Short-Radius Lateral Drilling System
Authors: Warren T.M. , Winters W.J. , Mount H.B. , Mason K.L. 
Published: December 2007

Abstract
Development of a rotary-guided short radius curve drilling tool is described. Improvements over prior tools include an anti-whirl PDC bit, a stronger and smoother flexible joint, a signalling valve to assist in tool face orientation, and a computer-aided system to monitor orientation while drilling. The tool drills a smooth radius of curvature which conforms to a simple relationship between the bit tilt angle and the distance between two points of contact with the wellbore. The authors advocate using this type of tool to economically enhance oil recovery in mature fields by laterally recompleting existing wells. Eight short radius lateral wells were drilled at 5000 ft depth in West Texas during field testing of the tool.

Introduction
There are numerous mature oil fields in the United States and other countries that are experiencing declining production. Unfortunately, even after the latest enhanced recovery methods are utilized, vast oil resources will be left unproduced.
Lateral wellbores drilled from existing wells offer the potential to drain more oil than would be recovered otherwise. Laterals may be used to tap fresh oil by intersecting fractures, penetrating pay discontinuities, and draining up-dip traps. Lateral recompletions can correct production problems such as water coning, gas coning, and excessive water cuts from hydraulic fractures which extend below the oil-water contact. Synergistic benefits may result from coupling lateral recompletions with enhanced recovery techniques to solve conformance problems, contact unswept oil by recompleting injection wells, and to redirect sweep by converting existing well patterns into line-drive configurations. Lateral recompletions strategies can take advantage of the current production infrastructure, capital resource of existing wellbores, known resources of oil in place, and secondary and tertiary recovery technology.
A major impediment to the widespread use of lateral re-entries is that drilling and completion of the laterals must be done relatively "cheaply." Workover economics in mature fields require substantial cost reductions over the methods most often used for drilling new horizontal wells. The need for a reliable reduced-cost drilling system that utilizes the equipment and cost structures of workover and repair services provided the impetus for a development and field test program in West Texas where laterals were drilled in 8 wells.
This paper primarily discusses development of the curve drilling portion of the re-entry system. Even though this is a small part of the overall effort to place a re-entry lateral in a well, it is a critical and costly part. Once the curve is drilled, the lateral is rotary drilled with a somewhat more conventional stabilized bottomhole assembly and the same articulated drillstring that is used for curve drilling.

Curve Drilling Tool Background
For a re-entry drilling system to be technically successful it must be capable of drilling a consistent radius of curvature and drilling the curve in the desired direction. These requirements arise from the necessity to (1) position the end of the curve within a precise depth interval so the lateral can traverse the payzone as desired, (2) place the lateral in a direction dictated by well spacing, desired sweep pattern, or other geological considerations, and (3) to establish a smooth curve to facilitate drilling the lateral and completing the well.
P. 693^