Abstract:
A method of inhibiting corrosion of metal equipment in wells comprises contacting the metal surfaces with an inhibiting amount of a corrosion inhibitor which is the reaction product of a compound containing a carbonyl group (e.g. aldehydes), an amine, and a thiocyanate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of inhibiting corrosion, particularly in oil field producing equipment. In one aspect, the method of the present invention employs a compound containing sulfur and nitrogen. 
     Wells producing from subterranean formations frequently produce high concentrations of salt water which present a severe corrosion problem, particularly at temperatures above 250° F. Corrosion is further increased with the presence of oxygen, carbon dioxide, hydrogen sulfide and/or organic and inorganic acids. 
     Nitrogen containing compounds are known to act as corrosion inhibitors. For example, various amines are effective to inhibit corrosion. A number of patents disclose corrosion inhibitors containing sulfur and/or nitrogen, e.g., sulfur - U.S. Pat. Nos. 3,809,655, 3,759,956, 3,755,176, 3,158,476, 2,880,180, 3,404,094, 3,197,403, 3,969,414; nitrogen - 3,445,441, 3,450,646, 3,976,593; sulfur and nitrogen - 3,414,521, 4,450,138. 
     U.S. Pat. No. 4,450,138, for example, discloses among other things, the reaction of thiols with epichlorohydrin followed by the reaction with amines. 
     U.S. Pat. No. 4,446,056 discloses S containing compositions prepared by reacting hexahydrotriazines, in the presence of a Lewis acid, with S or S containing compounds. 
     U.S. Pat. No. 4,673,436 discloses the use of a thio substituted quaternary ammonium salt. 
     There are several patents which disclose the use of N-S containing compounds for use as corrosion inhibitors in pickling operations. Pickling is a process for the removal of scale, oxides, and other impurities from metal surfaces by immersion into an inorganic acid. U.S. Pat. Nos. 2,425,320, 2,586,331, 2,606,155  are representatives of pickling inhibition patents. However, there is no teaching in these references that the N-S compounds are effective in inhibiting corrosion of oil field producing equipment. 
     Other U.S. Patents which disclose corrosion inhibitors include U.S. Pat. Nos. 3,634,270, 3,969,255, and 4,536,302. These references, however, do not disclose the corrosion inhibitors of the present invention. 
     SUMMARY OF THE INVENTION 
     It has surprisingly been discovered that a corrosion inhibitor prepared by the reaction of a carbonyl compound, an amine, and a thiocyanate provides exceptional protection against ferrous corrosion in severe environments. The method of the present invention, thus, involves the use of from 1 to 10,000, (preferably 1 to 1,000, and more preferably 1 to 500) wt ppm of the improved corrosion inhibitor based on the weight of the fluid treated. 
     The three components of the improved corrosion inhibitor may be reacted simultaneously or in any order. Preferably the mole ratio is from 1 to 2 moles each of the other two components. 
     The preferred carbonyl containing compound is selected from mono- and polyfunctional aldehydes and ketones, with monoaldehydes being the more preferred. The preferred amine is selected from monoamines and polyamines with alkyl monoamines being more preferred. The preferred thiocyanate is ammonioum thiocyanate. 
     The improved corrosion inhibitor is preferably employed in wells producing both oil and water and in high temperature environments (250° F.). The improved inhibitor may be injected into the crude stream by conventional equipment and techniques. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As mentioned previously, the improved corrosion inhibitor of the present invention is the reaction product of three compounds: (a) a carbonyl compound, (b) an amine, and (c) a thiocyanate. 
     The preferred carbonyl compounds are alkyl or aryl aldehydes and ketones. Alkyl and aryl aldehydes include C 1  -C 18  aldehydes, oiticia, benzaldehydes, substituted benzaldehydes, glutareldehyde, and glyoxyl, with formaldehyde to butanal being preferred. Alkyl and aryl ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, 2- and 3-hexanones, cyclohexanone and acylated aromatics such as acetophenone, propiophenone, butyrophenone, and salicylaldehyde. The preferred aldehydes are C 1  -C 6  aldehydes with formaldehyde being the most preferred. 
