Composition to reduce friction reducer fouling in wellbores

Abstract

A method of spearheading an acid into a wellbore is adapted to avoid the gelation of a friction reducer polymer. The method comprises injecting a synthetic or modified acid composition down a wellbore, the composition comprising: a synthetic or modified acid; a solvent; and a chelating agent. Optionally the composition may comprise a corrosion inhibitor package. The method further includes allowing sufficient time for the synthetic or modified acid composition to react with material which require acidic treatment and injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

Claims

1. A method of spearheading an acid into a wellbore adapted to avoid the gelation of a friction reducer polymer, wherein said method comprises: injecting a synthetic acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound selected from the group consisting of: sodium gluconate and gluconic acid; allowing sufficient time for the synthetic or modified acid composition to react with the friction reducer polymer in the wellbore which requires acidic treatment; injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

2. The method according to claim 1 where the modified acid is selected from the group consisting of: Urea-HCl; amino acid-HCl; and alkanolamine-HCl.

3. The method according to claim 1 where the synthetic acid is selected from the group consisting of: sulfonic acids.

4. The method according to claim 1 where the sulfonic acid is selected from the group consisting of: methansulfonic acid; and toluenesulfonic acid.

5. The method according to claim 1 where the modified acid comprises an amino acid-HCl where the amino acid is selected from the group consisting of: lysine; glycine; sarcosine, betaine (such as trimethyl glycine), dimethyl glycine (DMG), iminodiacetic acid (IDA), alanine, asparagine, aspartic acid, cysteine, glutamic acid, histidine, leucine, lysine, methionine, proline, serine, threonine or valine or combinations thereof.

6. The method according to claim 1 where the modified acid is lysine-HCL.

7. The method according to claim 1 where the modified acid comprises an alkanolamine-HCl, where the alkanolamine is selected from the group consisting of: monoethanolamine; diethanolamine; and triethanolamine.

8. The method according to claim 1 where the modified acid comprises an alkanolamine-HCl, where the alkanolamine is monoethanolamine.

9. The method according to claim 1 where the chelating agent compound is present in the synthetic or modified acid composition in an amount ranging from 0.1 wt % to 5 wt %.

10. The method according to claim 1 where the chelating agent compound is present in the synthetic or modified acid composition in an amount ranging from 0.5 wt % to 2 wt %.

11. The method according to claim 1 where the chelating agent compound is present in the synthetic or modified acid composition in an amount of about 1 wt %.

12. The method according to claim 1, wherein the composition further comprise a corrosion inhibitor package.

13. A method of spearheading an acid into a wellbore adapted to reduce the gelation of a friction reducer polymer, wherein said method comprises: injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound selected from the group consisting of: sodium gluconate and gluconic acid; allowing sufficient time for the synthetic or modified acid composition to react with the friction reducer polymer in the wellbore in the wellbore which requires acidic treatment; injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

14. The method according to claim 13, wherein the composition further comprise a corrosion inhibitor package.

15. A method of selectively depleting divalent cations present in a spent spearheading acid composition into a wellbore, wherein said method comprises: injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound selected from the group consisting of: sodium gluconate and gluconic acid; allowing sufficient time for the synthetic or modified acid composition to react with the divalent cations in the spent spearheading acid composition in the wellbore which requires acidic treatment; and allowing sufficient time for the chelating agent to remove cations of the spent spearheading acid.

16. The method according to claim 15, wherein said method further comprises the injection of a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

17. The method according to claim 15, wherein the composition further comprise a corrosion inhibitor package.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention may be more completely understood in consideration of the following description of various embodiments of the invention in connection with the accompanying figure, in which:

(2) FIG. 1 is a photograph of the reprecipitated solids from the addition of NaOH in spent acid blends;

(3) FIG. 2 is a photograph of the reprecipitated solids from the addition of NaOH in spent acid blends;

(4) FIG. 3 is a close-up of the reprecipitated solids from FIG. 1; and

(5) FIG. 4 is a close-up of the reprecipitated solids from FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not limitation, of those principles and of the invention.

