Subsea Completions for HPHT - Reality or Wishful Thinking
Authors: Garnham Dave , Taylor Bill 
Published: October 2008

The use of subsea completions for HPHI' fields has been discussed for several years. This paper will address the historical work which was performed at the time before there were immediate field applications, and the current development's status. The paper will then describe the work which has been performed under a study funded by Shell UK Exploration & Production, with requirements derived to meet the needs of a real HPHI' field. Under this study, the wellhead, the tubing suspension equipment, the xmas tree equipment and the installation equipment has been critically screened and classified. It was classified broadly as either a straight forward technical extension of existing equipment, equipment requiring design work without immediate qualification testing, or as a technical extension with "art" involved, therefore requiring qualification testing to guarantee a viable solution. An overview of the design goals, the resulting equipment, and the test program involved will be given. Finally, the authors will address the question, "is the technology sufficiently developed for an immediate commitment to a field development or is further work required?"

Introduction

In the early 1990's (Circa 1992) many of us felt that subsea High Pressure/High Temperature (HPHT) completions were just around the comer, where as in reality here we are in 1998 and a true Subsea HPHI' completion has not yet been built or installed. However, a number of potential prospects have been identified and work has been performed to qualify the design in readiness for these applications. Stepping back lets take a brief look at the history. In 1992 we performed a survey of the UK North Sea Operators to determine the valve size and operating conditions deemed most likely to be used in the North Sea. The results of this survey indicated that the industry would require 4 1/16" × 2 1/16" bore, 15,000 psi WP subsea trees with a temperature rating of 350 degrees F. Most operators also felt that the maximum casing size would be 7 5/8". This was born out by study work being done by others at about the same time, reference OTC paper 6993. Based on the above understanding a 4 1/16", 15,000 psi WP gate valve and actuator was built and prototype tested to qualify it for the above service. At that time it was assumed that if we had the valve and actuator, the remainder of the equipment would be relatively easy to design. No problems were experienced in the design and qualification of the valve and actuator, hence boosting our confidence in our ability to supply subsea HPHI' completions. In 1994 Shell U.K. Exploration and Production approached Cameron and another supplier and began detailed discussions on the requirements of Subsea HPHI' tree's with a potential for application in the Shearwater field. These discussions were followed by more detailed equipment investigations and in the latter part of 1996 resulted in Shell Expro awarding paid contracts to both suppliers, for the design and development of equipment, which would place Shell Expro in a position where they could confidently order Subsea HPHT Completions. Like most developments this was not an open-ended budget, therefore equipment was carefully selected for development.