     The amines useable to prepare the improved corrosion inhibitor include ammonia, primary and secondary and mono-and polyamines. The substituted hydrocarbon radical may be aliphatic (saturated or unsaturated), alicyclic, aromatic, heterocyclic, or combinations of these. The amines have the following formula ##STR1## where R and R&#39; are each H or C 1  to C 18  alkyl or aryl groups and are the same or different; n=2-3; and m=0-4. 
     The preferred amines are C 2  -C 18  alkyl monoamines. 
     The thiocyanates include alkyl and aryl thiocyanates and ammonium thiocyanate, with the latter being preferred. 
     Preparation Of The Corrosion Inhibitor 
     There are a number of ways for preparing the reaction product of the three components described above. The thiocyanate may be mixed with the amine in an appropriate solvent which then may be reacted with the aldehyde at sufficient reaction temperature. Alternatively, the aldehyde may be reacted with the amine followed by reacting the intermediate with the thiocyanate in an appropriate solvent with the application of heat. Also the three components may be mixed in an appropriate solvent and reacted simultaneously at reaction temperatures. 
     The mole ratio of the reactants may vary within a rather wide range but the preferred ratio ranges are as follows: 
     
         ______________________________________                   Preferred        Mole Ratio Range                   Mole Ratio Range______________________________________(a) Carbonyl compound          0.5-3.0      1.0-2.0(b) amine      0.5-3.0      1.0-2.0(c) thiocyanate          0.5-3.0      1.0-2.0______________________________________ 
    
     Thus in the preferred ranges the components (a):(b):(c) include the following combination 1:1:1, 1:1:2; 1:2:1; 2:1:1; 1:2:2; 2:1;2; and 2:2:1. 
     The corrosion inhibitor useful in the method of the present invention may be prepared by any of the following methods. One Step Method: The appropriate amounts of the selected amine, carbony-containing compound and thiocyanate are mixed together in a solvent such as xylene and heated to reflux. The water of reaction is removed by azeotropic distillation. After one to six hours at reflux, the reaction mixture is cooled to room temperature. The reaction product can be isolated by evaporation of the solvent or the product can be used in the aromatic solvent or it can be blended with other materials. Two Step Method: The appropriate amounts of the selected amine and carbonyl-containing compound are mixed together in a solvent such as xylene and heated to reflux. The water of reaction is removed by azeotropic distillation. After the theoretical amount of water has been collected, the reaction mixture is cooled and the thiocyanate is added. The mixture is then heated to reflux again for one to six hours, cooled to room temperature and worked up as described in the One Step Method. Three Step Method: The appropriate amounts of the selected amine and carbonyl-containing compound are mixed together in a solvent such as xylene and heated to about 60 degrees C. and held at this temperature for 20 to 120 minutes. The mixture is then heated to reflux and the water of reaction is removed azeotropically. After the theoretical amount of water has been collected, the reaction mixture is cooled and the thiocyanate is added. The mixture is then heated to reflux again for one to six hours, cooled to room temperature and worked up as described above. 
     All of the reactions can be done by any of the three Methods and the resulting reaction products provide substantially the same corrosion protection. However, each Method can be used to special benefit for certain reactants. The Three Step Method is especially useful when either the amine or aldehyde has a low boiling point and/or is in an aqueous or alcoholic solution. The reaction period at about 60 degrees C. allows the initial reaction of amine and aldehyde (to form the Schiff base) to proceed without the loss of either reactant. The Two Step Method was generally used because it allows the reaction to go through a known intermediate and also, if the formation of the Schiff base is incomplete for some reason, this lack of reaction can be readily detected because less than the theoretical amount of water will be liberated in the first step and, if this happens, the reaction can be terminated at that point. The One Step Method is physically and mechanically the easiest of the three Methods. 
     EXPERIMENTS 
     Samples were prepared by all three Methods described above and tested for corrosion inhibition performance in both dynamic tests (wheel test) and static tests. Table I presents the composition of some of the samples prepared and tested. 
