岩芯直径变形分析法及其在松科2井深部地应力调查中的应用

A method of diametrical core deformation analysis and its application on stress investigation in SK2 Well

介绍岩芯直径变形分析法(diametrical core deformation analysis,DCDA)的基本原理、基于激光测距仪的岩芯直径测试仪器和测试流程,并将该方法应用于松科2井6645~6846m深部地应力测试。研究结果表明:应力释放后的岩芯直径曲线均为正弦波型,呈π周期变化,且椭圆长轴和短轴近于正交,测试结果符合DCDA法理论结果,可反映原位地应力信息。岩芯截面椭圆长轴方向即水平最大主应力方向,结合岩芯黏滞剩磁定向结果,确定松科2井6645~6845m深度水平最大主应力方向为NE72°~83°;利用试验获取的岩芯弹性模量和泊松比,确定松科2井6645m水平主应力差约35MPa,6845~6846m水平主应力差约55MPa,与非弹性应变恢复法确定的结果吻合较好。DCDA地应力测试方法在松科2井6645~6846m的成功应用,为深部地应力信息的获取提供了新途径,特别是在超深或高温钻孔和地层较破碎的复杂地质条件下,应力解除法、水压致裂法等难以实施时,DCDA方法仍可获得较可靠的地应力数据。DCDA方法不受钻孔的深度和温度环境限制,只需要近均质且各向同性的圆柱岩芯,不需对岩芯进行切磨加工,有利于深部宝贵岩芯的重复利用。

The basic principle of diametrical core deformation analysis method(DCDA) in-situ stress testing method, core diameter testing instrument and testing process based on laser rangefinder were introduced, and the method was applied on the in-situ stress measurement of igneous rock strata on the base of 6 645-6 846 m in SK2. The results show that the core diameter curves after stress relief are sinusoidal with a periodic change of π,and the long axis and the short axis of the ellipse are nearly orthogonal. The test results conform with the theory results of DCDA method and can reflect the in-situ stress information. The direction of the elliptical long axis of core section is the direction of the maximum horizontal principal stress. According to the results of core paleomagnetic orientation, the maximum horizontal principal stress direction of 6 645-6 845 m in SK2 is determined to NE72°-83°. By taking into account the core elastic modulus and Poisson’s ratio, the horizontal principal stress difference of 6 645 m in SK2 is determined to be about 35 MPa, and the horizontal principal stress difference of 6 845-6 846 m is about 55 MPa, which are almost consistent with the results of ASR in situ stress measurement. The successful application of DCDA method in the field of 6 645-6 846 m in SK2 well provides a new way to obtain the information of the deep in-situ stress, especially in the complex geological conditions of ultra deep or high temperature drilling and relatively broken formation. In this case, when the stress relief method and hydraulic fracturing method are difficult to implement, while the method can still obtain more reliable in-situ stress data. At the same time, this method is not limited by the depth and temperature environment of the borehole,and only needs nearly homogeneous and isotropic cylindrical core, and does not involve cutting and grinding the core, which is conducive to the reuse of the deep precious core.