Waterflood process using alkoxylated low molecular weight acrylic acid polymers as scale inhibitors
United States Patent Watson Apr. 29, 1975 1 WATERFLOOD PROCESS USlNG 3.419.502 l2/l968 Newman 252/180 ALKOXYLATED ow MOLECULAR 3.480.083 lI/1969 Oleen lob/275 3.578.589 5/1971 Hwa 210 58 WEIGHT ACRYLIC POLYMERS AS 3.827.977 8/1974 Miles et al. 252/855 SCALE 3.841.401 10/1974 Restaino et al 1. 166/275 x Inventor: James D. Watson, Houston. Tex.  
 [73] Assignee: Nalco Chemical Company, Chicago.  
 Ill.  
 [22] Filed: Nov. l2, I973 [21] Appl. No.: 415,207  
 [52] U.S. Cl 252/8.55 D; l66/275; 2l0/58;  
  25218.55 B; 252/l; 260/88.7 B [51] Int. Cl. C02b 5/06; E2lb 43/20 [58] Field of Search 252/855 D, 8.55 B,  
 [56] References Cited UNITED STATES PATENT-S 1293.152 l2/l966 Herbert ct al. .5 252/!80 X Primary Examiner-Herbert B. Guynn Almrney, Agent, or Firm-John G. Premo; James F. Lambe [57] ABSTRACT Low molecular weight alkoxylated acrylic acid polymers are introduced into one or more water injection wells and forced through the underground formation to a producing well or wells without being destroyed during such passage.  
 2 Claims, No Drawings WATERFLOOD PROCESS USING ALKOXYLATED LOW MOLECULAR WEIGHT ACRYLIC ACID POLYMERS AS SCALE INHIBITORS The invention is concerned with the prevention of hardness scale deposits on metal surfaces in contact with hard water containing hardness scale-forming ions and with the preparation of compounds or compositions which are effective for this purpose. In particular. the invention is concerned with scale prevention in natural brines on ferrous metal walls and other surfaces in oil producing and waterflood systems.  
  Inorganic polyphosphates have long been the most effective and economical sequestering agents used for the prevention of alkaline deposits in both oil producing and waterflood systems. Inorganic polyphosphates have been added to water in waterflood systems in an effort to alleviate corrosion and scale formation.  
  The polyphosphates suffer from the objection that under the conditions present in an oil-bearing formation they can undergo reversion to orthophosphates which in turn form insoluble salts with calcium. magnesium. barium and strontium. Calcium and magnesium are usually present in substantial amounts in oil-bearing formations and barium and strontium salts are often present in smaller amounts. The formation of insoluble salts as previously indicated would tend to plug the oilbearing strata and reduce the chances of obtaining an improvement in the recovery of the oil.  
  lt would be desirable to provide a process in which a chemical is added to an injection well which will inhibit scaling of equipment and plugging of the well and will retain its identity while passing through the underground formation to the producing well or wells where it is also effective as a scale inhibitor. An object of this invention is to provide such a process.  
 THE INVENTION In accordance with the invention it has been found that low molecular weight. e.g. 3.000 to 20.000 watersoluble acrylic acid polymers. which have been reacted with from 5 to 60% by weight of an alkylene oxide are effective as scale inhibitors and can be added to an injection well or wells in a waterflood system and will pass through the underground formation to a producing well or wells without being precipitated or adsorbed in the formation during such passage. Thus. protection is afforded against scale formation in the producing well or wells as well as the injection well or wells. This protection is especially useful in a number of areas where scaling of metal surfaces. particularly ferrous metal surfaces. by barium sulfate. calcium sulfate and- /or calcium carbonate is a problem. By control of scale formation. breakdowns. maintenance. cleaning and repairs caused or necessitated by scale formation can be minimized.  
  The dosage of the low molecular weight alkoxylated water-soluble acrylic acid polymers should be sufficient to give a scale inhibiting amount in the producing well of at least 0.5 parts per million (ppm). Normally the amount added to the water in the injection well will be at least ppm but in some cases up to 100 ppm and even as high as 200 to 500 ppm can be used. They are particularly effective in treating injection waters which contain from 500 to l0.000 ppm of calcium.  