(7) According to an aspect of the present invention, there is provided a method of spearheading an acid into a wellbore adapted to avoid the gelation of a friction reducer polymer, wherein said method comprises:

(8) injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound, optionally the composition may comprise a corrosion inhibitor package;

(9) allowing sufficient time for the synthetic or modified acid composition to react with material which require acidic treatment;

(10) injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

(11) Water Analysis Laboratory Tests

(12) An operator requested specific tests for a wireline acid and the same acid further comprising a friction reducer polymer. A water analysis was performed on spent acid blends reacted with cuttings from Corbin (1608 5H-5X, 14800). A reprecipitation of solids was performed with the spent acid blends and the solids were sent for XRD analysis, while the filtered spent acid was sent for water analysis.

(13) The acid blends (15% HCl, 33% MEA-HCl (in a 1:4.1 ratio) and 33% MEA-HCl (in a 1:4.1 ratio)-FR (FR referring to a friction reducer polymer) were spent in excess with the cuttings. Half of the spent fluid was sent to a third-party laboratory for water analysis. The MEA-HCl blend were made by admixing 1 mole of MEA for each 4.1 moles of HCl. The stock solution of MEA-HCl (in a 1:4.1 ratio) is referred to the 100% blend. Normally, this blend can be diluted to be tailored to the intended application, in this case, the stock solution is diluted down to a third of its concentration for this application when used with a wireline. To obtain a 4.1:1 molar ratio of MEA to HCl, one must first mix 165 g of MEA with 835 g of water. This forms the monoethanolamine solution. Subsequently, one takes 370 ml of the previously prepared monoethanolamine solution and mixes with 350 ml of HCl aq. 36% (22 Baume). Circulation is maintained until all products have been solubilized. Additional products can now be added as required.

(14) Sodium hydroxide was then added to the other half of the spent fluids up to pH of 9-10. The fluids were then filtered and sent to a third-party laboratory for water analysis, while the reprecipitated solids from the addition of sodium hydroxide were dried and sent to a different third-party laboratory for XRD analysis.

(15) Procedure: The three acid blends (15% HCl, 33% MEA-HCl (in a 1:4.1 ratio), and 33% MEA-HCl (in a 1:4.1 ratio)-FR) were spent in excess with the drill cuttings (provided by Encana, Corbin 1608 5H-5X, 14800) at ambient temperature. The spent fluids were then filtered through P8 filter paper and packaged. The samples were sent to Bureau Veritas Laboratories for water analysis. Table 1 includes the results of the water analysis.

