Patent Description:
It is well known that steel and alloy made tubulars and equipment used in the production of oil and gas are exposed to corrosive environments. Such environments generally contain acid gases (CO<NUM> and H<NUM>S) and brines of various salinities. Under such conditions, the steel or alloy will corrode, possibly leading to equipment failures, injuries, environmental damage, and economic loss.

While the rate at which corrosion will occur depends on a number of factors, such as the type of metal or alloy, partial pressure of the acid gases, salinity, pH, temperature, etc., some sort of corrosion almost inevitably occurs. One way to mitigate this problem is to introduce corrosion inhibitors in the hydrocarbon production system.

Corrosion inhibitors are widely introduced into oil and gas production wells and pipeline transmission lines to help prevent or reduce corrosion of carbon steels surfaces coming into contact with fluids or gases produced from wells.

Methanol-based organic blends containing corrosion and scale inhibitors are sometimes delivered to production fluids or gases through capillary strings and umbilical tubing to aid in reducing or preventing corrosion of or formation of scale upon carbon steel surfaces in the well that come into contact with the production fluid or gas. However, the use of such methanol-based organic blends, because of the presence of chlorides, have been shown to generate pitting corrosion of (i.e. localized corrosion) and to reduce the repassivation ability of the stainless steel (e.g. <NUM>) and corrosion resistant alloy (e.g. Duplex <NUM>) capillary strings and umbilical tubing that are being used to deliver chemicals into the production well.

It would be advantageous to develop an organic chemical blend additive that would help to inhibit this localized corrosion of the stainless steel or corrosion resistant alloy made capillary string and umbilical tubing while still being useful to inhibit corrosion of and reduce scale formation upon other metal surfaces in a production well. <CIT> discloses scale inhibitors and methods of treating a subterranean formation with the same. <CIT> discloses a composition for inhibiting corrosion and/or removing hydrocarbonaceous deposits in oil and gas applications.

<CIT> discloses compositions including polyether-functionalized linear polysiloxanes and methods and systems for using the same to treat subterranean formations. <CIT> discloses a composition useful as corrosion inhibitor formulation for application in heavy brine systems, comprising at least one imidazoline; at least one sulfur synergist; at least one phosphate ester. <CIT> discloses a composition for inhibiting sulfide scale in oilfield operations.

There is provided, in one form, a method of inhibiting corrosion upon a metal surface of equipment used to deliver additives into a production well in which an organic chemical blend is introduced to the well through a conduit, such as a capillary string or umbilical tubing, the organic chemical blend additive being made up of a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt. % water and the amount of the organic chemical blend additive introduced being effective to inhibit localized corrosion of and to improve repassivation potential of a stainless steel and corrosion resistant alloy surface of the capillary string or umbilical tubing.

There is also provided, in another non-restrictive form, a treated system containing a conduit for delivering additives into a production well having a metal or metal alloy surface, and an organic chemical blend additive comprising a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt. % water, wherein the concentration of the organic chemical blend additive in the system ranges from <NUM> ppm to <NUM> ppm, based on a total amount of the production fluid present in the system.

In yet another form, is provided an organic chemical blend additive as defined in claim <NUM>. For example, an imidazoline may additionally be included in the organic chemical blend additive to aid in inhibiting corrosion or improving repassivation of metal surfaces of equipment and conduits used to deliver additives into a production well.

As previously noted, metal and metal alloy made conduits, pipes, tubing, and other equipment used to deliver chemicals and additives useful in the production of oil and gas from a well can experience localized corrosion (pitting) from the chemicals being delivered. It has been discovered that an effective amount of organic chemical blend additive made predominantly of an organic solvent containing a nitrate selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, less than <NUM> wt. % water, and optionally an imidazoline may be useful to inhibit localized corrosion and improve repassivation of metal and metal alloy surfaces of equipment used to deliver additives and chemicals to production wells.

The most commonly used equipment for delivering chemicals and additives to production wells are capillary strings and umbilical tubing. These conduits run down to the bottom of the well and the intake point of an electrical submersible pump to allow for delivery of chemicals and additives to the fluid in the well. Often, these pieces of equipment are made from stainless steel, such as <NUM>, or corrosion resistant alloys, such as Duplex <NUM>, but are not necessarily limited to these specific types of metal or metal alloys.

The organic chemical blend additive contains or includes a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt.

