Rock Permeability and Electrical Response Characteristics Under Different Effective Stress

Abstract:

The effective-pressure act on rock matrix mineral. The rock matrix mineral deform under effective-pressure which would have an impact on the pore structure. This paper studies and analysis the influence of effective-pressure on different rock pore structure firstly. And then analysis and deduce the influence of five pore structure parameters which include the effective stress pore coordination number z、the coefficient of variation of pore size distribution V_r、pore hydraulic radius r_H、pore length l and cross-section aspect ratio ε. Using Bernabé et al.’s formation factor and permeability formulas, we can find that there are power 、linear and log-linear relationship among effective-pressure formation factor and permeability formation factors. In order to verify the correctness of the conclusions, this paper selects the different properties in different parts of sandstone samples of formation factor and permeability effective pressure experimental data and have a comparative analysis. The fitting results shows that, when the sandstone is relatively high porosity and permeability, the reason why effective-pressure change cause formation factor and permeability change is mainly produced by the change of pore hydraulic radius; When the sandstone is low porosity and permeability, the reason why effective pressure change cause formation factor and permeability change is mainly produced by the change of pore hydraulic radius and coordination number, it shows two kinds of deformation mechanisms -- the pore deformation and coordination number change by fracture closure. Some experimental data of low permeability rocks will appear obvious segmentation and wave change phenomenon in log-log graph.