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| Rock brittleness evaluation based on stress dropping rate after peak stress and energy ratio |
| XIA Yingjie1，LI Lianchong1，TANG Chun?an1，MA Shou2，LI Ming2，BAO Chunyan3 |
(1. State Key Laboratory of Coastal and Offshore Engineering，Dalian University of Technology，Dalian，Liaoning 116024，China；
2. Petroleum Engineering Technology Research Institute of Shengli Oil Field，SINOPEC，Dongying，Shandong 257000，China；
3. College of Civil Engineering，Shaoxing University，Shaoxing，Zhejiang 312000，China) |
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Abstract Brittleness is one of the important mechanical properties for rock mass and is also the key index in hydraulic fracturing，rock breakage and rock burst prediction. The calculation methods of brittleness indexes of rock in China and abroad were therefore summarized and their applicability was discussed. In order to evaluate the brittleness of rock mass reasonably，a new index was proposed based on the stress dropping rate after peak stress of stress-strain curve and the ratio of elastic energy release at the point of rock failure to total energy that stored before the peak stress. Then laboratory tests under different confining pressures were carried out using rock cores collected from the isolated and reservoir layers in Shengli oil field. Through the analysis of test results，the validity and superiority of the new brittleness index were verified. In addition，the jump of brittleness index of reservoir core under the confining pressure of 15 MPa illustrated that internal defects of brittle rock mass should be given much attention in practical work.
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2016, Vol. 35 
