Disclosed apparatus and methods permit well-site operators to retrofit existing wells in order to comply with local regulations that restrict the escape of annular natural gas from hydrocarbon wells. Such allows sealing around an exterior of surface and concentric production casings, both above and below the point of their intersection, then assembling a pressure vessel around that point and between those seals so as to capture and hold gas rising up an intercasing annulus, for periodic controlled venting.
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