Composition Useful in Sulfate Scale Removal

Abstract

The present invention discloses a novel aqueous composition for use in removing petroleum-contaminated barium sulfate scale from a surface contaminated with such, said composition comprising: a chelating agent and a counterion component selected from the group consisting of: Li.sub.5DTPA; Na.sub.5DTPA; K.sub.5DTPA; Cs.sub.5DTPA; Na.sub.4EDTA; K.sub.4EDTA; TEAH.sub.4DTPA; and TBAH.sub.5DTPA; a scale removal enhancer; and a non-ionic surfactant. There is also disclosed methods to use such compositions.

Claims

1. A method of removing barium sulfate scale contaminated with at least one petroleum product, said method comprising: providing a liquid composition comprising: a chelating agent selected from the group consisting of: Li.sub.5DTPA; Na.sub.5DTPA; K.sub.5DTPA; Cs.sub.5DTPA; Na.sub.4EDTA; K.sub.4EDTA; TEAH.sub.4DTPA; and TBAH.sub.5DTPA; optionally, a scale removal enhancer; and a non-ionic surfactant; exposing a surface contaminated with said barium sulfate scale and said at least one petroleum product to the liquid composition; allowing sufficient time of exposure to remove said barium sulfate scale and said at least one petroleum product from the contaminated surface.

2. The method according to claim 1, wherein the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; CsCOOH; CsCO.sub.3; and combinations thereof.

3. An aqueous composition for use in removing petroleum-contaminated barium sulfate scale from a surface contaminated with such, said composition comprising: a chelating agent and a counterion component selected from the group consisting of: Li.sub.5DTPA; Na.sub.5DTPA; K.sub.5DTPA; Cs.sub.5DTPA; Na.sub.4EDTA; K.sub.4EDTA; TEAH.sub.4DTPA; and TBAH.sub.5DTPA; a scale removal enhancer; and a non-ionic surfactant.

4. The aqueous composition according to claim 3, wherein the scale removal enhancer is selected from the group consisting of: potassium carbonate; potassium formate; cesium formate and cesium carbonate and combinations thereof.

5. The aqueous composition according to claim 3, wherein the non-ionic surfactant is selected from the group consisting of: a linear alcohol ethoxylate surfactant and a branched alcohol ethoxylate surfactant.

6. The aqueous composition according to claim 3 where the non-ionic surfactant is a linear alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having a chain length of at least 6 carbon atoms.

7. The aqueous composition according to claim 3 where the non-ionic surfactant is a linear alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having a chain length of at least 8 carbon atoms.

8. The aqueous composition according to claim 3 where the non-ionic surfactant is a branched alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having at least 6 carbon atoms.

9. The aqueous composition according to claim 3 where the non-ionic surfactant is a branched alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having at least 8 carbon atoms.

10. The aqueous composition according to claim 3 where the non-ionic surfactant is an alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having a minimum degree of ethoxylation of 9 or higher.

11. The aqueous composition according to claim 3 where the non-ionic surfactant is an alcohol ethoxylate surfactant selected from the group consisting of: alcohol ethoxylate surfactants having a HLB value of 13 or higher.

12. The aqueous composition according to claim 3, wherein the scale removal enhancer is present in the composition in an amount ranging from 5 to 20 wt % of the composition.

13. The aqueous composition according to claim 3, wherein the scale removal enhancer is present in the composition in an amount ranging from 10 to 15 wt % of the composition.

14. The aqueous composition according to claim 3, wherein the scale removal enhancer is present in the composition in an amount of approximately 10 wt % of the composition.

15. The aqueous composition according to claim 3, wherein the chelating agent and counterion are present in the composition in an amount ranging from 5 to 40 wt % of the composition.

16. The aqueous composition according to claim 3, wherein the chelating agent and counterion are present in the composition in an amount ranging from 10 to 30 wt % of the composition.

17. The aqueous composition according to claim 3, wherein the chelating agent and counterion are present in the composition in an amount ranging from 10 to 20 wt % of the composition.

