ANALYSING OF ABNORMAL ANNULAR PRESSURE AND APPLICATION OF MITIGATATION TECHNOLOGIES TO PROTECT WELL INTEGRITY

During casing design operations there are product spaces generated between casings strings or between tubing and casing that are called annuli, it is the product as a result of design and not created purposely. The ideal case is these annuli must be filled with cement, but for some reasons such as limited cement technologies and weak formations, these annuli are filled with small-compressibility fluids (generally weighted mud, cement spacers, or transparent brines) to avoid fracturing of the weak formation and lost circulation during cementation. In high-pressure high-temperature wells (HPHT) these fluids will be heated during drilling operations and production activities by the fluids that coming from heat formations in the bottom of the well and as a result, it will expand and if the annulus was closed it will generate a trapped annulus pressure (TAP), it is the first type of annular pressure, this pressure can reach a very high value (10,000 - 12,000 psi or more). This pressure is more problematic in subsea wells (SSW) where the wellhead of SSW doesn’t permit annulus venting except for annulus ‘A’ (production casing - tubing). The second type of annular pressure is sustain casing/annular pressure (SC/AP), that caused by the failure of internal or external barriers of well integrity, involving casing and cement, in some cases when the annulus fluid pressurized by formation fluids invasion due to pressure difference between formation and annulus and there is a passageway through microfractures and channels in poor cement where there is a failure in the external barrier of well integrity, or it can be generated mechanically by tubing leak inside annulus or linking between annuli due to seals or casings damage, where there is an internal integrity barrier failure. Both of these two types of annular pressure are harmful when becoming abnormal annular pressure. Abnormal annular pressure is one of the most important issues that threaten the casing of wells from the annulus and may result in a casing failure. Because the casing is the major part of a well integrity system, so annular pressure impacts the well barriers and may lead to damage of the well integrity. Analysing the annular pressure by the source of this pressure, type, possible location, causes of generation, and calculation of permissible and present limits are more important during well design. The last conventional casing design for deep-water HPHT and SSW shows insufficient control of abnormal annular pressure and safety of well integrity by recording some accidents in most of the deep-water wells in the Gulf of Mexico (GOM) and other locations of the same problems. So, it is obligate to account for annular pressure in the new unconventional design that is provided in this research based on mitigating the effect of abnormal annular pressure and provide a complete risk plan to provide a robust design. We consider the annular pressure, apply risk analysis and define permissible limits to show the possible impaction to the well integrity, that study the case by identifying the possible risk, evaluate the risk level and probability of failure, then provide the ways to mitigate this risk to protect the well integrity barrier with applying risk treatment to the most critical (unacceptable) risk levels. Also, we apply an optimization strategy for mitigation devices selection for TAP and optimization for the new design and possible remediation for SCP.