(16) TABLE-US-00001 TABLE 1 Water analysis of spent acid blends COC Number Spent 33% Spent 33% MEA-HCl (in MEA-HCl (in a Spent 15% HCl a 1:4.1 ratio) 1:4.1 ratio)-FR UNITS TPL0004 RDL TPL0005 RDL TPL0006 RDL Calculated Parameters Anion Sum meq/L 4100 N/A 2000 N/A 1900 N/A Cation Sum meq/L 4200 N/A 1600 N/A 1600 N/A Hardness mg/L 150000 0.50 61000 0.50 62000 0.50 (CaCO.sub.3) Ion Balance % 0.75 N/A 11 N/A 6.4 N/A (% Difference) Dissolved mg/L ND 0.22 0.26 0.22 ND 0.89 Nitrate (NO.sub.3) Nitrate plus mg/L ND 0.071 ND 0.071 ND 0.28 Nitrite (N) Dissolved mg/L ND 0.16 ND 0.16 ND 0.66 Nitrite (NO.sub.2) Calculated mg/L 230000 1000 100000 500 99000 1000 Total Dissolved Solids Misc. Inorganics Conductivity uS/cm >110000 2.0 >110000 2.0 >110000 2.0 (1) (1) (1) pH pH 11.0 N/A 9.95 N/A 9.87 N/A Anions Alkalinity (PP mg/L 1300 1.0 8000 10 6500 10 as CaCO.sub.3) Alkalinity mg/L 1500 1.0 11000 10 9700 10 (Total as CaCO.sub.3) Bicarbonate mg/L ND 1.0 ND 10 ND 10 (HCO.sub.3) Carbonate mg/L 230 1.0 4200 10 3800 10 (CO.sub.3) Hydroxide mg/L 380 1.0 1500 10 1100 10 (OH) Dissolved mg/L 150000 1000 62000 500 59000 1000 Chloride (Cl) (2) (2) (2) Dissolved mg/L 200 1.0 150 1.0 160 10 Sulphate (3) (SO.sub.4) Nutrients Dissolved mg/L ND (4) 0.050 ND (4) 0.050 ND (4) 0.20 Nitrite (N) Dissolved mg/L ND (4) 0.050 0.058 0.050 ND (4) 0.20 Nitrate (N) (4) Lab Filtered Elements Dissolved mg/L 60000 150 24000 15 24000 15 Calcium (Ca) (2) (2) (2) Dissolved mg/L 0.27 0.060 0.17 0.060 130 0.60 Iron (Fe) Dissolved mg/L 0.22 0.20 130 0.20 460 2.0 Magnesium (Mg) Dissolved mg/L 0.024 0.0040 ND 0.0040 3.8 0.040 Manganese (Mn) Dissolved mg/L 210 0.30 150 0.30 160 3.0 Potassium (K) Dissolved mg/L 27000 50 8000 25 9000 25 Sodium (Na) (2) (2) (2)

(17) Water Analysis of Spent Acid Blends Re-Precipitation of Calcium Carbonate

(18) Procedure:

(19) The three acid blends (15% HCl, 33% MEA-HCl (in a 1:4.1 ratio), and 33% MEA-HCl (in a 1:4.1 ratio)-FR) were spent in excess with the drill cuttings (provided by Encana, Corbin 1608 5H-5X, 14800) at ambient temperature. The spent fluids were then filtered through P8 filter paper. Sodium hydroxide (NaOH) was then added dropwise to 450 mL of the spent acid blends to increase the pH. A pH probe was placed in the solution to monitor the pH of the solution as it was titrated. The test was performed at ambient temperature on a stir plate. The fluid was then filtered through P8 filter paper and packaged for water analysis. The solids collected from the filter paper were dried and packaged for XRD analysis. Table 2 includes the results of the water analysis.