18. The aqueous composition according to claim 3, wherein the pH of the composition ranges from 10 to 11.

19. The aqueous composition according to claim 3, wherein the scale removal enhancer is selected from the group consisting of: K.sub.5DTPA; Cs.sub.5DTPA; Na.sub.4EDTA; and K.sub.4EDTA.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] Features and advantages of embodiments of the present application will become apparent from the following detailed description and the appended figures, in which:

[0044] FIG. 1 is a picture showing the solubilization of barium sulfate scale covered in 40% crude oil in a solution of a known barium sulfate scale dissolver at 20 C. after 4 hours of exposure;

[0045] FIG. 2 is a picture showing the solubilization of barium sulfate scale covered in 40% crude oil in a solution of a barium sulfate scale dissolver according to a preferred embodiment of the present invention at 20 C. after 4 hours of exposure;

[0046] FIG. 3 is a picture showing the solubilization of barium sulfate scale covered in 40% crude oil in a solution of a barium sulfate scale dissolver according to another preferred embodiment of the present invention at 20 C. after 4 hours of exposure;

[0047] FIG. 4 is a picture showing the side-by-side solubilization of barium sulfate scale covered in 40% crude oil in a solution of the three barium sulfate scale dissolvers tested (as per FIG. 1, FIG. 2, and FIG. 3).

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0048] By the addition of potassium carbonate to K.sub.5DTPA, the same solubility numbers can be attained at a lower pH. Instead of 13.5, a pH of 11 was sufficient to obtain comparable solubility numbers. This represents a considerable difference. This allows to conduct scale removal operations at a lower pH and therefore increases the safety for the personnel handling the remover or anyone in the surrounding area.

[0049] According to a preferred embodiment of the present invention, the petroleum-contaminated barium sulfate scale removing composition provides improved rates of scale dissolution. This, in turn, reduces the down time for wells where the scale is being removed. It also reduces the cost of such treatment by limiting the treatment time.

[0050] As shown, the compositions tested for removing non-contaminated barium sulfate scale permits the removal thereof at a much lower pH than what has been practiced to date. Indeed, such a composition can effectively remove barium scale under conditions where the pH is 11, rather than other scale removal compositions which require conditions where the pH is 13. A preferred composition according to the present invention may remove up to 30 kg/m.sup.3 of non-contaminated BaSO.sub.4 scale with a pH of 10. When using the term non-contaminated BaSO.sub.4 scale, it should be understood to the person skilled in the art, that the barium sulfate scale is not contaminated by petroleum product or a petroleum-based product.

[0051] According to a preferred embodiment of the present invention, a composition for removing petroleum-contaminated barium sulfate scale permits the removal thereof with a higher dissolution capacity. This, in turn, allows reducing the volume of scale remover necessary. This also decreases transport costs and many other related items resulting from the usage of lower volumes of scale remover.

[0052] According to a preferred embodiment of the present invention, a composition for removing petroleum-contaminated barium sulfate scale permits the removal thereof at lower temperature than other barium sulfate scale removing treatments. This results in safer treatment conditions for individuals involved in this process.

[0053] According to a preferred embodiment of the present invention, a composition for removing petroleum-contaminated barium sulfate scale comprises a non-ionic surfactant. Alcohol ethoxylate-based surfactants are preferably used in the present invention because of their non-ionic character. However, because of this non-ionic character, long ethoxylate chains are necessary to make them water-soluble at a pH of 10 to 11. Examples of alcohol ethoxylate-based surfactant include, but are not limited to: aromatic ethoxylates and branched or linear ethoxylates of the following formula: H.sub.3C(CH.sub.2).sub.m(OC.sub.2H.sub.4).sub.nOH where m is between 6 and 12 and n is between 8 and 16, preferably m is 9 and n is between 9 to 14.

[0054] To prepare the base BSD solution, combine 334 g of distilled water with 300 g of potassium hydroxide (40% (w/v)) solution and 197 g of diethylenetriamine pentaacetate. Mix thoroughly. Measure 500 mL of the base solution and add 500 mL of distilled water with 50 g of potassium carbonate and 4 mL of XL 90. Mix thoroughly.

