Hard Rock Penetration - Summary

The theme of this review, ''Geothermal Energy and the Utility Market--The Opportunities and Challenges for Expanding Geothermal Energy in a Competitive Supply Market'', ties in directly with the subject of this session. That is, it follows immediately that the establishment, utilization and maintenance of the borehole for extracting energy and data are the first and continuing concerns of the geothermal industry in expanding that resource's role in the utility market. There is probably no portion of the utilization of the geothermal energy resource that more determines the cost competitiveness of that resource than the cost of reaching and delivering the heat energy. Therefore, there is probably no other area where advances in the state-of-the-art can be more directly and profitably applied to the theme of this review. The four subjects in this session feature the activities under the program conducted at the Sandia National Laboratories (Albuquerque). Specifically, an overview is presented, a discussion of advances in acoustic telemetry, the status of lost circulation technology development, and a description of downhole memory-logging tools. One of the points of emphasis in the overview concerned slimhole drilling. The cost advantages of a smaller diameter borehole are intuitively obvious. The possibility of cutting drilling costs by half opens up the possibility of conducting more detailed mapping of the thermal reserves. This is particularly attractive for the Pacific Northwest, where a power shortage looms in the future. There is substantial evidence of significant useful thermal reserves in the area. However, the capability of tapping them is, in many cases, dependent upon finding drilling locations not only advantageously related to the power grid, but suitably related to natural features and environmental considerations. These requirements demand a practical method of getting more accurate maps of the resource. Slimhole drilling could well provide the answer. As stated in the more comprehensive paper which follows, acoustic telemetry as a method of data retrieval from the bottom of the borehole has been a dream of the drilling industry for half a century. The problem up to now has been largely one of data rate. The result has been that the main practical use has been to provide directional data in offshore drilling, and limited use with gamma tools. These uses employed the drilling mud as the medium. The Sandia work has studied and developed the technique of using acoustic waves in the drill pipe, which, despite problems with wave reflections due to joints, etc., allows for substantial increases in the data rate. This technology is being transferred to industry. Working with industry, SNL is expecting to work with them to develop analysis codes, quantify attenuation, and prototype the critical hardware