Abstract:
The present invention generally relates to methods for decreasing viscosity, yield stress, or viscosity and yield stress of an asphaltene precipitate-containing aqueous mixture. More specifically, the method comprises applying an effective amount of a water-soluble polymer to an asphaltene precipitate-containing aqueous mixture. The water-soluble polymers comprise polyanion, polycation, and polar water-soluble polymer components. The present invention also relates to water-soluble asphaltene dispersants.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 62/235,982 filed on Oct. 1, 2015, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to methods for decreasing viscosity or yield stress of an asphaltene precipitate-containing aqueous mixture. More specifically, the method comprises applying an effective amount of a water-soluble polymer to an asphaltene precipitate-containing aqueous mixture. The water-soluble polymers comprise polyanion, polycation, and polar water-soluble polymer components. The present invention also relates to water-soluble asphaltene dispersants. 
       BACKGROUND OF THE INVENTION 
       [0003]    Paraffinic froth treatments are used within the petroleum industry to eliminate aqueous and solid contaminants (i.e., asphaltenes) from the froth to form a clean bitumen product. Paraffinic solvents can be added to reduce viscosity and density of the oil phase, to produce a diluted bitumen product. The diluted bitumen can be transported more effectively and economically through pipelines. 
         [0004]    Even though, paraffinic froth treatments are able to clean the bitumen product and reject asphaltene deposits, large asphaltene, and solid aggregates can still form in the bottom of the froth settling units (FSU), which can lead to plugging of equipment and pipelines. Large asphaltene and solid aggregates that are carried over to the tailings solvent recovery system (TSRU) can hinder solvent recovery and cause foaming within the TSRU. 
         [0005]    Asphaltenes are defined as the crude oil fraction that is soluble in aromatic solvents and insoluble in low-boiling straight chain alkanes. Asphaltene molecules have complex structures and are typically polar molecules with relatively high molecular weights (approximately 700 to 1,000 g/mole). Asphaltenes can contain carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts of vanadium and nickel. 
         [0006]    Asphaltenes are typically stable under virgin reservoir conditions, but can be destabilized and precipitate from crude oil during production due to changes in temperature, pressure, chemical composition, and shear rate. Asphaltene deposits can occur throughout the production system, from inside the reservoir formation to pumps, tubing, wellheads, safety valves, flow lines, and surface facilities used in the extraction process. Asphaltene deposits can cause production rate decline and other operational problems, such as increased fluid viscosity and density, and stabilization of oil-water emulsions. The nature of asphaltene deposits, which can appear hard and coal-like or sticky and tar-like, is determined by the composition of the crude oil and the conditions under which precipitation occurred. Asphaltene deposits can block reservoir pores in near-well formations, production tubing, and downstream pipelines. 
         [0007]    Therefore, a need exits to develop methods and chemistries for increasing the fluidity of the underflow, decreasing asphaltene formation, and enhancing solvent recovery. 
       SUMMARY OF THE INVENTION 
       [0008]    One aspect of the invention is a method for decreasing viscosity, decreasing yield stress, or decreasing viscosity and yield stress of an asphaltene precipitate-containing aqueous mixture. The method comprises mixing an asphaltene-containing hydrocarbon with paraffinic solvent to form the asphaltene precipitate-containing aqueous mixture and contacting an effective amount of a water-soluble polymer with the asphaltene precipitate-containing aqueous mixture whereby the viscosity, the yield stress, or the viscosity and the yield stress of the asphaltene precipitate-containing aqueous mixture is reduced as compared to an otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a temperature from about 20° C. to about 150° C. 
         [0009]    Another aspect of the invention is a method for determining viscosity or yield stress of an asphaltene precipitate-containing aqueous mixture. The method comprises charging a bitumen froth into a high pressure reactor fitted with a mixer and a temperature controller; charging a paraffinic solvent into a sampling cylinder in fluid contact with the high pressure reactor; heating the high pressure reactor to a temperature of from about 30° C. to about 95° C.; pressurizing the high pressure reactor by adding gas from a gas source in fluid contact with the high pressure reactor; contacting the paraffinic solvent with the bitumen froth to form a reaction mixture; mixing the reaction mixture; stopping the mixing and allowing the solids, water, and asphaltene precipitates to separate from the bitumen forming a bitumen layer and an aqueous layer; removing at least a portion of the bitumen layer from the high pressure reactor; contacting an effective amount of a water-soluble polymer for reducing viscosity, yield stress, or viscosity and yield stress with the aqueous layer; contacting additional paraffinic solvent with the remaining bitumen layer and aqueous layer to form a second reaction mixture; reheating the high pressure reactor to a temperature of from about 30° C. to about 95° C.; repressurizing the high pressure reactor by adding gas from a gas source in fluid contact with the high pressure reactor; mixing the second reaction mixture; stopping the mixing and allowing the water and asphaltene precipitates to separate from the bitumen forming a second bitumen layer and a second aqueous layer; removing at least a portion of the second bitumen layer from the high pressure reactor; and measuring viscosity or yield stress of the second aqueous layer. 
         [0010]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram of the high temperature paraffinic froth treatment process. 
           [0012]      FIG. 2  is a diagram of a laboratory bench unit used to simulate the paraffinic froth treatment process. 
       