[0055] Lutensol surfactants are ethoxylates of alkyl polyethylene glycol ethers based on the C10-Guerbet alcohol. They are non-ionic surfactants. The LutensolXL BASF C.sub.10-Guerbet Alcohol used for the experiments can be better described as follows: the chemical formula is C.sub.5H.sub.11CH(C.sub.3H.sub.7)CH.sub.2OH with the restriction that for 70-99 weight % of compound C.sub.5H.sub.11 means n-C.sub.5H.sub.11 and for 1-30 weight % C.sub.5H.sub.11 means C.sub.2H.sub.5(CH.sub.3)CH.sub.2 and/or CH.sub.3CH(CH.sub.3)CH.sub.2CH.sub.2. Produced by BASF via dimerization of slightly branched C5-aldehyde via aldol reaction followed by hydrogenation. The various surfactant tested in this description are listed and characterized in Table 1 below.

TABLE-US-00001 TABLE 1 Characterization of the various surfactants used in the contaminated barium sulfate scale dissolution tests Lutensol Lutensol Lutensol XL 90 XL 100 XL 140 C-Chain C.sub.10-Guerbet C.sub.10-Guerbet C.sub.10-Guerbet Degree of 9 10 14 ethoxylation HLB number 14 14.5 16

[0056] The content of the compositions according to preferred embodiments of the present invention are listed in Table 2 below. The method of preparing such compositions requiring the initial preparation of the barium sulfate scale dissolver (referred to base BSD) which is then admixed with the appropriate surfactant as per the compositions listed in Table 2.

TABLE-US-00002 TABLE 2 Preferred Compositions according to the present invention Base BSD with XL Base BSD with XL Base BSD with XL 90 100 140 100 mL of base BSD 100 mL of base BSD 100 mL of base BSD with 0.4% XL 90 with 0.4% XL 100 with 0.4% XL 140 Or or or 100 mL of base BSD 100 mL of base BSD 100 mL of base BSD with 400 L XL 90 with 400 L XL 100 with 400 L XL 140

[0057] The hydrophilic-lipophilic balance numbers (hereinafter referred to as HLB value) are understood to help determine the character of a surfactant. Originating from the work of Griffin in the 1950's, the HLB values are calculated according to the following formula: HLB=20*Mh/M, where Mh is the molecular mass of the hydrophilic portion of the surfactant molecule and M represents the total mass of the surfactant.

[0058] As mentioned the XL C-chain is a branched C10, which was the only this type tested as it is readily commercially available. But different types are possible (longer or shorter). As will be understood by the person skilled in the art, the Guerbet alcohol describes only the name reaction how to synthesize a branched hydrocarbon. It is understood that different types are available. The branched C-chain is preferable to achieve a better oil emulsification and better wettability of hydrophobic surfaces, compared to a straight C-chain.

[0059] According to a preferred embodiment of the present invention, the surfactants are selected form the group of non-ionic surfactants. Preferably, the surfactants are ethyleneoxides (also referred to as alcohol ethoxylates. More preferably, the surfactant being ethoxylate alcohols have a chain length of at least 6 carbon atoms. More preferably, the ethoxylate alcohols have a chain length of at least 8 carbon atoms. More preferably, the ethoxylate alcohols have a chain length of at least 6 carbon atoms with a minimum degree of ethoxylation of 9 or higher.

[0060] Preferably also, the surfactant are selected based on their HLB value, which, as mentioned above with respect to non-ionic surfactants, can be easily calculated. The inventors have noted that it is desirable to have a fairly high HLB value, preferably of 13 or higher at the high pH of the barium sulfate scale dissolver. It is believed that the reason for this is that the hydrate layer around the ethoxylate chain form differently depending on the pH which leads to a less hydrophilic character of the ethoxylate chain at a higher pH. It is therefore thought to be preferable to have a surfactant with a longer chain in order to achieve a sufficient solubilisation at a pH of 10 or higher.

[0061] Absolute Solubility of Barium Sulfate Scale

[0062] The inventors have previously noted that chelating agents such as EDTA (Ethylenediaminetetraacetic acid) or DTPA (diethylenetriamine, pentaacetic acid) have the ability to dissolve non-contaminated barium sulfate depends substantially on the size and ion strength of the counterion.

