The purpose of this research is to investigate the potential of Enhanced Geothermal Systems (EGS) heat extraction using directional wells. Analyses of EGS systems have typically assumed vertical well configurations that are set up in either a 2-point, or 3-point, or 5-point injection scheme. Our previous research demonstrates that the performance of vertical wells is greatly affected by the well separation, thickness of the injection interval, vertical anisotropy in reservoir permeability, and fracture properties and orientation. The near-vertical orientation of fractures often found in EGS environments means that vertical wells cannot optimally exploit the geothermal resources. In addition, vertical well performance can be impacted by density differences that cause the colder injected water to sink to the bottom of the injection interval. The potential of directional well drilling to overcome these problems has led to an investigation of their thermal and economic performance across a variety of EGS environments. This paper presents the thermal performance results of that investigation. In our analysis we simulate an injection and production pair of wells with three different orientations: vertical, 450 inclination, and horizontal. The design specifications and costs were developed for Sandia National Laboratories as part of a separate study by Baker Hughes Inc. For both the 450 inclination and horizontal orientations, the production well is assumed to be at the top. To insure that the performance comparisons are valid, the injection intervals and well separation distances are equal across all three orientations. A total of 30 simulations were run by varying the injection interval, reservoir permeability, and fracture orientation with respect to the well-pair plane. Our results indicate that the 450 and horizontal wells perform significantly better than the vertical wells. They perform slightly better when the injection interval is large (1,000 m or greater). Furthermore, as the well inclination increases (i.e., goes from vertical to 450 to horizontal), the sensitivity of the thermal performance to changes in the injection interval, reservoir permeability, and fracture orientation decreases. We conclude that from a thermal performance standpoint, directional drilling has great potential for EGS because it may (1) significantly reduce the risks associated with the uncertainty in fracture parameters; (2) allow for using shorter well lengths; and (3) require only moderate reservoir stimulation. Work investigating these three points further is currently underway. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

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