Horizontal Drilling is now a well established technique with growing popularity for exploiting a number of reservoirs which would otherwise be noncommercial. However a horizontal well requires a substantial engineering work compared to conventional directional drilling. Significant advances in drilling technology have made it possible to drill horizontally in almost any situation by using very specialized tools. But some inherent weaknesses to this technique still exist, like casing design. Most of the reported horizontal wells are completed with open hole or slotted liner. This type of completion is simple and inexpensive, but may not furnish enough support to the walls of the well to allow for long well life.

This paper discusses casing design considerations for horizontal wells. It addresses the type and nature of loads applied on casing strings set in horizontal wells; examples of these loads are torque and drag, formation subsidence, effect of perforations, and bending loads. A design method for casing string under loads that prevail in horizontal wells is also included. The proposed design method shows that the horizontal section needs high collapse resistance pipe or thick-wall pipe to avoid casing failure due to non-conventional loads that prevails in horizontal wells.

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