[0063] In Tables 3 and 4 (absolute solubility testing) the absolute (or maximum) solubility of non-contaminated barium sulfate increases with the size of the counterion from lithium to cesium. TEAH (Tetraethylammonium hydroxide) and TBAH (Tetrabuthylammonium hydroxide) as organic bases (counterions) are showing the same trend. Information indicates that the size of the TBAH cation (including the hydrate layer) is comparable to potassium.

[0064] The solubility numbers for both were found to be very similar. In order to quantitatively compare the kg/solubility properly, the BaSO.sub.4:chelating agent ratio was calculated in g/mol and the Ba.sup.2+:chelating agent ratio was calculated in mol/mol. The mol:mol ratio indicates the number of molecules of the chelating agent needed to dissolve one ion of Ba.sup.2+ (complex). The highest ratio which was found was almost 0.5, which means that there needs to be, on average, 2 molecules of DTPA to dissolve 1 Ba.sup.2+ ion but mostly it can be much less.

[0065] Tests performed have indicated that besides the nature of the counterion, an excess of the counterion also improves the solubility. K.sub.5DTPA was tested in conjunction with KCl, K.sub.2CO.sub.3, and KOOCH (potassium formate). It seems that the counterion also plays a large role as K.sub.2CO.sub.3 (with the larger anion) was much more effective than KCl (with a small anion).

TABLE-US-00003 TABLE 3 Absolute solubility of non-contaminated barium sulfate scale (when using a 40% solution of the scale removing composition) 40 wt % sol BaSO.sub.4 BaSO.sub.4 Ba.sup.2+ pH (kg/m3) (g/mol) (mol/mol) Li.sub.5DTPA 2 Na.sub.5DTPA 13.01 17 20.24 0.088 K.sub.5DTPA 13.25 46 62.16 0.266 K.sub.5DTPA + 10 wt % 13.21 38 51.35 0.22 K.sub.2CO.sub.3 Cs.sub.5DTPA 13.4 52 72.2 0.309 Na.sub.4EDTA 13.11 9 7.89 0.034 K.sub.4EDTA 13.32 31 32.98 0.141 TEAH.sub.4DTPA 13.1 14 43.75 0.187 TBAH.sub.5DTPA 13.33 18 64.28 0.275

TABLE-US-00004 TABLE 4 Absolute solubility of non-contaminated barium sulfate scale (when using a 20% solution of the scale removing composition) at 60 C. 20 wt % sol BaSO4 BaSO4 Ba2.sup.+ pH (kg/m3) (g/mol) (mol/mol) K.sub.5DTPA 13.19 27 72.97 0.313 K.sub.5DTPA + 5 wt % K.sub.2CO.sub.3 13.32 41 110.81 0.475 K.sub.5DTPA + 5 wt % K.sub.2CO.sub.3 11.25 40 108.11 0.463 K.sub.5DTPA + 5 wt % K.sub.2CO.sub.3 10 33 89.19 0.3821 Cs5DTPA + 5 wt % CsCO3 35 Cs5DTPA + 10 wt % 35 CsCO.sub.3 Cs5DTPA + 10 wt % 30 HCOOCs TEAH4DTPA + 10 wt % 21 K.sub.2CO.sub.3 TBAH5DTPA + 10 wt % 25 K.sub.2CO.sub.3

[0066] Moreover, the K.sub.5DTPA composition (at 40%) was determined to dissolve 30 kg/m.sup.3 of FeS for a g/mol total of 40.54.

[0067] Preferably, the dissolution of non-contaminated barium sulfate in an amount above 20 kg/m.sup.3. More preferably, dissolution of barium sulfate above 30 kg/m.sup.3 is desired.

[0068] Speed of Barium Scale Dissolution

[0069] A second set of tests were performed to study the speed of dissolution of non-contaminated barium sulfate scale. In order to determine the speed, a relatively small amount of BaSO.sub.4 (0.25 gthis equates to 10 kg/m.sup.3) was used and the time was measured until the solution became clear. Large differences were noted. The best results involved the combination of K.sub.5DTPA with K.sub.2CO.sub.3. This combination provided a dissolution time which was almost 4 times faster than K.sub.5DTPA alone.

