A technique facilitates use of acoustic measurements to enable geo-steering during a well operation. A steerable well string is provided with acoustic systems used to collect data which is then processed to determine geo-steering inputs. In some applications, the well string may comprise a coiled tubing drilling tool. The coiled tubing drilling tool or other well string tool is combined with an azimuthally distributed pitch-catch micro-sonic sensor system and an azimuthally distributed ultrasonic pulse-echo transducer system. Data from these two systems is provided to a processing system which processes the data to determine, for example, real-time, geo-steering inputs. These inputs may then be used to more effectively steer the coiled tubing drilling tool or other well string tool.