TECHNICAL FIELD

[001] This invention relates generally to methods of using foamer compositions for treatment of oil and gas wells to enhance production. More specifically, the invention relates to foamer compositions including an imidazoline-based compound. The invention has particular relevance to such compositions that also include corrosion-reducing properties.

BACKGROUND

[002] Declining reservoir pressure in natural gas wells may lead to gas production decreases. The typical cause of this decrease is liquid loading that occurs when water and condensate enter the bottom of the well. Foaming agents (sometimes referred to as "foamers") are frequently used to aid in the unloading of water and condensate accumulated in the wellbore, thereby increasing production from a loaded well. Such agents are generally applied either by batch treatments or continuous applications via injecting down a capillary string or via the casing/tubing annulus. Foamers function by reducing the surface tension and fluid density in the wellbore, and may also be used in conjunction with a lift gas to enhance oil recovery from oil wells.

[003] U.S. Pat. App. Pub. No. 2006/0128990 teaches a method of treating a gas well comprising a chloride-free amphoteric surfactant. U.S. Pat. No 7,122,509 discloses a method of preparing a foamer composition having an anionic surfactant and a neutralizing amine. In U.S. Pat. App. Pub. 2005/0137114 an aqueous foaming composition comprising an anionic surfactant, a cationic surfactant, and a zwitterionic compound is disclosed. PCT App. Pub. No. WO 02/092963 and U.S. Pat. App. Pub. No. 2007/0079963 disclose methods for recovering oil from a gas-lifted oil well using a lift gas and a foaming surfactant which consists of nonionic surfactants, anionic surfactants, betaines, and siloxanes.

[004] While such foamers represent a significant contribution to the art of unloading fluids in oil and gas wells, there still remains a need for improved foamers and methods of using improved foamers. It is thus an objective of this invention to provide a cost-effective foamer for unloading oil, water, or mixtures thereof from oil and/or gas wells. Such improved foamers would also ideally be compatible with anti-corrosive and anti-scale agents. SUMMARY

[005] This invention provides a method of foaming a fluid. The method includes introducing into the fluid a foam-forming amount of a composition comprising at least one imidazo line-based compound of the general formula:

wherein R4 has the following structure:

R ₃ — (CR ₅ )— CHCH ₂ —

[006] In a preferred aspect, the variables of the above general formula are defined as follows: (i) Ri is a moiety selected from the group consisting of: substituted or unsubstituted branched, chain, or ring alkyl or alkenyl having from 5 to about 29 carbon atoms in its main chain; (ii) each R ₂ is independently hydrogen or a linear alkyl or alkenyl moiety having from 1 to about 10 carbon atoms; (iii) each R ₃ is independently a moiety selected from the group consisting of: — C0 ₂ H, — S0 ₃ H, — P0 ₃ H ₂ , — C0 ₂ R _5i — CONH ₂ , — CONHR ₅ , — CON(R ₅ ) ₂ , and combinations thereof; (iv) at least one is R4, and the other ¾ is H or R4; (v) each R ₅ is independently a moiety selected from the group consisting of: hydrogen, substituted and unsubstituted linear alkyi, branched alkyl, aryl, alkylaryl, cycloalkyl, and heteroaromatic groups having from 1 to about 10 carbon atoms in the main chain; (vi) n is from 0 to about 8; (vii) each o is independently from 0 to about 10; (viii) x is 0 or 1; and (ix) y is from 0 to about 4.

[007] In another aspect, the imidazoline-based compound is formed from a reaction between at least one long chain fatty acid and at least one polyalkylene poiyamine. The intermediate imidazoline produced by this reaction is then further reacted with at least one unsaturated acid or acid derivative to form the imidazoline-based compound.

[008] It is an advantage of the invention to provide novel foaming agents for downhole injection in oil and gas wells. Upon separation of the phases from the w/o emulsion, the crude is commonly drawn off the top of the desalter and sent to the fractionator tower in crude units or other refinery processes. The water phase containing water-soluble metal salt compounds and sediment is discharged as effluent.

This invention is an improved refinery desalting operation comprising (i) providing crude oil; (ii) adding wash water to the crude oil and mixing to form and emulsion; and (iii) resolving the emulsion to provide an aqueous phase and crude oil having a reduced metal and amine content in which the improvement comprises adding an effective metal removing amount of one or more hydroxycarboxylic acids selected from malic acid and lactic acid and salts thereof to the crude oil separately from the wash water. Salts of the hydroxycarboxylic acids include, for example, alkali metal salts such as sodium and potassium salts and ammonium salts. "Separately from the wash water" means a separate addition point which may be upstream or downstream of the wash water addition.

"Crude oil" means any hydrocarbon feedstock used in refinery operations including crude petroleum, atmospheric or vacuum residua, solvent deasphalted oils derived from these crudes and residua, shale oil, liquefied coal, beneficiated tar sand, and the like and blends thereof. The crude oil may also be treated with one or more processing aids including solvents, demulsifiers, corrosion inhibitors, and the like. In embodiment, the crude oil is petroleum crude. In an embodiment, the petroleum crude is Doba crude or a crude oil slate comprising Doba crude.

