The most important parameter in the cathodic protection of
oil well casing is the penetration depth of the protection current and its magnitude, which depend on the geological structure and the resistivity of each layer. Insulating ground is a disadvantage because it limits the scope of the protected area.
When planning the cathodic protection of oil and gas fields, according to the geological data of the pipeline, the required data is the diameter, wall thickness, depth, cementing state and surrounding geological conditions of the tubing and casing. Other factors that need to be considered are operating data, such as oil layer temperature, wellhead temperature, electric heating status of oil field crude oil, etc.
The cathode cable must always be connected to the oil well to be protected, and the oil collection pipeline must be equipped with pipe current measurement points to calculate the amount of current obtained by the casing of each oil well.
When the pipeline does not carry the electrolyte medium, an insulating device can be used to electrically separate the casing and the oil collection line. For oil collecting pipelines with high protection current requirements, it is usually reasonable to build a special anode bed for oil well casings and oil collecting pipelines. For oil outlet pipelines with low protection current requirements, they can be connected to the protection current device by means of diodes and balancing resistors, or connected to the insulation device of the bushing for cathodic protection via a potential connection device. In these two cases, the on-off current method can be used to determine the no-IR drop tube ground potential of the oil collection line. For potential connection, the jumper wire of the insulation device can be connected or disconnected.
The structure of the anode bed depends on the specific conditions of the oil field. The distance between the anode bed should be greater than 100m, so that a uniform potential distribution can be obtained on the oil well casing. If possible, the distance from other oil well casings without cathodic protection should be larger to avoid harmful interference.
