System and method for electrical resistivity tomography and/or electrical impedance tomography
In electrical resistivity tomography and electrical impedance tomography, interference effects of the metal well casing can be reduced by disposing measurement electrodes in the form of conductive bands around a region of primary insulation on the well casing. Secondary insulation can be provided longitudinally adjacent the primary insulation to further reduce the interference effects. Parameters of the primary and secondary insulation may be determined using finite element methods. The conductive band electrode can connect to a wire of a multi-strand cable using a novel takeout arrangement. Novel measurement methods are also described.
1. An arrangement for subsurface electrical measurements comprising:
(A) a cable comprising an exposed metal connector that is electrically connected to at least one internal cable wire of the cable;
(B) a metal well casing;
(C) primary insulation on at least a first portion of the well casing; and
(D) a first conductive band;
(E) wherein the first conductive band is affixed to the well casing about the primary insulation such that the first conductive band is electrically isolated from the well casing;
(F) wherein the first conductive band electrically and physically engages the exposed metal connector; and
(G) wherein the cable comprises a takeout that electrically connects to the at least one internal wire of the cable, the takeout comprising a clip that electrically engages the first conductive band.
2. The arrangement of claim 1 comprising a conductive contact that extends from the first conductive band and is configured to contact a formation when the arrangement is disposed in the formation.
3. The arrangement of claim 1 comprising secondary insulation on at least one second portion of the well casing longitudinally adjacent the first portion, wherein one or more parameters of the primary insulation are different from one or more parameters of the secondary insulation.
4. An arrangement for subsurface electrical measurements comprising:
(A) a well casing;
(B) a cable;
(C) at least one conductive band provided at least partially around the well casing, the conductive band being electrically isolated from the well casing, the conductive band providing electrical engagement with at least one wire of the cable; and
(D) a contact extending from the at least one conductive band and configured to contact a sidewall of a borehole when the well casing is disposed in the borehole, the contact comprising an arcuate band that arcs from the first conductive band to a second band provided at least partially around the well casing, the arcuate band being the most radially projecting component of the arrangement.
5. The arrangement of claim 4 wherein the well casing comprising at least one first region of primary insulation on an exterior of the well casing, wherein the conductive band is disposed about the primary insulation.
6. The arrangement of claim 5 comprising at least one region of secondary insulation disposed longitudinally adjacent the at least one first region, wherein one or more parameters of the secondary insulation are different from one or more parameters of the primary insulation.
7. The arrangement of claim 4 wherein the cable comprises a takeout that electrically connects to the at least one wire of the cable, the takeout comprising a clip that electrically engages the conductive band.