Performance of Doppler ultrasound for fluid influx/efflux velocity estimation from borehole fractures in water-based and oil-based muds

Abstract

Ultrasonic logging tools are used for several imaging applications in borehole operations. Recent studies, including from the authors of this work, have evaluated Doppler ultrasound as a potential method for obtaining greater information about influx/efflux of fluids between the borehole and formation. This work aims to further the development of Doppler ultrasound for application in borehole operations by evaluating its performance in various drilling muds. Water-based (WBM) and oil-based (OBM) drilling muds within the mud weight range of 1200 kg/m3–1800 kg/m3 are considered in this study. The study has been done experimentally using a laboratory setup pumping the drilling muds in orthogonal directions, viz. annular flow, and influx/efflux flow. Procedurally generated 3D printed fracture shapes are used for emulating the influx/efflux from borehole walls. The effect of attenuation on the signal to noise ratio (SNR) of Doppler flow images and subsequent impact on flow velocity estimates is discussed. An SNR of 1.1 dB was achieved at 45 mm depth for the heaviest OBM with a mud weight of 1640 kg/m3. Doppler flow velocity estimates could be obtained with a standard deviation of 0.528 m/s at SNR of 1.1 dB. The standard deviation reduced with increasing SNR and a minimum standard deviation of 0.209 m/s was obtained at SNR of 21.6 dB for the lightest WBM with a mud weight of 1200 kg/m3. No significant effect on the standard deviation of influx/efflux velocity estimates were observed for changes in annular flow rate.