     
                       TABLE I______________________________________Sample            Carbonyl     X-SCN   MoleNo.    Amine      compound     X=      Ratio______________________________________ 1     ammonia    formaldehyde NH4     1:1:1 2     ammonia    propionaldehyde                          NH4     1:1:1 3     ammonia    butyraldehyde                          NH4     1:1:1 4     ammonia    butyraldehyde                          NH4     2:1:1 5     ammonia    butyraldehyde                          NH4     1:2:1 6     ammonia    octyl aldehyde                          NH4     1:1:1 7     ammonia    octyl aldehyde                          NH4     2:1:1 8     ammonia    octyl aldehyde                          NH4     1:2:1 9     ammonia    decyl aldehyde                          NH4     1:1:110     ammonia    dodecyl aldehyde                          NH4     1:1:111     butyl      formaldehyde NH4     1:1:112     butyl      butyraldehyde                          NH4     1:1:113     ethylene   salicylaldehyde                          NH4     1:1:1  diamine14     butyl      octyl aldehyde                          NH4     1:1:115     octadecyl  acetone      NH4     1:1:116     ethylene   oiticia oil  NH4     1:1:1  diamine17     octyl      formaldehyde NH4     1:1:118     octyl      butyraldehyde                          NH4     1:1:119     octyl      octyl aldehyde                          NH4     1:1:120     octyl      octyl aldehyde                          Na      1:1:121     dodecyl    formaldehyde NH4     1:1:122     dodecyl    butyraldehyde                          NH4     1:1:123     dodecyl    octyl aldehyde                          NH4     1:1:124     coco       formaldehyde NH4     1:1:125     coco       formaldehyde NH4     2:1:126     coco       formaldehyde NH4     1:2:127     coco       propionaldehyde                          NH4     1:1:128     coco       butyraldehyde                          NH4     1:1:129     coco       butyraldehyde                          NH4     2:1:130     coco       butyraldehyde                          NH4     1:2:131     coco       hexyl aldehyde                          NH4     1:1:132     coco       octyl aldehyde                          NH4     1:1:133     coco       octyl aldehyde                          NH4     2:1:134     coco       octyl aldehyde                          NH4     1:2:135     coco       dodecyl aldehyde                          NH4     1:1:136     octadecyl  formaldehyde NH4     1:1:137     octadecyl  butyraldehyde                          NH4     1:1:138     octadecyl  octyl aldehyde                          NH4     1:1:139     tallow     formaldehyde NH4     1:1:140     tallow     butyraldehyde                          NH4     1:1:141     tallow     octyl aldehyde                          NH4     1:1:142     tallow     octyl aldehyde                          NH4     2:1:143     tallow     octyl aldehyde                          NH4     1:2:144     oleyl      formaldehyde NH4     1:1:145     oleyl      butyraldehyde                          NH4     1:1:146     oleyl      octyl aldehyde                          NH4     1:1:147     ethylene   butyraldehyde                          NH4     1:1:1  diamine48     ethylene   butyraldehyde                          NH4     1:2:1  diamine49     ethylene   butyraldehyde                          NH4     1:2:2  diamine50     ethylene   octyl aldehyde                          NH4     1:1:1  diamine51     ethylene   octyl aldehyde                          NH4     1:2:1  diamine52     ethylene   octyl aldehyde                          NH4     1:2:2  diamine53     diethylene butyraldehyde                          NH4     1:1:1  triamine54     diethylene butyraldehyde                          NH4     1:2:2  triamine55     diethylene butyraldehyde                          NH4     1:3:3  triamine56     diethylene octyl aldehyde                          NH4     1:1:1  triamine57     diethylene octyl aldehyde                          NH4     1:2:2  triamine58     diethylene octyl aldehyde                          NH4     1:3:3  triamine59     