Abstract

The increasingly active exploitation of tight gas shale resources has resulted in new and improved processes to more effectively recover the vast reserves. Horizontal well construction, multi-stage interval isolation, and fracturing techniques are among the more prominent. However, for such otherwise leading-edge engineering and operational processes, 'minimalistic' fracturing system technologies such as high rate, large fluid volume, low sand concentration slickwater treatments have been the norm.

The Big Sandy is a productive field of more than 25,000 wells, located in the eastern USA. Production is dominated by ultra-low permeability Berea tight gas sands and Devonian Ohio shales such as the Huron formation. Post-frac commingled production from area wells typically ranges from 20 to 500 Mcf/D. Due to the low reservoir pressures exhibited by the Lower and Upper Huron, they are considered to be fluid sensitive, and consequently, have historically been stimulated with high-velocity nitrogen or nitrogen foam fracturing treatments. Previous studies indicated the long-term production was better in the stimulations including proppant than in those treated with nitrogen alone. Additional studies concluded that clean-up effectiveness was critical to maximizing net present value. Therefore, it was believed that treatments providing proper proppant placement with a minimized amount of liquid loading would be the best route to improving well performance.

Recently, two vertical wells were fractured using a new process incorporating a pre-slurried proppant concentrate foamed to 93–99 quality with nitrogen, and pumped to place ultra-lightweight in partial monolayer concentrations. Cumulative production after the first 30 days was observed to be approximately 200% greater than offsets. Less equipment, tank storage, and water volume are required for the process, providing for a much smaller location footprint, minimal water-hauling expenses, and significantly lower recovered fluid disposal costs.

Following the successes of the process in the vertical wells, several horizontal wells having 8 to 9 intervals each were treated using the new process in the Big Sandy. This paper provides case histories of those horizontal well stimulations, along with comparison to offset wells treated with nitrogen fracs and conventional foam fracs.

Introduction

Advances in horizontal well drilling, multi-stage interval isolation, and hydraulic fracturing stimulation techniques have recently led to the increasingly active exploitation of unconventional resources, perhaps most notably in the tight gas shales. Fracturing applications incorporating large volumes of slickwater pumped at high rate with low sand concentrations have been the norm for treatment of horizontal gas shales in most basins. However, in fluid sensitive and/or low pressure formations the large fluid volumes can often lead to post-frac cleanup problems and less than optimal well performance.

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