Development and Achievements of a Computerized System for Inventory Control and Failure Analysis of Subsurface Safety Valves
Authors: Linton Fred W. , Durrett Ed G. 
Published: December 2007

Summary
To improve safety and reduce costs of subsurface safety valve (SSSV) operations at Ekofisk, offshore Norway, a computer system was developed for inventory control and failure analysis. Improvements and identification of problem areas in SSSV operations have been realized from changes made problem areas in SSSV operations have been realized from changes made during development and use of the system.

Introduction
The Ekofisk field was discovered in the Norwegian sector of the North Sea in late 1969 by the Phillips Norway Group. This group is composed of Phillips Petroleum Co. Norway (PPCoN) (37%), Norske Agip A/S (30%), Norsk Phillips Petroleum Co. Norway (PPCoN) (37%), Norske Agip A/S (30%), Norsk Agip A/S (13%), and the Petronord Group (20%). A total of seven geologically separate fields have been developed in three phases with 11 producing and 11 support platforms as illustrated in Fig. 1. Greater Ekofisk was developed over a 10-year period, from discovery until the last platform came on production in 1979. There are a total of 118 producing wells, 6 gas-injection wells, and 1 water injection well. These wells were completed with several schemes utilizing mostly 4 1/2-in. [114-mm] tubing and some 3 1/2-in. [89-mm], 5-in. [127-mm] and 5 1/2-in. [140-mm] tubing. Wireline retrievable SSSV's are used as pall of the completion equipment in all Ekofisk wells. Many sizes and models of SSSV's were necessary because of the various completion types and sizes.

SSSV Operations at Ekofisk
SSSV assemblies at Ekofisk consist of a valve and lock, each having its own serial number. The lock and valve when considered separately have been defined within this paper as "devices." When the lock and valve are considered as an assembly, they will be referred to as an SSSV. Fifteen models of locks and valves in sizes of 3.68 in. [93.4 mm], 3.81 in. [96.8 mm], and 4.56 in. [115.8 mm] have been used. These devices are produced by three SSSV manufacturers. Ten of these models continue in use today. Surplus inventory must be maintained for each of the SSSV models in use. The total inventory of locks and valves is 460. Approximately 240 devices are in service in wells and 220 devices are required as spare inventory to ensure that a device will be available when a replacement is needed. An average of 450 SSSV's are run and pulled in wells each year at Ekofisk and as many as 90 replacements have occurred in 1 month. Reservoir pressure monitoring, production logging, tubing caliper inspection, and pressure monitoring, production logging, tubing caliper inspection, and other operations requiring wireline work below the SSSV cause most of the running and pulling of these SSSV's. Failures and malfunctions of SSSV's contribute to only 15 % of total replacements. SSSV's pulled from wells are transported to the onshore Norway base for repair. Many of the lock-and-valve combinations must be separated and sent to their respective repair shops, since the lock and valve of an assembly are not all from the same manufacturer. This requires separate tracking of the lock and valve.
JPT
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