SEMBLANCE PROCESSING FOR AN ACOUSTIC MEASUREMENT-WHILE-DRILLING SYSTEM FOR IMAGING OF FORMATION BOUNDARIES

摘要

The present invention provides a system for drilling boreholes having adownhole subassembly which contains an acousticmeasurement-while-drilling system. It uses the acoustic velocity through theformations surrounding the borehole and an acoustic transmitterand a set of receivers for determining the bed boundaries surrounding theborehole formation. An acoustic isolator on the tool may be used toattenuate body waves traveling between the transmitter and the receivers.Additional attenuation of the body waves is provided by a thresholdfilter based upon the absolute maximum of the received signals. Semblance ofthe data is determined in a slowness/intercept-time domain.Coherence and semblance filtering methods are used to differentiate betweenreflection signals and noise. The position and orientation ofthe bed boundary relative to the tool are determined. A further processingstep uses the relative position and orientation determined for anumber of tool positions to further discriminate against noise and obtain anabsolute position and depth of the bed boundaries.