GALVESTON, Texas – Emerson Process Management, exhibiting at Subsea Tieback 2012, has developed the Roxar Downhole Wireless PT Sensor System–Annulus B instrument. It measures online and in real-time previously inaccessible pressure and temperature information behind the casing in subsea production wells, providing operators with an important new tool for well integrity monitoring.
The annulus of an oil well is the space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow. In a completed well, there are normally at least two annuli. The A annulus is the space between the production tubing and the smallest casing string with the B annulus located between different casing strings.
Cement seals behind the wellbore casing provide a barrier against the high pressures encountered deeper in the well. Poor or deteriorating cement sealing or casing collapse (the casing will heat up and thermally expand due to the production flow), however, can lead to a loss in casing integrity, allowing oil or gas to migrate vertically towards the surface along the outside of the casing. This can result in potentially hazardous situations, especially during workover operations, where uncontrolled gas may escape at the surface. In the worst case scenarios, a shallow gas blow out might evolve due to the failed barriers in the casing systems.
With online pressure monitoring, the Roxar Downhole Wireless PT Sensor System–Annulus B can provide positive confirmation of the pressure barrier’s integrity. The tool will also negate the sometimes excessive and expensive over dimensioning of casings that can take place to compensate for worst case scenarios and will also potentially provide operators with significant cost savings previously incurred in shutting in wells, due to their lack of ability to verify barrier integrity. The new wireless PT Sensor System and its permanent monitoring capabilities will give added certainty to the well integrity monitoring process as well as valuable input during well trouble-shooting.
The Roxar Downhole Wireless PT Sensor System monitors the B Annulus pressure and temperature without any degradation to the original barrier element consisting of the A casing system and can be retrofitted to the monitoring system design of current subsea systems.