采用等效介质模型研究地应力场中套管井周波速的空间分布

在以往的工作中,利用弹性力学理论获得了地应力场中套管—水泥环—地层系统应力分布的解析表达式。在此基础之上,应用等效介质模型的速度—应力关系式,研究了地应力场中套管井周弹性波速的空间分布规律。分析结果表明,相对裸眼井,套管井应力集中的程度更加明显,由于套管和水泥环的存在,地层应力集中的范围明显缩小到井眼附近。应力集中将导致套管井周波速空间分布的各向异性,对应不同方位径向偏振的横波速度的交叉点明显向井孔附近移动,这意味着垂直偏振的两种弯曲波频散曲线的交点会向高频移动。这一结果表明,在高频情况下,在套管井中应用正交偶极子声测井检测应力导致的各向异性是可行的。

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.