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

注册调查员开发了一种特殊的双层封隔器。在水力压裂作业中，裂缝的开闭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的张开度。新型封隔器由两根独立移动的同轴管组成。由于密封元件分别固定在两根管道上，因此可以通过两根同轴管道的相对位移来测量裂缝的开度。对两种密封材料进行了试验。一种材料是橡胶，另一种是铅。前者被称为橡胶密封封隔器，后者被称为金属密封封隔器。1998年，在神冈矿进行了常规双封隔器、橡胶封隔器和金属封隔器的现场试验。在这个矿井里，为了估计地应力，水力压裂实验是在1996年用一个水平钻孔从一个巷道中钻出来的。新开发的封隔器用于重新打开先前存在的人工裂缝。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眼附近测得的巷道壁面膨胀有较好的相关性。关井压力，被认为相当于正应力分量的大小，是根据两根同轴管道的相对位移估计的。金属密封封隔器估算的关井压力与Muskut法和Hayashi & Haimson法测定的结果吻合良好。采用三维边界元法对流体注入引起的裂缝孔径和巷道壁面位移变化进行了数值模拟。数值结果与实测结果基本吻合。

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.