This Handbook is a description of the complex process that comprises drilling a geothermal well. The focus of the detailed Chapters covering various aspects of the process (casing design, cementing, logging and instrumentation, etc) is on techniques and hardware that have proven successful in geothermal reservoirs around the world. The Handbook will eventually be linked to the GIA web site, with the hope and expectation that it can be continually updated as new methods are demonstrated or proven.

Electricity production from geothermal resources is currently based on the exploitation of hydrothermal reservoirs. Hydrothermal reservoirs possess three ingredients critical to present day commercial extraction of subsurface heat: high temperature, in-situ fluid and high permeability. Relative to the total subsurface heat resource available, hydrothermal resources are geographically and quantitatively limited.A 2006 DOE sponsored study led by MIT entitled "The Future of Geothermal Energy" estimates the thermal resource underlying the United States at depths between 3 km and 10 km to be on the order of 14 million EJ. For comparison purposes, total U.S. energy consumption in 2005 was 100 EJ. The overwhelming majority of this resource is present in geological formations which lack either in-situ fluid, permeability or both. Economical extraction of the heat in non-hydrothermal situations is termed Enhanced or Engineered Geothermal Systems (EGS). The technologies and processes required for EGS are currently in a developmental stage. Accessing the vast thermal resource between 3 km and 10 km in particular requires a significant extension of current hydrothermal practice, where wells rarely reach 3 km in depth.This report provides an assessment of well construction technology for EGS with two primary objectives: 1. Determining the ability of existing technologies to develop EGS wells. 2. Identifying critical well construction research lines and development technologies that are likely to enhance prospects for EGS viability and improve overall economics. 4Towards these ends, a methodology is followed in which a case study is developed to systematically and quantitatively evaluate EGS well construction technology needs. A baseline EGS well specification is first formulated. The steps, tasks and tools involved in the construction of this prospective baseline EGS well are then explicitly defined by a geothermal drilling contractor in terms of sequence, time and cost. A task and cost based analysis of the exercise is subsequently conducted to develop a deeper understanding of the key technical and economic drivers of the well construction process. Finally, future research & development recommendations are provided and ranked based on their economic and technical significance.5

The search for silicic magma in the upper crust is converging on the Long Valley Caldera of eastern California, where several lines of geophysical evidence show that an active magma chamber exists at mid‐to lower‐crustal depths. There are also other strong indications that magma may be present at depths no greater than about 5 km below the surface. In this paper, we review the history of the search for magma at Long Valley. We also present the preliminary results from a coordinated suite of seismic experiments, conducted by a consortium of institutions in the summer and fall of 1984, that were designed to refine our knowledge of the upper extent of the magma chamber. Major funding for the experiments was provided by the Geothermal Research Program of the U.S. Geological Survey (USGS) and by the Magma Energy Technology Program of the U.S. Department of Energy (DOE), a program to develop the technology necessary to extract energy directly from crustal magma. Additional funding came from DOE's Office of Basic Energy Sciences and the National Science Foundation (NSF). Also, because extensive use was made of a 0.9‐km‐deep well lent to us by Santa Fe Geothermal, Inc., the project was conducted partly under the auspices of the Continental Scientific Drilling Program (CSDP). As an integrated seismic study of the crust within the caldera that involved the close cooperation of a large number of institutions, the project was moreover viewed as a prototype for future scientific experiments to be conducted under the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL). The experiment thus represented a unique blend of CSDP and PASSCAL methods, and achieved goals consistent with both programs.

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This report documents the results of a study of advanced drilling concepts conducted jointly for the Natural Gas Technology Branch and the Geothermal Division of the U.S. Department of Energy. A number of alternative rock cutting concepts and drilling systems are examined. The systems cover the range from current technology, through ongoing efforts in drilling research, to highly speculative concepts. Cutting mechanisms that induce stress mechanically, hydraulically, and thermally are included. All functions necessary to drill and case a well are considered. Capital and operating costs are estimated and performance requirements, based on comparisons of the costs for alternative systems to conventional drilling technology, are developed. A number of problems common to several alternatives and to current technology are identified and discussed. ACKNOWLEDGMENTS Through the course of this study, the authors have discussed advanceddrilling concepts and systems with a large number of people closely involved with drilling, drilling operations, and drilling research. Some of these people we have known and been associated with for some time; others we met only in the course of this effort. Almost without exception, these individuals were completely open in discussing their knowledge and experience with drilling systems and in providing the authors with data and documentation on both current and past efforts. Without this cooperation and courtesy, this study would not have been possible. Work performed at Sandia National Laboratories is supported by the U.S. Department of Energy under contract DE-AC04-94AL8500.