Corrosion inhibitors with low environmental toxicity

Details Corrosion inhibitors with low environmental toxicity Corrosion inhibitors with low environmental toxicity

1999-04-09

2002-11-05

McKane, Elizabeth (Department: 1744)

Chemical apparatus and process disinfecting, deodorizing, preser

Process disinfecting, preserving, deodorizing, or sterilizing

Maintaining environment nondestructive to metal

C422S016000, C422S017000, C507S243000, C507S939000, C252S394000

Reexamination Certificate

active

06475431

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
The present invention relates generally to the protection of metallic surfaces from corrosion. The invention addresses prevention of corrosion of metallic surfaces with environmentally less damaging inhibitors.
It is a known fact that many oil and gas producing formations yield hydrocarbon, brine, carbon dioxide and/or hydrogen sulfide, which are very corrosive on metal tubing, pumps, casing and other production equipment. This is especially true of metal surfaces, which are exposed to aqueous solutions along with other corrosive chemicals. Corrosion is higher in wells producing brine containing a high percentage of dissolved acidic gases such as carbon dioxide or hydrogen sulfide and inorganic salts, or low molecular weight organic acids such as acetic formic or propionic acid. These chemical ingredients dissolved in water at elevated temperature increases the corrosivity of the medium.
Traditionally, the most common way to reduce corrosion is to add a corrosion inhibitor to a corrosive system to preserve metals. Inhibitors of the corrosion metals are chemical compounds and formulations of these which, when present in small quantities in an aggressive medium, inhibit corrosion by bringing about changes in the surface condition of the metal. The commercially available corrosion inhibitors are less friendly to the environment. Increasingly, operating companies, the government and the public have become concerned about toxicity and environment impact of oil field chemicals, especially in offshore. In offshore operations such as in North Sea, environmentally sounds chemicals are very important. To protect marine environment, corrosion inhibitor should be non-toxic to fish, plants and organisms, and should be biodegradable and reasonably water soluble (it is desired that the partition coefficient of octanol and water should be less than three). Furthermore, the flash point of the solvent and the solvent evaporating factor of the chemical are considered in designing these inhibitors.
For this, corrosion inhibitors, the inventive focus has been a corrosion inhibitors, which have low toxicity in a marine environment. The present invention is related to compounds and compositions, which are very effective corrosion inhibitors in oil and gas field applications, and have less impact on the natural environment.
The low toxicity inhibitor of the present disclosure finds application in tropical waters where the temperature remains relatively high around the offshore production platform. Likewise, it can be used in colder waters including the North Sea and elsewhere. These are waters where temperatures get down to freezing, and yet still support different types of marine life. In both instances, the corrosion inhibitor of the present disclosure is a fluid which can be discharged with the salt water and yet have low toxicity for the marine life.
In general terms, the present disclosure sets forth a reaction product, which is obtained by a relatively straight forward reaction and does not involve extreme difficulties in manufacture.
Consider a production situation in which a production stream of oil droplets suspended in salt water is recovered at 185° F. This is not an uncommon circumstance. This stream will be produced up through the production tubing string in the well, and it is then directed through the well head equipment, a set of valves enabling connection to horizontal gathering lines that extend to a separator tank. A separator tank is commonly a tall, relatively thin upstanding cylinder. It is sometimes called a shotgun tank. Depending on the volume, the tank may be 20 to 30 feet in height. Again, depending on the volume, the diameter may be as small as about 3 feet up to some large diameter. With the passage of time, the oil collects on the top surface of accumulated liquid, and the hot salt water collects at the bottom. While it may cool in that interval, and may actually become quite cool dependent on the northern latitude of the tank and the season of the year, the interior of the tank is exposed to strong salt water solutions, often at elevated temperatures. It is necessary to protect against corrosion the production tubing stream, the well head equipment, and everything made of metal which comes into contact with the flowing fluid. While at the first blush it might appear that produced oil is relatively benign, this is far from the situation that normally occurs. Rather, the produced fluid is typically quite corrosive and will react to damage the metal surfaces.
In some instances, an offshore production platform will produce a large quantity of salt water along with the produced oil. The separator tank on the platform is filled substantially with produced salt water. The salt water can be returned to the ocean, or perhaps to an injection well. In some instances, return of this to the ocean is the only practical solution. Where the produced mix of fluids includes a lot of salt water, and the salt water is returned to the ocean, the operator is placed in a pinch by the desirability of returning produced salt water back to the ocean which does not create a pollution risk, and on the other hand, the pinch relates to the need to add corrosion inhibitors. Successful corrosion inhibitors have been provided heretofore which are quite good and are exemplified in the U.S. Pat. Nos. 5,611,991, 5,611,992, and 5,779,938. These inhibitors are quite successful. They are, however, not readily discharged into a ocean or other salt water environment. Effectively, these inhibitors are handicapped by being somewhat toxic to marine life. The present invention set out an inhibitor compound, more accurately, a family of compounds which has reduced toxicity. Effectively, toxic compounds which include fatty amines, fatty poly amines, fatty amides, fatty poly amides, imidazolines and poly imidazolines are all reacted with both acrylic acid and monochloro acetic acid in such a way that the base nitrogen atoms present in these compounds are reacted with acrylic acid and monochloro acetic acid, or their salts. This converts a highly toxic base molecule (being an amine as exemplified above) and yields a product which provides a quality corrosion inhibitor but which is less toxic.
The need for corrosion inhibitors is accelerated when a well produces something other than the expected flowing oil (with out without natural gas). Often, salt water is produced as mentioned. In addition to that in liquid form, added gases are produced which sometimes create problems. These added gases include CO
2
and H
2
S. Small bubbles of these two gases are often entrained in the produced oil at substantial depths, and the bubbles, while not readily apparent at great depths where the pressure reduces bubble size, become something of a problem as the containment pressure is reduced while flowing to the surface. At the surface, what would appear to be a flowing stream of liquid becomes a froth as the dissolved gases come out of solution, thereby exposing the pipe to corrosion. These gases create problems, thereby shortening the life of the metal goods. Effectively, this attacks the production tubing and any other metal exposed to the flow. The flowing produced oil, with or without the above mentioned gases, and with or without bubbles of entrained natural gas, may also occasionally include low molecular weight organic acids. These are exemplified by acids such as acetic, formic and propionic acid. These acids will attack any exposed metal surface.
Inhibitors can be provided that overcome the problems just mentioned which are grouped in three general groups, the problems derived from: 1) produced gases; 2) produced salt water; and 3) produced acids. The concentration or amount of each may vary, but these are especially problematic depending on pH of the flow, temperature, relative concentrations, and the intervals between servicing of the well. For instance, it is necessary to service the well by adding the corrosion inhibitor exemplified by this present disclosure to the flow periodically. Withou

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