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Chen Q.,3D Geoscience Inc. | Wu D.,Tiandi Science And Technology | Xu J.,Chongqing University | Mizuta Y.,3D Geoscience Inc. | Mizuta Y.,Yamaguchi University
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering | Year: 2012

In the rock stress measurement with stress relief method of embedded strain gauge, both the size of core diameter and the packed thickness of elastic mortar affect the accuracy of measuring precision. In order to discuss the issue, the authors analyzed three cases of stress relief method of embedded strain gauge in secondary stress field, which are over-coring model, practical sensitivity test model and theoretical sensitivity test model. By the comparison of the exact solutions of three cases and calculation of two measurement systems, it could be found that the packing core diameter is not large enough, then measured values of ground stress of rock mass will be significantly underestimated compared with the actual stress field.

Bennour Z.,Kyoto University | Ishida T.,Kyoto University | Nagaya Y.,Kyoto University | Chen Y.,Kyoto University | And 5 more authors.
Rock Mechanics and Rock Engineering | Year: 2015

We performed hydraulic fracturing experiments on cylindrical cores of anisotropic shale obtained by drilling normal to the sedimentary plane. Experiments were conducted under ambient condition and uniaxial stresses, using three types of fracturing fluid: viscous oil, water, and liquid carbon dioxide (L-CO2). In the experiments using water and oil, cracks extended along the loading direction normal to the sedimentary plane under the uniaxial loading and extended along the sedimentary plane without loading. These results suggest that the direction of crack extension is strongly affected by in situ stress conditions. Fluorescent microscopy revealed that hydraulic fracturing with viscous oil produced linear cracks with few branches, whereas that with water produced cracks with many branches inclining from the loading axis. Statistical analysis of P wave polarity of acoustic emission waveforms showed that viscous oil tended to induce Mode I fracture, whereas both water and L-CO2 tended to induce Mode II fracture. Crack extension upon injection of L-CO2 was independent of loading condition unlike extension for the other two fluids. This result seemed attributable to the low viscosity of L-CO2 and was consistent with previous observations for granite specimens that low-viscosity fluids like CO2 tend to induce widely extending cracks with many branches, with Mode II fractures being dominant. These features are more advantageous for shale gas production than those induced by injection of conventional slick water. © 2015, Springer-Verlag Wien.

Bennour Z.,Kyoto University | Ishida T.,Kyoto University | Nagaya Y.,Kyoto University | Nara Y.,Kyoto University | And 5 more authors.
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

Hydraulic fracturing experiments were run on cylindrical cores from a shale stratum at a coal mine in Japan. Experiments were made under two uniaxial stresses 0 and 3 MPa and by using three types of fluids: viscous oil, water and liquid carbon dioxide (L-CO2). As for results, from the crack observation and AE source distribution, in the experiments used water and oil as fracturing fluid, fractures extend along the sedimentary plane if tests were run without loading, while they extend along the loading direction normal to the sedimentary plane under the uniaxial loading. These results suggest that the direction of crack extension is strongly affected by in-situ stress condition. However, the L-CO2 fracturing didn't show this tendency, this might be related to the low viscosity of L-CO2. From the analysis of the ratio of polarity of P-wave initial motions, it was found that viscous oil injection tends to induce Mode-I fracture while both water and L-CO2 injection tend to induce Mode-II fracture. Copyright (2014) ARMA, American Rock Mechanics Association

Inui S.,Kyoto University | Ishida T.,Kyoto University | Nagaya Y.,Kyoto University | Nara Y.,Kyoto University | And 2 more authors.
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

Tri-axial hydraulic fracturing experiments using supercritical CO2 (SC-CO2), water and viscous oil have been conducted in order to investigate how the viscosity of fracturing fluid affects fracture propagation and fracture mode. We performed these experiments on cubic granite specimens and monitored acoustic emission (AE) with 16 sensors. AE data analysis allows us to clarify fracture propagation and its mode. The effects of fluid viscosity on the distribution of AE sources and the fracture mode are discussed. Macroscopic observations of the surface fractures were consistent with located AE sources. The distribution of AE sources indicated that fracturing with low viscosity fluid such as SC-CO2 can induce more widely and complexly extending fractures than those with higher viscosity fluid like water and oil. In addition, the analysis of the fracture mechanism showed that low viscosity fluid such as SC-CO2 induces shear dominant fracture, while high viscosity fluid induces tensile dominant fracture. Thus, since CO2 has a higher affinity to shale than methane and enhances methane desorption, O2 fracturing could be an effective technique particularly for shale gas recovery. Copyright (2014) ARMA, American Rock Mechanics Association

