Dry Tree and Drilling Riser System for Hoover DDCV
Authors: Bates John B. , Kan Wan C. , Allegra Allen P. , Yu C. Alan 
Published: October 2008

The Hoover Deep Draft Caisson Vessel (DDCV) includes six production risers connecting the subsea wellhead with surfacebased trees, setting a water depth record for dry tree completions. The six wells are drilled by the DDCV platform rig and surface BOPs using a dual barrier drilling riser that does not require recovery and re-deployment between wells. This paper summarizes the overall riser systems design and execution effort culminating in the successful installation and operation.

The riser global design and analysis efforts included previously unrecognized load effects for buoyancy cansupported risers, refined the understanding of riser, buoyancy can, and hull structure load interactions, and assessed requirements for separation between deployed risers. The non-integral buoyancy can system design was developed to best integrate with the overall DDCV installation and HUC sequence, minimizing impact on both the installation and field drilling time requirements. Assessment of the riser joint connection design and validation of the fabrication practices assured that designs would meet the field performance requirements. A number of new riser components were designed and developed to meet this field's requirements and provide ready capability for extension to additional worldwide deepwater field development opportunities.

Introduction

The Hoover-Diana Project is a co-development of two deepwater fields approximately 16 miles apart. The Hoover DDCV drilling and production facility is installed in Alaminos Canyon Block 25 in 4800 feet water depth. ExxonMobil is operator on behalf of itself and BP for both fields. Several papers are presented detailing various aspects of technical development and execution of these fields.

This paper details the design and development of the drilling riser and dry tree production riser systems. Each of the six Hoover wells is completed using the production riser and surface wellhead and tree. The trees are accessible from the central wellbay in the DDCV.

A riser team was organized within the integrated project team, made up of both company and key contract technical staff. The team had overall responsibility for all aspects of riser design and execution, comprising the following main elements:Concept evaluation and developmentGlobal riser design and assessmentCoordination with hull, deck and facility groups on all interfacesDevelopment of functional, technical and procurement specification for riser system and componentsStewardship of vendor detailed design and manufacturingAssessment and qualification of new or modified designsProcedures for, and technical support to, the Drilling Organization for riser installationTechnical verification and validation of both in-house andvendor design work

The comprehensive scope of work and dedicated team effort ensured the successful execution and delivery of risersfor field development.

Drilling Riser System

Concept Selection.

The drill riser system for the Hoover DDCV utilizes the dual casing concept with surface BOPs similar to deepwater TLP applications1. This technologyfacilitates the use of platform drill rigs requiring specific modifications for riser handling. The Hoover drill riser consists of a 21" OD × 3/4" wall × 3,000 psi outer riser and a13-3/8" OD × .514" wall × 6,000 psi inner riser shown in Figure 1.