With the increase in the number of horizontal well projects worldwide. several reviews of the potential applications of the technology have been published_ However, contrary La much of the established literature, horizontal well technology is still in its infancy. Horizontal drilling may he commonplace, but still requires considerable improvements. Many field applications have not provided the extra-ordinary production increases that were expected. This review of the Slate of the art of horizontal well technology focuses on the shortcomings in the knowledge base in such areas as drilling, well completion, recovery strategies, and reservoir performance predictions. Various field results and experiences have been evaluated and compared to the expectations based on literature publications. A set of recommendations is proposed on areas requiring further research and development to:

  • ensure better realization of the expectations,

  • expand the application to new areas, and

  • improve the potential for commercial success based on the combination of conventional and horizontal wells.


Horizontal wells were used over forty years ago for hydrocarbon production mainly in Russia. The concept was revived recently due to improvements in directional drilling and the requirements for large offshore developments. The increase in popularity can be associated with proven and expected capability for improving production in some applications. Despite this popularity, there is still a great deal of apprehension towards the application of horizontal wells due partly to:

  • cost,

  • lack of understanding of the technology, and

  • insufficient published production data on the successful applications.

Horizontal wells are generally more expensive, risky, and more difficult to drill than conventional vertical wells. However. the cost of horizontal drilling has decreased substantially in recent years from about 3 times the comparable vertical well in 1984 to about 1.5 times in 19861.

A recent survey of worldwide horizontal drilling projects reported 133 medium and long radius wells with lengths of 300 m or more along the horizontal section2. This listing excluded the large number of short radius wells (with lengths under 300 m) as well as those wells drilled from subsurface shafts and tunnels. From the widely diverse applications cited in this survey, no generic well or development can typify the current horizontal well technology. Hence, the scope exists for innovative applications to a wide range of reservoir types and recovery processes.

Extensive publications of the application of horizontal wells have appeared in literature. The potential of horizontal wells for both conventional oil recovery and for the recovery of heavy oil and oil sands are well documented 3, 4 Reservoir scenarios where horizontal wells present clear advantages over conventional wells include: thin reservoirs (less than 15 m), reservoir with high vertical permeabilities, naturally fractured reservoirs, reservoirs in environmentally sensitive or restricted areas, and reservoirs where gas or water coning problems preclude efficient operation of vertical wells.

It would therefore: appear that no new reviews arc called for, until new developments are made. However. the approach in this review is slightly different.

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