Annual Report: Support Research for Development of Improved Geothermal Drill Bits

The work reported herein is a continuation of the program initiated under DOE contract E(10-1)-1546* entitled "Program to Design and Experimentally Test an Improved Geothermal Bit"; the program is now DOE Contract EG-76-C-1546*. The objective of the program has been to accelerate the commercial availability of a tolling cutter drill bit for geothermal applications. Data and experimental tests needed to develop a bit suited to the harsh thermal, abrasive, and chemical environment of the more problematic geothermal wells, including those drilled with air, have been obtained. Efforts were directed at the improvement of both the sealed (lubricated) and unsealed types of bits. The unsealed bit effort included determination of the rationale for materials selection, the selection of steels for the bit body, cutters, and bearings, the selection of tungsten carbide alloys for the friction bearing, and preliminary investigation of optimized tungsten carbide drilling inserts. Bits build** with the new materials were tested under stimulated wellbore conditions. The sealed bit effort provided for the evaluation of candidate high temperature seals and lubricants, utilizing two specially developed test apparatus which simulate the conditions found in a sealed bit operating in a geothermal wellbore. Phase I of the program was devoted largely to (1) the study of the geothermal environment and the failure mechanisms of existing geothermal drill bits, (2) the design and construction of separate facilities for testing both drill-bit seals and full-scale drill bits under simulated geothermal drilling conditions, and (3) fabrication of the MK-I research drill bits from high-temperature steels, and testing in the geothermal drill-bit test facility. The work accomplished in Phase I is reported in References 1 through 9. In Phase II, the first generation experimental bits were tested in the geothermal drill-bit test facility. Test results indicated that hardness retention at temperature, but not at the expense of fracture toughness, was a primary requirement for geothermal bit bearings. Materials selections for the MK-II bit were made based on these results. Also in Phase II, effort was directed at the screening of elastomers for use as a high-temperature seal for sealed bits. References 10 though 13 report the work performed in Phase II. This report summarizes the work on Phase III, encompassing the period from May 18, 1977, to May 19, 1978. There were two major tasks in Phase III which consisted of material selection, fabrication and testing of MK-III bits and Seal and lubricant evaluation. [DJE -2005