Directional Drilling Limitations

Any drilling limit described in a textbook written today would be simply broken tomorrow by some operator. We have drilled horizontal wells with laterals over 6,100m long; extended reach wells with over 10,000m of horizontal reach (horizontal to vertical ratio of 6 or 7 to 1); multi-lateral horizontal wells with 10 legs; purposefully turned horizontal wells 180° in bearing; drilled 27 wells off a single land based pad location; re-entered just about every wellbore configuration to drill to a new target and are now drilling stacked well pairs within 3m (10') of each other. Coiled tubing drilled wells are also setting new records with lateral sections in excess of 1,200m. Just about anything can be drilled provided you have the financial support. It is better to know the potential equipment or wellbore limitations. The following is a list of some of the factors considered when planning a directional well:

  1. Through experience many operators have established their own maximum inclination and/or dogleg severity limits to minimize rod and casing wear.
  2. Open-hole and cased hole logging equipment have limits on dogleg severity the tools can safely pass through that depends upon the tool OD, hole OD and tool length.
  3. It may be impossible to get sufficient weight on bit (WOB) to drill the well depending upon factors such as drag, drill string assembly design, mud type and hole geometry to name a few.
  4. Key seat and differential sticking potentials.
  5. Maximum dogleg directional equipment can be rotated or slid through (bending stresses).
  6. Wellbore stability (tectonic conditions, sloughing, boulders)
  7. Ability to steer the BHA along the required course (reactive torque).
  8. Ability for equipment to build inclination at the required rates

As directional drilling technologies continue to develop, new applications will emerge. Although oil and gas drilling applications will continue to dominate the future of the directional industry, environmental and economic considerations will force other industries to consider directional drilling alternatives to conventional technologies.

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