doi:10.16186/j.cnki.1673-9787.2020010065

Received:2020/01/21

Revised:2020/04/21

Published:2021/09/15

Study on brittleness index of shale based on stress-strain curve

SANG Fengjun1, CHENG Hanlie2, ZHANG Xiaoyan3, YANG Guoping3, ZHAO Jianfeng3, FU Caiyun3, ZHANG Chong3

1.Petroleum Engineering Management Co. Ltd， Sinopec Zhong-yuan Oilfield Service Corporation， Puyang  457001 ， Henan， China;2.COSL-EXPRO Testing Services（Tianjin） Co. ， Ltd. ， Tianjin  300457 ， China;3.PetroChina Changqing Oilfield Company， Yulin  719000 ， Shaanxi， China

Abstract:The brittleness of shale is a key indicator for evaluating the compressibility of shale reservoirs ， and is the key to decide whether shale reservoirs can be commercialized. In this work ， the uniaxial and triaxial com-pression tests of organic rich shale of marine Longmaxi formation in South China were carried out ， a new brittle-ness evaluation index was established and verified according to the rock stress-strain curve. On this basis ， the brittleness anisotropy characteristics of shale were studied. The results showed that the brittleness index could commendably reflect the brittleness characteristics of shale ， and the best results could be obtained when the normalization coefficients were λ =0.4 and n =0. 6 ， respectively； The shale reservoir of marine Longmaxi formation in south China had strong brittleness， which could be divided into high compressibility reservoir； The brittleness index decreased With the increase of confining pressure ， and the decreasing rate decreased gradually ； With the increase of confining pressure ， the compaction stage shortened and the yield stage became longer. The residual strength increased almost linearly with the increase of confining pressure ； With the increase of confining pressure ， the peak strength ， elastic modulus and softening modulus of shale showed a significant in-creasing trend ， with growing rate of 105.17% ，71.74% and 97.75% ， respectively. With the increase of the bedding angle ， the brittleness index of shale decreased first and then increased ， showing a “U” shape change law ， whose maximum value and minimum value were obtained when the bedding angle θ=0° and θ= 30° ， respectively. The anisotropy coefficient was as high as 1.991 ， which showed that the brittleness of shale had obvious anisotropic characteristics.

Key words:Longmaxi formation shale;brittleness index;uniaxial compression test and triaxial compression test;mechanical parameter;stress-strain curve;anisotropic characteristic

基于应力应变曲线的页岩脆性指标分析_桑峰军.pdf