Field application of near-borehole fracture acoustic imaging using a three-dimensional scanning inversion method

Abstract

Borehole acoustic remote imaging can help identify and evaluate abnormal geological bodies within tens of meters of a well, which has a very important application prospect in fracture imaging. Compared to the borehole mode wave, the echo amplitude from a near-borehole fracture is considerably small, and the currently used wave field separation method cannot completely filter the borehole mode wave. Due to the influence of the large amplitude of the remaining borehole mode wave, several artifacts are often produced near the well when using traditional migration imaging. Thus, imaging and characterizing near-borehole fractures via acoustic imaging becomes difficult. To overcome this, we propose a three-dimensional scanning inversion method that attenuates the effects of remaining refracted waves on borehole acoustic imaging. We then perform data processing and imaging of field-logging data based on this method, and multimode echoes are used to identify and evaluate fractures. Finally, a comparison of the inversion results of the borehole acoustic and borehole electrical imaging showed that the three-dimensional scanning inversion method can effectively attenuate the remaining refracted wave and better realize the clear imaging of near-borehole fractures. Different modes of echoes illuminate different areas of fractures near wells. Therefore, based on scattered S-waves, the proposed imaging method can effectively detect fractures that cross-cut a well. Moreover, based on multimode waves, the method can suppress artifacts and highlight the azimuth characteristics of near-borehole fractures. Using the proposed method, high-precision positioning and fine characterization of formation fractures in near and far wells can be achieved simultaneously. Further, near-borehole fracture parameters—such as tendency, dip, and depth—can be inverted, and the results are consistent with the inversion results obtained through borehole electrical imaging. Thus, the proposed method enables the quantitative evaluation of near-borehole fractures.