The Development of a System to Restore Full Safety Valve Functionality to Wells With Blocked and Damaged Control Line

Abstract

A significant problem confronting Operators in modern field development and production is that created by loss of functionality of the surface controlled subsurface safety valve (SCSSV) due to blockage of, or damage to, the hydraulic control line. The consequent loss of hydraulic pressure to the valve means its closure, the resultant loss of production and the need to provide an alternative safety system in order to continue exploiting the wells reserves Currently two alternatives are available:○A full scale workover to pull tubing, replace the inoperable control line and restore functionality to the SCSSV.○Installation of a velocity or dome charged subsurface controlled subsurface safety valve (SSCSSV). The former approach requires a major expense, which may not be justifiable in a mature well, while the reliability offered by the latter approach typically does not meet well integrity requirements and can sometimes lead to reduced production. Nederlandse Aardolie Maatschappij (NAM) has been faced with this problem in many onshore and offshore wells and was determined to find an alternative solution. Based on the successful completion of a previous development project, NAM asked Weatherford to jointly develop a solution to this problem, which would allow the installation of an alternative control line without the expense of a workover. In this paper the authors will review the problems associated with loss of control line functionality and consequent SCSSV malfunction. They will go on to describe in detail the joint project which led to the development, testing, and eventual field deployment of the Weatherford Damaged Control Line (WDCL) Safety Valve featuring surface control, which can be installed using wireline and capillary string techniques. Introduction In any and all field developments which incorporate surface controlled subsurface safety valves a significant potential problem exists with the hydraulic access conduit. When a control line is used to provide hydraulic power to the safety valve, the danger is ever present that it could become blocked or damaged thus rendering the safety valve inoperable. When such a situation occurs there are normally two possible alternatives to be considered in order to restore safety valve control to the well and thereby facilitate continued safe production:○The well can be worked over to pull the tubing, replace the damaged control line and recomplete the well with a functioning safety system. This approach involves major expenditure which, in more mature wells, can often be financially unjustifiable because the remaining reserves may be insufficient. In the case of NAM operations the approximate cost of such a workover is in the range 6 - 8 million Euros which makes it a fiscally unattractive approach.