CA2184240A1

CA2184240A1 - Method for treating oil production systems

Info

Publication number: CA2184240A1
Application number: CA002184240A
Authority: CA
Inventors: Charles L. Kissel
Original assignee: Amvac Chemical Corp
Current assignee: Amvac Chemical Corp
Priority date: 1995-08-29
Filing date: 1996-08-28
Publication date: 1997-03-01
Also published as: GB2304731A; NO963601D0; NO963601L; GB9617954D0; GB2304731B

Abstract

Solutions of dithiocarbamate salts, such as the sodium salts of N-methyl dithiocarbamate and N,N-dimethyl dithiocarbamate, can be utilized as admixtures with acids, to provide admixtures that are non-corrosive to mild steels in the treatment of oil production systems. Some admixtures are even corrosion inhibiting. Both general corrosion and pitting corrosion forms are affected by the dithiocarbamate admixtures. As a consequence, petroleum production is facilitated as evidenced by the lowering of pour points, the reduction of pressures in flow lines, the reduction of separation problems, and increased crude oil yields.

Description

PATENT

METHOD FOR TREATING OIL PRODUCTION SYSTEMS

Field of the Invention The present invention is related to methods for dewaxing oil in steel systems without causing corrosion of the steel. More particularly, the invention relates to methods for providing aqueous solutions of dithiocarbamates with aqueous acids to form admixtures that are non-corrosive to mild steels.

Back~round of the Invention In the production of oil from subte,~ ean formations penetrated by a well, paraffins are often deposited from the oil and tend to clog the pores of the reservoir rock, well casing, and piping through which the oil flows to the surface. Problems involving plugging and lost production yields can be caused by the formation of solid, waxy, asphaltenic, and/or colloidal sulfur deposits. In a two-phased oil-water system, additional interfacial problems can arise which adversely affect separation processes.
Various techniques have been employed in the removal of these paraffin deposits from ~u~Jte.ldilean formations, wells and piping penetrating these formations. These techniques include the use of heating devices, mechanical scraping, specialty polymers and solvents. Various types of solvents which have been used to dissolve the paraffins include benzene, xylene, toluene, gasoline and heavier ~ till~tes~ carbon tetrachloride and carbon disulfide.

Carbon disulfide is considered one of the most effective solvents for paraffins of widely different compositions. Carbon disulfide is known for preventing the deposition of waxes, asphaltenes, and/or sulfur, as well as in the removing of these deposits once formed. Enhanced oil recovery is also assisted when carbon disulfide is utilized. While some of these systems are made of specialized steels, the vast majority of the world-wide ones are of mild steels.
Carbon disulfide is also identified as being useful in many other applications.
Some of the uses include: viscosé rayons, cellophanes, m~nl~f~cture of carbon tetrachloride and sulfur-cont~ining chemicals such as x~nth~tes and thiocarb~m~tes, agricultural fungicides, rodenticides, insecticides, nematocides, fumig~nt~, soil conditioners, ph~rm~ceuticals, rubbers, polymer industrial plepaldlions, electroplating, metal treatment, wastewater treating, semiconductors, photography, food preservation, ore flotation, paper-making and catalysts. In addition to petroleum production, carbon disulfide can also provide its useful solvent prope.lies in such areas as: petroleum refining, iodine recovery, sulfuric acid reclamation, sulfur extraction and the recycling of plastics. Most of these uses occur in systems fabricated in metals, particularly steels.
Use of carbon disulfide is difficult and hazardous, however. The hazards includefl~mm~bilit,v and toxicity, which have led to certain bans on its usage. A water-based carbon disulfide precursor would provide all of the above utility, while being safer to handle. Dithiocarbamates represent a class of chemicals that can be water-based, and can yield carbon disulfide under controlled conditiorls. Acidification of dithiocarbamate salts is usually required to liberate the carbon disulfide agent. Aqueous, acidic solutions are generally corrosive to the vast majority of mild steels present in the above mentioned carbon disulfide industries and applications, which would require special metallurgy or periodic replacement of steel pipe.
lt is an object of the present invention to provide a method for safely releasing carbon disulfide for oil field dewaxing, enhanced oil recovery and other services without the need for special precautions, metallurgy or periodic replacement of steel pipe. It is a further object of the invention to provide admixtures of aqueous dithiocarbamates and acids that are not corrosive to mild steel systems.

