Emerson Process Management today launched the Roxar downhole wireless PT sensor system – annulus B at OTC 2011. The new instrument will measure 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 – annulus B represents a real step change in protecting subsea well integrity, as it tracks pressure in an area which was previously off limits for all operators,” said Terje Baustad of Emerson Process Management.

“The new wireless instrument attaches to the same cable as the reservoir monitoring gauges and will detect any variations in pressure behind the casing string. It will provide early warning of these conditions and allow intervention or other remedial actions to be planned and implemented in a timely manner. For oil and gas operators planning subsea production or injection wells and looking for improved well integrity monitoring, and for government regulatory agencies overseeing safety and environmental protection, the Roxar downhole wireless PT sensor system represents a milestone moment.”

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.

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 ¼in 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 +- 2.5psi – +- 0.18°F.

The system is qualified to last for a minimum of 20 years at temperatures of up to 302°F and pressures up to 10,000psi. The system is also based on an electronic wireless system, where the signals and power are transmitted wirelessly, ensuring a long life.

Emerson has considerable, long-term experience in downhole monitoring going back two decades. Emerson’s first Roxar downhole gauges on Statoil’s Gullfaks C production platform in the North Sea were installed in 1990 and the same instrumentation is providing continuous and reliable downhole reservoir information on the field today.

Terje Baustad from Emerson Process Management will be introducing the Roxar downhole wireless PT sensor system as part of the OTC technical program in the ‘Well Testing and Reservoir Evaluation Concepts’ session during the morning of Thursday 5 May 2011.