Over the past several years the industry hits encountered many production problems in the Antrim play. Among these are calcium carbonate scale, NORM and CO2 removal. One problem, the corrosion of steel within the production system, has developed due to the chemical nature of the Antrim gas and water. This corrosion hits become a major problem for NOMECO and other operators. This paper will discuss the problem, its source and effects and some possible solutions.
Corrosion of steel within a production system is the result of various chemical reactions between the steel, gas and other fluids it comes in contact with. This chemical reaction can be in the form of iron sulfide or iron oxide, both of which are reactive with acids and other chemicals, The corrosion can also be a reaction of the steel coming in contact with acids themselves. One such acid is known as carbonic acid. It is formed when CO2 dissolves in the water at lower Ph levels. This reaction is further described in a book entitled "Oilfield Water Systems" by Dr. C. C. Patton, According to Dr. Patton, the following equations explain how CO2 dissolves in water:
This ionization of carbonic add liberates hydrogen ions. An excess of these hydrogen ions causes the ph to decrease and the water solution to become more acidic (ph C 7), The continued reaction can cause significant corrosion, metal loss and ultimately tubing failure. The chemical nature of the Antrim gas and water, i.e., high CO2 content in the gas and low ph levels, hits contributed greatly to the problem. The natural Antrim water already hits a low Ph and the mixing of CO2 with this water reduces the Ph even further. In other words, where there is water and CO2 there is corrosion. The extent of the corrosion will depend on the answers to the following questions:
How much water is present?
What is the ph of the water?
What is the chloride content of the water?
what is the CO2 content of the gas?
The answers to these questions will relate to the severity of the corrosion present in the system. As the CO2 content of the gas continues to increase, the potential for the formation of carbonic acid increases significantly. Artificial lift systems that use steel tubulars and other steel down hole equipment will have corrosion problems. In addition to the CO2, some wells also make H2S that will accelerate the corrosion rates in these wells significantly. This accelerates the failure rates of any steel tubulars, pipelines and equipment that comes into contact with the produced waters.
NOMECO first noted a problem might be present as early as 1992 in our Chester East AI-10 which had a sill hole in the stator, or the outer casing of the PC pump.