ANALYSIS OF WAVE VELOCITY SPATIAL DISTRIBUTION AROUND A CASED HOLE IN TECTONIC STRESS FIELD USING EQUIVALENT MEDIUM MODEL

In our previous work, the stress distribution analytic solution of a casing-cement-stratum system in tectonic stress field is obtained by elastic theory. Based on it, the elastic wave velocity spatial distribution around a cased hole in tectonic stress field is studied by applying the velocity-stress formula of equivalent medium model. The results show that the cased hole stress concentration is more obvious than that of the open hole, and the casing and the cement lead to obvious reduction of the stratum stress concentration range near the borehole. The stress concentration also causes the wave velocity spatial distribution anisotropy around a cased hole. The two shear wave velocity crossover point polarized along radial direction with different azimuth angle moves towards the borehole, which means that the orthogonally polarized crossing point of the two flexural wave dispersion curves will move to high frequency. The result indicates that in high frequency, the detection of the anisotropy induced by tectonic stress through cross-dipole logging in a cased hole is feasible.