    
    
       [0013]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The present invention is directed towards methods for decreasing viscosity, yield stress, or viscosity and yield stress of an asphaltene precipitate-containing aqueous mixture. An effective amount of a water-soluble polymer that is not ethoxylated is contacted with the asphaltene precipitate-containing aqueous mixture whereby the viscosity, yield stress, or viscosity and yield stress of the aqueous mixture is reduced as compared to an otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a temperature from about 20° C. to about 150° C. 
         [0015]    The asphaltene precipitate-containing aqueous mixture can further comprise solids, and hydrocarbons. 
         [0016]    The asphaltene precipitate-containing aqueous mixture can be from the underflow of a froth settling unit in a paraffinic solvent froth treatment. 
         [0017]    The underflow can be from a second froth settling unit in the paraffinic solvent froth treatment. 
         [0018]    The underflow from the second froth settling unit can be transferred to the tailings solvent recovery unit. 
         [0019]    The asphaltene precipitate-containing aqueous mixture in the tailings solvent recovery unit can have a reduced viscosity as compared to the otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a temperature from about 20° C. to about 150° C., from about 20° C. to about 120° C., from about 20° C. to about 100° C., from about 20° C. to about 80° C., from about 40° C. to about 150° C., from about 40° C. to about 120° C., from about 40° C. to about 100° C., from about 40° C. to about 80° C., from about 50° C. to about 150° C., from about 50° C. to about 120° C., from about 50° C. to about 100° C., from about 50° C. to about 80° C., from about 50° C. to about 70° C., from about 55° C. to about 65° C., or about 60° C. 
         [0020]    The asphaltene precipitate-containing aqueous mixture in the tailings solvent recovery unit can have a reduced viscosity as compared to the otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a pressure from about 15 psi to about 150 psi, from about 15 psi to about 130 psi, from about 15 psi to about 110 psi, from about 15 psi to about 90 psi, from about 15 psi to about 80 psi, from about 30 psi to about 150 psi, from about 30 psi to about 130 psi, from about 30 psi to about 110 psi, from about 30 psi to about 90 psi, from about 30 psi to about 85 psi, from about 50 psi to about 150 psi, from about 50 psi to about 130 psi, from about 50 psi to about 110 psi, from about 50 psi to about 90 psi, from about 50 psi to about 85 psi, from about 70 psi to about 150 psi, from about 70 psi to about 130 psi, from about 70 psi to about 110 psi, from about 70 psi to about 90 psi, from about 70 psi to about 85 psi, from about 75 psi to about 85 psi, or about 80 psi. 
         [0021]    When the viscosity is measured at a temperature from about 55° C. to about 65° C., a pressure from about 75 psi to about 85 psi, and a mixing rate from about 550 rpm to about 650 rpm, the viscosity is reduced by about 75%, about 70%, about 65%, about 60%, about 55%, about 50%, about 45%, about 40%, about 35%, about 30%, about 25%, or about 20%. 
         [0022]    The asphaltene precipitate-containing aqueous mixture in the tailing solvent recovery unit has a reduced yield stress as compared to an otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a temperature from about 20° C. to about 150° C., from about 20° C. to about 120° C., from about 20° C. to about 100° C., from about 20° C. to about 80° C., from about 40° C. to about 150° C., from about 40° C. to about 120° C., from about 40° C. to about 100° C., from about 40° C. to about 80° C., from about 50° C. to about 150° C., from about 50° C. to about 120° C., from about 50° C. to about 100° C., from about 50° C. to about 80° C., from about 50° C. to about 70° C., from about 55° C. to about 65° C., or about 60° C. 