coco       butyraldehyde                          NH4     1:1:1  diamine60     coco       butyraldehyde                          NH4     1:2:1  diamine61     coco       butyraldehyde                          NH4     1:2:2  diamine62     coco       octyl aldehyde                          NH4     1:1:1  diamine63     coco       octyl aldehyde                          NH4     1:2:1  diamine64     coco       octyl aldehyde                          NH4     1:2:2  diamine65     tallow     butyraldehyde                          NH4     1:1:1  diamine66     tallow     butyraldehyde                          NH4     1:2:1  diamine67     tallow     butyraldehyde                          NH4     1:2:2  diamine68     tallow     octyl aldehyde                          NH4     1:1:1  diamine69     tallow     octyl aldehyde                          NH4     1:2:1  diamine70     tallow     octyl aldehyde                          NH4     1:2:2  diamine71     butyl      glyoxal      NH4     1:1:172     butyl      glyoxal      NH4     1:1:273     butyl      glyoxal      NH4     2:1:174     butyl      glyoxal      NH4     2:1:275     butyl      glutaraldehyde                          NH4     1:1:176     butyl      glutaraldehyde                          NH4     2:1:177     butyl      glutaraldehyde                          NH4     2:1:278     octyl      glyoxal      NH4     1:1:179     octyl                   NH4     2:1:180     octyl      glyoxal      NH4     2:1:281     octyl      glutaraldehyde                          NH4     1:1:182     octyl      glutaraldehyde                          NH4     2:1:183     octyl      glutaraldehyde                          NH4     2:1:284     coco       glyoxal      NH4     1:1:185     coco       glyoxal      NH4     2:1:186     coco       glyoxal      NH4     2:1:287     coco       glutaraldehyde                          NH4     1:1:188     coco       glutaraldehyde                          NH4     2:1:189     coco       glutaraldehyde                          NH4     2:1:290     butyl      acetone      NH4     1:1:191     octyl      cyclohexanone                          NH4     1:1:1______________________________________ 
    
     High Temperature and Pressure Tests 
     The high temperature and pressure tests were run in 50 ml and 500 ml pressure containers. Temperatures tested were from 250 to 350 degrees F.; oil/water ratios were from 0 to 0.5; the salinity of the brine (as sodium chloride) ranged from 0 to 25 wt %. Corrosive gases were hydrogen sulfide and/or carbon dioxide at mole fractions of up to 0.4 for each gas (balance being methane); the total pressures in the system were from 1000 to 4000 psig at ambient temperature. The pressure containers with corrosion coupons inserted therein were rotated in a heated oven for about 24 hours. At the end of each test, the coupons were removed, cleaned and weighed. 
     Representative, but not exclusive, conditions under which many of the corrosion inhibitors were tested include: Test Series A: 
     Temperature=260 degrees F. 
     Brine comp.=25% NaCl 
     Oil/water=0 
     Gas mixture=16% H 2  S, 3% CO 2 , 81% CH 4   
     Total pres.=1250 psig 
     Test Series B: 
     Temperature=430 degrees F. 
     Brine comp.=20% NaCl 
     Oil/water=0 
     Gas mixture=10% H 2  S, 4% CO 2 , 86% CH 4   
     Total pres.=2000 psig 
     Test Series C: 
     Temperature=350 degrees F. 
     Brine comp.=5% NaCl 
     Oil/water=1/9 
     Gas mixture=10% H 2  S, 10% CO 2 , 80% CH 4   
     Total pres.=1000 psig 
     Test Series D: 
     Temperature=295 degrees F. 
     Brine comp.=0% NaCl 
     Oil/water=0 
     Gas mixture=4% H 2  S, 6% CO 2 , 90% CH 4   
     Total pres.=2000 psig 
     Test Series E: 
     Temperature=290 degrees F. 
     Brine comp.=0% NaCl 
     Oil/water=0 
     Gas mixture=21% H 2  S, 40% CO 2 , 39% CH 4   
     Total pres.=950 psig 
     Under each test, the corrosion inhibitor, unless otherwise indicated, was used at a concentration of 250 ppm actives based on the total weight of the liquids. Each test was run in duplicate. Table II presents representative test results. 
