New Testing Methods Resolve the Mysteries of Integrity in Hydraulic Systems for Downhole Safety Equipment
Authors: Rowntree Richard , Banks Richard , Smith Roddie R. 
Published: October 2008

Abstract
The subsurface safety valve is a critical component in the performance of subsea production systems. Until recently, wellbore temperatures and pressures have been low, and control fluids and subsurface safety valves to satisfactorily meet the reservoir conditions could be selected with fewproblems. As developments were expanded into wellbore conditions with higher temperatures and pressures, however, the traditional testing methods did not provide satisfactory results, and integrity problems were experienced. More stringent testing processes as well as capability to test valves and fluids in combination and for extended periods were obviously needed. A cooperative effort has recently been undertaken by a team of fluid suppliers, a safety valve supplier and operators in the U.K. to provide awareness to the industry concerning the need to provide more effective testing for safety systems. This group has performed extensive investigation to determine answers to some of the mysteries encountered with hydraulic systems in high pressure high temperature environments, targeting specific commercial targets. The results of the extensive testing program have confirmed that the combination of the safety valve and subsea control fluid is critical to maintaining integrity and reliability of the subsurface safety valve hydraulic system for the life of the well.

Introduction
The development of high pressure/high temperature (HPIHT) environments has challenged the integrity of traditional completion scenarios. The proper combination of subsurface safety valve and hydraulic control fluid is critical to maintaining the integrity and reliability of the subsurface safety valve hydraulic system for the life of the well.1 Current HPMT systems are currently in operation in wellbore conditions up to 180°C and 15,000 psi. This service environment requires a careful analysis of both the hydraulic system within safety valves as well as their interaction with the control line fluids. Most of the developmental work performed up to now by the fluid suppliers and the safety valve suppliers has been performed independently. Realizing that more interaction was needed in this field, the British Hydromechanic Research (BHR) Group pioneered a program to coordinate the resulting data from the independent efforts and to coordinate these efforts. The intent of the program was to bring the level of reliability in ensuring the life of well systems up to new standards.

Objectives
The primary objective of the testing program was to assess the stability of the control fluid and ensure that the operation of the valve would not be compromised. To enable this program to provide the necessary information, team members identified the specific areas to target and developed the following list of program objectives:Test the control fluid under realistic and extreme conditionsExamine fluid and valve performance as a combined unit.Provide end users with an envelope under which the valve / fluid combination would be qualifiedEvaluate new materials and technologyDefine an analytical process to ensure compatibility between the control fluid and safety valve for most applications

Requirements of the Safety System
The design of the sub surface safety valve must take into account the operating conditions downhole in the most severe environments for an expected 20-year life cycle.