Experimental study on the permeability characteristics of impure salt rock

The percolation test of whole process to the impure salt rock of a natural gas reservoir in China was carried out using the THMC rock triaxial test system in Sichuan university. A multi-factor coupled percolation model considering simultaneously the confining pressure, dilation and impurity content was established by curve fitting the test results. The experimental research shows that the content, distribution and composition of the impurity all have the significant influence on the permeability of the salt rock. The permeability of salt rock with different impurity decreased after damage recovered. The plastic deformation can be divided into two stages. In stage one, the permeability increased rapidly, while in stage two, the permeability increased slowly and even decreased. The permeability increased significantly after the sample failure and the permeability maintained at a stable level in the residual phase. The low permeability interlayer restricts the vertical permeability. The salt rock with the mud component has the lower permeability than the salt rock with glauberite impurity. The multi-factor coupled percolation model shows that the higher the confining pressure, the lower the permeability, and the greater the volumetric strain dilation, the higher the permeability. When the impurity content is more than 0.46, the permeability increases with the increase of impurity content. When the impurity content is less than 0.46, the permeability decreases with the increase of impurity content. © 2017, Science Press. All right reserved.