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| Mechanical property and bedding inclination effect on gas fracturing of black shale |
| HOU Peng1，2，GAO Feng1，2，ZHANG Zhizhen2，LIN Bin2，YANG Yugui1，GAO Yanan2 |
(1. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University of Mining and Technology，Xuzhou，Jiangsu 221116，China；2. School of Mechanics and Civil Engineering，China University of Mining and Technology，
Xuzhou，Jiangsu 221116，China) |
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Abstract Gas fracturing，as a new type of waterless fracturing technology，is important to the exploitation of shale gas. In order to explore the failure mechanism of shale with bedding planes of different directions due to the gas fracturing，the anisotropic mechanical properties of black shale from Pengshui were systematically analyzed. The gas fracturing tests on the axis of the shale samples parallel to and perpendicular to the direction of bedding plane were performed using the reformed assembly of high pressure gas fracturing system respectively. The effect of the directions of bedding plane on the deformation，strength，AE characteristic and failure modes was discussed and failure mechanism of shale was revealed. The effect of layer on the shale strength under different loading modes was discussed. The effect of bedding plane directions on the tension-compression properties of black shale is obvious. The ratios in compressive strength，tensile strength，elastic modulus and shear modulus of the samples with the axis vertical to bedding plane direction and the samples with the axis parallel to bedding plane direction are 138.22%，44.37%，169.17%，173.27%，respectively. However，the effect of bedding inclination on Poisson?s ratio of shale is not apparent. The failure strength and failure time of the samples with the axis vertical to bedding plane direction are 4.2 times and 3.35 times greater than the samples with the axis parallel to bedding plane direction respectively. The former appeared the tensile failure along a weaker bedding layer and the latter mainly produced the tensile failure，but the shear failure can be also found in the latter resulting in an uneven fracture surface. The deformation carves are nonlinear. The deformation of the samples with the axis vertical to bedding plane direction is larger，and the abnormal inflection point and down concave trend in the lateral deformation curves were shown clearly in this case. While for the samples with the axis parallel to bedding plane direction，the deformation curves are relatively smooth and the concave trend was shown in the lateral deformation curves. The samples with the axial vertical to bedding plane direction were failed more violently according to the results of AE energy rate. The loading modes affected the bedding effect coefficient of shale strength significantly，and the gas fracturing test affected the most and the uniaxial compression test affected the least.
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2016, Vol. 35 