Metals suitable for removal using the process of this invention include, but are not limited to calcium, iron, zinc, silicon, nickel, sodium, potassium, vanadium, and the like and mixtures thereof. In an embodiment, the metals include iron and calcium. In an embodiment, the metal is calcium in its bound and unbound forms.

Amines suitable for removal using the process of this invention include, but are not limited to, monoethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, N,N- dimethyiethanolamine, morpholine, N-methyl morpholine, ethylenediamine,

methoxypropylamine, N-ethyl morpholine, N-methyl ethanolamine, N-methyl diethanolamine, and the like and mixtures thereof.

The malic and/or lactic acid may be added as an aqueous solution. In an embodiment, the aqueous solution comprises about 40 to about 70 weight percent of the acids.

The effective amount of malic and/or lactic acid is the amount of acid required to achieve the desired amount of metal or amine removal from the crude oil and can be determined by one of skill in the art taking into account the characteristics of the acids, the crude oil being treated and any additional process parameters. In an embodiment, the amount of acid added to the crude oil is an amount sufficient to result in a pH of about 3 to about 6 in the separated aqueous solution.

In general, about 1 to about 2,000 ppm of the hydroxycarboxylic acids are added to the crude oil. In an embodiment, about 10 to about 500 ppm of the hydroxycarboxylic acids are added to the crude oil.

In an embodiment, the hydroxycarboxylic acid is malic acid.

The hydroxycarboxylic acids may be used in combination with one or more adjuvants employed in refinery desalting processes including corrosion inhibitors, demulsifiers, pH adjusters, metal complexing agents, scale inhibitors, hydrocarbon solvents, and the like. The adjuvants may be independently added to the crude oil, to the wash water or formulated with the acid solution. For example, oil soluble adjuvants such as demulsifiers and corrosion inhibitors may be added directly to the crude oil while water soluble adjuvants may be formulated with the acids or added to the wash water.

In an embodiment, one or more demulsifiers are added to the crude oil or the wash water.

In an embodiment, one or more corrosion inhibitors are added to the crude oil or the wash water.

In an embodiment, one or more corrosion inhibitors are added to the wash water.

In an embodiment, the hydroxycarboxylic acids are added to the crude oil upstream of the corrosion inhibitor-containing wash water.

In an embodiment, the hydroxycarboxylic acids are added to the crude oil downstream of the corrosion inhibitor-containing wash water.

In an embodiment, one or more metal complexing agents, not including malic acid and lactic acid, to the crude oil or the wash water.

Metal complexing agents include a broad class of chemicals that coordinate or complex metal ions. Representative metal complexing agents include, but are not limited to

ethylenediaminetetra acetic acid (EDTA), glycolic acid, gluconic acid, thioglycolic acid, tartaric acid, mandelic acid, citric acid, acetic acid, oxalic acid, nitrolotriacetic acid (NTA),

ethylenediamine (EDA), methanesuifonic acid, malonic acid, succinic acid, maleic acid, dithiocarbamates and polymeric dithiocarbamates, and the like and salts thereof.

In a representative refinery application, crude oil containing about 70 ppm calcium is processed in a conventional desalting operation which comprises a preheat train which includes preheat exchangers, a mix valve downstream of the preheat train and an electrostatic desalter. Upwards of 150,000 bbl/day of crude oil containing about 20% (30,000 bbls) of Doba crude oil are processed. Wash water treated with a corrosion inhibitor is added to the crude oil stream at a rate of about 5% (7,500 bbl/day). A 50% aqueous solution of hydroxycarboxylic acid is added to the crude charge at a dosage rate of about 2,000 to about 3500 gal/day upstream of wash water. The crude oil emulsion formed by the mix valve is resolved by electrostatic coalescence in the desalter to effect removal of up to about 95% of the calcium from the crude oil.

The foregoing may be better understood by reference to the following Example, which is presented for purposes of illustration and are not intended to limit the scope of this invention.

Example 1

A 50 weight percent solution of crude oil in toluene is heated for about 20 minutes at 180 °F and the heated crude oil sample is then mixed with a 10 weight percent aqueous solution of hydroxycarboxylic acid. The mixture is heated and shaken for about 30 minutes. At the end of the extraction cycle, the samples are immediately heated for a second, 10-minute heating cycle, after which, the phases are allowed to separate in a separatory funnel. The calcium and iron content of the recovered phases is determined by ICP analysis. The results are summarized in Table 1.

Table 1

While the present invention is described above in connection with representative or illustrative embodiments, these embodiments are not intended to be exhaustive or limiting of the invention. Rather, the invention is intended to cover all alternatives, modifications and equivalents included within its spirit and scope, as defined by the appended claims.