Suitable nitrates salts for use in the present invention are calcium nitrate, sodium nitrate, potassium nitrate, or a combination thereof. Calcium nitrate, in particular, is shown to have better solubility in organic solvents such as methanol or ethylene glycol.

An example of the maleic acid copolymer that may be used in the organic chemical blend additive is, without limitation, propenoic acid, ethyl ester, polymer with ethenyl acetate, and/or <NUM>,<NUM>-furandione, hydrolyzed. This copolymer is included to aid in the reduction of scale formation in the production fluid or any metal surfaces in contact with production fluid. The amount of maleic acid copolymer in the organic chemical blend additive ranges from about <NUM> wt. % to about <NUM> wt.

Suitable organic solvents useful in the organic chemical blend additive may include methanol, ethylene glycol, isopropyl alcohol, <NUM>-butoxyethanol, propylene glycol, butyl carbitol, and combinations thereof.

The blend is organic-solvent based. That is, the amount of the organic solvent in the organic chemical blend additive is greater than <NUM> wt. % and alternatively, greater than <NUM> wt. %, based on the total amount of organic chemical blend additive. Water is present in a small amount, namely in an amount less than <NUM> wt. %, and alternatively less than <NUM> wt. %, based on the total amount of organic chemical blend additive.

In one non-limiting embodiment, the amount of nitrate present in the blend ranges from about <NUM>% of a <NUM>% aqueous solution of nitrate salt to about <NUM>% of a <NUM>% aqueous solution of the nitrate salt. In yet another embodiment, the nitrate salt is present in the organic chemical blend additive in an amount less <NUM> % of a <NUM>% aqueous solution of nitrate.

In an alternative embodiment, the organic chemical blend additive further comprises an imidazoline to help improve corrosion inhibition and repassivation potential of the metal surface of a conduit used to deliver chemicals and additives to a production well.

Imidazolines useful in the organic chemical blend additive for this purpose may have the following general formula:
<CHM>.

In this formula, R describes the hydrophobic tail portion of the molecule and P describes the pendant group of the molecule. In one embodiment, R is a tall oil fatty acid. The pendant group, P, may be selected from a group consisting of (CH<NUM>-CH<NUM>)-X or (CH<NUM>-CH<NUM>-O)nH, wherein X may be NH<NUM> or OH and n is <NUM>. The proportions of the optional imidazoline in the organic chemical blend additive may range from about <NUM> wt. % independently to about <NUM> wt.

It is difficult to predict in advance what amount of organic chemical blend additive should be introduced to the production well to achieve an optimum corrosion inhibition and repassivation improvement because such amount is dependent upon many interrelated variables such as, for example, the nature of the production fluid being extracted from the production well, the nature of other the oilfield chemicals being delivered, and nature of the metal surface of the conduits and other equipment used to deliver chemicals to the production well or to carry the production fluid, etc. Nevertheless, in one non-limiting example, the amount of organic chemical blend additive being delivered ranges from <NUM> ppm independently to <NUM> ppm independently. Alternatively, the amount of organic chemical blend additive being delivered may range from about <NUM> ppm independently to about <NUM> ppm independently or range from about <NUM> ppm independently to about <NUM> ppm independently. The amounts in this paragraph are based on the total amount of production fluid in the well. As used herein with respect to a range, "independently" means that any threshold may be used together with another threshold to give a suitable alternative range, e.g. about <NUM> ppm independently to about <NUM> ppm independently is also considered a suitable alternative range.

For purposes of this disclosure, the term "inhibit" is defined to mean reduce, suppress, or prevent. It is not necessary for the corrosion, localized or general, and scaling of the metal surfaces of capillary string, umbilical, tubing, or other oil and gas production or piping having metal surfaces to be entirely prevented for the chemical blend additives discussion herein to be considered effective, although complete prevention is a desirable goal.

The invention will be further described with respect to the following Examples, which are not meant to limit the invention, but rather to further illustrate the various embodiments.

The Cyclic Potentiodynamic Polarization ("CPP") graphs in <FIG> and <FIG> depict the pitting potential, repassivation potential, and open circuit potential performance of organic chemical blend additives having the compositions set forth in Table <NUM> below upon a Duplex <NUM> alloy surface and upon a stainless steel <NUM> surface of a capillary string. Erep - Eocp is the difference between the repassivation potential (Erep) and the open circuit potential (Eocp). The larger the difference in these values, the more the metal tends to repassivate. An Erep - Eocp > <NUM> mV represents an effective protection of the metal surface.

