Field Evaluation of Cathodic Production of Casing

Abstract

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 354–360. Abstract A full scale field experiment on cathodic protection of casing answers questions concerning (1) the proper criteria for determining current requirements, (2) the amount of protection provided by different currents, and (3) the transfer of current at the base of the surface pipe. Three dry holes in the Trico pool in Rooks County, Kans., were selected for cathodic protection tests. The three holes were in an area where casing failures opposite the Dakota water sand often occur in less than a year. Examination of the electric logs showed the wells to be similar to other wells in the field where casing in four of seven producing wells has failed. The three holes were cleaned out and cased with 75 joints of new 5l/:z-in. 14-lb I–55. Each joint was visually inspected and marked before it was run. The casing was bull plugged and floated in the hole so that the inside might remain dry and free of excessive attack. Also, if a leak occurred, a pressure increase could be observed on gauge at the surface. Extensive testing was done, including potential profiles, log current-potential curves and electrode measurements from both surface and downhole connections. Based on these data, a current of 12 amps was applied to one well and 4 amps to another. The third well was left to corrode. During the two-year period when the casing was in the ground, the applied current was checked weekly and reference electrode measurements were made about every two months. Three sets of casing potential profiles were run. When the three strings were pulled, each joint was examined for type of scale formed, presence of sulfate-reducing bacteria, extent of corrosion attack and pit depth. Since the pipe was new when run, quantitative determination of the protection provided by current was possible. This is the first concrete field evidence to help resolve the many arguments about the proper method for selecting adequate current for cathodic protection of oilwell casing.