Class II Saltwater Disposal Well Completions in Open and Cased Hole: Which is Better and why?

Abstract

The scope of this paper is to use publicly and privately sourced data to compare openhole versus cased hole completion techniques and injection results in select Ohio Class II saltwater injection wells (SWIW). The vast majority of the SWIWs drilled in Ohio the past 10 years have been completed openhole, typically by drilling to total depth and then carefully selecting a large diameter greater than 7-inch casing shoe depth and cementing casing above the Cambrian-Ordovician age reservoirs. That allows for 1,000 feet plus of openhole and multiple targets for injection. There have been successful cased hole completions. Cased hole completions open the door to an operator’s ability to stimulate multiple injection zones more effectively than in an openhole using a non-selective stimulation of a long interval. A large public oil & gas well database was used to gather data for an ‘area of interest’. A private company offered greater operational details and testing information to assist in the evaluation of which completion technique is most effective for large volume fluid injection. Hall Plots were generated to compare openhole and cased hole SWIWs, but will not be the focus of this paper. A review of physical reservoir properties and fracture modeling were used to estimate three-dimensional stimulation or frac geometries and to approximate radial or linear saltwater travel over the life of a disposal well. This paper will attempt to answer several questions. Was the result of the cased hole completion better than previous offset well’s openhole completion. How could results be improved over what procedures were done? What was the pressure response of the openhole and cased hole injections following stimulation? Finally, a comparison of well costs and economics was done to evaluate and make recommendations about improving injectivity, and when to consider remedial treatments.