Stimulation of Deep Gas and Gas-Distillate Wells

Abstract

Abstract This paper discusses recently developed gas and gas-distillate producing wells, deeper than 10,000 ft, in West Texas and Southeast New Mexico. High bottom-hole pressures and temperatures above 200F require modification of conventional completion and stimulation techniques. The problem of formation damage due to solid infiltration from drilling fluids and cement slurries is particularly severe. The use of high-density brines as completion fluids is described and recommended to minimize such formation damage. During completion, mud dispersal and removal acids are usually employed to clean up the critical area next to the wellbore. In case of severe permeability damage, it may be necessary to employ supplementary stimulation treatments using acids with retarded reaction rates. Pressure limitations usually require that such treatments be conducted through tubing. When treating acids can be pumped down the casing, utilization of large-volume, high-injection-rate treatments have resulted in increased benefits. Such treatments in the Azalea Devonian field have proven equivalent to fracturing treatments employing propping agents. Comparative lab tests of post-treatment fracture flow capacities indicate that propping sand may undergo crushing or embedment when subjected to high overburden pressures. Although the use of malleable propping agents such as walnut shells or aluminum pellets often results in considerable improvement in productive capacity following fracturing, even better results sometimes are obtained with acid. Nonuniform acid solubility of the fracture faces results in self-propping, thus providing highly permeable flow channels which are unblocked by propping material. High bottom-hole temperatures require the use of special inhibitors to avoid excessive corrosion of metal well equipment. In some cases, the problem of gyp deposition resulting from contact between spent acid and incompatible brine has been overcome by the use of suitable chelating chemicals. Case histories are included, illustrating treating procedures and results obtained under various circumstances. Correlation of reservoir conditions and treatment data have made possible the evaluation of various stimulation methods and selection of optimum treating techniques. Introduction Well stimulation has played an important part in the development and exploration of deep gas reservoirs in the West Texas-Southeast New Mexico area. Most of the recent activity has occurred in the Delaware basin, Sheffield channel, and in the Val Verde basin area. Two important West Texas discoveries, both near the eastern mouth of the Delaware basin in Pecos County, have triggered a new era of deep search throughout the region. Mobil Oil Co.'s No. 1 Kathleen Moore was completed in the Pennsylvanian at 15,041 to 15,047 ft for a calculated open flow of 102 MMcf/D for the discovery of the Rojo Caballos pool. Shut-in bottom- hole pressure was reported to be 12,590 psi. About 20 miles southwest of the Mobil well, another strike was made in The Atlantic Refining Co. No. 1 Kelly, to inaugurate the Hershey pool. This well became the deepest producer in Texas when it potentialed a combined flow of 52 MMcf/D from the Fusselman, Devonian and Montoya between 15,800 and 16,680 ft. Another significant gas discovery was the triplycompleted Shell Oil Co. and Humble Oil and Refining Co. No. 1 Blackstone-Slaughter in the Yucca Butte area, five miles southeast of Sheffield. This well had a calculated absolute open flow of 5.6 MMcf/D from the Pennsylvanian detrital at 8,190 to 8,310 ft, 12 MMcf/D from the Connell at 9,993 to 10,012 ft and 16.5 MMcf/D from the Ellenburger at 10,050 to 10,092 ft. Gas-distillate ratios were 67,000:1 for the Pennsylvanian, 16,500:1 for the Connell and 22,600:1 for the Ellenburger. Other important deep gas pools in the area under consideration include the Vinagerone, Brown-Bassett, Puckett, Emperor, Reeves, Remuda, Azalea, Henshaw, Lancaster Hill, Baggett Ranch, Kermit, Cobblestone, Joe T., Custer, Midland Farms, Jack Herbert, Vacuum, Stiles, Gladiola, Scharb, King, Lusk, Denton, Lea, Mescalero and Coyanosa. JPT P. 841^