ABSTRACT
Many South Texas low permeability Vicksburg gas completions have been made economical through hydraulic fracturing. Between 1981 and 1984, 36 Vicksburg completions by Sun Exploration and Production Company were evaluated and subsequently fraced based on the results of pre-frac testing and frac optimization studies. These completions are located in 14 gas fields in Jim Wells, Brooks, Starr, and Hidalgo Counties of South Texas at depths ranging from 4,500' to 12,200' (1,372 m to 3,719 m).
This paper details a post-audit of well performance for these 36 Vicksburg completions, introduced by a review of Vicksburg reservoir characteristics and Sun's pre-frac evaluation methods. An example of the frac optimization and selection process is presented. The post-audit reviews predicted/actual initial deliverability, ultimate gas recovery, and frac length. An economic post-audit is also presented to illustrate the profitability of Sun's Vicksburg fracturing program. Finally, the conclusions of the post-audit as they relate to future Vicksburg frac candidates are presented and discussed.
The results of the post-audit generally indicate that the accuracy of post-frac initial deliverability projections provides a good correlation to the accuracy of projected ultimate recovery and the accuracy of frac length calculations. Also, the average ratio of predicted/actual initial deliverability provides a good overall indicator of a confidence factor that can be applied to Sun's reservoir simulator's projections of fractured well performance. Finally, statistical data infers that there is an evolution of skill in projections of post-frac well performance.