[0070] The speed of dissolution of compositions according to preferred embodiment of the present invention were tested and studied. Table 5 summarizes the findings of the testing. The experiment involved the dissolution of 0.25 g of BaSO.sub.4 in a volume of 50 ml fluid at 60 C. under gentle stirring by magnetic stir bar.

TABLE-US-00005 TABLE 5 Speed of dissolution of non-contaminated barium sulfate scale Fluid Time pH K.sub.5DTPA (40%) 1 h 44 min 13.26 K.sub.5DTPA (40%) + 10% TBAH 1 h 38 min 13.4 K.sub.5DTPA (40%) + 20% TBAH 1 h 21 min 13.43 K.sub.5DTPA (40%) + 30% TBAH 1 h 20 min 13.49 K.sub.5DTPA (40%) + 10 wt % KCl 1 h 24 min 13.27 K.sub.5DTPA (40%) + 10% K.sub.2CO.sub.3 30 min 13.22 K.sub.5DTPA (20%) + 5% K.sub.2CO.sub.3 22-23 min 10.5-11

[0071] This testing indicates that both the extent of barium scale dissolution and the speed at which it is dissolved represent marked improvements over known compositions.

[0072] Preferrably, the scale removal enhancer is selected from the group consisting of: K.sub.2CO.sub.3; KOOCH; CsCO.sub.3; CsCOOH and combinations thereof. Preferably, the scale removal enhancer is K.sub.2CO.sub.3. Preferably also, the scale removal enhancer is present in an amount ranging from 5 to 30% by weight of the scale removal composition. More preferably from 10 to 20% by weight and even more preferably, the scale removal enhancer would be present in an amount of approximately 10% by weight.

[0073] Impact of Temperature

[0074] The speed of dissolution of a barium scale dissolver composition was tested and studied under different temperature conditions on non-contaminated barium sulfate scale. Table 6 summarizes the findings of the testing. The experiment involved the dissolution of 0.25 g of BaSO.sub.4 in a volume of 50 ml fluid at various temperatures under gentle stirring by magnetic stir bar. The composition tested comprised a 20 wt % solution of K.sub.5DTPA and 5 wt % K.sub.2CO.sub.3.

TABLE-US-00006 TABLE 6 Impact of Temperature on the Dissolution of Barium Sulfate Temperature in C. ( F.) Time (minutes) 25 (77) 225 40 (104) 50 60 (140) 22 80 (176) 3.5 90 (194) 1.5

[0075] Laboratory Testing of Scale Dissolution

[0076] The sample selected for the solubility testing origins from an oilfield tubular containing sulfate scale crystals originally used for demonstration purposes. Crystals of non-contaminated barium sulfate scale were removed from the tubular to be used for the solubility testing. 200 mL of the composition (K.sub.5DTPA 20 wt % and 5 wt % K.sub.2CO.sub.3) was used. A weighted portion of oilfield sulfate scale sample was submerged in 200 mL of each de-scaling composition. A small magnetic stirrer is added to create a very minimal vortex, creating a small movement of fluid without rigorously stirring the fluid. The fluid was heated to 70 Celsius.

[0077] Results

[0078] 25.165 grams of non-contaminated oilfield sulfate scale was weighted and added to the fluid. The stirrer and heater were started. After 1 hour a slight colouring of the fluid was observed. After 4 hours at temperature when no continued visual reduction of scale was observed, the fluid was filtered and the filter rinsed with water, dried and weighted. The maximum scale solubility was reached and subsequently calculated.

[0079] The base barium scale dissolver composition (used in later testing and referred to as base BSD) comprises a 20 wt % solution of K.sub.5DTPA and 5 wt % K.sub.2CO.sub.3. The base BSD was able to dissolve 52.97 grams per litre of scale at 70 C. The testing was also carried out with a commercially available product (Barsol NS), which is alkali/EDTA based and with EDTA. The Barsol NS product was capable of dissolving 24.19 grams per litre. While EDTA alone only dissolved around 6 grams per litre. Under identical conditions, BSD-40 was shown to have more than double the performance of Barsol NS

[0080] Extent of Dissolution of Petroleum-Contaminated Barium Scale

[0081] In order to assess the extent and efficacy of barium sulfate scale dissolvers according to preferred embodiments of the present invention, testing using petroleum-contaminated barium sulfate was carried out. The dissolution of barium sulfate contaminated with petroleum products to mimick the real-life situations encountered in the oilfield was studied by comparing a barium sulfate dissolver (the base BSD) to various preferred compositions according to the present invention (base BSD with XL 90, base BSD with XL 100, and base BSD with XL 140).