Ishida T.,Kyoto University | Aoyagi K.,Kyoto University | Niwa T.,Kyoto University | Chen Y.,Kyoto University | And 3 more authors.
Geophysical Research Letters | Year: 2012

Carbon dioxide (CO 2) is often used for enhanced oil recovery in depleted petroleum reservoirs, and its behavior in rock is also of interest in CO 2 capture and storage projects. CO 2 usually becomes supercritical (SC-CO 2) at depths greater than 1,000 m, while it is liquid (L-CO 2) at low temperatures. The viscosity of L-CO 2 is one order lower than that of normal liquid water, and that of SC-CO 2 is much lower still. To clarify fracture behavior induced with injection of the low viscosity fluids, we conducted hydraulic fracturing experiments using 17 cm cubic granite blocks. The AE sources with the SC-and L-CO 2 injections tend to distribute in a larger area than those with water injection, and furthermore, SC-CO 2 tended to generate cracks extending more three dimensionally rather than along a flat plane than L-CO 2. It was also found that the breakdown pressures for SC-and L-CO2 injections are expected to be considerably lower than for water. © 2012. American Geophysical Union. All Rights Reserved.

Chen Y.,Kyoto University | Suzuki T.,Kyoto University | Bennour Z.,Kyoto University | Nagaya Y.,Kyoto University | And 3 more authors.
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

To examine the features of fractures induced by hydraulic fracturing and the surrounding stimulated regions, a hydraulic fracturing experiment was conducted using shale samples. In this experiment, the fracturing fluid was a thermosetting resin, methyl metaacrylate (MMA), mixed with a fluorescent paint, and just after fracturing the resin was immediately fixed within the sample by heating. Cut sections of the samples were observed under ultraviolet light irradiation. It is expected that the hydraulically induced fractures and the surrounding fractured region will be detected because the induced fractures filled with resin should emit light, while the other parts will not. The samples, which were collected from the Kushiro Coal Mine in Hokkaido, Japan at the depth around 275 m, were roughly 85 mm in diameter, 170 mm in length, and cored normal to the sedimentary planes. An injection hole with a 10-mm diameter was drilled onto the center of the sample parallel to the sedimentary plane to simulate hydraulic fracturing in shale gas development. The experiment was conducted under a uniaxial loading condition of 3 MPa and the fracturing fluid was injected into the sealed injection hole at a constant flow rate. The main fracture induced by hydraulic fracturing, which was subsequently filled and fixed with the resin, is clearly observed. Detailed microscopic observations show that the main fracture is accompanied by many thinner secondary branches. Furthermore, fractured regions around the induced main fracture, which penetrate with the resin and emitted light under ultraviolet light irradiation, are also observed. It is confirmed that the region influenced by hydraulic fracturing around the main fractures exists. This fractured region is considered to be the stimulated region where the permeability is improved, presumably because the main fracture forms a new fracture network and/or activates a preexisting one. © 2014 by Japanese Committee for Rock Mechanics.

Yokoyama T.,OYO Corporation | Sano O.,University of Tokyo | Hirata A.,Sojo University | Ogawa K.,OYO Corporation | And 3 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

In order to measure crustal stresses at great depths of more than 1000. m from the ground surface, we have been promoting research and development of borehole-jack fracturing technique. When a borehole wall is loaded by a borehole-jack, a pair of new fractures will be induced oppositely in parallel to the borehole axis. After unloading, if the same place on the borehole wall is loaded again by the jack, the pair of fractures will be opened again. Two principal stresses and the orientation of crustal stress in the plane perpendicular to the borehole axis are determined by the re-opening pressures and the orientation of the fractures respectively. This technique is similar to a hydraulic fracturing from the viewpoint of analysis. The features of this technique are that it is possible to produce a pair of axial fractures in an arbitrary direction, possible to measure a displacement of the fracture opening, and, as a result, it is possible to determine the re-opening pressure accurately. This paper describes our results of numerical analyses, laboratory experiments, and field tests. © 2014 Elsevier Ltd.

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