21 ~4240 Summary of the Invention Contrary to expectations, the addition of aqueous acids to certain aqueous dithiocarbamate salts produces admixtures that are not corrosive, and in some cases corrosion-inhibiting, even though the resulting pH realized in these admixtures is acidic.
These results are also realized for admixtures cont~ining adjuvants such as surfactants and alcoholic winterization agents.
The dithiocarbamates have the formula R S
R
The dithiocarbamates can also have a polymeric form, and can further be homopolymeric or copolymeric.
The method comprises the steps of forming an aqueous solution of the dithiocarbamate, admixing an acid, and applying the ~ lixlllle to the oil production system to be dewaxed. The acid is added in an amount sufficient to provide about 0.5 to 7.0 equivalents of acid for every one equivalent of carbon disulfide in the dithiocarbamate. This allows for about 90% or more of the carbon disulfide to beliberated. The liberated carbon disulfide may be present as a neat phase, dissolved in a hydrocarbon phase, dissolved in an aqueous cosolvent phase or distributed among any of the above. The a~ lixlul~ can be applied to mild steel systems without causing corrosion of the mild steel.

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of S illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and theinvention includes all such modifications.

Detailed Description of the Preferred Embodiments Aqueous solutions of dithiocarbamate salts can be utilized as admixtures with aqueous acids, to provide admixtures that are non-corrosive to mild steels. Someadmixtures are even corrosion inhibiting. Both general corrosion and pitting corrosion forms are affected by the dithiocarbamate admixtures. As a consequence, petroleum production is facilitated as evidenced by the lowering of pour points, the reduction of pressures in flow lines, the reduction of separation problems, and increased crude oil yields.
The dithiocarbamates useful in the present invention have the formula R S
Rl/

wherein R and Rl are each independently a hydrogen, an alkyl radical or an aryl radical.
An example of an aryl radical is benzyl. M can be any cation with plef, .~d cations being an alkali metal, such as lithium, sodium, potassium, cesium, or rubidium or a substituent compound having the formula NR2R3R4R5. R2, R3, R4 and R5 can each independently be hydrogen, an alkyl radical, or an aryl radical. Preferred dithiocarb~m~t~s are sodium salts of N-methyldithiocarbamate and _,_-dimethyldithiocarbamate .
The method comprises the steps of prepaling an aqueous solution of the dithiocarbamate, combining an acid with the dithiocarbamate solution to form an admixture, and delivering the a~lmixtllre to oil production equipment in a mild steel system. The amount of acid admixed with the aqueous dithiocarbamate will vary depending on the strength of the acid and the equivalents of carbon disulfide in the dithiocarbamate. In general, the amount of acid admixed with the dithiocarbamate will be an amount sufficient to provide about 0.5 to 7.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate, preferably about l .S to 3.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate. Most preferably, the amount of acid added provides about 2.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate. In this manner, at least 90% of the theoretical carbon disulfide is released and available for treating the oil. The liberated carbon disulfide may l O be present as a neat phase, dissolved in a hydrocarbon phase, dissolved in an aqueous cosolvent phase or distributed among any of the above.
The decomposition or reconversion reaction in which carbon disulfide is releasedfrom the admixture of a dithiocarbamate with acid (HA) can be represented by theequation R S + 2HA = CS2 + NH2 A~ + MA

Rl/ Rl/

When sodium _-methyldithiocarbamate is used, methylamine salt is produced along with the release of carbon disulfide. Methylamine salts are listed in the tables published by the National Association of Corrosion Engineers as agents known to cause corrosion in mild steels. Likewise, use of sodium _,_-dimethyl dithiocarbamate releases known corrosive agents, dimethylamine salts, in the carbon disulfide liberation reaction.

It has surprisingly been discovered that acids can be admixed with the aqueous dithiocarbamates of the present invention to release carbon disulfide and known corrosive agents, yet the resulting admixtures are not corrosive to mild steels.
Preferably, the dithiocarbarnates of the present invention have low molecular weight Lower molecular weight dithiocarbamates will be water soluble, and have a high proportion of carbon disulfide potential. In particular, dithiocarbamates of formula I in which R or Rl each has six carbons or less are plef~.~ed. The reconversion reaction products of these dithiocarbamates have correspondingly low molecular weight and are known corrosive agents in mild steel systems. The resulting admixtures of the present invention, however, do not cause corrosion in mild steels.
The dithiocarbamates utilized in the present invention can also be polymeric materials with the formula ~C--C~n II