         [0023]    The asphaltene precipitate-containing aqueous mixture in the tailing solvent recovery unit has a reduced yield stress as compared to an otherwise identical asphaltene precipitate-containing aqueous mixture without the water-soluble polymer when measured at a pressure from about 15 psi to about 150 psi, from about 15 psi to about 130 psi, from about 15 psi to about 110 psi, from about 15 psi to about 90 psi, from about 15 psi to about 80 psi, from about 30 psi to about 150 psi, from about 30 psi to about 130 psi, from about 30 psi to about 110 psi, from about 30 psi to about 90 psi, from about 30 psi to about 85 psi, from about 50 psi to about 150 psi, from about 50 psi to about 130 psi, from about 50 psi to about 110 psi, from about 50 psi to about 90 psi, from about 50 psi to about 85 psi, from about 70 psi to about 150 psi, from about 70 psi to about 130 psi, from about 70 psi to about 110 psi, from about 70 psi to about 90 psi, from about 70 psi to about 85 psi, from about 75 psi to about 85 psi, or about 80 psi. 
         [0024]    When the yield stress is measured at a temperature from about 55° C. to about 65° C., a pressure from about 75 psi to about 85 psi, in a vane geometry rheometer at a rate of about 550 rpm to about 650 rpm, the viscosity is reduced by about 80%, about 75%, about 70%, about 65%, about 60%, about 55%, about 50%, about 45%, about 40%, about 35%, about 30%, about 25%, or about 20%. 
         [0025]    The water-soluble polymer disperses the asphaltene/solid aggregates into the aqueous mixture. 
         [0026]    The effective amount of the water-soluble polymer can be from about 20 ppm to about 500 ppm, from about 20 ppm to about 400 ppm, from about 20 ppm to about 300 ppm, from about 20 ppm to about 200 ppm, from about 20 ppm to about 100 ppm, from about 50 ppm to about 500 ppm, from about 50 ppm to about 400 ppm, from about 50 ppm to about 300 ppm, from about 50 ppm to about 200 ppm, from about 50 ppm to about 100 ppm, from about 80 ppm to about 500 ppm, from about 80 ppm to about 400 ppm, from about 80 ppm to about 300 ppm, from about 80 ppm to about 200 ppm, from about 80 ppm to about 150 ppm, from about 80 ppm to about 120 ppm, based on the total weight of the aqueous mixture comprising asphaltene/solid aggregates. 
         [0027]    The water-soluble polymer can comprise a polyanion, a polycation, a polar water-soluble polymer. 
         [0028]    The water-soluble polymer can comprise a polyanion. 
         [0029]    The polyanion can comprise a polyacrylic acid, poly(methyl methacrylate), a polystyrene carboxylic acid, a poly(maleic acid), a polystyrene sulfonic acid, a polyvinyl sulfonic acid, a poly(2-acrylamido-2-methylpropane sulfonic acid), a poly(3-acrylamido-3-methylbutanoic acid), or a combination thereof. 
         [0030]    The water-soluble polymer can comprise a sulfonated water-soluble polymer. 
         [0031]    The water-soluble polymer can comprise a polystyrene sulfonic acid, a polyvinyl sulfonic acid, a poly(2-acrylamido-2-methylpropane sulfonic acid), a poly(3-acrylamido-3-methylbutanoic acid), or a combination thereof. 
         [0032]    The water-soluble polymer can comprise a polystyrene sulfonic acid. 
         [0033]    The water-soluble polymer can comprise a poly(styrene sulfonic acid-co-maleic acid). 
         [0034]    The water-soluble polymer can comprise a polycation. 
         [0035]    The water-soluble polymer can comprise poly(melamine formaldehyde), poly(diallyldimethylammonium chloride), poly(diallyldiethylammonium chloride), poly(diethylaminoethyl methacrylate), poly(dimethylaminoethyl methacrylate), poly(methacryloyloxyethyltrimethyl ammonium sulfate), poly(methacryloyloxyethyltrimethyl ammonium chloride), poly(3-(methyacrylamido)propyltrimethyl ammonium chloride), or a combination thereof. 
         [0036]    The water-soluble polymer can comprise poly(melamine formaldehyde). 
         [0037]    The water-soluble polymer can comprise a polar water-soluble polymer. 
         [0038]    The polar water-soluble polymer comprises polyacrylamide, a poly(vinyl alcohol), a poly(vinvylpyrrolidone), or a poly(hydroxymethyl acrylate), or a combination thereof. 
