Surface Controlled Subsurface Safety Valve failure data from 14 North Sea fields have been collected and failure rates for the various valve types and makes calculated. Failure rates have been compared to well data in order to identify critical well parameters and give guidance to operators when selecting valves for new fields.
Finally, models are developed for calculating well safety and production availabilities. Input to these models is failure rates, testing and maintenance routines, frequency of other well service operations etc.
Output from the models is:
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The proportion of the time the valve acts as a safety barrier, i.e. safety availability
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The proportion of the time that the valve is causing production shutdown, i.e. production unavailability
Most people involved in production of oil and gas from high pressure reservoirs will probably agree that the Down Hole Safety Valve is one of the most important components for controlling blowout risk. In particular this is the case offshore where one platform may be producing from more than 30 wells. In such situations it is very important to be able to shut off the wells with a down hole device if a hazardous situation should arise on the platform.
In spite of this importance, there are still endless arguments regarding what kind of safety valve to use, e.g. from which manufacturer, flapper or ball valve, or maybe to install two valves in series. No clear cut criteria for selecting valves for various types of fields and uses exists. The study documented this paper was aiming at recommending such criteria, based on an investigation of past safety valve performance in North Sea fields. In this area only surface Controlled Subsurface-Safety Valves (SCSSV) are used, and the study is therefore restricted to this type of valves.
The selection criteria that were sought, should reflect both well safety and production availability. Disregarding one of these factors will inevitably result in suboptimal solutions.
To obtain a reasonably correct picture of past SCSSV performance, all major operators in the North Sea area were contacted, and asked to participate in the study by releasing their data regarding valve failure statistics and field parameters. Fortunately, most operators were willing to release their data, provided the information was published in a pooled manner. The information necessary was
Valve type, make and dimensions
Operating time
Number of failures and failure modes
Field data (e.g. reservoir type, pressure, temp., H2S and CO2 content, GOR, oil gravity)
Wire line Retrievable (WR) valves:
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Otis DD, Otis DK, Otis DB, Otis QO
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Baker BFX-Ol (Super "e")
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Camco B-6
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Folderol PA
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Tubing Retrievable (TR) valves:
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Camco TRB-8FSR
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