This paper assesses the current state of the art in horizontal directional drilling (HDD) for pipeline installation, reviews analytical methods associated with HDD pipeline design and installation, and presents concepts useful in the application of HDD techniques to pipeline construction in the arctic. The current state of the art is defined by a review of recent commercial applications of HDD to pipeline construction. Details on completed projects defining feasibility limits with respect to length and pipe diameter are presented. Restrictions with respect to subsurface conditions are examined. Theoretical limits on HDD pipeline installation are explored including a discussion of analytical methods available to calculate pulling loads associated with very long HDD Installations. The paper concludes with conceptual design examples of how HDD installation might be applied to obstacles presented by the arctic environment.
Three primary characteristics govern the feasibility of an HDD installation:
pipe diameter, and
These three characteristics work in combination to limit what can be accomplished using existing HDD tools and techniques. Individual limits for each of these characteristics are discussed in the following paragraphs. It should be noted that, consistent with the objectives of this paper, this discussion is founded on commercial experience within the HDD Industry. The limits of directional drilling technology applied to drilling oil wells are not considered. While such tools and techniques may be applied to pipeline installation in the future, this paper discusses what is being utilized in the Pipeline Industry today.
The nature of the subsurface material through which the drilled path must pass is critical in determining the technical feasibility of an HDD pipeline installation. For a pipeline to be installed by HDD, either an open hole must be cut into the subsurface material so that installation of a pipeline by the pullback method is possible, or the properties of the subsurface material must be modified so that the soil behaves in a fluid manner allowing a pipeline to pass through it.
In the open hole condition a cylindrical hole is drilled through the subsurface. Drilling fluid flows to the surface in the annulus between the pipe and the wall of the hole. Drilled spoil is transported in the drilling fluid to the surface. This is generally applicable to rock and cohesive soils. It may also apply to some sandy or silty soils depending on the density of the material, the specific makeup of the coarse fraction, and the binding or structural capacity of the fine fraction.