Optimization and Evaluation of Openhole Cavity Completion Techniques for Coal Gas Wells

Abstract

Abstract An innovative completion technique that has been used to effectively complete coal gas wells is an open-hole completion in which the coal is encouraged to slough into the wellbore. During the completion process, the wellbore is effectively linked to the reservoir due to the creation of numerous multi-directional self-propped fractures. The technique has been commonly called an "open-hole cavity completion." However, the cavity is a by-product of the process and not the primary objective of the completion. A more suitable terminology for the technique is "dynamic open-hole completion." The majority of the dynamic open-hole completions have been performed in the Fruitland Formation of the San Juan Basin, Colorado and New Mexico. Dynamic open-hole completed coal gas wells in some areas, but not all, produce at significantly greater rates than wells completed using other techniques such as hydraulic fracturing. Because of the success in the San Juan Basin, dynamic open-hole completions have been attempted in other basins including the Piceance, Powder River, Arkoma, Uinta, and Black Warrior. This paper presents a conceptual model and a working hypothesis concerning what takes place in the coal reservoir during the dynamic open-hole completion process. Based upon this model and hypothesis, techniques to: i) optimize the completion, ii) evaluate the effectiveness of the technique, and iii) how to determine when to terminate completion operations will be presented.