Short Turn Radius Drilling
The build rate angle on a short radius well may range from 5 to 10 degrees per three feet (roughly one meter). The radius of curvature may be as small as 20 ft, with a hole size of between 4 3/4 inches and 6 1/2 inches. Figure 1 (Short radius angle-building assembly) illustrates a short radius angle-build assembly that employs curved, articulated tubulars.
Short-radius applications include infill drilling in depleted reservoirs draining the very top of undrained reservoirs (attic oil), drilling shaly intervals or other trouble-prone formations and drilling multiple drainholes from one vertical wellbore. They are also proving useful for enhanced oil recovery, particularly steam flooding.
Short-radius wells are relatively inexpensive. They provide easy, precise entries to the horizontal sections, and can reach lateral displacement at a minimum measured depth. This makes them particularly appropriate, and sometimes necessary, for shallow reservoirs.
Disadvantages of short radius wells include special drilling equipment requirements such as articulated tubulars, limits on hole size and reach, limited azimuth control, and a limited ability to run logging tools or casing. Coring abilities are limited to 3-foot sections of 1-inch diameter core, and diamond or PDC bits must be used when drilling with a short, articulated motor.
