(1. State Key Laboratory of Coastal and Offshore Engineering，Dalian University of Technology，Dalian，Liaoning 116024，China；
2. College of Civil Engineering，Shaoxing University，Shaoxing，Zhejiang 312000，China；3. Petroleum Engineering Technology Research Institute of Shengli Oil Field，SINOPEC，Dongying，Shandong 257000，China)
Abstract：Failure characteristics and brittle evaluation of reservoir sandstone are of great significance in oil and gas drilling engineering. The sandstone cores from the well of Shengli Oil Field were studied with the developed physical tests under condition of triaxial compression and numerical simulation. The results show that the failure mode of interlayer and reservoir cores under the effect of confining pressure is mainly the shear failure. Under the same level of confining pressure，the interlayer cores are more brittle than reservoir cores. The brittleness tendency can be evaluated by the brittleness index B effectively. Besides，the relevance between the main mechanical parameters of sandstone and the brittleness index B is analyzed as well. Under the condition of the same confining pressure，the peak strength，expansion point，elastic modulus，Poisson?s ratio，residual strength and residual strength coefficients of cores decrease with the increase of brittleness index B. The relationship between index B and parameters is linearly fitted well. The intrinsic factor of low brittleness is the high clay mineral content of the oil layer rock. The microscopic brittle characteristics of two kinds of sandstone are shown in the CT scans under uniaxial compression. In the case that other parameters are fixed，the numerical cores are more brittle with the increase of the elastic modulus，ratio of compressive strength to tensile strength and internal friction angle. However，the brittleness of cores reduces with the increase of Poisson's ratio，residual strength and residual strength coefficient. In addition，there is little relationship between the brittleness of cores and its strength. The modes of acoustic emission are dominant by the pre-main-after shocks and group shocks. The essential relationship between the index B and the acoustic emission modes is summarized based on the results of physical experiment and numerical calculation. Under the condition of same loading rate，the acoustic emission modes in the low brittleness zone，middle brittleness zone and high brittleness zone are swarm shocks，pre-main-after shocks and mass shock. Lastly，the mechanism of acoustic emission modes was verified with those of limestone and different types of coals.
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2017, Vol. 36 