 THE ALKOXYLATED WATER-SOLUBLE ACRYLIC ACID POLYMERS The low molecular weight water-soluble acrylic acid polymers include the homoand copolymers of acrylic acid. These polymeric intermediates to be effective in the proximities of the invention should have a molecular weight within the range of 3,000 to 20.000 and preferably within the weight range of 5.000 to 15.000. These starting polymers may be prepared by a wide variety of known synthetic techniques which includes the polymerization of acrylic acid or methacrylic acid or by hydrolysis of polyacrylonitriles or polyacrylamides.  
  The starting copolymers of acrylic acid should contain at least 50% by weight of these monomeric moieties and preferably should contain from to thereof. The copolymers may be prepared copolymerizing acrylic acid and another vinyl monomer such as, for instance. acrylamide vinyl acetate. maleic anhydride and the like.  
  A preferred group of copolymers are produced by the hydrolysis of low molecular weight polyacrylonitriles. Polymers of this type contain from 20 to 30% by weight of amide groups and from 70 to 80% by weight of carboxyl groups. Their molecular weight is within the range of from 5.000 to 40.000. Polymers of this type are described in detail in U.S. Pat. No. 3.419.503. the disclosure of which is incorporated herein by reference.  
 ALKOXYLATION OF THE COPOLYMERS The starting copolymers previously described when used to practice this invention must be reacted with a lower alkylene oxide with ethylene oxide being most preferred. The amount of alkylene oxide which will hereinafter be described in relation to ethylene oxide which is intended to include the lower alltylene oxides including propylene oxide. may vary between 2 to 607r by weight of the starting polymer and preferably is within the range of 3 to 30% by weight of the starting polymer. While it is possible to react the starting polymers with ethylene oxide. it is also possible to prepare the ethoxylated polymers by first reacting the starting monomer with ethylene oxide and then conducting an appropriate polymerization reaction to produce the fin ished ethoxylated polymer.  
  To illustrate the two different techniques for preparing the ethoxylated polymer the following examples are presented below:  
 EXAMPLE l (ETHOXYLATION METHOD ll To a homopolymer of acrylic acid. which may be prepared by polymerizing acrylic acid or by the hydrolysis of an appropriate molecular weight acrylonitrile there is added a small amount of potassium hydroxide or other base into an autoclave. The polymer which previously has been added to the autoclave is in the presence of from about 5 to 60% by weight of water. The temperature of the autoclave is elevated to about l00C. and maintained throughout the entire ethoxylation procedure. Upon reaching l00C. an appropriate weight percent of ethylene oxide is added using nitrogen pressure. The ethylene oxide is added over a period of time ranging between 20 minutes to 2 hours. At the end of the addition the autoclave is allowed to cool and is then vented. After this process the ethoxylation product is EXAMPLE 2 (ETHOXYLATION METHOD 2) Neat acrylic acid and a small amount of catalyst usually BF was added to an autoclave and heated to 40C. With water coils on for cooling the ethylene oxide was slowly added using nitrogen pressure. The addition rate was regulated so that the temperature stayed 40 to 80C. After all of the ethylene oxide was added. the product was cooled to room temperature. After the ethoxylated acrylic acid is recovered it is then polymerized with a free radical initiator using known polymerization techniques to produce an ethoxylated polyacrylic acid polymer having specifications of the type previously described.  
