This paper describes case histories of wells drilled primarily in two fields in Southern Oklahoma, Southwest Davis and Cottonwood Creek, which are located in an area of known deviation problems. Past operations in this "crooked hole country" have employed conventional means of drilling these problem wells, including running relatively light weights and problem wells, including running relatively light weights and stiff, packed hole assemblies. Ordinarily, conventional directional tools are used to direct the hole to a specified location. In an attempt to control deviation problems and increase penetration rates, a steerable system was incorporated into the penetration rates, a steerable system was incorporated into the drilling program for the 8-3/4" hole size, at depths that ranged from 2000 to more than 8000 feet. While directional tools were used to direct the hole to a specified location, use of the steerable system resulted in a drastic reduction in the number of days required to drill the interval. Introduction Drilling through strata with significant dip angles can result in numerous hole problems because of appreciable and sometimes rapid hole deviation, which can increase drilling costs sharply. However, introduction of steerable "navigation" drilling technology has been found to help reduce unwanted hole deviation in the complex geology of the Southwest Davis and Cottonwood Creek fields of Southern Oklahoma (Figure 1). Prior to application of the steerable system, conventional Prior to application of the steerable system, conventional means of controlling deviation problems were employed, such as fanning bottom - reducing weight on bit while increasing rotational speed - to reduce unwanted angle build. However, as a result of the lighter WOB, penetration rates often were reduced to uneconomical levels. In most wells in the Southwest Davis and Cottonwood Creek fields, pendulum or packed hole assemblies were employed to reduce hole deviation. Their performance, however, was often unpredictable and, because they also require lower weight on bit, penetration rate was limited. Excessive torque and drag also has been a problem when packed hole assemblies are used. Because it is usually possible to predict the direction a well will drift, the surface location of a well sometimes can be placed so the well will drift into the target. However, in the placed so the well will drift into the target. However, in the region of the subject wells, it is more difficult to predict the magnitude of the drift; that is, the horizontal displacement that results from wellbore drift. Another option often employed was use of a bent sub and motor to turn the hole down to eliminate unwanted angle build. where formation tendencies are strong, however, a high-angle bent sub is necessary, which can itself create severe doglegs. Extensive reaming often was required when such bent sub assemblies were followed by stabilized assemblies. While each of these solutions may have provided an optimal approach from an engineering standpoint, it was found that the steerable system provided a cost effective method of maintaining directional control without decreased penetration rates or excessive doglegs. Background Steerable System By incorporating a steerable downhole motor, the navigation drilling system is capable of changing the course of the hole without requiring a trip to change the BHA, thus reducing significantly the time required to drill a hole interval. A measurement-while-drilling (MWD) system also is employed to provide real-time updates of hole trajectory and toolface orientation. P. 299
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