A Case Study of the Upper Cotton Valley in the Oak Hill Field of East Texas

This paper summarizes a study of Upper Cotton Valley completions in the northern half of the Oak Hill Field in the East Texas Basin. The study involved the evaluation of full core, sidewall core, special permeability measurements, x-ray diffraction, thin sections, SEM, conventional open hole logs, magnetic resonance imaging tools, micro-resistivity imaging tools, production logs, build-up data, and forty-eight Upper Cotton Valley completions. The overall goal of the project was to improve the completion economics of the Upper Cotton Valley in Oak Hill. This paper details improvements made towards the identification and prediction of productive Upper Cotton Valley sands. An in-depth analysis of the stimulation and completion procedures for the Upper Cotton Valley was also undertaken. That portion of the Upper Cotton Valley study primarily involved the development of a new low sand concentration fracture stimulation technique. These results are presented in a separate paper, SPE 38611. In this paper, a method is described that could be applied to the development of other stacked tight gas sand reservoirs where conventional open hole logs or other conventional evaluation methods have proven to be unreliable. The method resulted in a 50% reduction in average completion costs, with no loss in average initial production rates or reserves per Upper Cotton Valley completion.