Control of Subsea Satellite Wells at Extreme Offset Distances
Authors: Savage Bill , Hibbs David 
Published: October 2008

As the offshore industry extends the use of subsea production technology, more complex systems are being considered for their economic viability. Deeper water, longer offsets, multiple well templates and clusters, manifolds, and system combinations demand control systems of higher performance levels. The electrical cable is an important component of the control systemaffecting performance levels and system cost. Refinements and upgrade of cable design and materials have resulted in cables with lower circuit loss and constructions that minimize circuit degradation that can result when the likely seawater flooding of the cable occurs during the to twenty-five (15-25) year system design life. Component design geometry coupled with material selections result in cables having lower circuit capacitance while sealing insulated conductors against the radial water entry that degrades circuit performance of components of conventional design/construction cables. These low loss cables can provide system savings when the most cost 'friendly' electronic system/cable combination are brought together.

Introduction

Subsea production system development began in earnest in the early 1970s. Competing one atmosphere 'dry tree' consortiums and various 'wet tree' systems went from the drawing board to field trial testing of the systems and their component parts. These early subsea systems were typically of modest offset distances being no more than a few thousand feet from the surface host control station. As a true development effort of testing and forcing technology, most of the systems used some form of electrical control and/or monitoring of the subsea well, The work since these early days and continued systemsrefinements have resulted in reliability levels that prove economically attractive to the operator for many applications. The recent requirement of longer offset distances present more demands on the control system to communicate detectable. intelligent information and commands over these distances.

The earliest subsea production systems using electrical control of the well functions were of short offset distances, and associated cable losses were minimal. For these systems the focus of development was on the subsea electrical terminations, both dry and underwater make and break, in the form of conductive and inductive connections. Hardware and cable/connection developments/improvements have resulted in improved connection hardware reliability. With hardware and system improvements, the number of subsea production projects have steadily grown over the pest fifteen years at an accelerating pace. The successes of these system have buoyed confidence levels, encouraging operators to utilize subsea production in more and more complex and demanding projects.

This is particularly true in early production/floating production projects and deepwater production tiebacks to structures in shallower water. Some of the deepwater tiebacks involve offset distances far beyond anything seriously considered not that many years ago. Today there are ongoing studies for projects having requirements of up to 100 mile offsets. At these offset distances, all control system components are subject to scrutiny, particularly the electrical cable which represents a significant investment that can only be recovered through a reliable operational life of many years.