Novel Approach to Combat the B-annulus Pressure Build-up Challenge

Abstract

Abstract In December 2014 a metal annular packer equipped with sealing elastomers, was installed and verified in an offshore platform well in Norway. The annular packer was installed to function as a barrier element against pressure buildup from shallow formations in the overburden with limited flow potential, containing liquid only (no gas). The packer was installed between the intermediate casing and the production casing. Upfront the installation the packer was tested and qualified according to ISO 14310 V3. This paper describes the operation, which was a world’s first, as well as the implications this achievement has for the industry in terms of preventing the plague of sustained casing pressure (SCP). SCP can be defined as pressure in any annulus that is measurable at the wellhead and rebuilds when bled down, not caused solely by temperature fluctuations or imposed by the operator. The wells were facing B-annulus pressure build-up. Studies revealed that it originated from shallow formations in the overburden. A project team was challenged to investigate find and verify a barrier for the 9 5/8’’ x 13 3/8’’ annulus. The initial, two main methods attempted were second stage cementing and long primary cement jobs. Second stage cementing had operational limitations while long primary cement jobs were subject to narrow ECD margins. Alternative methods were evaluated because of these challenges and the concept of the metal packer was considered being the most suitable option. This new type of packer had already been qualified for use in this operator’s wells; however, further testing was required before installing the packer as a barrier element. These tests extended the qualification from 345 bar ISO 14310 V3 rating within the load envelope and needs defined for the well. In addition, an ISO 14310 V6 test was performed (V0 gas test without axial load). One of the potential limitations of the packer was that it was an anchor-less design lacking a dedicated axial load- bearing element. Simulations had shown significant axial movement during casing pressure tests in green cement. The concern was that this might result in damaging the packer seal area during expansion. This risk was in the end mitigated by testing the annular barrier in fully set cement. The packer was mounted on a 9 5/8’’ casing joint and installed as a part of the casing string. The casing was successfully run to total depth (TD) and cemented around the shoe as planned without any losses. After cement had fully set, the casing was tested to 345 bar, simultaneously setting the packer. The packer was successfully verified by pressure testing the B-annulus to 100 bar for 10 minutes. The packer’s sealing capability will continue to be monitored during production (B-annulus monitoring) for ongoing verification of integrity. SCP is a concern throughout the industry, where it is of vital importance to evaluate the flow potential and associated risk. In wells where it can be concluded that both the flow potential and the associated risk is limited, the operator may operate the wells with SCP. In all other cases the SCP should be eliminated. With the introduction of this new type of annular barrier element, operators will not only save money on costly slot recovery - but it will construct safer wells without SCP.