| Title | New Drilling System Concept Could Reduce Geothermal Drilling Costs |
|---|---|
| Authors | John C. Rowley, Seiji Saito, Roy Long |
| Year | 1997 |
| Conference | Japan International Geothermal Symposium |
| Keywords | |
| Abstract | The energy price for one kilogram of hOl geothermal fluid is far less than for one kilogram of hydrocarbon production. But the costs for drilling average geothermal wells arc nearly two to four. or more. times those for oil wells drilled to a comparable depth. Therefore, the incentives for geothermal well drilling cost reductions are far greater because well costs are a significant 40 to 60% of total geothermal electric power projects. Incremenlal improvements by use of specilic technology have made some cosl reductions possible over the past two decades. However, these short-term modifications of presently used oilfield drilling equipment and practices. have not provided the major gains needed. Therefore, an innovative purpose-designed advanced geothermal drilling system has been proposed. It is based upon the development of a new, high-temperature, hydraulic percussion hammer. This hammer is designed for deep drilling in the very hard volcanic, metamorphic. and crystalline rocks of geothermal reservoirs. This percussion hammer, an all-metal downhole drilling motor, will improve the rate of penetration by at least a factor of five increasing from a current low of < 3 mlh to perhaps 15 mIh. A dual-wall corrosion resisl.aI1t alloy drillslring configuration is proposed. This type of drill string will solve two major problems of geothermal drilling: severe lost circulation to highly fractured rocks, and also control the bottom hole circulating temperature of the boreholes by using reverse circulation. A depth capacity of 4 km, and a temperature rating of 4000 C. are targeted. An international team has been conducting a feasibility design study for such a purpose-developed advanced geothermal drilling system. Thus far the results indicate that significant operating cost reductions are possible. The time frame for this development is considered a midterm effort. realizable in 5 to 10 years. Details of the design. components of the system and analytical results thus far are presented, and the present stalus of the project reviewed. Currcnt activities and future directions are presented. |