THE PERMEABILITY FACTOR IN COALBED METHANE WELL COMPLETIONS AND PRODUCTION

Description: After 30 years of CBM production in the USA, general principles and decision trees have emerged to guide an operator in choosing a well completion based on permeability. This paper discusses the role of permeability in choosing CBM well completions, as well as examples of those completions. We also re‑examine the striking observations of permeability increases with depletion (10‑100 times) in the San Juan basin. Application. If enough permeability measurements are made, well completions can be prioritized, and hybrid well completions evaluated. The benefits of horizontal and multi‑lateral wells are made clear. Low permeability is a serious challenge for CBM ventures, and success will entail finding regions of enhanced permeability, utilizing horizontal wells, and "creating" permeability by new‑paradigm methods. Industry results have led to two benchmarks for evaluating, ahead of full‑field development, (1) commercial success from reservoir parameters, and (2) effectiveness of well completions by comparing early production with reservoir parameters. The latest attempts to model and match the strong permeability increases with depletion in the San Juan basin are reconciled, although there remain differences. Results and Conclusions. (1) guidelines for CBM well completions are given, which include permeability bands, benchmarks, and decision trees, (2) options are evaluated for CBM completions in low‑permeability "tight" coals, (3) a concensus has been obtained for some reservoir parameters after matching the strong permeability increases with depletion in the San Juan basin. Significance: The guidelines, including permeability bands and benchmarks, are simple and practical, and should benefit any CBM completions strategy. The concensus from modeling permeability increases in the San Juan basin will assure better predictability of CBM production, and of greenhouse gas injection into coalbeds.