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

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. © 2019, Central South University Press. All right reserved.