Although design concepts for tubing retrievable safety valves (TRSV) have improved considerably over the last decade, the demands imposed by deep-water, high-pressure/high-temperature (HP/HT) environments, high-flow-rate gas reservoirs and remote subsea applications have also increased. In spite of the use of non-elastomeric and metal-to-metal (M-t-M) sealing materials and enhanced validation testing, all of which have improved drastically TRSV performance over the last decade, equipment has continued to be pushed to its limits.
This paper reviews the unique capabilities of a new TRSV concept that uses a magnetic coupler. The discussion will focus on the targeted applications and specific issues that this technology addresses. In addition, the paper will cover the development and preparation of the magnetic coupled TRSV for field installation.
The magnetic-coupler concept was developed for deep and ultra deep completions. As the TRSV is set deeper, it typically requires additional operating pressure. By using the magnetic coupler design, the operating pressure required for the TRSV is drastically reduced by removing any interaction between the hydraulic operating piston and the internal tubing-wellbore pressure. This is especially beneficial for deepwater systems where a lower operating pressure simplifies the overall operating system. This simplification is important both for safety and costs since the magnetic coupler design could eliminate the need for high-pressure equipment and the associated high-pressure umbilicals in subsea systems. The benefits of this new, intrinsically simple design go beyond the initially targeted deep completions and include:
Increased environmental and personnel safety
Reduced system costs
Reduced service demands for seals
An extremely reliable tubing-retrievable safety valve
Enhanced well life.
Reliability is a critical issue and of prime importance for SCSSVs because of the very nature of their role in overall well safety. It is universally agreed that the following attributes are important for overall SCSSV design:
Design simplicity
Elimination of seals
Increased use of M-t-M sealing.1
Engineers have always felt that design simplification and the elimination of seals are important contributors to reliability. However, as well completions have become increasingly more challenging from the demands of deep-water, high-pressure/high-temperature (HPHT) environments,2 and high-flow-rate gas reservoirs; greater emphasis has been placed on M-t-M sealing. These efforts have resulted in the significant increase in safety-valve reliability, and in all probability, this has been one of the factors along with design simplification, more intense consideration of operational constraints, and capabilities for enhanced performance testing and monitoring that have resulted in the significant improvement in reliability. Unfortunately, the improvements have not been sufficient to eliminate all the inherent safety-valve problems that have been intensified by the more corrosive deepwater environments.3
In conventional design solutions, wellbore isolation traditionally has focused on balancing the safety-valve piston area. That mechanism requires additional seals and/or gas-charged chambers, which are heavily dependent on elastomeric seals and the permanent, long-term containment of a dome charge, to maintain reliability. Dynamic elastomeric seals pose a major limitation when trying to design for life of the well reliability.