         [0039]    Another aspect of method for determining viscosity, yield stress, or viscosity and yield stress of an asphaltene precipitate-containing aqueous mixture comprising charging a bitumen froth into a high pressure reactor fitted with a mixer and a temperature controller; charging a paraffinic solvent into a sampling cylinder in fluid contact with the high pressure reactor; heating the high pressure reactor to a temperature of from about 30° C. to about 95° C.; pressurizing the high pressure reactor by adding gas from a gas source in fluid contact with the high pressure reactor; contacting the paraffinic solvent with the bitumen froth to form a reaction mixture; mixing the reaction mixture; stopping the mixing and allowing the solids, water, and asphaltene precipitates to separate from the bitumen forming a bitumen layer and an aqueous layer; removing at least a portion of the bitumen layer from the high pressure reactor; contacting an effective amount of a water-soluble polymer for reducing viscosity, yield stress, or viscosity and yield stress with the aqueous layer; contacting additional paraffinic solvent with the remaining bitumen layer and aqueous layer to form a second reaction mixture; reheating the high pressure reactor to a temperature of from about 30° C. to about 95° C.; repressurizing the high pressure reactor by adding gas from a gas source in fluid contact with the high pressure reactor; mixing the second reaction mixture; stopping the mixing and allowing the water and asphaltene precipitates to separate from the bitumen forming a second bitumen layer and a second aqueous layer; removing at least a portion of the second bitumen layer from the high pressure reactor; and measuring viscosity, yield stress, or viscosity and yield stress of the second aqueous layer. 
         [0040]    The paraffinic solvent is a C 5  to C 7  paraffinic hydrocarbon solvent or a combination thereof. 
         [0041]    The temperature within the high pressure reactor ranges from about 30° C. to about 95° C., from about 30° C. to about 85° C., from about 30° C. to about 75° C., from about 40° C. to about 95° C., from about 40° C. to about 85° C., from about 40° C. to about 75° C., from about 50° C. to about 95° C., from about 50° C. to about 85° C., or from about 50° C. to about 75° C. 
         [0042]    The absolute pressure within the high pressure reactor is from about 50 psi to about 200 psi, from about 50 psi to about 180 psi, from about 50 psi to about 160 psi, from about 50 psi to about 150 psi, from about 70 psi to about 200 psi, from about 70 psi to about 180 psi, from about 70 psi to about 150 psi, from about 100 psi to about 200 psi, from about 100 psi to about 180 psi, or from about 100 psi to about 150 psi. 
         [0043]    The inert gas is nitrogen, argon, helium, or a combination thereof. Preferably, the inert gas is nitrogen. 
         [0044]    Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 
       EXAMPLES 
       [0045]    The following non-limiting examples are provided to further illustrate the present invention. 
       Example 1: High Temperature Paraffinic Froth Treatment (HTPFT) 
       [0046]    A simple laboratory bench unit was designed and built to evaluate treatment methods and new chemistries. This laboratory bench unit is represented by  FIG. 2 , which comprises a bench top reactor 65, a magnetic drive or mixer 60 with a power controller 55, a water bath 75 connected to a water jacket 70, a sampling cylinder 40, an ice bath 80, a cooling coil 85, an overflow sample collector 90, connecting lines and valves and an inert gas cylinder with a pressure regulator. 
         [0047]    The testing apparatus is used to evaluate various methods and new chemistries to obtain data with respect to performance and various method parameters (i.e., temperature, concentration, and time). 
         [0048]    Froth samples were collected, divided into 120 g samples, and analyzed using a Dean-Stark apparatus for various components (e.g., bitumen, water, and solids content). 
         [0049]    The amount of paraffinic solvent needed was based on the type of solvent and the solvent to bitumen ratio (S/B). 
         [0050]    The test method consisted of placing a reactor vessel 65 into a water jacket 70 that was preheated to 90° C. A 120 g sample of froth was placed into a glass jar and heated to 70° C. using a separate water bath. A paraffinic solvent was then added into a sampling cylinder 40 through the funnel, followed by closing both valves and increasing the temperature to 70° C. Once the glass jar containing the froth sample reached 70° C., it was then poured into the reactor vessel 65. 
         [0051]    At this point, known as chemical injection point one, a desired amount of water-soluble polymer was added into the reactor vessel 65. 
