Basic Theory And Applied Research Of Borehole Acoustic Remote Sensing Technology

Borehole acoustic remote sensing technology could supply imaging results of geological structures far-away from the borehole,which expand the acoustic logging data from onedimensional space to two-dimensional or even three-dimensional space,thus it will provide geological information on particular spatial scales different from other geophysical methods for the developing of oil&gas exploration and geological theory.With the development of borehole acoustic remote sensing technology,especially the so-called dipole shear wave remote sensing technology,it has been widely used in the detection of fractures and karst caves of reservoirs and has made great contribution to seek for sweet spot zone and discover hidden oil&gas reservoirs.As a mature but evolving technology,borehole acoustic remote sensing technology has two main development directions.The first one is to broaden its application enviroments,and the other is to obtain deeper radial detection distance and clearer imaging results.Aiming at the above two development directions,this thesis studies the theory of borehole acoustic imaging technology in cased boreholes and forms a set of hydraulic fracturing evaluation method based on acoustic logging.The radiation and receiving characteristics of the dipole source in a ultra-slow formation is also researched which provides a theoretical basis for broadening its application environments in shallow formations.Meanwhile,a hybrid method,which could provide forward support for improving detection distance and imaging accuracy,is proposed for solving the multi-scale problem in the numerical simulation of borehole acoustic remote sensing technology.This thesis is divided into the following three parts.The first part studies the feasibility to do the acoustic imaging in cased boreholes,analyzes the influence of cenment bonding quality,source frequency and formation shear velocity on the signal-to-nosie ratio of reflected waves,numerically simulates the dipole shear wave remote sensing response of fractured formation,summarizes the effects of fracturing fractures on the monopole sliding compressional waves and diopole flexural waves.On these basis,a fracturing results evaluation method of using the orthogonal dipole anisotropy and radial velocity tomography in the near well and dipole shear wave remote sensing techonology in the far well is finally formed.In the second part,for the shallow ultra-slow formation,the radiation characteristics of various polarized waves excited by a dipole source are studied.The amplitued variation of these types of polarized wavs reflected from the impedance interface is compared and analyzed.It will provided theoretical basis and guidance for the application in shallow formations of borehole acoustic remote sensing technology.At the same time,considering the advantages of logging while drilling(LWD),this part also theoretically analyzes the feasibility of performing acoustic imaging in LWD enviroments in ultra-slow formation.In the third part,the research on numerical simualtion method of borehole acoustic remote sensing technology is carried out.Aiming at the multi-scale problem in numerical simulation of borehole acoustic remote sensing technology,a hybrid method based on three-dimensional finite-difference method and elastic wave surface integral equivalence principle is proposed.This method can avoid the mesh of homogeneous region and obtain far-field scattering results of complex geological structures efficiently.Based on this,the far-field scattering response and rules of karst caves is numerically simulated and analyzed.It provides an efficient forward modeling method for improving the radial detection distance and imging accuracy of the borehole acoustic remote sensing technology.