Method and apparatus for filtering noise from data signals

Abstract

The filtering technique of the present invention cancels or minimizes noise in data signals found to be caused by dynamic variations in the drilling process. It has been discovered that the measurement of surface vibrations in the drill string and their effects on certain drilling equipment such as rotary table torque contains information that can be used to remove some or all of the pressure disturbance caused by these dynamic variations (vibrations). The result of removing some or all of the dynamic variation induced noise from the measurment-while-drilling (MWD) data signal yields a better signal to noise ratio (SNR) and therefore improves decoding of the MWD signal. In accordance with another important feature of the present invention, it has been found that improved SNR results from taking the first derivative with respect to time of the torque measurement. This first derivative measurement more closely resembles the actual disturbance in the standpipe pressure (SPP). In addition, even greater improvements in SNR may be obtained if the torque measurement is processed by a low-pass filter to equalize the effects of the two different channels. In this case, the torque measurement still better approximates the disturbance in the SPP.