Deep Ground Bed for Casing Cathodic Protection
- John P. Daly (Sunray Mid-Continent Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 1961
- Document Type
- Journal Paper
- 16 - 18
- 1961. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 4.2.3 Materials and Corrosion, 2.2.2 Perforating, 4.2 Pipelines, Flowlines and Risers, 1.14 Casing and Cementing, 1.6 Drilling Operations
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This paper deals with the application of a deep ground bed (1,000 ft) for casing cathodic protection. While several ground beds of this type have been used successfully in the cathodic protection of surface lines, this is the first attempt to control external casing corrosion with a ground bed located in the corrosive zone.
Early and incomplete data indicate favorable results, with certain minor mechanical problems still to be solved. Actual corrosion protection has not been determined, but field surveys correlate with anticipated equipment performance.
Severe external casing corrosion has been apparent for years in the West Kansas area, more precisely through the Dakota sandstone, a large water-bearing reservoir. New casing has been known to fail within a year, and repair costs average $5,000 per failure. Since casing corrosion protection is a relatively new field and has frequently shown poor results, the majority of the wells drilled in this area are still without protection of any kind.
A cathodic protection program study indicated that conventional ground bed designs have three major disadvantages.
1. Poor current distribution occurs along the casing string. The conventional rectifier-ground bed system involves burying numerous non-sacrificial anodes about 100 ft from the well head and some 10- to 20-ft deep. It is from these anodes that current is supplied to the casing. However, corrosion usually occurs opposite, water-bearing formations located at a remote distance from the ground bed. Logically, a large amount of current is ineffective in the protection of the corrosive areas.
2. High top-soil resistances during dry seasons result in overdesign of equipment and expensive electric-power bills or insufficient current densities.
3. Interference with surface equipment occurs. Since the immediate ground bed area is highly corrosive to all structures not electrically connected to the system, it is always time-consuming and expensive to locate and protect all buried equipment in the vicinity of the anodes.
The logical solution to these three problems is to locate the ground bed in the Dakota water, approximately 1,000-ft deep. Early investigation indicates that satisfactory results can be anticipated from this type installation.
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