This paper describes evaluation of the possible causes of Sustainable Annular Pressure (SAP) in a sour gas field in the Middle East. It explains the diagnostic testing undertaken and describes how evidence was used to identify the cause of the SAP. The steps taken to prevent the occurrence of SAP in new wells and to remedy the problem in existing wells are described.
This practical approach, based on critical assessment of many aspects of the whole well condition put the SAP problem under total control, covering the process from well design through the lifecycle of the well. This allencompassing approach is regarded to be essential for all sour gas wells, but especially for HPHT designs.
Varying magnitudes of annular pressure exist in wells in some of the fields of the Middle East. The sources of this pressure vary along with the particular affected casing string in the well. In some high rate wells casing pressure is caused by thermal expansion of annular fluid. However, once a well is flowing at steady state conditions, the pressure from all casing strings should bleed through a needle valve to, and remain at, atmospheric conditions. If the casing pressure builds up when the valve is closed, then the casing exhibits sustainable annular pressure (SAP).
The general policy adopted internationally is that departure approval is automatic as long as the SAP is less than 20% of the minimum internal yield pressure and can be bled down to zero through a 0.5-in. needle valve in less than 24 hours.
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