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

注册的研究人员开发了一种特殊的双包装机。在水力压裂操作中，裂缝的打开和闭合行为与原地应力状态有关。新型封隔器的目的之一是直接测量裂缝开度。新封隔器由两个独立移动的同轴管组成。由于密封元件固定到两个管道中的每一个，裂缝开口可以通过两个同轴管道的相对位移来测量。对两种密封材料进行了试验研究。其中一种材料是橡胶，另一种是铅。1998年在神冈矿分别采用常规双封隔器、橡胶封隔器和金属封隔器进行了现场试验。1996年，在该矿井中，利用从巷道水平钻出的钻孔进行了水力压裂实验，以估计地应力。金属密封封隔器的实验结果表明，两个同轴管的相对位移与井眼附近测得的巷道壁膨胀量有很好的相关性。关井压力被认为与正应力分量的大小相当，由两个同轴管的相对位移估计。用金属封隔器估算的关井压力与Muskut法和Hayashi & Haimson法计算的关井压力吻合较好，并采用三维边界元法对注液引起的裂缝口和廊道壁面位移变化进行了数值模拟。数值计算结果与实测结果基本一致。

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.