坑底情報解析技術に関する研究 第１報 ビット振動による岩石強度の推定

Abstract

Drilling tests for several types of rock were conducted to investigate the relationship between bit vibration and rock strength. An insert bit, a tooth bit and a PDC bit of 3-7/8 in. diameter were used for the tests. Rocks drilled are tuff, sandstone, granite and two types of andesite whose uniaxial compressive strength ranges from 16.5 to 167 MPa. The bit vibration while drilling was measured by two accelerometers for horizontal and vertical directions set in a rod above the bit. The magnitude of the bit vibration was obtained by the calculation of RMS (root mean square) value of acceleration. The bit weight, penetration rate, torque and rotary speed were also measured while drilling, in addition to the bit vibration.From the results of tests, it became obvious that the bit vibration reflects well the change of rock strength. Moreover, the bit vibration, penetration rate and torque at the same bit weight were compared to understand the feature of the bit vibration. The comparison revealed that the change of the bit vibration and penetration rate with the change of rock strength are larger as compared to that of the torque in two types of roller cone bit. It also revealed that the increase and decrease of bit vibration for the change of rock strength are opposite to those of the penetration rate in the roller cone bits.