Rg S
or ~CI--I ~n R9 III

Il C--S--M
where n is an integer greater than 1. R6, R~, R8 and Rg are each indepen~l~ontly hydrogen, an alkyl radical or an aryl radical. Again, these radicals are of a relatively low molecular 2 1 8l~243 weight, having from 1 to 6 carbon atoms. For both formulae II and III, Z is an alkyl radical, for example methylene or ethylene, an aryl radical, for example phenylene, or need not be present in formula II.
The dithiocarbamate of formula I, II, or III can also be a polymer where M has the formula R~ R8 ~C ¢ ~n IV
R~ I R
~N' R

or ~1 ¢~n ~3 R

R~ C--O--Z--N--Rl Still further, the dithiocarbamates of formula I, II, or III can be polymers where M has the formula ~N VI
R

and p is greater than 1.
20The repeating units of the polymeric dithiocarbamates should have a high proportion of latent carbon disulfide. These polymeric dithiocarbamates may also have a co-monomer character which improves their water solubility. An example of a polymeric dithiocarbamate having a co-monomer character is one of the above formula with abackbone having appendant ammonium groups.
The polymeric dithiocarbamates having any of the formula 1, II, or III, may alsobe used with a copolymer. These copolymers could be, for example, methacrylic acid, acrylic acid, allyl alcohol, methacrylamide, acrylamide, alkyl methacrylates, alkyl acrylates, crotonic acid, itaconic acid, maleic acld, maleic anhydride, fumaric acid, styrene, butadiene, vinyl acetate, carboxyethylmethacrylate, carboxyethylacrylate, sulfoethyl-methacrylate, sulfoethyl-acrylate, hydroxyethylmethacrylate, hydroxyethylacrylate, oxyalkylated methacrylates, oxyalkylated acrylates, oxyalkylated allyl alcohol and acrolein. The oxyalkylation could contain ethylene oxide, propylene oxide or butylene oxide or mixtures thereof.
While wholly aqueous dithiocarbamate solutions are preferred, it may be advantageous to use a cosolvent and/or emulsifying agent together with the dithiocarbamate to provide additional benefits. Examples of such cosolvents include organic materials that are water miscible, exemplified in alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof.
Examples of emulsifying agents are surfactants, dispersion agents, suspension agents and the like. The sllrfActAnt~ can be nonionic, anionic or cationic.
The dithiocarbamate for use in the present method could further comprise any combination or a~lmixtllre of dithiocarbamates given above.
When the acidic materials utilized in the present invention are water soluble enough to produce concentrated aqueous solutions, these acid solutions are also known to be corrosive to mild steels. The corrosive tendencies of specific acids in various systems are presented in tables published by the National Association of Corrosion Engineers (NACE) Corrosion Data Survey, 5th ed., National Associations of Corrosion Engineers, 1981. The admixtures of the present invention, however, which contain aqueous dithiocarbamates and acid are surprisingly not corrosive to mild steel systems.
The acidic agents liberate carbon disulfide from the aqueous dithiocarbamate salts. These acidic agents may be typical mineral acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, boric acid, fluoboric acid or sulfurous acid. Typical polyacids such as polyphosphoric acid or polysilicic acid may also be used.
Organic acids, such as acetic acid, hydroxyacetic acid, oxalic acid, citric acid, tartaric acid, maleic acid, acrylic acid or benzoic acid, also have application in the present invention. A preferred acid is acetic acid. Likewise, polyorganic acids such as polyacrylic acid or polymethacrylic acid may be used.
Although wholly aqueous acid solutions are plere.led, it may be advantageous to use a cosolvent and/or emulsifying agent together with the acid to provide additional benefits. For example, acid agents with low or no water solubility could be emulsified with surf~ct~ntc and utilized in the present invention. Examples of such cosolvents include organic materials that are water miscible, exemplified in alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof. Examples of emulsifying agents are surfactants, dispersion agents, suspension agents and the like. Nonionic, anionic and cationic surfactants could be used. These agents may also be monomeric (such as oleic acid) or polymeric (such as poly-fatty 21 ~424U

