Short Normal Log (SN Log)

• Short Normal Log is the Type of Electrical Survey which was invented by the Schlumberger Brothers in 1927.

• The tool required a conductive mud, but worked poorly in salty mud. It did not work in cased holes.

• If the formation is uniform, the formation resistivity, Rt, can be computed from the formula Rt = K * V / I.

• Where V is the voltage between M and N, and I the intensity of the current flowing from A to B.

• K is a geometric factor that depends upon the relative distance between A, B, M, and N and is a constant for a given electrode arrangement.

• Electrodes A and M are on an insulating mandrel, called the probe or sonde or logging tool, which is suspended at the end of the logging cable.

• Electrodes B and N are placed far from A and M, and are either at the surface of the ground or on the cable at a long distance from A and M.

• The distance AM is known as the spacing. The depth reference point of the measurement is the midpoint between A and M.

Thanks…