24 - Plugging of CBM wells

Abstract

Horizontal degasification boreholes drilled from within the mine or from surface coal bed methane (CBM) horizontal wells have proven to be effective in recovering coal mine methane and coal bed methane for degasification and commercialization. However, the inability to completely plug horizontal boreholes still producing methane gas prior to mine-through can cause unsafe situations and significant coal production delays. To date, cement slurry has commonly been used to plug underground horizontal degasification boreholes <2000ft. with varying results. The purpose of this chapter is to describe the successful plugging of horizontal underground degasification boreholes and CBM wells each with multiple horizontal laterals drilled in the coal, including sidetracks. To date 1,451,398gal of crosslinked polymer gel have been pumped to plug 97 underground horizontal boreholes and 36 CBM wells’ coal bed laterals, totaling 182miles! This includes in-mine remediation plugging whereby polymer gel is mixed and pumped underground to plug client's boreholes or coal bed laterals after mine through determined other plugging materials were not successful. The quantity of gel pumped is almost two times the calculated volume of the boreholes and coal bed laterals, including sidetracks. The polymer gel effectively squeezes into the fracture system of the coal displacing gas and water demonstrating an affinity to attach itself to everything, including adhering to the inner wall of the borehole providing an impenetrable skin, minimizing gas and water migrating back into the borehole as evidenced by mining into the boreholes and coal laterals.