Abstract: 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.

Abstract: A plug and process for use in well abandonment is taught. The plug includes a retaining structure, such as a cement plug, which is placed in the well borehole and an amount of a viscous substance, such as sand and fines in bitumen, above the retaining structure. The viscous substance prevents the passage of fluids vertically through the well borehole. The plug remains viscous over time and can flow to fill void which may open up in the well adjacent the plug. To enhance the sealing characteristics of the plug, the process for placement of the plug includes the removal of a section of the well casing and possibly also the sheath and a layer of the borehole wall behind the removed section of the casing at the position of the plug to prevent the flow of fluids around the plug.