         [0052]    The reactor vessel 65 was then placed on its holder, engaged, and secured to the head unit. The water jacket 70 was then placed underneath the reactor vessel 65 in order to maintain the desired operating temperature. An inert gas was then added through line 1 and valve 20 to the reaction vessel 65 in order to increase the pressure to 80 psi. Following a leak check, the inert gas was vented from the reactor 65 through the vent valve 30 and the vent valve 30 was returned to the closed position. The bottom of the warmed sampling cylinder 40 was then connected to the sample inlet line 2 of the reactor vessel 65. The gas supply was then connected to the top side of the sampling cylinder 40 through valve 10. When the gas valve 10 was opened, the sampling cylinder 40 became pressurized which forced the hot paraffinic solvent into the reactor vessel 65. After the pressure inside the reactor vessel 65 reached 110 psi, the inlet valve 10 on the sampling cylinder was closed. After the reactor vessel 65 temperature reached 75° C., the motor was set to 40% power and turned on. The mixer speed was then set at 600 rpm. After five minutes of mixing, the motor was turned off. Once the solids/water/asphaltene aggregates settled, approximately two minutes, the sample outlet valve 35 was opened to allow the flow of the first stage overflow. The overflow was then collected after it passed through a cooling coil 85 immersed in an ice bath. After the pressure within the reactor vessel had dropped to 40 psi, the sample outlet valve 35 was closed. 
         [0053]    At this point, known as chemical injection point two, a desired amount of a water-soluble polymer could be added to the inlet line 2 without opening the reaction vessel 65. 
         [0054]    Hot paraffinic solvent was then added to the reactor vessel 65 by pairing it with a pre-heated pressure cylinder to the inlet line 2. An inert gas was used to pressurize the cylinder. The reactor vessel 65 was heated to 70° C. After the reactor vessel 65 reached the desired temperature, the motor was turned on and allowed to mix the contents for five minutes. Once the solids/water/asphaltene aggregates settled, approximately two minutes, the sample outlet valve 35 was opened to allow the flow of the second stage overflow. The overflow was then collected after it passed through a cooling coil 85 immersed in an ice bath. After the pressure within the reactor vessel had dropped to 40 psi, the sample outlet valve 35 was closed. 
         [0055]    At this point, also known as chemical injection point three, without opening the reaction vessel 65, a desired amount of a water-soluble polymer could be added to the inlet tubing 2 through valve 15. Nitrogen supply line 1 was used to pressurize the water-soluble polymer into the vessel 65. 
         [0056]    The impeller was run at 600 rpm for three minutes followed by depressurizing the system. After depressurizing, the vessel was opened and the second stage underflow sample was collected. The remaining tailings were removed with toluene and transferred to a HDPE bottle. 
         [0057]    The first and second stage overflow samples were subjected to Karl Fisher water content, solids/ash, and asphaltene suspension determination. 
         [0058]    The temperature of the reactor vessel and sampling cylinder was measured using a Type J thermocouple. 
       Example 2: Evaluation of Compositions Using the Bench-Scale HTPFT Setup 
       [0059]    The bench-scale HTPFT setup was used to evaluate compositions for their efficacy of increasing the fluidity of underflow stream and solvent recovery. The composition tested comprised 89.6595 wt. % water, 0.3959 wt. % hydroxymethyl urea, 0.3959 wt. % N,N′-bis(hydroxymethyl) urea, 0.9895 wt. % hydrochloric acid, 7.9162 wt. % formaldehyde-melamine copolymer hydrochloride, 0.09 wt. % formaldehyde, and 0.553 wt % melamine formaldehyde resin (identified as composition A hereinafter and commercially available from Nalco as Product No. PK-9512). 
         [0060]    The bench-scale HTPFT setup was used to evaluate composition A using the method described in Example 1. The key parameters used during the testing procedure are shown in Table 1. The amount of composition A used was 100 ppm of water-soluble polymer based on the total aqueous mixture treated. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Bench-scale HTPFT test parameters for composition A. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Temperature 
                 60° C. 
               