(20) TABLE-US-00002 TABLE 2 Water analysis results for spent acid blends reprecipitated with NaOH and filtered COC Number Spent 33% Spent 33% MEA-HCl (in MEA-HCl (in a Spent 15% HCl a 1:4.1 ratio) 1:4.1 ratio)-FR UNITS TPL0004 RDL TPL0005 RDL TPL0006 RDL Calculated Parameters Anion Sum meq/L 4100 N/A 2000 N/A 1900 N/A Cation Sum meq/L 4200 N/A 1600 N/A 1600 N/A Hardness (CaCO.sub.3) mg/L 150000 0.50 61000 0.50 62000 0.50 Ion Balance % 0.75 N/A 11 N/A 6.4 N/A (% Difference) Dissolved mg/L ND 0.22 0.26 0.22 ND 0.89 Nitrate (NO.sub.3) Nitrate plus mg/L ND 0.071 ND 0.071 ND 0.28 Nitrite (N) Dissolved mg/L ND 0.16 ND 0.16 ND 0.66 Nitrite (NO.sub.2) Calculated mg/L 230000 1000 100000 500 99000 1000 Total Dissolved Solids Misc. Inorganics Conductivity uS/cm >110000 2.0 >110000 2.0 >110000 2.0 (1) (1) (1) pH pH 11.0 N/A 9.95 N/A 9.87 N/A Anions Alkalinity (PP as mg/L 1300 1.0 8000 10 6500 10 CaCO.sub.3) Alkalinity mg/L 1500 1.0 11000 10 9700 10 (Total as CaCO.sub.3) Bicarbonate mg/L ND 1.0 ND 10 ND 10 (HCO.sub.3) Carbonate mg/L 230 1.0 4200 10 3800 10 (CO.sub.3) Hydroxide mg/L 380 1.0 1500 10 1100 10 (OH) Dissolved mg/L 150000 1000 62000 500 59000 1000 Chloride (Cl) (2) (2) (2) Dissolved mg/L 200 1.0 150 1.0 160 10 Sulphate (3) (SO.sub.4) Nutrients Dissolved mg/L ND (4) 0.050 ND (4) 0.050 ND (4) 0.20 Nitrite (N) Dissolved mg/L ND (4) 0.050 0.058 0.050 ND (4) 0.20 Nitrate (N) (4) Lab Filtered Elements Dissolved mg/L 60000 150 24000 15 24000 15 Calcium (Ca) (2) (2) (2) Dissolved mg/L 0.27 0.060 0.17 0.060 130 0.60 Iron (Fe) Dissolved mg/L 0.22 0.20 130 0.20 460 2.0 Magnesium (Mg) Dissolved mg/L 0.024 0.0040 ND 0.0040 3.8 0.040 Manganese (Mn) Dissolved mg/L 210 0.30 150 0.30 160 3.0 Potassium (K) Dissolved mg/L 27000 50 8000 25 9000 25 Sodium (Na) (2) (2) (2)

(21) Study of the Solids Re-Precipitated from NaOH with Spent Acid Blends

(22) Procedure:

(23) X-Ray diffraction (XRD) analysis at Calgary Rock and Materials Services Inc. was performed. The X-ray diffraction data for bulk and clay mineralogy was performed for three samples:

(24) Solids re-precipitated from the addition of NaOH to 15% HCl spent with cuttings from Corbin 1608 5H-5X, 14800

(25) Solids re-precipitated from the addition of NaOH to 33% MEA-HCl (in a 1:4.1 ratio) spent with cuttings from Corbin 1608 5H-5X, 14800

(26) 3) Solids re-precipitated from the addition of NaOH to 33% MEA-HCl (in a 1:4.1 ratio)-FR spent with cuttings from Corbin 1608 5H-5X, 14800

(27) TABLE-US-00003 TABLE 3 Summary of XRD results of reprecipitated solid with NaOH Sample 1) Solids Sample 2) Solids Sample 3) Solids reprecipitated reprecipitated from reprecipitated from from addition addition of NaOH to addition of NaOH to of NaOH to spent 33% MEA-HCl spent 33% MEA-HCl spent 15% HCl (in a 1:4.1 ratio) (in a 1:4.1 ratio)-FR Weight % Weight % Weight % Bischofite 43.1 — — Brucite 20.7 — — Calcite — 28.2 0.0 Halite — 71.8 100.0 Halite 9.7 — — Iowaite 26.5 — — Total % 100 100 100 These test results indicate that the composition used in Sample 3 has effectively sequestered all of the multivalent cations (Mg.sup.2+, Ca.sup.2+, Fe.sup.2+ and Fe.sup.3+) from the solution to which it was exposed. Bischofite is a hydrous magnesium chloride mineral having a formula of MgCl.sub.2.6H.sub.2O. Brucite is the mineral form of magnesium hydroxide having a formula of Mg(OH).sub.2. Calcite is the mineral form of calcium carbonate hydroxide having a formula of CaCO.sub.3. Halite is the mineral form of sodium chloride having a formula of NaCl. Iowaite is a mineral form of magnesium containing iron chlorine among other elements, it has a chemical formula of Mg.sub.4Fe(OH).sub.8OCl.sub.2.4H.sub.2O. The removal of the divalent and multivalent cations from solution indicates a high potential for gelling inhibition of the friction reducer present in the spearhead acid.

