API RP 90:2006 pdf download

API RP 90:2006 pdf download.Annular Casing Pressure Management for Offshore Wells.
If a casing string has significant rotating time, suspected or known erosion or corrosion, or is operating under high temperature, then the operator should consider applying a de-rating factor to the wall thickness or material properties in calculating the MIYP.
In most cases, the MAWOP will be established by either 50 percent of MIYP of the casing string being evaluated or by 80 percent of the MIYP criteria of the next outer casing string. However, the collapse pressure of the tubular within the annulus being evaluated should be considered, since collapsing the inner tubular is an undesirable event. For the MAWOP calculation, a safety factor of 75 percent of the MCP provides a reasonable and conservative measure of the risk of collapsing the inner tubular.
In some cases, pressure communication between the “A” and “B” annuli can exist, normally because of either a leak in the production casing string or in the wellhead. In these cases, the MAWOP formula is not applicable and these wells should be evaluated on a case-by-case basis.
If there is pressure communication between two or more outer casing annuli (e.g., communication between the “B” and “C” annuli or between the “C” and “D” annuli, etc.); then the casing separating these annuli is not considered a competent barrier and should not be used in the MAWOP calculation. See Appendix B for example calculations.
Example MAWOP calculations for each well type are shown in Appendix B. Examples of the annular casing pressure management program using the MAWOP calculations are shown in Appendix A.
5 Fixed Platform Wells
5.1 SYSTEM OVERVIEW
5.1.1 Typical Well Schematic
As defined in Section 1.3, a fixed platform well is characterized as having a surface wellhead and Christmas tree with all the casing strings tied back to the surface welihead. Typical well schematics arc shown in Appendix C.
5.1.2 Key Component Overview
The surface welihead is typically composed of casing heads that suspend the weight of the casing strings and seal the top of the casing annulus at the casing head. Access to each annulus should be available at each casing head, which provides a means to monitor casing pressure and to bleed or to inject fluids.
The tubing head suspends the weight of the tubing, provides a seal at the top of the “A” annulus and provides access to the “A” annulus for monitoring casing pressure, as well as bleeding or injecting fluids.
Unitized or unihead weliheads may also be used for fixed platform wells. The functions and design requirements described above are also met by these types of weliheads.
The christmas tree is typically mounted on the tubing spool, which seals to the tubing string and provides sealed outlets for control and monitoring lines. The christmas tree includes the master, production and swab valves.
5.1.3 Potential Leak Paths in the “A” Annulus
The potential leak paths into the “A” annulus include the following:
• A cement seal integrity failure in the “B” annulus combined with a casing leak in the production casing string.
• Uncemented section in the “B” annulus combined with a casing leak in the production casing string.
• Production tubing connection leak.
• Hole in production tubing or parting of the production tubing string.
• Leak in gas lift mandrels, chemical injection mandrels, SCSSV and control lines.
• Production packer seal leak.
• Production casing hanger leak.
• Tubing hanger leak.
5.1.5 Design Considerations
5.1.5.1 Casing Strings
When first brought on production, all new wells with liquid packed annuli will normally exhibit a pressure increase caused by heating and the subsequent thermal expansion of the fluids. This annular pressure build-up is referred to as thermal casing pressure. This pressure may be bled off as the well is brought up to the operating temperature level. The outer casing string should be designed to withstand all potential thermal casing pressure. When practical. the design should also provide means for thermal casing pressure to he bled off. If thermal pressure is left on a casing string, it should be evaluated to ensure that it is not masking SCP.
5.1.5.2 Production String.