Study on the influence factors of shale reservoir brittleness based on grey correlation analysis

Many factors affect the shale brittleness, and their weight distribution is fuzzy.Considering that, this paper uses 15 shale samples from Yanchang formation of southern Erdos Basin to test the stress-strain curve, and use linear regression and gray correlation method on the 10 factors which affect the brittleness of the shale to have the qualitative and quantitative analysis.Finally, 10 factors weight allocation can be calculated in the brittleness evaluation.The results show that confining pressure, Poisson ratio, modulus of elasticity are positively associated with shale brittleness, and peak strain, peak stress, rupture time, residual stress, residual strain, differential stress, numbers of surfaces of rupture are negatively related with the shale brittleness; the peak strain has the greatest impact on the shale brittleness, and residual stress, residual strain, etc are the secondary, and modulus of elasticity with the minimal impact on shale brittleness; the mechanical parameters(peak strain, peak stress, fracture time and differential stress) at the peak have the greatest impact on the shale brittleness, and the after-peak mechanical parameters(residual stress, residual strain, broken noodles number) are the secondary, and pre-peak mechanical parameters(elastic modulus, Poisson ratio and confining pressure) have the minimal impact on brittleness three weight ratio of 0.181∶0.499∶0.319.The weight analysis of the influence factors of shale brittleness can not only simplify the formula of brittleness evaluation, but also improve the accuracy of brittleness evaluation.