Using an acoustic sensor and accelerometer to measure the downhole impact frequency of a hydraulic impactor

Abstract

As an efficient drilling technology, percussion-rotary drilling technology depends extensively on the core component, a hydraulic impactor located at the bottom of the well, to realize its performance. As the most important parameter of the hydraulic impactor, the impact frequency directly reflects the efficiency with which rocks are broken. Furthermore, the impact frequency of the impactor running at the bottom of the well most accurately reflects the real working situation of the hydraulic impactor and the actual drilling process. Several methods have been employed to measure impact frequencies, including a stress wave method, a displacement measurement, and an electromagnetic induction method. However, given the limitations of the testing principle and the test equipment size, most of these methods can only be used to measure the impact frequency of the hydraulic impactor on the ground, i.e., outside the well. To directly obtain the impact frequency of the hydraulic impactor at the bottom of the well, this paper suggests two new test methods, namely, an acoustic sensor method and an accelerometer method, based on actual project experience. The acoustic sensor method measures the impact frequency by processing the acoustic data resulting from the hydraulic impactor's vibration, while the accelerometer method measures the impact frequency by processing the accelerometer data of the hydraulic impactor's vibration. The acoustic sensor method is simple and practical with regard to its programming and operation and can be further divided into two methods, namely, a non-threshold decibel sensor method and a threshold acoustic sensor method. The accelerometer method can be applied both downhole and on the ground. In addition, the ballistic work value obtained using the accelerometer method can be compared to that obtained using the acceleration sensor under the same conditions (including the impact of the pump, the shock shape, the formation conditions, and the hole deviation angle). Laboratory tests and field works were performed after the testing equipment was calibrated. The test results show that both test methods can meet the requirements in terms of required measurement errors. Moreover, the measurements obtained using the accelerometer method and the non-threshold decibel sensor method are more accurate than those obtained using the threshold acoustic sensor method when working downhole, and the threshold acoustic sensor method is more suitable for impact frequency measurements obtained on the ground.