contractors (Figure 1). The team had the overall responsibility of delivering the riser and well system to Operations with the following main tasks:
Concept evaluation and development.
System design and analysis
Interface management (drilling, hull, subsurface, topsides and operations).
Development of technical specifications
Bid evaluations and award
Technical assurance and support to hardware fabricators
Quality assurance and third party inspection
Equipment shipping and logistics management
Onshore and offshore HUC and installation support
Development of well system manuals
Ensure the overall project goals and HSE requirements are met.