               
                   
                 Pressure 
                 80 psi 
               
               
                   
                 1 st  stage D/B (wt./wt., diluent 
                    1.75 
               
               
                   
                 to bitumen ratio) 
               
               
                   
                 2 nd  stage D/B (wt./wt.) 
                 20 
               
               
                   
                 estimation 
               
               
                   
                 Mixing at 1 st  and 2 nd  stage 
                 600 rpm for 5 min. 
               
               
                   
                   
               
             
          
         
       
     
         [0061]    A summary of the test results are shown in Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Bench-scale HTPFT test results using compositions A. 
               
             
          
           
               
                   
                   
                 100 ppm 
                 100 ppm 
                   
               
               
                   
                   
                 of A 
                 of A 
                 100 ppm 
               
               
                   
                   
                 added to 
                 added to 
                 of A 
               
               
                   
                   
                 1 st  stage 
                 2 nd  stage 
                 added to 
               
               
                 Simulation 
                 Blank 
                 underflow 
                 underflow 
                 froth 
               
               
                   
               
               
                 Test number 
                 1 
                 2 
                 3 
                 4 
               
               
                 Water % in first stage 
                 0.20% 
                 0.35% 
                 0.25% 
                 0.06% 
               
               
                 overflow 
               
               
                 Asphaltene suspension 
                  1.8% 
                  1.6% 
                  1.6% 
                  1.8% 
               
               
                 % in first stage overflow 
               
               
                 Solids content % in first 
                 ~250 ppm 
                 ~250 ppm 
                 ~250 ppm 
                 ~250 ppm 
               
               
                 stage overflow (volume 
               
               
                 reading) 
               
               
                 Maltene/asphaltene % in 
                 25.6% 
                 22.7% 
                 24.7% 
                 50.0% 
               
               
                 second underflow 
               
             
          
           
               
                 Physical 
                 Color 
                 Shining 
                 Black 
                 Matt black 
                 Black 
               
               
                 appearance 
                   
                 black 
               
               
                 of second 
                 Size 
                 Relatively 
                 Medium 
                 Medium 
                 Small 
               
               
                 underflow 
                   
                 big 
               
               
                   
                 Shape 
                 Irregular 
                 Granular 
                 Granular 
                 Granular 
               
               
                   
                 Stickiness 
                 Medium 
                 Low 
                 Low 
                 Medium 
               
               
                   
               
             
          
         
       
     
       Example 3: Evaluation of Compositions by Rheology Analysis of Underflow Samples Using the HTPFT Apparatus 
       [0062]    The bench scale HTPFT setup was used to evaluate various compositions for their efficacy of enhancing the rheology of underflow streams using the method described in Example 1. The compositions tested comprised composition A, 82 wt. % water and 18 wt. % polystyrene sulfonic acid (identified as composition B hereinafter), 75 wt. % water and 25 wt. % poly(styrene sulfonic acid-co-maleic acid) (identified as composition C hereinafter). 
         [0063]    The key parameters used during the testing procedure are shown in Table 1. A summary of the rheology test results are shown in Table 3. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Bench scale HTPFT rheology test results 
               
             
          
           
               
                 Sample 
                 Yield stress (Pa) 
                 Viscosity (cP) 
               
               
                   
               
             
          
           
               
                 Blank 
                 187 
                 341 
               
               
                 A 
                 48 
                 125 
               
               
                 B 
                 39 
                 92 
               
               
                 C 
                 35 
                 83 
               
               
                   
               
             
          
         
       
     
         [0064]    When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0065]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
         [0066]    As various changes could be made in the above methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.