Dictionary:Static self-potential (SSP)

The maximum SP that would be recorded when the borehole logging sonde passes from within a very thick, porous, permeable, clean sand to a point that is well within a thick shale. The electrochemical SSP (the electrokinetic SP is often neglected) is approximately given by:

$SSP=-Klog_{10}{\frac {a_{w}}{a_{mf}}}$,

where a_w is the activity of the formation water and a_mf that of the mud filtrate. Because of the inverse relationship between activity and equivalent resistivity, this equation can be written:

$SSP=-Klog_{10}{\frac {a_{mfe}}{a_{we}}}$.

where R_mfe=equivalent mud filtrate resistivity, R_we= equivalent water resistivity. For NaCl muds that are not too saline, R_mfe=R_mf; for other muds an activity correction should be made. In these equations ${\textstyle K=60+0.133T}$ where T=Fahrenheit temperature. See also SP and pseudostatic SP.