When setting two deep wellbore barriers in close proximity it can be difficult to be assured that the upper barrier has integrity. Only by measuring the pressure between the barriers can the integrity of the shallower barrier be verified.
Well abandonment practice is dictated by territory specific regulations which are largely based on historic practices. However, emerging technologies and methodologies are gradually changing the outlook, affecting the way we carry out future P&A operations.
With the introduction of any new methodology or technology there is a need for verification and testing of the permanent barrier. Currently, the typical concept is to use an anchoring or plug device to build a barrier above.
The wireless BVS (Barrier Verification System) uses ELF (Extreme Low Frequency) telemetry and has the capacity to transfer signals through the barrier or surrounding wellbore/lithology to a receiver above the established seal. The system consists of a pressure sensor with a transmitter attached below an anchoring device. A receiver is lowered on slickline or electric-wireline above the barrier to be tested. The receiver wirelessly records the pressure measurements transmitted from below the anchoring sealing device. An additional pressure sensor in the receiver forms part of the toolstring to provide an accurate pressure reference above the established barrier for verification testing.
The transmitter can record for multiple days depending on battery configuration, wellbore temperature and logging frequency. The receiver can transmit real time data or it can be deployed in memory mode for slickline, coiled tubing and pipe-deployment applications.
The objective of this paper is to examine and explore the technology of the BVS, the design and development, the qualification tests carried out, and the execution and results of an operation in the North Sea.
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