According to API RP 90-2, Annular Casing Pressure (ACP) is “the pressure measured at the wellhead in the space between the tubing and casing or in the space between other casing strings that terminate in the wellhead.”
ACP can be classified depending on its source as:
- Thermally Induced Pressure
- Operator-Imposed Pressure
- Sustained Casing Pressure (SCP)
Typically, well design ensures that annuli are not exposed to abnormal pressures. When production starts, Annular Pressure Buildup (APB) might be experienced due to thermal expansion of the tubing/casing; however, once it is bled off, it must not rebuild if the well integrity is to be assured.
SCP is caused by flow from a formation in open communication with an annulus (absence of a barrier), or a barrier failure that creates an unplanned flow path. SCP is the only type of ACP that will rebuild once bled off.
SCP is “pressure in any well annulus that is measurable at the wellhead and rebuilds when bled down, not caused solely by temperature fluctuations or imposed by the operator.”
Figure 1: Pressure buildup test analysis in a well with sustained casing pressure in B and C Annuli
Industrial experience with SCP shows that typically most serious consequences have resulted from tubing leaks leading to unacceptable pressure buildup in the A annulus. A tubing leak can cause failure of the production casing, which can have a catastrophic outcome as typically, only the production casing is designed to withstand the pressure of the deepest producing formation (the outer casing strings could also quickly fail, resulting in an underground blowout with potential for escalation).
AIE is currently supporting a major well operator in setting an Annuli Pressure Management programme for multiple wells on two offshore platforms that are being batch drilled and are showing early signs of SCP issues.
Our well integrity experts prepared a diagnostic process to analyse annuli pressure data and investigate the root causes of the SCP issue. Using our Veracity Well integrity software analysis was performed with corrective actions and a logical mitigation plan developed.
Some of the potential causes of SCP investigated:
- Well element barrier failure
- Thermal expansion
- Casing deformation
- Poor seal integrity
During this study our client was required to conduct significant annuli pressure testing across all affected wells, resulting in a large volume of pressure data being collected. Our extensive experience in operational integrity management has consistently demonstrated that manual extraction analysis and storage of large volumes of integrity data is inefficient and usually fails to identify trends correctly and quickly.
Throughout the operational life of these wells, regular pressure monitoring, data collection and analysis will be required, resulting in a data set, which if stored and analysed reliably, can significantly contribute to the overall demonstration of well integrity.
MANAGING WELL INTEGRITY DATA EFFECIENTLY
Our VeracityWells software package allows clients to evaluate whether their wells are fit for operations and long-term containment systematically and efficiently. Additionally, it allows the management of a large amount of well data, such as:
- Annuli pressures
- Tubing pressures
- Safety critical elements testing results
- Well barrier elements assurance tasks
The Real-time Data and pressure trending functions/or features against safe operating limits such as maximum allowable annulus surface pressure (MAASP) and maximum allowable working operating pressure (MAWOP) in VeracityWells are extremely effective in assisting clients to manage the SCP/SAP issues. These features allow clients to have accurate 24/7 well data to predict potential tubing or casing, burst / collapse issues, and many other potential well integrity threats.
Pressure buildup test analysis in wells with sustained casing pressure R. Xu a, *, A.K. Wojtanowicz