acids). The added acidic agents may also be a buffering material with an acidic pH when made up in water.
It will be appreciated that admixtures of any combination of the aforementioned acid agents and dithiocarbamates could also be used.
S Since the largely aqueous solutions of the present invention are commonly used in cold climates where wax formation is a problem, it is advantageous to apply a winterizing agent to the dithiocarbamate, acid or their admixture. Winterizing agents lower the freezing point of the solution, making it easier to pump the material. Commonly used winterizing agents are alcohols, which can be either monomeric or polymeric. Examples l O are methanol, isopropanol, ethylene glycol, propylene glycol, polyethylene glycol and mixtures thereof.
The above-described solutions of the present invention may be utilized in steel systems without experiencing corrosion. The steels can be mild steels, cast irons, and galvanized, with mild steels being the most plefe.led.
l S The invention is further embodied in the following non-limiting examples.

Ex~n~le I
The amount of acid relative to the amount of winterized, aqueous sodium N-methyldithiocd~ .late can be determined by ex~rnining different ratios of acid to dithiocarbamate and measuring the point at which the maximum theoretical amount of carbon disulfide is released upon adrnixing.
25 mL of a solution of 39% sodium N-methyldithiocarbamate, 24% ethylene 2 1 &4240 glycol and 36% water was admixed with an equal volume of acetic acid at varying strengths and the amount of carbon disulfide converted was determined. The following data was obtained.
Acetic Acid Amount (mL) of Concentration (%)Neat Carbon Disulfide 0.4 1.6 1.9 2.4 3.0 3.0 The theoretical carbon disulfide value is 5.5 mL. Distillation of the aqueous layer when 30% acetic acid was used afforded 2.5 mL of carbon disulfide, bp 45C. ThisI S demonstrates that the carbon disulfide was held in the aqueous solution by the ethylene glycol.
These data show that 25 mL of about 30% aqueous acetic acid will convert 39%
sodium N-methyldithiocarbamate to the theoretical amount of carbon disulfide.
The pH was observed to proceed from 11 to 3.6 upon the addition of the acid to the dithiocarbamate, followed by a rise to 7Ø Aqueous acetic acid is known to be corrosive to mild steels.

Ex~ ple 2 The corrosive nature of dithioc~b~ tes, acids and their admixtures was dete rninecl under dynamic conditions by the use of a recirculating flow-loop. In this case, a reservoir was connected to a corrosion test cell via a pump. The test cell housed a Corrater probe fitted with mild steel elements (available from Rohrback-Cosasco, Santa Fe Springs, CA). Flow meters, thermometers and a pH probe were also part of the system. The entire loop held at least 300 mL fluid, and is run at speeds of 4 to 10 gph.
Normally, the flow rate was 6 gph. The data for the sodium _-methyldithiocarbamate/
acetic acid system are displayed in the following Table 1.

Tablel 21 8424U

Temp. Corrosion (mpy)2 System Measured (C)pH(am)/pH(eq)' General Plttmg 300 g deioniæd (DI) water 22 5.8/5.9 3.6 0.5 150 g 39% sodium ~- 23 11.0/10.9 - 3.7 0.4 methyldithiocarbamate in - glycol/water;
150 g DI water 150 g 50% acetic acid; 22 1.9/1.9 27.0 8.0 150 g DI water 150 g sodium ~1- 23 3.6/7.0 3.4 0.2 methyldithiocarbamate in glycol/water;
150 g 50% acetic acid 150 g 50% acetic acid; 23 5.6/5.6 11.9 5.6 128 g DI water;
21.6 g 86% NaOH
150 g 50% acetic acid; 23 5.0/5.1 13.5 6.1 120 g DI water;
30 g 40% aqueous MeNH2 150 g 50% acetic acid; 23 5.1/5.0 10.3 5.8 98 g DI water;
21.6 g 86% NaOH;
30 g 40% aqueous MeNH2 ' The pH(am) is the value immedi~tely after ~.l..,;";l.g the system, and the pH(eq) is the value after the system ~ched equilibrium.
2 The corrosion rates were determined after the Corrat,~r e~ t reached a stable reading. ~ d~4~
These data indicate the sodium N-methyldithioc~l~ ate in glycol/water with the equivalent amount of 50% aqueous acetic acid is not corrosive. This is evident by comparisons with the acetic acid systems cont~inin~ equivalent amounts of sodium hydroxide and methylamine, which result from the reconversion process yielding concurrent carbon disulfide.

