A Sustainable Solution for Preventing Sustained Casing Pressure: A Gas-Tight Metal to Metal Seal

Abstract

Abstract The engineering of an extremely unique metal alloy can avail solutions for downhole sustained casing pressure which is a common well integrity concern. SCP pressure takes place when pressure communication from the reservoir reaches to surface. This happens due to cement channeling or casing-cement micro-annulus. The performance of the proposed system, the Thermally Deformable Annulus Packer (TDAP), has been lab-tested under downhole conditions. In particular, a full-scale version of the packer has been set in a full-scale replica of the targeted Casing Casing Annulus (the 9-5/8" × 13-3/8" CCA), in the three potential fluid medias for setting; 1) in clear brine, 2) in typical fluid formula, and 3) in a typical cement slurry. The sealing capacity of each packer has been pressure tested with both a hydro-test and a gas test with the maximum pressure allowed by the casing strength. Examples of Eutectic alloys are those that contain Bismuth. A Bismuth-based alloy can be molten downhole to a liquid with the viscosity of water and ten times its density. Upon solidification, like the behavior of ice, these alloys expand. In the proposed methodology, this expansion is utilized to provide a metal-to-metal seal in fluid leaking-channels. During the well construction phase, the packer is run in hole as a sleeve on the 9 5/8’’ casing. It is optimally operated in areas with higher likelihood of observing SCP pressure. The created seal would eliminate the risk fluid migration. This prevents the fluid from reaching surface when a leakage occurs. The pressure rating of the Bismuth-alloy packer, as well as its ability to seal gas, was shown to strongly depend on the medium in which the packer was set. The best performance was observed when the packer was set in clean brine. Under such condition, the packer was able to hold the maximum pressure allowed by the casing strength with both the hydro and the gas pressure tests. The bismuth alloy packer was able to withstand pressure that exceeds the casing rated pressure. The sealing of the pressure leakage from formation was achieved successfully and the methodology was availed as a SCP preventative practice. Finding other zonal isolation methods is key to availing more strategies for mitigating SCP issues. This technology is aimed for casing designs that have 9 5/8’’ casing as a production casing and this TDAP method, working on a pro-active prevention of SCP, is new in the industry.