A modified determination method of rock 's abrasiveness for well drilling using diamond bits

Key words:  diamond bit  rock abrasiveness  determination method  standard wear specimen  abrasiveness index  abrasiveness classification

Abstract:

In order to classify the rock 's abrasiveness in oil well drilling using diamond or PDC bits, a conventional equipment used for rock 's abrasiveness testing was modified based on the wear mechanisms of diamond bits, and a new kind of standard wear specimen made of diamond bit materials was manufactured. The volume worn of the standard wear specimen for breaking per unit volume of rocks was taken as the abrasiveness index, and a new experimental method was proposed. An optimized diamond volume fraction of the standard wear specimen was determined as 25% with size of 0.3 mm diamond grains, and the matrix was formulated with phenolic resin 55%, Cu 25%, Cr₂O₃ 38%, ZnO 6%, SiC 5% and with 1% volume of pores. For the standard wear testing, the suggested weight on the wear specimen is of 500 N, and the rotation speed is 198 r/min with a circulation rate of drilling fluid of 0.2 L/s. The abrasiveness index of the representative rock samples from different formations encountered in oil well drilling has been determined, which was found to be in the range of 0.80 to 45.78. The logarithm value of the abrasiveness index was used for the classification of the rock 's abrasiveness, defined as the abrasiveness grade value. The rocks encountered in oil well drilling in China can be divided into six grades according to the abrasiveness grade values.