Example 3 S A petroleum-producing well was selected as a site to apply aqueous sodium N-methyldithiocarbamate cont~ining ethylene glycol as a winterizing agent described in Example l. An equal volume of 30% acetic acid was applied concurrently. The wellproduced 10 bbl/day gross production, with a 5% water cut. The crude oil had an API
gravity of 28.2, and contained about 8.1% wax and about 4.0% asphaltenes. The produced brine had a pH of 7.2, and a total dissolved solids level of 6,400 ppm. The chemicals were pumped down the backside of the well using a beam-driven pump equipped with two heads. Each chemical was pumped separately, and admixed after the pump heads before entering the well casing. No flush was used. Historically, about 10-14 days are required for the p~lÇo~,nance of the product to appear at the wellhead with the gross production. The data for this application are shown in Table 2. The corrosion measurements were made on a Corrosometer probe (Rohrback-Cosasco, Santa Fe Springs, CA).

Table 2 Elapsed Time (days) Amount of Pour Point (C) Corrosion (mpy) Dithiocarbamate Solution Applied (gal) 0 +6 2 0.9 +5 2 - 3 2.2 +5 2 4.1 +4 2 7 6.0 +5 9 8.1 +5 9.0 +3 12 1 1.1 -2 2 14 13.0 -9 2 16 15.2 -I 1 17 16.0 -14 19 17.9 -15 21 20.1 -14 22 21.0 -13 2 24 21.0 -13 2 These data demonstrate the sodium N-methyldithiocarbamate can be applied with concurrent use of acetic acid, and yield a pour point depression for this crude oil.
Furth~rmore, no change in the corrosive nature of the production was observed when the dewaxing performance was realized.

Example4 21 ~240 The amount of numerous acids relative to the amount of winterized aqueous sodium N,N-dimethyldithiocarbamate can also be determined by eY~mining the different ratios of acid to dithiocarbarnate and measuring the point at which the maximum amount of carbon disulfide is realized upon admixing. In this case, the precursor contained 33%
sodium N,N-dimethyldithiocarbamate, 20% ethylene glycol, and 47% water. Graduated tubes were charged with 6.5 g dithiocarbamate solution and admixed with various amounts of acids at different concentrations. The theoretical amount of carbon disulfide is 0.9 mL. The data are shown in Table 3.

21 84~4~
Table 3 Aqueous Acid System Arnount (mL) Carbon Disulfide from Amount Acid Examined 2g 4g 6g 7g 8g 9g 12g 16g 25 % Acetic Acid 0.25 0.5 0.75 0.9 - -50% Acrylic Acid 0.15 0.45 0.85 0.9 25% Citric Acid 0.2 0.5 0.8 0.85 0.9 20% Fluoboric Acid 0.1 0.35 0.5 0.6 0.7 0.8 0.9 88% Formic Acid 0.7 0.9 35% Glycolic Acid 0.4 0.7 0.9 50% Glycolic Acid 0.5 0.8 0.9 - - - - -50% Glyoxylic Acid 0.35 0.6 0.9 49% Hydrobromic Acid 0.35 0.75 0.9 18% Hydrochloric Acid 0.3 0.7 0.9 50% Hypophosphorous Acid 0.3 0.55 0.8 0.9 50% Methacrylic Acid 0.3 0.6 0.8 0.9 35% Nitric Acid 0.4 0.8 0.9 - - - - -50% Phosphoric Acid 0.4 0.6 0.85 0.9 20% Propionic Acid 0.2 0.35 0.5 0.6 0.7 0.8 0.9 15% Sulfamic Acid 0.1 0.2 0.3 0.35 0.4 0.45 0.6 0.9 50% Sulfuric Acid 0.45 0.8 0.9 20% Tartaric Acid 0.15 0.3 0.5 0.7 0.75 0.8 0.9 As it can be seen, several inorganic and organic acids can be used to liberate carbon disulfide from the sodium _,_-dimethyldithiocarbamate. Most of these acids are corrosive to mild steels, which is easily verified by reference to the Corrosion Data Survey issued by the National Association of Corrosion F,ngin~ers.

Example S
The acid/sodium N,N-dimethyldithiocarbamate admixtures at acid levels sufficient to yield maximum amounts of carbon disulfide were examined for their corrosion tendencies using the test loop described in Example 2. The data are described in Table 4.

