A total of five carbon dioxide (CO2) /sand well stimulations were successfully executed with two Devonian shale operators in Perry and Pike Counties, Kentucky. This new stimulation method offers a minimum formation damage proppant stimulation approach for natural gas producers in the United States.

Some operators have been concerned about the frac fluid formation damage associated with the water and chemicals used in conventional foam stimulations, whereas other operators have been concerned about the lack of proppant in straight nitrogen fracs used by service companies today. Two carefully screened geological areas of established Devonian shale production were selected based on active ongoing drilling and completion operations. One selected control area contained an existing set of wells with established production histories.

More specifically, one operator furnished three offset wells which were stimulated with the carbon dioxide/sand frac method. The quantity of proppant and fluids pumped during each well stimulation ranged from 23,000 to 43,000 pounds of proppant and from 120 to 160 tons of liquid carbon dioxide. Another operator furnished two offset wells which were each stimulated with approximately 47,000 pounds of proppant and 120 tons of carbon dioxide.

The logistics and field layout of a typical carbon dioxide/sand frac treatment has been described and highlighted. The importance and unique aspects of the closed system blender that is required for job execution is discussed. Five stimulation treatments have been reviewed, and stimulation and preliminary production data compared to offset wells stimulated with nitrogen, and explosives. Initial production results indicate more than a 50 percent increase in production rate compared to nitrogen fraced wells in the Pike County area. In addition, production is also 4.8 times better than conventional shot wells in the same area. These results are encouraging enough to formally combine existing pumping equipment, a closed system blender, and liquid carbon dioxide supplies to develop a new fracturing service in the eastern U.S. A total of 22 additional jobs are planned in the eastern U.S. in low permeability gas formations over the next year.

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