(28) Friction Reducer-Acid Incompatibility

(29) This study was carried out to assess an apparent incompatibility of friction reducer with acid. Initial experiments showed that 0.1 wt % friction reducer could be homogenized in 33% MEA-HCl (in a 1:4.1 ratio), but over time precipitation of the friction reducer was observed (ca. 3 days). This occurred with 0.1 wt % Fe.sup.3+ and without Fe.sup.3+ present in the mixture. The precipitate is likely polyacrylic acid which can crosslink through carboxylic acid groups and/or complex to cations in the solution (i.e. Fe.sup.3+). To test this, 3 000 000 g/mol polyacrylic acid (PAA) was added to a spent 50% solution of MEA-HCl (include the ratio for MEA-HCl (in a 1:4.1 ratio), where, after homogenization of the solution, rapid precipitation of PAA was observed.

(30) Two chelates at 0.1 wt % loadings were tested in mixtures containing a spent solution of 50% MEA-HCl (in a 1:4.1 ratio), where the acid was neutralized with either CaCO.sub.3 (s) or the provided cuttings (Corbin 1608—cleaned and washed). To the neutralized acid combinations of friction reducer, Fe.sup.3+ and chelate were added (Table 2). When chelate is added to the mixture the residue formed a powder; whereas, without chelate a more gel-like precipitate is observed on the filter paper. Note that these reactions are very slow and after filtration there was still precipitate forming in the filtrate, therefore numeric values of precipitate and Fe.sup.3+ concentrations are not provided.

(31) Procedure:

(32) The first experiment studied the compatibility of friction reducer with FLOJET DR 22430 (FLOJET) and 33% MEA-HCl (incl. 1:4.1 ratio). The samples were mixed with an IKA T18 UltraTuraxx at 25,000 rpm. This was done for several minutes to ensure complete homogenization of the samples. Table 4 contains a sample list. Images after three days were taken to show acid compatibility.

(33) TABLE-US-00004 TABLE 4 Compatibility test samples and loadings Sample Acid Friction reducer Fe.sup.3+ (aq) 1 33% MEA-HCl (in a 0.1% FloJet ® 0.0% 1:4.1 ratio) 2 33% MEA-HCl (in a 0.1% FloJet ® 0.1% 1:4.1 ratio)

(34) In the second experiment the performance of two chelates are tested in order to prevent or reduce the formation of gel-like precipitates. Firstly, 50% MEA-HCl (in a 1:4.1 ratio) is neutralized by addition to CaCO.sub.3 (s) or cuttings, the resulting pH of the spent acid is 5.95 and 5.60 respectively. The spent acid is then filtered and divided into separate Nalgene bottles where FLOJET®, Fe.sup.3+ and chelate are added. The resultant solutions were heated to 90° C. for approximately 72 hrs, cooled to ambient temperature and filtered. A sample list follows in Table 5 below.

(35) TABLE-US-00005 TABLE 5 Spent acid testing Friction Fe.sup.3+ Chelate Sample Base Acid reducer (aq) 3 Poultry 50% MEA-HCl 0.1% FLOJET 0.1% 0.0% grit (in a 1:4.1 ratio) 4 Poultry 50% MEA-HCl 0.1% FLOJET 0.1% 0.1% CH1 grit (in a 1:4.1 ratio) 5 Poultry 50% MEA-HCl 0.1% FLOJET 0.1% 0.1% CH2 grit (in a 1:4.1 ratio) 6 Cuttings 50% MEA-HCl 0.1% FLOJET 0.1% 0.0% (in a 1:4.1 ratio) 7 Cuttings 50% MEA-HCl 0.1% FLOJET 0.1% 0.1% CH1 (in a 1:4.1 ratio) 8 Cuttings 50% MEA-HCl 0.1% FLOJET 0.1% 0.1% CH2 (in a 1:4.1 ratio) 9 Cuttings 50% MEA-HCl 0.1% FLOJET 0.0% 0.0% (in a 1:4.1 ratio)

