Sustained Casing Pressure (SCP), also referred to as Sustained Annular Pressure (SAP) or Annulus Pressure Buildup, affects >30% wells globally and is present within multiple annuli. Since 2009, well integrity has cost operators over USD 75 billion and this has provided the impetus for the industry to focus on and rework, international standards on well integrity management.
SCP is excessive casing pressure in wells that persistently rebuilds after bleed-down. It is defined as a 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.
SCP is caused by gas migration from a high-pressured subsurface formation through the leaking cement sheath in one of the well’s casing annuli.
In contrast, an unsustained casing pressure determination is made if either the casing pressure on a well is self-imposed (e.g. gas-lift pressure, gas- or water-injection pressure) or if the pressure is entirely thermally induced.
It may also be caused by:
- Defective or leaking tubing connections, downhole accessories or wellhead seals
- Degradation or failure of well barriers
- Leaks that develop either due to:
- Poor primary cementing job
- Temperature and pressure fluctuations during production
- Corrosion/erosion of casing or tubing
- Other type of Well integrity failures