The curves on <FIG> demonstrate that an organic chemical blend additive containing a maleic acid copolymer, at least <NUM> wt. % organic solvent, and less than <NUM> wt. % water, and <NUM>% of a <NUM>% aqueous solution of calcium nitrate achieves the same amount of corrosion inhibition and repassivation improvement on Duplex <NUM> metal surface as an organic chemical blend additive containing a maleic acid copolymer, at least <NUM> wt. % organic solvent, and less than <NUM> wt. % water, and <NUM> or <NUM>% of a <NUM>% aqueous solution of calcium nitrate on the same type metal surface.

The performance was a bit different when the organic chemical blend additive was applied to a stainless steel <NUM> surface. While an additive containing only <NUM>% of a <NUM>% aqueous solution of calcium nitrate performed just as well in inhibiting corrosion and improving repassivation potential as an additive that contained <NUM>% of a <NUM>% aqueous solution of calcium nitrate, the results were not as good when an additive with <NUM>% of a <NUM>% aqueous solution of calcium nitrate was applied to the stainless steel surface, as shown the curves in <FIG>. These results indicate that determining what amount of components is necessary to achieve good results may depend on the stainless steel or alloy used on a given capillary string or umbilical tubing.

In addition, the CPP graph in <FIG> indicates that there is a significant improvement in corrosion inhibition and repassivation improvement with an organic chemical blend additive that contains both the nitrate salt and a maleic acid copolymer, Blend B, represented by curve B as compared to an organic chemical blend additive that doesn't include a maleic acid copolymer, Blend D, represented by curve D. These results suggest that the maleic acid co-polymer may act synergistically with the nitrate salt to improve repassivation behavior and inhibit localized corrosion.

Table <NUM> shows the composition of Blends A, B, C, D, and E, the CPP graphs of which are shown in <FIG>, <FIG>, and <FIG>.

The CPP graphs in <FIG> depict the pitting potential, repassivation potential, and open circuit potential curves of the organic chemical blend additives further containing an ethoxylated imidazoline, as set forth in the compositions in Table <NUM> below, upon a Duplex <NUM> alloy surface and upon a stainless steel <NUM> surface.

<FIG> demonstrates that the addition of an ethoxylated imidazoline to the organic chemical blend additive, for example, greatly improves the repassivation behavior of Duplex <NUM> even when the organic chemical blend additive contains only <NUM>% of a <NUM>% aqueous solution of calcium nitrate, a smaller amount than otherwise employed or expected to achieve an Erep - Eocp larger than <NUM> mV. These results suggest that the imidazoline may act synergistically with the nitrate salt and the maleic acid copolymer to improve repassivation behavior and inhibit localized corrosion.

The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For example, the method may consist of or consist essentially of introducing an organic chemical blend additive to a production well via a conduit having a metal surface, the organic chemical blend additive consisting essentially of or consisting of a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt. As another example, the treated system may comprise, consist of, or consist essentially of: a conduit for delivering additives to a production well having a metal or metal alloy surface; and organic chemical blend additive consisting essentially of or consisting of a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt.

In another non-limiting embodiment, the additive may comprise, consist essentially of, or consist of a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt.

In a different non-restrictive version, the additive may comprise, consist essentially of, or consist of, a nitrate salt selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof, a maleic acid copolymer, an imidazoline, greater than <NUM> wt. % of an organic solvent, and less than <NUM> wt.

As used herein, the terms "comprising," "including," "containing," "characterized by," and grammatical equivalents thereof are inclusive or open-ended terms that do not exclude additional, unrecited elements or method acts, but also include the more restrictive terms "consisting of" and "consisting essentially of" and grammatical equivalents thereof.

Claim 1:
A method of inhibiting corrosion of a metal or metal alloy comprising:
introducing an organic chemical blend additive to a production well, where the organic chemical blend additive comprises:
a nitrate selected from a group consisting of calcium nitrate, sodium nitrate, potassium nitrate, and a combination thereof,
a maleic acid copolymer,
an organic solvent in an amount greater than <NUM> wt.%, based on a total amount of the organic chemical blend additive, and
less than <NUM> wt.% water, based on a total amount of the organic chemical blend additive.