Experiments on mechanics and friction characteristics of shale under soaking conditions
For the problem of fault slip during shale hydraulic fracturing,the mechanical and friction characteristics of shale under immersion conditions were analyzed by laboratory experiments,and the evolution laws of shale friction coefficient were studied.The results show that:(1)The compressive strength,tensile strength,modulus of elasticity and cohesion of shale decrease with the increase of soaking time;Poisson's ratio of shale increases with the increase of soaking time,and the variation law of internal friction angle is not obvious.(2)The shale friction coefficient decreases with the increase of soaking time,normal stress and coring angle,and the shale friction coefficient decreases more within 6 h of soaking and then stabilizes.(3)After the interfacial pressure is greater than 5 MPa,the friction coefficient of shale does not change with the increase of interfacial pressure,but only decreases with the increase of soaking time.(4)After the end of hydraulic fracturing,the friction coefficient continues to decrease,and the fault still has the risk of slipping.Shortening the length of fracturing operation can avoid the influence of the continuous decrease of friction coefficient on the slip of the fault.The research results in this paper can provide a scientific basis for shale fault slip prediction.
rock mechanicsshalestrengthfriction coefficientsoaking time
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