Coarse sediment in transport along a riverbed gradually reduces in size as a result of grain-to-grain collisions (Daubrée, 1879). This process is termed abrasion and represents the combined effects of attrition, the gradual wear of the surface into fine particles, and fragmentation, the loss of larger particles (Attal & Lavé, 2009;Kuenen, 1956). Downstream abrasion is commonly modeled as an exponential decay of either the grain diameter or mass,where M o is the original grain mass, M x is the grain mass at a given distance downstream, x is the downstream transport distance (commonly, in km), and α is a mass loss coefficient (1/km) representing abrasion rate (Sternberg, 1875). α is generally defined for a particular lithology either via laboratory experiments (e.g., Attal &

The use of a newly-designed bottomhole assembly in the Kuparuk River Field on Alaska's North Slope has proven to be a cost-effective improvement over traditional rotary drilling methods. The bottomhole assembly consists of a polycrystalline diamond compact bit, a positive-displacement downhole motor with specially-designed tilted drive sub (called a navigation sub), and a measurement while drilling system. The use of these tools in combination allows the driller to constantly monitor the well path and either drill straight ahead or make necessary course corrections, while drilling continues uninterrupted. The savings from such a system have proven to be substantial, with significant reductions in drilling time, increases in rate of penetration, and average savings to the operating company of over $50,000 per well.

While traditional definitions classify short-, medium- and long-radius lateral wells by angle build rates, the technology now employed to achieve those build rates suggests an industry definition which characterizes lateral wells not only in terms of wellbore geometry, but in engineering terms as well. In proposing such a definition, this paper examines new developments in downhole technology, focusing on short- and medium-radius systems to show how choice of drilling hardware can determine the type of curve drilled, as well as how it is planned and completed. New horizontal well-planning techniques developed in light of recent hardware improvements are also discussed, while technicaf innovations still in development are noted. Field results of recent lateral wells present examples of problem-solving, since a detailed discussion of lateral applications exceeds the scope of this paper. Concluding remarks suggest areas for further development to improve economics and performance in lateral drilling.

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