[0082] The preparation of contaminated petroleum involved the following: use 10 g of lab grade 98% pure Barium Sulfate and add to that 3 g of a low viscous crude oil into a beaker. The ingredients were mixed with a stir rod until a homogenous, dry, powdered mixture was achieved. The mixture were allowed to sit for 24 hours.

[0083] The amount of liquid used was 100 ml to which was added 0.25 g of contaminated BaSO.sub.4. Therefore, the 1500 mg/L Ba below is just the maximum of available Ba under these experimental conditions and not a maximum for the barium sulfate scale dissolver. This experiment shows that the solubility is improved and the oil layer can be successfully removed, it was not designed as a measure of the extent of dissolution of barium sulfate scale by the barium scale dissolver with surfactant.

[0084] The results of the analysis of the solution was done by atomic spectroscopy which analyzed the amount of barium dissolved in the solution are listed in Table 7 below.

TABLE-US-00007 TABLE 7 Elemental analysis of dissolved barium by Atomic Spectroscopy Base Base Base BSD BSD BSD Lab Filtered Base with with with Elements UNITS BSD XL 90 XL 100 XL 140 Dissolved mg/L 1100 (1) 1500 (1) 1500 (1) 1500 (1) Barium (Ba)

[0085] RDL=Reportable Detection Limit

[0086] (1) Detection limits raised due to dilution to bring analyte within the calibrated range.

[0087] Moreover, the compositions according to the present invention used are quite environmentally safe. This represents a major advantage over any known chemically-based methods of the removal of petroleum-contaminated barium scale. Another advantage to the compositions according to preferred embodiments of the present invention includes the speed of dissolution which is considerably faster than any known commercial compositions. Another advantage of preferred compositions according to the present invention is that they can be employed on wells according to a one-step process and thus are very desirable to operators which deal with petroleum-contaminated barium sulfate scale issues.

[0088] According to a preferred embodiment of the present invention, there is provided a onestep process for removing petroleum-contaminated barium sulfate scale inside a wellbore, said process comprising:

[0089] providing a liquid composition comprising:

[0090] a chelating agent selected from the group consisting of: Li.sub.5DTPA; Na.sub.5DTPA; K.sub.5DTPA; Cs.sub.5DTPA; Na.sub.4EDTA; K.sub.4EDTA; TEAH.sub.4DTPA; and TBAH.sub.5DTPA;

[0091] a scale removal enhancer;

[0092] a non-ionic surfactant;

[0093] exposing a surface contaminated with petroleum-contaminated barium sulfate scale to the liquid composition;

[0094] allowing sufficient time of exposure to remove some or all of the petroleum-contaminated barium sulfate scale from the contaminated surface. The person skilled in the art will understand that what is meant by one-step is that there is a single treatment step in the process (or method) to remove barium sulfate scale.

[0095] When the surface contaminated with barium sulfate scale is deep underground or a hard to access tubing or piping, the exposure consists of circulating the liquid composition through the tubing or piping until it has been established that the scale has been removed beyond a desirable predetermined point. Hence, in some cases, it is quite possible that the entirety of the scale present is not removed but the amount of removal is sufficient to re-start operations and provide the desired productivity and/or circulation through the affected tubing/piping. The liquid composition can also be heated in order to improve the removal of the scale and the speed at which the removal is effected.

[0096] According to another preferred embodiment of the present invention, the method of treatment of petroleum-contaminated BaSO.sub.4 scale wherein the fluid is spotted, i.e. placed in a tube/tank/pipe/equipment in a soaking operation. This may in some instances be somewhat less efficient than circulating the fluid due to the surface reaction nature of the fluid, but it is used in some cases to remove enough scale to run tools, for example.

[0097] While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.