Wireless Tool for Measuring Pressure In Offshore Well Casings

Emerson Process Management's Roxar Downhole Wireless PT Sensor System – Annulus B measures online and in real-time previously inaccessible pressure and temperature information behind the casing in subsea production wells. 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. With online pressure monitoring, the Roxar Downhole Wireless system can provide positive confirmation of the pressure barrier’s integrity. The 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 system consists of an Integrated Downhole Network (IDN) system to carry signals from the wellbore to the customer monitoring system with a Downhole Network Controller Card (DHNC) placed in the subsea structure and connected to a 1/4" electrical cable coupled to a tubing hanger penetrator and a series of up to 32 sensors distributed throughout the completion string. Other key components of the system include a wireless reader, a wireless PT Transponder and antennae to monitor activity in the B Annulus, and a transponder and reader carrier. The system has an accuracy of +/-2.5 PSI and +/-0.18 F.