Lithologic Reservoirs ›› 2019, Vol. 31 ›› Issue (4): 54-61.doi: 10.12108/yxyqc.20190406

• PETROLEUM GEOLOGY • Previous Articles     Next Articles

An improved method for evaluating rock brittleness index based on stress-strain curve characteristics

CAO Qian1,2, QI Minghui1,2, ZHANG Haotian3, HUANG Yi1,2, ZHANG Yeyu1,2   

  1. 1. Sichuan Province Key Laboratory of Shale Gas Evaluation and Exploitation, Chengdu 610091, China;
    2. Sichuan Keyuan Testing Center of Engineering Technology, Chengdu 610091, China;
    3. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
  • Received:2018-12-21 Revised:2019-03-29 Online:2019-07-21 Published:2019-06-21

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Abstract: As one of the important indexes for rock mechanics evaluation,the evaluation of brittleness index is of great significance to rock characteristics. 21 rock samples of the fifth member of Xujiahe Formation of Xinchang Gas Field in Sichuan Basin were selected to carry out laboratory triaxial rock mechanics experiments. Triaxial saturation hydraulics and acoustic tests of samples under confining pressure of 0 MPa,12 MPa,22 MPa and 32 MPa were simulated respectively. Based on the stress-strain curve characteristics,the differences of different brittleness characteristic parameters were analyzed. The brittleness factors such as BYm,Bμ,BRε and BRσ respectively based on Young's modulus,Poisson's ratio,recoverable strain and total strain,and yield strength and compressive strength,were calculated. The existing brittleness evaluation methods based on stress-strain curves were compared and analyzed,and the functional relationships of brittleness index Bn with BYm,Bμ,BRε and BRσ were established according to the laboratory rock mechanics test results. A new brittleness index model was established by multiple regression method to evaluate the brittleness of rock samples. The results show that the conventional brittleness index evaluation method is not effective in distinguishing brittleness of rock samples,and the improved model can better distinguish high brittle mudstone,low brittle mudstone and sandstone in the study area. The study results have guiding significance for accurately evaluating the brittleness characteristics of rocks.

Key words: brittleness index evaluation, stress-strain curves, improved method, normalization

CLC Number: 

  • TU45
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