Electrochemical activity of shaly sands

Tenchov, G.G., 1991. Electrochemical activity of shaly sands. J. Pet. Sci. Eng., 6: 81-89. The electrochemical activity of shaly sandstone is principally confined to the bound water volume Per unit pore volume at standard conditions. On the basis of the dual water model and sample data, the electrochemical activity is shown lobe related to the cation exchange capacity. The advantage of the electrochemical activity, with respect to the cation exchange capacity, is that the former can be obtained by nondestructive techniques of core samples by measuring their electrical conductivities. A relationship between water permeability, formation factor, pore radius and shaly sandstone electrochemical activity is theoretically obtained using the fluid flow and the electrical conductivity analogy in shaly sands. It is compared to the sample data. A statistical relationship between mean pore channel radius and electrochemical activity of shaly sandstone is stated. Both the upper limit of cation exchange concentration per unit pore volume and the probable radii of the pore channels in ideal shale are stated. The results yield the possibility that the electrochemical activity can be used instead of the cation exchange capacity as a parameter relating reservoir and structural parameters of shaly sandstones.