A major component Well Integrity issue will be the annular pressure limits to make sure our operating condition still below the safety limits. In order to determine what these limits are, the Maximum Allowable Wellhead Operating Pressure (MAWOP) must be calculated for each well.
The MAWOP will be the measure of how much pressure can be safely applied to an annulus according to the API Recommended Practice 90.
If two or more weights or grades are used in a string, the minimum weight or grade should be used in the MAWOP calculation.
We can use the following definitions when determining the MAWOP for each annulus:
"A" Annulus - The annulus designation between the production tubing and the production casing
"B" Annulus - The annulus designation between the production casing and the next outer casing. The letter designation continues in sequence for each and every outer annular space encountered between casing strings up to and including the surface casing and conductor casing.
How to Calculate MAWOP according to API RP90:
The MAWOP for annulus being evaluated is the lesser of the following:
· 50 percent of the minimum Internal Yield Pressure of the pipe body for the casing or production riser stated or
· 80 percent of the minimum Internal Yield Pressure of the pipe body of the next outer casing or production
· 75 percent of the minimum Collapse Pressure of the inner tubular pipe body
For the last casing or production riser string in the well, the MAWOP is the lesser of the following:
· 30 percent of the minimum Internal Yield Pressure of the pipe body for the casing or production riser stated; or 75 percent of the minimum Collapse Pressure of the inner tubular pipe body