     
                       TABLE II______________________________________Test  Sample  Ave. weight Test  Sample                                 Ave. weightCond. No.     loss (mg)   Cond. No.   loss (mg)______________________________________A     blank   115         B     blank 157 11      53                11    62 24      55                36    36 25      42                38    39 26      45                24    59 36      22                25    63 38      30                26    59 39      42C     blank   119         D     blank 92 3       50                11    8 6       30                24    7 11      72                25    18 17      30                26    20 19      45                28    6 24      25                36    7 35      35                39    6 36      12 37      35 38      40E     blank   80 11      44 24      11 25      9 26      25 36      15 38      13 39      10______________________________________ 
    
     Wheel Tests 
     Wheel tests consisted of the following: The brine and hydrocarbon liquids were saturated with the corrosive gas by bubbling the gas therethrough. In the case of gas mixtures, a saturated solution of hydrogen sulfide in brine was added to a brine saturated with carbon dioxide to produce the desired ratio of gases. The inhibitor was added (at 100 ppm based on total fluids unless otherwise noted), a metal coupon was inserted into the bottle, the bottle capped and placed on a &#34;wheel&#34; in an oven at the selected temperature. The &#34;wheel&#34; was rotated at 30 rpm for 24 hours. At the end of the test period, the coupons were removed, cleaned and weighed. 
     Test Series AA: 
     Temperature=200 degrees F. 
     Brine comp.=3% NaCl 
     Oil/water=0 
     Corrosives=saturated H 2  S 
     Test Series BB: 
     Temperature=200 degrees F. 
     Brine comp.=205 NaCl 
     Oil/water=0 
     Corrosives=saturated H 2  S 
     Test Series CC: 
     Temperature=200 degrees F. 
     Brine comp.=20% NaCl 
     Oil/water=1/19 
     Corrosives=saturated H 2  S 
     Test Series DD: 
     Temperature=200 degrees F. 
     Brine comp.=3% NaCl 
     Oil/water=0 
     Corrosives=saturated CO 2  +500 ppm H 2  S 
     Test Series EE: 
     Temperature=200 degrees F. 
     Brine comp.=20% NaCl 
     Oil/water=0 
     Corrosives=saturated CO 2  +500 ppm H 2  S 
     Test Series FF: 
     Temperature=200 degrees F. 
     Brine comp.=3% NaCl 
     Oil/water=0 
     Corrosives=saturated CO 2   
     Test Series GG: 
     Temperature=200 degrees F. 
     Brine comp.=20% NaCl 
     Oil/water=0 
     Corrosives=saturated CO 2   
     Test Series HH: 
     Temperature=200 degrees F. 
     Brine comp.=20% NaCl 
     Oil/water=1/19 
     Corrosives=saturated CO 2   
     
                       TABLE III______________________________________Test  Sample  Ave. weight Test  Sample                                 Ave. weightCond. No.     loss (mg)   Cond. No.   loss (mg)______________________________________AA    blank   36          BB    blank 33  1      10                 1    4  3      6                  3    3  6      10                 6    5 11      6                 11    4 17      4                 12    8 21      6                 17    3 22      7                 21    6 36      13                22    7 37      7                 24    5 38      10                27    6AA    39      6           BB    28    6 43      10                36    3                           27    6CC    blank   33                28    6 11      6                 36    3 36      6                 37    4 38      8                 38    4 39      5                 39    4                           40    4DD    blank   44                43    6  1      12                71    10  3      4                 72    8  6      7                 73    8 11      10                74    8 17      7                 78    6 21      7                 79    5 36      7                 80    8 37      7                 87    4 38      6                 89    6 39      4EE    blank   34          FF    blank 104  1      10                 1    48  3      4                  3    16  6      5                  6    16 11      5                 11    32 17      5                 17    16 21      5                 21    10 36      6                 22    10 37      5                 36    10 38      5                 37    16 39      4                 38    16                           39    10                           43    10GG    blank   56          HH    blank 77  1      5                 11    36  3      2                 36    22  6      2                 38    30 11      2                 39    28 12      16 17      2 21      2 22      4 24      6 27      10 28      11 35      10 36      2 37      3 38      2 39      2 43      30 40      7 71      11 72      13 73      9 74      14 78      13 79      13 80      13 87      13 89      12______________________________________ 
    
     The above tests demonstrate the effectiveness of a variety of compositions under a variety of test conditions. It again is emphasized that these materials and tests are only representative. As will be appreciated by those skilled in the art, variations and modifications of the materials exemplified above may be made without departing from the scope of the invention as hereinafter claimed.