Patent ID: 7984755

Claim:
An electrical cased-well logging method, comprising using a sonde in the form of two current electrodes located on the opposite sides of at least three measuring electrodes; alternately applying electric current; measuring, with the use of a measuring device, during each current application, the current applied, the potential across the central measuring electrode, the potential difference between the two outer electrodes and the central measuring electrode; using the specific electrical resistivity of formation beds surrounding the well as an electrical logging parameter of cased wells, wherein use is made of a sonde having measuring electrodes spaced at distances that are required to be equal; additional measuring devices are used to measure the differences in electrical field potentials between a current electrode that is not supplied with current on connection and the central measuring electrodes, and the specific electrical resistivity is found from the formula: = · [ 2 Ia 1 · ( Ub 3 + Δ ⁢ ⁢ Ub 13 ) + Ib 5 · ( Ua 3 + Δ ⁢ ⁢ Ua 53 ) ] × × [ ( Ua 3 · Δ ⁢ ⁢ Ub 23 - Ub 3 · Δ ⁢ ⁢ Ua 23 ) · ( Ua 3 · Δ ⁢ ⁢ Ub 43 - Ub 3 · Δ ⁢ ⁢ Ua 43 ) ( Δ ⁢ ⁢ Ua 43 · Δ ⁢ ⁢ Ub 23 - Δ ⁢ ⁢ Ua 23 · Δ ⁢ ⁢ Ub 43 ) ] wherein ρ bed is specific electrical resistivity, Ohm·m; K sonde is the geometrical coefficient of the sonde, m; I a1 and I b5 are currents applied on the first connection to the upper current electrode and on the second connection to the lower current electrode, respectively, A; Ua 3 and Ub 3 are electrical field potentials across the central measuring electrode relative to ground on the first and second connections, respectively, V; ΔUa 23 , ΔUa 43 , ΔUb 23 , and ΔUb 43 are electrical field potential differences on the first and second connections between the upper measuring electrode and the central measuring electrode, and between the lower measuring electrode and the central measuring electrode, respectively, V; and ΔUa 53 and ΔUb 13 are electrical field potential differences between the lower current electrode to which current is not applied on this first connection and the central measuring electrode, and between the upper current electrode to which current is not applied on this second connection and the central measuring electrode, respectively, V.