Deepwater Completion/Workover Riser and Control System
Authors: Parks W.C. , Smith J.D. , Weathers G.G. 
Published: October 2008

ABSTRACT
Sonsub Inc. designed and built a Completion/Workover Riser and Control System which is being offered to the industry on a lease basis for use in deepwater subsea development applications. The riser is based upon a unique, concentric design with a 4" nominal production bore and a 2" equivalent annular flow area. The control system is comprised of a combination of direct and piloted hydraulic control functions and a hard-wired electronic data acquisition system.
The system includes all of the equipment required for use in well completion operations to run and install the tubing hanger and subsea tree and during workover operations to provide wireline and/or coiled tubing access into both the production and annulus bores. Clearly defined, standardized interfaces allow the system to be readily adapted to any vendor?s running tools.
The system is designed for use in water depths from 1,000? to 6,000? and is rated for 10,000 psi working pressure. The unique, concentric design of the riser combined with a fully integrated controls system results in a simple, high-strength system that is easy to handle and run.
The availability of the system on a lease basis offers the offshore industry a cost effective solution for conducting completion and workover operations in deepwater.

INTRODUCTION
This paper describes a deepwater Completion/Workover(C/WO) Riser and Control System which was designed and built by Sonsub Inc. and is being offered to the industry on a lease basis. The system includes all of the equipment required for use in well completion operations to run and install the tubing hanger and subsea tree and during workover operations to provide wireline and/or coiled tubing access into both the production and annulus bores,
The riser system is based upon a unique, concentric riser design and includes several new and enhanced features and capabilities. The control system, comprised of a combination of direct and piloted hydraulic control functions and a hard-wired electronic data acquisition system, also features several unique enhancements.

BACKGROUND
Prior to beginning the design of the Completion/Workover Riser and Control System, Sonsub performed a market survey to identify potential subsea development projects in the Gulf of Mexico. A survey was then conducted of several operators with projects scheduled for development to determine both operator requirements and preferences for a C/WO system. The results of this survey were used to establish a design basis for a "Universal" C/WO Riser and Control System that satisfiedat least 90?% of these requirements/preferences. Sonsub also discussed the various types of riser designs, e.g. integral vs. non-integral, jacketed vs. non-jacketed, dual-bore vs. concentric, etc., and riser coupling designs, e.g. flanged, threaded, dog-type, etc. with the operators. While several of the operators indicated a preference for a conventional dual-bore, integral, non-jacketed riser, most of the operators also recognized that the existing designs for these types of risers were not adequate for deepwater applications.
Moreover, a number of operators expressed strong interest in the concentric riser, provided that a simple, reliable means of accessing the annulus bore was available.