Introduction

Deep, high-pressure Morrow sands in the western Oklahoma portion of the Anadarko Basin indicate the area's potential to become one of the more prolific natural gas producing areas in the continental United States. In the past several years, there have been a number of major deep Upper-Morrow gas discoveries in the Oklahoma counties of Beckham, Roger Mills, and Washita. Fig. I illustrates the major Upper Morrow fields in the three-county area.

El Paso Natural Gas Co. has been engaged in an active exploration program in this area during the past 6 years. This paper is based on the company's accumulated drilling experience in the area combined with the knowledge and experience of drilling contractors, service companies, and other operators active in the area. The area is unique in that almost every conceivable problem known to the drilling industry can occur during the drilling and completing of a single Upper Morrow well. This paper will summarize a few of the most frequent and most troublesome problems encountered by El Paso Natural Gas Co. in western Oklahoma. This paper will also discuss methods used by the company to prevent, overcome, or alleviate the problems.

SUBNORMAL AND ABNORMAL PRESSURES

The most important and most critical drilling problem in the western Oklahoma area of the Anadarko is abnormal pressure. All Morrow tests in the area must be designed basically to hold formation pressures ranging from the equivalent of 16.3-ppg to 18.1-ppg gradients. To add to the problem, in the area there are many fractured loss circulation zones with fracture pressure gradients of lower than the gradient of saturated salt water. Also, many areas of regressive fracture gradients add to the complexity of selecting the proper casing points. points. Fig. II is an equivalent pore pressure plot of the El Paso-Hunt Cross No. 1 located in Section 22, T-13-N, R-24-W in Roger Mills County, Okla. This well was the discovery well of the West Cheyenne field. The actual casing program is also shown. The area has normal program is also shown. The area has normal pressures (0.433 psi/ft) to an approximate depth pressures (0.433 psi/ft) to an approximate depth of 10,500 ft. At 10,500 ft, the gradient starts building rapidly, reaching 13.8 ppg at approximately 11,000 ft in the Granite Wash section. Below this interval, formation pore pressures continue steadily increasing throughout the Granite Wash and Atoka sections, reaching 15.5-ppg equivalent at 15,000 ft.

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