Horizontal wells with lengths up to 8,000 ft are capturing an ever-increasing share of all wells drilled. However, the performance of many of these wells is significantly less than what is predicted by published well performance models. The factors causing this variance must be understood if horizontal wells are to produce at their potential.

Methods are presented in this paper that demonstrate which reservoirs may benefit from horizontal wells instead of fractured vertical wells. Additionally, an extensive analysis of expected performance shows that many horizontal wells may also benefit from fracture stimulation, and that the vast majority of reservoirs that have traditionally been candidates for vertical well fracturing are obvious candidates for horizontal well fracturing.

There is a need to determine the in-situ stress directions before a horizontal section is drilled, even if hydraulic fracturing is considered unattractive. These contrasting stresses can greatly affect the producing potential of a horizontal well. Analytical approximations are offered which can account for the permeability anisotropγ expected in these cases. Performance comparisons demonstrate that a horizontal well must be drilled in accordance with these stress measurements to maximize production rates.

Case histories are used to demonstrate both successes and failures of hydraulically fractured horizontal wells. Various completion practices are reviewed and their corresponding results are explained.

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