(36) Subsequently each one of samples 3 to 9 were filtered. The major difference in the samples is the formation of a powdered precipitate in the case of mixtures with chelate, versus gel-like precipitate in the cases where no chelate was added. As stated previously these reactions are very slow so the precipitates final mass and the filtrates final Fe.sup.3+ concentration has not been quantified. The formation of powder precipitates is desirable over the formation of a gel as a powder may be flowed back out of a well without causing clogging within the wellbore.

(37) Re-Precipitation of Calcium Carbonate in Spent Synthetic or Modified Acid

(38) In order to assess the performance of two chelating agents used in a composition according to the present invention, the re-precipitation of solids from the addition of sodium hydroxide were performed with acid blends spent with cuttings provided by an operator at ambient temperature.

(39) Gluconic acid and lab grade sodium gluconate were tested head-to-head in order to determine their capacity to chelate iron while in the presence of a spent synthetic acid. This is a laboratory method intended on mimicking some of the potential interactions between the chemicals present downhole during a spearhead acid stage. With a loading of 1.0% sodium gluconate vs 1.67% gluconic acid (60% active material), both blends had relatively similar performances. A cloudy haze was observed and once filtered and dried, the precipitate weighed in the range of 0.7 g-1.1 g. This represents approximately 0.2 w % of re-precipitated solid from the total volume of solution.

(40) Procedure:

(41) Two acid blends: 33% MEA-HCl (in a 1:4.1 ratio)-FR with 1.67% gluconic acid and 33% MEA-HCl (in a 1:4.1 ratio)-FR with 1% sodium gluconate, were spent with excess drill cuttings (provided by Encana, Corbin 1608 5H-5X) at ambient temperature. The spent fluids were then filtered through P8 and P2 filter paper. Sodium hydroxide (NaOH) was then added dropwise to 500 mL of the spent acid blends to increase the pH up to 9. A pH probe was placed in the solution to monitor the pH of the solution as it was titrated. The test was performed at ambient temperature on a stir plate. The fluid was then filtered through P2 filter paper and the solids were collected and dried, the results are reported in Table 6. Photos were taken of the solids at 1× and 20× zoom for visual comparison (see FIGS. 1, 2, 3 and 4).

(42) TABLE-US-00006 TABLE 6 Results of the re-precipitation testing Weight of Reprecipitated Test Fluid Additive Solids (g) A 33% MEA-HCl 1.61 w % Gluconic Acid 0.7807 (in a 1:4.1 ratio)-FR B 33% MEA-HCl 1.0 w % Sodium 1.0296 (in a 1:4.1 ratio)-FR Gluconate NB: the loading of gluconic acid is derived from a commercially available composition which comes in a concentration of 60 wt % gluconic acid. The actual content of gluconic acid is approximately 0.97 wt %.

(43) The re-precipitated solids consisted of halite with impurities which explains their black color. The value of using gluconic acid or sodium gluconate is two-fold. It is a very selective cation chelator and contrary to EDTA and derivatives thereof, it is readily biodegradable.

(44) The value of the present invention is even more attractive when considering that some in the industry have expressed a desire to increase the loading of friction reducing polymer in the fracking fluid in order to minimize the occurrence of seismic events (i.e. fracking-induced earthquakes). Currently, some fields have shown a 20% occurrence of friction reducing polymer fouling (i.e. sufficient gelling to cause production shutdowns). Estimates for the treatment of a single instance of polymer fouling range from 50,000 $ to 200,000 $, figures which do not take into account the loss production caused by such an event.

(45) The embodiments described herein are to be understood to be exemplary and numerous modification and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the claims appended hereto, the invention may be practiced otherwise than as specifically disclosed herein.