Sustained Casing Pressure (SCP) due to integrity concerns on a deepwater subsea producer in US GoM required the operator to isolate the reservoir. During a previous intervention, an R-nipple plug & prong had been installed and tested to isolate the reservoir pressure. Within six months after the plug installation, tubing and annulus pressure began increasing, indicating fluid was leaking past the plug & prong. As a result, the well required a new barrier with an additional integrity verification method.
A V0 rated Medium Expansion Retrievable Bridge Plug (ME) was chosen to remediate the SCP. The ME was conveyed open water on E-Line, via a Riserless Light Well Intervention vessel. The operator performed extensive testing to confirm the integrity of the new barrier, relying on a novel Barrier Verification System (BVS) to wirelessly transmit pressure data from below the ME. This technology allowed barrier testing to be performed while directly monitoring pressure on either side of the ME. A second barrier was established by setting another ME, using data from the DHPGs for integrity verification.
The distinguishing factor of this intervention was utilizing the barrier verification system to confirm barrier integrity. The BVS allowed the pressure differential across the plug to be read at surface in real-time. During the positive pressure test, the BVS readings showed that additional pressure had to be applied to achieve the required differential across the ME. During the twelve-hour extended inflow test, pressure on the BVS gauge below the ME gradually increased. This pressure signature confirmed that the SCP was due to fluid leaking across the previously installed R-profile plug. Based on these results, the operator concluded the R-profile plug was likely impaired during its original pressure test, but the leak rate had been too low to detect in the pressure test. The ability of the BVS to monitor the pressure beneath the ME confirmed that the ME was holding pressure in both directions, and this data provided additional verification that the ME had successfully isolated the reservoir. Thus, the BVS assured the operator that the ME would prevent further SCP on the well.
The BVS provided comprehensive downhole barrier verification that exceeded the operator’s isolation standards as well as the regulator’s. As a result, the operator now has the assurance they will not have to return to the well until it is time to plug and abandon.
This GoM job was performed with web-based execution and remote monitoring from the product technical support team in Norway, giving extra confidence to the novel technology in this high-profile operation.