ABSTRACT
A rule of thumb that is often mentioned is that drilling accounts for about 50% of the cost of a geothermal project. Although the accuracy of such a statement may not be high, it is a certainty that drilling is expensive. Figure 8.1 is a graph that shows the drilling costs for various types of geothermal drilling projects. For comparison, the costs of completing oil and gas holes by the petroleum industry are also shown. Note that the curve for completing boreholes for ground source heat pumps, which are discussed in Chapter 10, is extrapolated to depths much greater than most such boreholes are drilled. It is shown for comparison.
