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为了测量距地表1 000m以下位置的地壳应力状态,我们研究并开发了钻孔千斤顶压裂技术。技术的原理是:当钻孔千斤顶对钻孔壁加载时,与钻孔轴向平行的方向将会产生两个相对的新裂隙;卸载之后,如果千斤顶对钻孔壁的同一个地方进行施压,这对裂隙将会再次张开。与钻孔轴向垂直的平面上的两个主应力的大小和方向分别是由重张压力和裂隙的方向决定的。这个技术与水压致裂法相似。因此,测量深度没有理论上的限制。这个技术的特点就是它可以产生一对任意方向的轴向裂隙,可以测量裂隙张开的位移大小,根据测量结果可以精确计算重张压力的大小。在实地测试中,先用水压致裂法形成裂隙,再用钻孔压力千斤顶法加以与水压近似相等的压力值使之重张。本文介绍了我们的数值分析结果、实验室实验和现场测试。
In order to measure the crustal stress state below 1 000 m from the earth’s surface, we have researched and developed drilling jack fracturing technology. The principle of the technique is that when the drilling jack is loaded against the borehole wall, two opposite new fractures will be created in the direction parallel to the axial direction of the borehole; after unloading, if the jack presses the same place on the borehole wall This crack will open again. The magnitude and direction of the two principal stresses in the plane perpendicular to the axial direction of the borehole are determined by the direction of the stress and fracture, respectively. This technique is similar to the hydraulic fracturing method. Therefore, there is no theoretical limit to the depth of measurement. The characteristic of this technology is that it can generate a pair of axial cracks in any direction, which can measure the displacement of the crack opening. According to the measurement results, the magnitude of the resetting pressure can be precisely calculated. In the field test, fractures were first formed by hydraulic fracturing, and then the drilling pressure jack method was used to make the pressure equal to the pressure of water approximately. This article presents our numerical analysis results, laboratory experiments and field tests.