Abstract

Successful development of the Frontier formation in southwest Wyoming begins with the hydraulic fracture treatment design and implementation. Without a design to effectively stimulate the Frontier formation and a proper implementation of that design in the field, production rates will be limited. This paper will describe the results from an extensive drilling and completion program conducted by Bannon Energy Incorporated in the Frontier formation on the Moxa Arch.

Information from over 100 fracture treatments and the production response from over 550 wells will be used to demonstrate the significant improvement in gas production resulting from the fracture treatment designs and implementation methods employed. The effect of fracture conductivity on gas recovery from this formation will be demonstrated along with the effect of multi-phase flow on fracture conductivity.

Introduction

The Moxa Arch area Frontier formation has been under steady development since the mid 1970's. Over 600 Frontier completions have been made in the study area of this paper. Figure 1 indicates the completion activity by year since 1976. Over half of the total completions have been made since January 1992. Completion activity in the early 1990's was elevated due to incentives for "tight" gas development. The continued activity in 1994 however is due to successful drilling and completion practices which have made the formation more attractive for development.

Production from the Frontier is centered along the axis of the Moxa Arch which plunges north to south. Figure 2 is a map indicating the study area along the arch along with the productive sections, Bannon Energy Incorporated (BEI) developed acreage and a boundary between what we will define as Interior wells and field Delineation wells. The geology of the Frontier has been described in great detail in previous publications and studies. While we have not conducted an independent geological study, we have noted from production response and log analysis that north-south offsetting wells have a greater tendency to be similar than east-west offsets.

Hydraulic fracturing treatment designs used on the Frontier formation in the late 1970's and early 1980's consisted primarily of cross-linked water based gels with sand as the proppant Production response from these treatments did not exhibit the type of decline associated with a simulated "tight" gas sand. This unexpected behavior was attributed to formation clay swelling and damage caused by the water based fracturing fluids. In the late 1980's, foamed fracturing fluids were used to reduce the amount of fluid in the fracturing treatment. Intermediate strength proppants (ISP) were utilized in these treatments.

Observed production response from the foamed fluid treatments was not perceived to be much better than the previous water-based fluid treatments. The cost of the foamed treatments with ISP were significantly higher than the earlier treatments with sand ($300,000 vs. $110,000). Therefore, a return to water-based fluids and the use of sand was determined to be more economic. Production response from these recent treatments has been similar to the response noted in the early 1980's, which were, again, not typical of stimulated "tight" gas sands and thought to be damaged.

The goal of the authors efforts during the BEI Frontier development program has been to place a highly conductive propped fracture through the use of intermediate strength proppants and modern fracturing techniques.

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