Given that a cap rock, by definition, is a formation with a sufficiently low permeability to prevent gas flow from deeper sources, it is logical to place a remediation annular plug in a well with SCVF within the cap rock interval if the sealant comprising the plug is capable of forming an effective seal against the impermeable cap rock surface. It is unreasonable to expect that Class G well cement that shrinks upon setting can form an effective seal against a cap rock. However, a fluid sealant that is squeezed into the annulus through suitable access openings in the well casing and that expands upon solidification is ideal if the residual stresses from the expansion are high enough, its compressive strength is good, and if the solidified sealant has a very long service life. The report to the Climate Change and Emissions Management Corporation (“CCEMC”) entitled “Permanent Sealing of GHG Emitting Wells”, and resident on the CSGM web site, describes such a sealant, a fusible bismuth-tin metal alloy. The expansion characteristics of this material are well-known and are listed as fundamental properties by its several vendors. The report contains the results of a computed stress analysis carried out by an independent numerical simulation firm, and the very long service life has been measured at the University of Calgary in a comprehensive corrosion study under a spectrum of expected well environments. The report also contains a description of the methods used to deploy the alloy and several laboratory and field tests conducted to demonstrate its effectiveness.
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