  To illustrate the various compositions of the invention, TABLE I is presented below:  
 TABLE I 7? Acrylic &#34;/2 Ethylene Ethoxylation Chemical No. Acid Oxide Method l 22 20 l 2 24 II I 3 26 5.9 l 4 24 II I S 23 I6 I 6 22 20 l 7 2t] 27 l 8 ll&#39;l 4.3 2 III 4.3 2 It] I8 42 2 ll 17 5.6 2 l2 l 7.2 2 l3 l4 8.8 2 l4 l8 4.| 2 l5 l4 8.6 2 lb to 6.3 2 l7 I5 85 2 I8 I) I3 I l&#39;-) 21 4.7 l 20 9.l l 2! 19 8.9 l 22 I) I3 I 23 l9 I7 I 24 I8 24 l 25 17 5.6 2 2h 22 I4 2 27 27 I6 2 2B 27 I6 2 29 24 I4 2 30 22 I3 2 3| 2| l2 2 32 2! I2 2 33 24 1-4 2 34 22 I3 2 35 2I l2 2 36 21 I2 2 37 27 I6 2 EVALUATION OF THE INVENTION The ethoxylated polymers of the invention are particularly good scale inhibitors and tend to remain in solution in the presence of large quantities ofcalcium salts. This particular and unique property of the compounds allows them to stabilize large quantities of heavy metal ions which would normally tend to precipitate or plug an underground formation yet. at the same time. the compounds remaining in solution do not form precipitates with heavy metals, particularly calcium. Thus. by maintaining good solubility characteristics in high brine type waters, the ethoxylated polymers used in the prac tice ofthe invention are able to carry through an entire underground formation without precipitating thus effectively allowing treatment of a large area of subterranean formation which characteristic has not heretofore been available by using most known scale inhibiting chemicals.  
  To evaluate the effectiveness ofthe compositions two tests were employed. One is a Calcium Stability Test while the other is a Calcium Carbonate Deposition Test. These test procedures are set forth below:  
 CALCIUM STABILITY TEST Relative calcium stabilities were determined using a F. test. Five percent NaCl brines containing various amounts of calcium and 1% of the chemicals under test were heated in a 160F. water bath for at least 1 hour. Then while constantly stirring and monitoring the pH ofeach solution with a pH meter the pH ofeach solution was raised using sodium hydroxide solution until the solution became slightly cloudy or hazy. The pH at which a slight haze or cloud developed was called the cloud point.  
  The CaCO Brine C was used for a room temperature calcium stability test. The cloud point of l7r chemical 9971 Brine C solutions were determined.  
 Brine C l2.l60 mg CaCl 2 H- .O  
 3.680 mg MgCl 2 H- O per liter of distilled water fi6.000 mg NaCl Various chemicals were subjected to the Calcium Stability Test with the results being shown in TABLE II below:  
 TABLE II Test A Calcium Stability Test using CaCO No. l brine l7r chemical Room Temperature pH at Cloud Point Chemical pH at Cloud Point I I03 2 I04 5.5  
 Test B Calcium Stability Test on chemical 2 ppm Calcium Carbonate 7&#39; No. l Brine Cloud Pt. at pH Test C Chemical Calciuml mg/l) pH at Cloud Point 8 l l 7 1 s TABLE ll-Continued TABLE ll-Continued Test D 1e-t J COCO] No. 1 hrine (no dilution) at 160F. I; chemicai linntw \.r(l1 healed to 100! before adding 1&#39;! Chemical pH After 30 Min. After Hrs. &#39;m &#39;H 5 Chemical (&#39;alciuml rug/1| pH .it (loud Pt 23 1&#39;1. 1, c *33 5000 10.7 9 7 H 7000 9.2 10000 5.9 Test E I I 2000 I 1.6 3000 I 1.4 5000 mg/l Ca Brine in 5&#39;71 NaCl at room temperature 10 4000 l H Chemical pH .11 Cloud Pt. 11 4000 l 5000 l 1.3 22 11.7 t. 000  
  F 13 mean 1 1.2 0 r Ex used 1); solution in 5000 mg/l Ca brine and straight HL LL g ig l i g utg gi firefi 1 thumb l5 chen&#39;iical to 3000?. for three days. then checked cloud (.hcmiwl l iunflmgll pH at Cloud Pt. points. Both solutions had cloud pt. at pH 4.9 on 5000 mg/l Ca&#34;.  
