Logging while drilling

Abstract: A LWD tool is disclosed for providing an image of the borehole during drilling or during removal of the tool from the borehole. The tool includes imaging transducers which are fired based upon either time or direction. Borehole reflections are processed to determine time-of-flight to give an indication of standoff with respect to each transducer from which the borehole geometry can be obtained. The reflections also are analyzed for other information, such as the amplitude of the reflected signal. The time-of-flight and amplitude values are encoded and stored in memory for retrieval later. In addition to the imaging transducers, the imaging assembly also includes depth transducers to obtain a micro measurement of depth downhole. The micro-depth measurements are stored and/or transmitted to the surface. In addition, a directional sensor and clock are provided downhole to correlate the firing of the transducers and the receipt of reflections. The micro-depth measurements and directional measurements preferably are used with one more image signals to check for the presence of bed boundaries intersecting the borehole. If a boundary is present, the imaging assembly applies a best fit sine wave to the image signal, from which dip angle α and dip direction are obtained. In the preferred embodiment, acoustic transducers are used as the imaging transducers, although electromagnetic transducers or other suitable transducers may be used.