Underbalance or extreme overbalance

Application of an extreme overbalance, sufficient to fracture the reservoir formation, applied either Juring or after perforating was first presented as an alternate completion technique during the 1993 Fall SPE Conference.(1 ) During the ensuing two years, a number of jobs have been run by different operators in a variety of formations with varying applications. The primar y question asked by an operator relates to the benefit of extreme overbalan ce (EOB) versus current perforation techniques of underbalance (UB) or mode st overbalance for well control. Of course this question spawns a whole set of new questions about when and how to use and the benefits and risks of t he EOB. EOB, as used in this paper, includes extreme overbalance perforatin g and rapid overpressured perforation extension. This paper compares and co ntrasts UB and EOB strengths and weaknesses and provides recommendations of when and why to use the different techniques. Field examples are provided of successful and unsuccessful application of EOB completions.