 23 5000 I 1.1 Test K 7000 5.0  
  8 2000 8.4 Added V/i chemical to different Calcium le\el hrines 3000 5.2 )0 (containing 591 NaCll and heated at 160F. 1 hr. before 10 1000 I 1.8 running cloud point 9 3000 5.3 Chemical CaIeiumImg/l] pH at Cloud Pt. 1 1 2000 1 1.7 5000 5.4 33 5000 10.6 5000 10.3 Test (1 7000 5.8 g 7000 5.8 Chemical Calciumlmg/ll pH at Cloud Pt. 10000 4.7 12 5000 l 1.0 9 2000 11.5 5000 10.) 10 2000 5.8 I 7000 4.7 25 4000 1 1.3 7000 4.1. I I 3000 0.0 33 6000 11.2 12 4000 l 1.4 (1000 7.9 5000 5.6 12 6000 10.7 13 10000 11.2 (1000 10.7 25 3000 1 1.4  
 &#34; 4000 5.5 Test L Test H Checked Chemical 33 in 1091 NaCl at 160F.  
  15 Used 100 mls. total volume Heated hrines to 160F. prior to adding 1% chemical Mls. Brine M&#34; Calcium (mg/ P 111 Clvud Brincs made with 5&#39;1 NaCl Chemical Calciumtmg/ll pH at Cloud Pt. 12.6 5000 10.3 15.1 6000 5.4 23 5000 11.3 1 7000 .3 7000 5.4 25.2 10000 5.3 13 10000 l 1,1 Heated 1% chemical 33 in 1091 NaCl at 265F. 3 days. then 211 10000 1,] checked cloud pt. at 160F. using 6.3 mls. brine M and 17 7000 1].] 43.7 mls. 1% chemical 33 pH 4.3 at cloud pt. 10000 5.0 29 5000 10.6 7000 5.8 M :33 Chemical 33 calcium stability in 1001 NaCl at pH 13 H l 0000 and room temperature Cloud Pt. Te 1 Mls. Brine &#34;M&#34; CalciumImg/l) Appearance Heated hrines to 1h0F. rior to addin 1% chemical Brincs madc with 5% Naii l fi Chemmal Caluum(mg/1] pH at Cloud Pt. [4 h y 23 5mm L3 Heated 1% chemical 33 at .7. fi5F. 1 hour and checked 7000 5.3 &#34;1&#34;&#34; 39 5mm m3 M15. Brine M Calcrum(mg/l1 Appearance 1. o 33 [15 .06 23.8 S1. Haze 7000 L4 55 Adjusted 10&#39; NaCl to pH 13 at NaOH W000 Then added 1% chemical and ran cloud pt. by adding is 2mm 1 1.3 bt&#39;nc 3000 5.1  
 Test N J Calcium stability of chemical 33 at pH 13 K s! a 1&#39;); 1 131.33g? F Tested at 265F. in NaCl adjusted an NaCl 1. Chemical (u|cium(mg/n pH m d p pH 13 with NaOH. Then added 1% chemical and ran visual cloud pt. by adding Brine -M&#34; of CaSO Brine 23 5000 1 1.2 Time at 7000 10.8 265F. Mls. Brine &#34;M&#34; Calciumtmg/l) Appearance 10000 4.6 25 4000 1 1.1 (,5 0 min. .06 23.14 Clear 5000 5.1 10 39.7 Hay 29 5000 111- 15 min. .06 23.8 Clear 7000 8.6 .10 39.7 Halt TABLE ll-Continued I est N (alumni stabillh of chemical 33 at pH l3 I&#39;cstcd at 2b5F in It); Natl ad usted lll&#39;i Nafl to pH l3 uith NnOH Then added l&#39;i chemical and ran \isunl cloud pt by adding Brine M&#34; of (2:50, Brine CALCIUM CARBONATE DEPOSITION TEST APPARATUS:  
  l. Constant temperature bath 100 to 200F.) 2. Glass test cells (4 oz. bottles with screw lid) 3. Synthetic brines 4. Graduated cylinders 2-100 ml 5. I /r solutions of inhibitors to be tested 6. Pipettes: l0.l ml. ll.0 ml and l-l ml 7. 125 ml Erlenmeyer flasks for each inhibitor to be tested 8. Standard EDTA solution (l ml =1 mg of CaCO 9. 1 Normal sodium hydroxide l0. Ammonium purpurate indicator l l. l0 ml micro buret PROCEDURE:  
 1. Using the 1% solutions of inhibitors. pipette the desired amount of inhibitor into each test cell. (Duplicates should be run of each concentration.)  
