coupler 120 may have a thickened fiberglass body and incorporate an inner threaded steel ring 122 which threads coupler 120 to the end of casing segment 106 u2032 in the illustrated embodiment female threads 123 of ring 122 are dimensioned to mate with male threads 124 of casing 106 u2032 of course the arrangement of the threads could be reversed and other known mechanical couplings could be employed at this point it should also be recognized that the present invention can be employed in connection with both a new well and in retrofitting an existing well in the case of a new well it will be appreciated that both a coated intermediate production casing and an uncoated bottom end section would be specified along with the inclusion of the insulative coupler 120 of the invention such as illustrated in fig3 and 4 on the other hand for use with existing uncoated steel cased wells another approach is required for delivery of a current to the bottom of the well in this additional embodiment a smaller diameter production casing or tubing coated with an electrically insulating material can be lowered into the existing well with the bottom end segment of the tubing left uncoated the upper coated end would be similarly attached to an insulative coupler like coupler 120 illustrated at fig4 therefore this embodiment includes corresponding first second and third interconnected segments and the current is again supplied to the second or intermediate segment for transmission to the third segment at the bottom section of the well and into nearby geological zones adjacent the well while being prevented from dissipating to.