Table 4 System Evaluated T~.. lpeldlllre Corrosion (mpy)2 (C)pH(am)/PH(eq)' General Pitting 300 g DI water 22 5.8/5.9 3.6 0.5 23S g sodium N, N- 19 11.0/10.9 5.0 0.5 dimethyldithiocarbamate;
200 g DI water 235 g sodiumN,N- 19 5.0/7.0 0.04 0.02 dimethyldithiocarbamate;
200 g 25% acetic acid 235gsodiumN,N- 20 4.4/6.0 4.1 0.2 dimethyldithiocarbamate;
250 g 25% acetic acid 200 g DI water; 21 2.7/2.9 20.0 5.0 250 g 25% acetic acid 235 g sodium ~, ~- 20 3.2/3.9 0.11 0.02 dimethyldithioc~balllate;
200 g 35% glycolic acid 235 g sodiu n ~ 20 2.3/3.8 0.7 0.3 dimethyldithiocall,alnate;
92 g 88% formic acid 235 g sodium N, N- 19 4.4/5.2 1.9 0.6 dimethyldithiocarbamate;
492 g 20% propionic acid Table 4 (Continued) 2 1 8 4 2 ~ O

System Evaluated Temperature Corrosion(mpy)2 (C) pH(am)/pH(eq)' General Plttmg 235 g sodium N, N- 20 0.2/0.8 0.3 0. l dimethyldithiocarbamate;
185 g 18% hydrochloric acid 235 g sodium N, N- 20 2.4/2.3 3.0 2.0 dimethyldithiocarbamate;
215 g 50% phosphoric acid 235 gsodiumN,N- 20 3.9/4.6 1.3 1.5 dimethyldithiocarbamate;
215 g 50% acrylic acid 235 g sodium N, N- 21 3.9/4.6 1.2 0.2 dimethyldithiocarbamate;
369 g 20% tartaric acid 235 g sodium N, N- 20 1.2/6.7 2.8 0.6 dimethyldithiocarbamate;
523 g 15% sulfamic acid 235 g sodiumN,N- 20 4.6/5.0 1.3 1.2 dimethyldithiocarbamate;
246 g 50% methacrylic acid 235gsodiumN,N- 20 3.9/5.6 0.2 0.1 dimethyldithiocarbamate;
267 g 25% citric acid ' The pH(am) is the value immediately after ~flmixing the system, and the pH(eq) is the value after the system reached equilibrium.
2 The corrosion rates were clete rnined after the Corrator equipment reached a stable reading.
The above examples indicate that the use of acids with sodium N, N-dimethyldithiocarbarnate in ethylene glycol/water admixtures, yield lower general corrosion rates for all acids reported. There are some increases in pitting corrosion for 21 842~0 the acrylic, methacrylic, and phosphoric cases. In the case of 25% acetic acid, general corrosion rates did change appreciably when a 25% increase in acid was used, but that the observed values were below the blank water example.

Example 6 The winterized version of sodium ~I,N-dimethyldithiocarbamate was applied at a rate of one gallon per day, with a concurrent amount of 20% acetic acid at the petroleum-producing well under the conditions described in Example 3. After 51 days at one gallon per day, the rates were increased to 1.5 gallons per day. The data are shown in Table 5.

Table 5 Applied Chemical Cumulative Amount Pour Point (C) Corrosion (mpy) Rate (gallons per Dithiocarbamate S day) Solution Applied (gal) 0 +6 +5 2 - I 6 +5 2 11 +1 1.5 42.5 -2 1 5 1 .5 50.0 -2 2 1.5 57.5 -3 1.5 65.0 -3 2 1.5 72.5 -6 1.5 80.0 -8 2 1.5 81.5 -8 The data demonstrate that the aLl~ixlu.e of acetic acid and sodium N, N-dimethyldithioc~l,dl,late can be applied downhole, and that no corrosion increases were realized dunng the times that dewaxing ~clro,lnance was observed in the gross production.

