The Terzaghi effective stress principle only considers the deformation of soil structure. To adapt to more general situations, Li Chuang-liang proposed the dual effective stresses in porous media: the primary effective stress and the structural effective stress. The concept of dual effective stresses is easy to understand and has been widely cited. However, the two effective stress expressions and the pore compression coefficient and stress sensitivity theory derived from them contradict the test results. Based on the analysis and comparison of commonly used effective stress expressions, the stress-strain of porous media is closely analyzed. The new dual effective stress expressions are derived, their comprehensive effect is analyzed and the total effective stress expression is obtained. Compared with the Laughton et al. experiment and the Hall chart, the applicability of the new dual effective stresses is demonstrated and an application example is given. The results show that the previous two effective stress expressions are the same as the effective stress expressions earlier proposed by Biot and Bishop, which is contradictory to the Laughton et al. experiments. The new dual effective stress first proposed grain shape deformation and its significant influence on the total volumetric strain of the rock. The failure to take into account intergranular deformation and grain shape deformation is the fundamental reason that the theoretical value of the previous pore compression coefficient is far less than the experimental value. The dual effective stresses have the same connotation as the Skempton effective stress, which comprehensively considers grain deformation and intergranular deformation. The comprehensive effect total effective stress expression is the same as the Skempton effective stress. The expressions of the new dual effective stresses can explain well the results of Laughton et al. experiments. The pore compressibility coefficient is consistent with the Hall chart, which theoretically demonstrated that the rock pore compression coefficient is negatively correlated with the porosity and a low-permeability reservoir is more sensitive to stress.
MAO Xiaolong, LIU Yuetian, FENG Yueli, ZHENG Wenkuan, LIU Siping. Re-recognition of dual effective stresses and the comprehensive effect. Petroleum Science Bulletin, 2018, 04: 390-398.