 2. Two controls (blanks) are set up with each test.  
 Control contains no inhibitorv 3. Brines A and B should be saturated with CO for 30 minutes before using.  
 4. Add ml of Brine A and B to each test cell.  
 5. Cap test cells and agitate to thoroughly mix brines and chemicals.  
 6. Put test cell in water batch at 160F. for 24 hours.  
 7. After exposure at the temperature for 24 hours, the test cells are removed and allowed to cool to room temperature.  
 8. Pipette l ml of the brine from each test cell and transfer to the Erlenmeyer flask.  
 9. Add 50 ml of distilled water to the Erlenmeyer.  
 l0. Add 2 ml of IN sodium hydroxide.  
 l 1. Add a small amount of ammonium purpurate indicator and titrate with the EDTA solution. The color changes from pink to violet.  
 12. The amount of CaCO retained in solution is computed by multiplying the ml of standard EDTA solution used by I000. The results are expressed as calcium carbonate.  
 13. A typical scale evaluation is found below:  
 Calcium Carbonate Retained in Solution (mg/L) pp pp Chemical C 3.600 4.300 Blank (after precipitation) 2.600 Blank (before precipitation) 4.300  
 TABLE III CALCIUM CARBONATE DEPOSITION TEST (Dosage in Parts Per Million) 7 8 9 CHEMICAL 3 4 5 6 l0 I5 20 30 50 l 3 I00 3 500 3600 3 700 3700 4000 4000 4 I00 2 3300 3400 3 800 4200 4200 4200 X 3 700 4 4 l 00 3900 4200 9 3900 4200 I0 3600 4 I00 4200 l I 3400 3700 4100 4200 I2 3300 3700 4000 4000 4 [00 4200 I3 3200 3500 3600 3700 3900 4100 4200 l 4 3 800 4000 4000 4000 4200 l 4 Top 2 700 2700 2700 3000 3 300 I 4 Bottom 3600 3900 4 200 4200 l 5 3400 3800 3000 4 l 00 4200 l 5 Top 3800 4000 4200 4200 I5 3400 3700 4200 4200 4200 Bottom l 6 4200 I7 3500 4100 4200 2 l 4 l 00 4200 22 3600 4200 22 3200 3400 3900 4200 TABLE III -Continued CALCIUM CARBONATE DEPOSITION TEST (Dosage in Parts Per Million) CHEMICAL 3 4 5 o 7 8 9 it) IS 30 50 23 3200 3500 3900 4000 4100 4200 23 3x00 4200 24 3400 3500 24 3100 3500 25 3400 3700 4100 4200 It 3400 3000 3700 29 4000 4100 4200 33 4100 4200 I claim: molecular weight within the range of 3,000 to 20.000,  
  1. In a waterflood system in which water is added to one or more injection wells in order to force oil from underground formations to one or more producing wells, the process which comprises introducing into at least one of said injection wells a water flooding composition containing a scale inhibiting amount of an alkoxylated water-soluble acrylic acid polymer having 21 said acrylic acid polymer being alkoxylated with from 2-60&#39;71 by weight of ethylene oxide or propylene oxide.  
  2. The method of claim 1 where the alkoxylated water-soluble polymer is an acrylic acid polymer which has been ethoxylated with from 2 to 60% by weight of ethylene oxide, said starting polymer having a molecular weight range of from 5,000 to 15,000.