Exarnple 7 An oil well having a gross production of oil and water rate of about 100 bbl/day, with an oil content comprising about 40 bbl/day of an API 20 crude, was treated with a solution of 33% aqueous dithiocarbamate admixed with a 25% acetic acid at a ratio of l: I . The treatment comprised squeezing 2 bbl of solution (equivalent to about 0.17 bbl carbon disulfide) at a pH of about 4.5 into the well bore, after which the well was shut-in for about 24 hours. Twelve months prior to this treatrnent, the total production for the well was about 60 bbl/day. In the first 24 hour period after the squeeze, the production was resumed. The gross production rate had risen to about 135 bbl/day comprising about 74 bbl/day crude oil (187% improvement), after about one month, while the gross production had declined to about 108 bbl/day, the crude oil rate was about 48 bbl/day (120% improvement). The corrosion rate prior to this squeeze application was about 1 -2 mpy. At the time of the restart of production of crude after the shut-down condition, and during the month thereafter, no change in the corrosion rate was observed.
Example 8 The corrosion test loop described in Example 2 was used to evaluate various winterized acid/sodium dithiocarbamate admixtures. The data are described in Table 6, and use 235 g 33% sodium dimethyldithiocarbamate and 200 g 20% acetic acid, with the winterizing agent at a level of 25% in the 235 g dithiocarbamate solution.

2 1 842~0 Table 6 Corrosion (mpy)' Winteri7in~ Agent General Pitting None 0.10 0.05 Ethyleneglycol 0.04 0.02 Isopropanol 0.09 0.04 Methanol 0.09 0.07 Propylene glycol 0.05 0.01 Polyethylene glycol (MW=400)0.10 0 03 ' The corrosion rates were determined after the Corrator equipment reached a stable reading.
These data suggest that alcoholic-based winterizing agents do not affect the low levels of corrosion realized by acid/dithiocarbamate admixtures.

Claims

1. A method for treating oil without causing corrosion in a mild steel system comprising the steps of:
preparing an aqueous solution of a dithiocarbamate of the formula wherein R and R1 are each independently H, C1-6 alkyl or aryl, M is Li, Na, K, Cs, Rb or NR2R3R4R5, R2, R3, R4 and R5 are each independently H, C1-6 alkyl or aryl;
combining acid with said dithiocarbamate solution to form an admixture, said acid being added in an amount effective to provide about 0.5 to 7.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate; and delivering the admixture to the oil in the mild steel system, wherein the treating method is selected from the group consisting of dewaxing, desulfurizing and deasphalting.

2. The method of claim 1 wherein the acid is added in an amount effective to provide about 1.5 to 3.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate.

3. The method of claim 2 wherein the acid is added in an amount effective to provide about 2.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate.

4. The method of claim 1 wherein the acid is in aqueous solution.

5. The method of claim 1 wherein the acid is selected from the group consisting of hydrochloric, sulfuric, phosphoric, boric, fluoboric, sulfurous, polyphosphoric, polysilicic, acetic, hydroxyacetic, oxalic, citric, tartaric, maleic, acrylic, benzoic, polyacrylic, polymethacrylic, oleic, poly-fatty acids and combinations thereof.

6. The method of claim 5 wherein the acid is acetic acid.

7. The method of claim 1 wherein the acid is emulsified with an agent selected from the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, emulsification agents and dispersion agents.

8. The method of claim 1 wherein a cosolvent selected from the group consisting of alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof is added to the acid.

9. The method of claim 1 wherein M is Na.

10. The method of claim 1 wherein the dithiocarbamate is emulsified with an agent selected from the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, emulsification agents and dispersion agents.

11. The method of claim 1 wherein a cosolvent selected from the group consisting of alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof is added to the dithiocarbamate.

12. The method of claim 1 further comprising adding a winterizing agent selected from the group consisting of methanol, isopropanol, ethylene glycol, propylene glycol, polyethylene glycol and mixtures thereof to the admixture.

13. The method of claim 1 wherein the dithiocarbamate is a polymer having the formula wherein n is an integer greater than 1;
R6, R7, R8 and R9 are each independently H, C1-6 alkyl or aryl; and Z is alkyl, aryl or absent.

14. The method of claim 13 wherein the dithiocarbamate polymer has the formula

15. The method of claim 1, 13 or 14 wherein M is a polymer of the formula

16. The method of claim 1, 13 or 14 wherein M is a polymer of the formula

17. The method of claim 1, 13 or 14 wherein M is a polymer of the formula wherein p is an integer greater than 1.

18. The method of claim 13 or 14 wherein the dithiocarbamate is a copolymer with a compound of the group consisting of methacrylic acid, acrylic acid, allyl alcohol, methacrylamide, acrylamide, alkyl methacrylates, alkyl acrylates, crotonic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, styrene, butadiene, vinyl acetate, carboxyethylmethacrylate, carboxyethylacrylate, sulfoethyl-methacrylate, sulfoethyl-acrylate, hydroxyethylmethacrylate, hydroxyethylacrylate, oxyalkylated methacrylates, oxyalkylated acrylates, oxyalkylated allyl alcohol, acrolein and combinations thereof.

