New Composite Fracturing Plug Improves Efficiency in Coalbed Methane Completions

Abstract

Abstract Success in coalbed methane (CBM) development projects can be attributed to efficient hydraulic fracturing of multiple coal seams and quick online gas production. Because the coal can be naturally fractured, friable, and somewhat plastic in nature, successful stimulation can be challenging.1 Typical cased or openhole completion methods involve hydraulic fracturing of the coal seams. The seams may either be commingled and fractured together or isolated to perform staged fracturing treatments. Zonal isolation historically has been achieved when operators set inflatable plugs in the openhole or cast iron plugs in casing between stimulation intervals. Many operators use foamed fracturing fluids to enhance flowback and fracture closure after the initial treatment. Inflatable packers have not been reliable in openhole completions, and this technology is developing at a slow pace in the industry. Difficulties also occur in either drilling or retrieving cast iron plugs used to isolate stimulation intervals in cased hole CBM completions. When multiple cast iron plugs are used in a single well, the difficulty in drilling out these plugs increases with the number of plugs. The increased difficulty is caused when the steel slips are drilled through and the remaining portion of the plugs drop on top of the undrilled plug or plugs left below. This remaining portion of the upper plug rotates freely on the fracturing sand and lower plug, increasing the drillout time on successive plugs. Retrievable plugs are difficult to remove because the fracturing sand left in the wellbore frequently enters the retrievable plug, creating releasing problems. Removal of cast iron plugs has taken as long as 8 days in some CBM completions. A new composite epoxy-glass fracture plug was designed for use as an aid in the completion of multiple coal seams, allowing staged zonal treatment with flowback capabilities after treatment. The fracturing plug is made of an easily drillable, lightweight, composite material with no metal. The composite plug greatly reduces drilling time and drilling difficulties. Case histories of more than 100 CBM wells that were completed with composite fracturing plugs are summarized in this paper. The new plug, combined with nitrogen-foam stimulation, improves completion efficiency and greatly reduces associated rig time in CBM operations. In addition, the new plug design greatly reduces the potential for downhole tool problems, including wellbore debris. Use of the new plug allows the operator to achieve wellstream production 30 days sooner than with previous plugs, allowing more rapid degasification of the coal. P. 603