Process and seal for minimizing interzonal migration in boreholes

摘要

A process and a material for use in sealing casing lining in a borehole is taught. The process includes the placement of a bitumen sealant material in a position between the casing tube and the wall of the borehole to be maintained in this annulus by means of a retaining devise such as an external casing packer or with the placement of a retainer made of cement grout and situated at the lower end of the casing tube. The bitumen sealant material prevents the passage of fluids vertically through the borehole. The sealant material remains viscous over time and can flow to fill voids which may occur in the rock formations adjacent to the borehole, or in the steel casing of the casing tube. To improve the sealing capabilities of the bitumen material a measured amount of fine grain weight material can be added to the bitumen to increase the density of the sealant material and thereby increase the hydrostatic pressure that the column of bitumen sealant will exert on the bottom and the walls of the borehole.