19. The method of claim 1 wherein the dithiocarbamate is sodium N-methyldithiocarbamate.

20. The method of claim 1 wherein the dithiocarbamate is sodium N,N-dimethyldithiocarbamate.

21. A method for enhancing the recovery of petroleum from a production well penetrating a petroleum-bearing formation without causing corrosion in a mild steel system comprising the steps of:
preparing an aqueous solution of a dithiocarbamate of the formula wherein R and R1 are each independently H, C1-6 alkyl or aryl, M is Li, Na, K, Cs, Rb or NR2R3R4R5, R2, R3, R4 and R5 are each independently H, C1-6 alkyl or aryl;
combining acid with said dithiocarbamate solution to form an admixture, said acid being added in an amount effective to provide about 0.5 to 7.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate;
introducing the admixture into the petroleum-bearing formation through the mild steel system; and removing petroleum from the petroleum-bearing formation at a daily crude oil production rate.

22. The method of claim 21 wherein the acid is added in an amount effective to provide about 1.5 to 3.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate.

23. The method of claim 22 wherein the acid is added in an amount effective to provide about 2.0 equivalents of acid for one equivalent of carbon disulfide in the dithiocarbamate.

24. The method of claim 21 wherein the acid is in aqueous solution.

25. The method of claim 21 wherein the acid is selected from the group consisting of hydrochloric, sulfuric, phosphoric, boric, fluoboric, sulfurous, polyphosphoric, polysilicic, acetic, hydroxyacetic, oxalic, citric, tartaric, maleic, acrylic, benzoic, polyacrylic, polymethacrylic, oleic, poly-fatty acids and combinations thereof.

26. The method of claim 25 wherein the acid is acetic acid.

27. The method of claim 21 wherein the acid is emulsified with an agent selected from the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, emulsification agents and dispersion agents.

28. The method of claim 21 wherein a cosolvent selected from the group consisting of alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof is added to the acid.

29. The method of claim 21 wherein M is Na.

30. The method of claim 21 wherein the dithiocarbamate is emulsified with an agent selected from the group consisting of nonionic surfactants, cationic surfactants, anionic surfactants, emulsification agents and dispersion agents.

31. The method of claim 21 wherein a cosolvent selected from the group consisting of alcohols, glycols, ketones, ethers, esters, amides, amines and calcogenide and phosphorous derivatives thereof is added to the dithiocarbamate.

32. The method of claim 21 further comprising adding a winterizing agent selected from the group consisting of methanol, isopropanol, ethylene glycol, propylene glycol, polyethylene glycol and mixtures thereof to the admixture.

33. The method of claim 21 wherein the dithiocarbamate is a polymer having the formula wherein n is an integer greater than 1;
R6, R7, R8 and R9 are each independently H, C1-6 alkyl or aryl; and Z is alkyl, aryl or absent.

34. The method of claim 33 wherein the dithiocarbamate polymer has the formula

35. The method of claim 21, 33 or 34 wherein M is a polymer of the formula

36. The method of claim 21, 33 or 34 wherein M is a polymer of the formula

37. The method of claim 21, 33 or 34 wherein M is a polymer of the formula wherein p is an integer greater than 1.

38. The method of claim 33 or 34 wherein the dithiocarbamate is a copolymer with a compound of the group consisting of methacrylic acid, acrylic acid, allyl alcohol, methacrylamide, acrylamide, alkyl methacrylates, alkyl acrylates, crotonic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, styrene, butadiene, vinyl acetate, carboxyethylmethacrylate, carboxyethylacrylate, sulfoethyl-methacrylate, sulfoethyl-acrylate, hydroxyethylmethacrylate, hydroxyethylacrylate, oxyalkylated methacrylates, oxyalkylated acrylates, oxyalkylated allyl alcohol, acrolein and combinations thereof.

39. The method of claim 21 wherein the dithiocarbamate is sodium N-methyldithiocarbamate.

40. The method of claim 21 wherein the dithiocarbamate is sodium N,N-dimethyldithiocarbamate.

41. The method of claim 21 wherein the admixture is delivered to the petroleum-bearing formation at a sufficient rate to increase the crude oil production rate by at least about 10 percent.