Development of a system to measure fracture aperture of artificial fracture produced in-situ

注册调查人员开发了一种特殊的双层封隔器。在水力压裂施工中，裂缝的开合行为与地应力状态有关。新型封隔器的一个目的是直接测量裂缝开度。新型封隔器由两根可独立移动的同轴管道组成。当密封件分别固定在两根管子上时，可以通过两根同轴管的相对位移来测量裂缝开度。对两种材料作为密封件进行了检测。其中一种材料是橡胶，另一种是铅。前者称为橡胶密封封隔器，后者称为金属密封封隔器。1998年在神冈煤矿进行了现场试验，分别采用常规双层封隔器、橡胶密封封隔器和金属密封封隔器。在这个矿井中，为了估计地应力，进行了一次水力压裂试验，试验使用的是1996年从巷道水平钻出的一个钻孔。金属密封封隔器实验结果表明，两根同轴管的相对位移与井筒附近测得的孔壁膨胀率有很好的相关性。关井压力被认为相当于一个法向应力分量的量级，由两个同轴管的相对位移来估算。金属密封封隔器测得的关井压力与Muskut法和Hayashi&Haimson法测得的关井压力吻合较好。利用三维边界元方法对注液引起的裂缝孔和孔壁表面位移变化进行了数值模拟。数值计算结果与实测值基本吻合。

The registered investigators have developed a special double packer. In hydraulic fracturing operation, an opening and closing behavior of a fracture is related to in-situ stress state. A purpose of new packer was to measure the fracture opening directly. The new packer consisted of two co-axial pipes that move independently. As sealing elements were fixed to each of two pipes, fracture opening could be measure by relative displacements of two co-axial pipes. Two types of the materials as sealing element were examined. One of the materials was rubber and the other was lead. The former was named rubber-seal packer, and the latter is named metal-seal packer.A conventional double packer, the rubber-seal packer and the metal-seal packer were used for in-situ experiment carried out in the Kamioka mine in 1998. IN this mine, a hydraulic fracturing experiment in order to estimate an earth stress was done using a borehole that was drilled horizontally from a gallery in 1996. The newly developed packers were used to re-open the pre-existed artifical fracture.The result of the metal-seal packer experiments showed that relative displacements of two co-axial pipes had a good correlation with the gallery wall expansion that was measured at vicinity of the borehole. The shut-in pressure, that is thought to be equivaient to a magnitude of normal stress component, was estimated from the relative displacements of two co-axial pipes. This shut-in pressure estimated from the metal-seal packer agreed well with those determined from the Muskut method and Hayashi & Haimson method.Numerial simulation of displacement variations of fracture aperture and gallery wall surface, which were caused by fluid injection, was carried out by using three dimensional boundary element method. Numerical results nearly agreed with the measured results.