When the casing pressure can not be permanently bled off through needle valves at wellhead, the casing is said to exhibit Sustained Casing Pressure (SCP). Since high values of SCP may threaten worker safety and environmental protection, MMS regulations require remedial treatment. Testing of SCP could provide information on parameters causing gas migration and SCP.

A mathematical model for testing SCP buildup has been developed. The objective of the model to identify the flow mechanism of external leak leading to SCP. The model also determines critical parameters of the leak to be used in selecting some remedial actions. Also presented in the paper are two examples of using this model to analyze actual SCP field tests. The analysis gives acceptable estimates of the depth of gas invasion zone, formation pressure, cement conductivity, and expected maximum value of casing pressure.

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