EASILY DISPERSIBLE POLYMER POWDER FOR HYDROCARBON EXTRACTION

Abstract

A dry polymer powder for use in enhanced petroleum recovery without being prehydrated before being added to water or brine to be introduced into a wellhead. The dry polymer powder consisting of at least one of a polyacrylamide, a copolymer of acrylamide and acrylic acid, a functionalized derivatives thereof, a galactomannan, or cellulosic polymer or derivatives thereof, and the polymer can be crosslinked or not crosslinked, provided that if they are homo- or co-polymers of acrylic acid, they are not crosslinked. The dry polymer powder is sized between two size limits, namely at least about 85 wt % of particles of a size smaller than about 40-mesh, and at least 75 wt % of particles of a size greater than 200-mesh, which size range ensures that the dry polymer powder will efficiently hydrate in the water or brine within about one minute without forming fisheyes.

Claims

1. A dry polymer powder for use in the petroleum industry for enhanced petroleum recovery, comprising dry polymer powder sized between two size limits, namely at least about 85 wt % of particles of a size smaller than 40-mesh, and at least 75 wt % of particles of a size greater than 200-mesh.

2. The dry polymer powder of claim 1, the polymer size range ensures that the dry polymer powder will efficiently hydrate in the water or brine within about one minute without forming fisheyes.

3. The dry polymer powder of claim 1, further comprising at least one additive selected from the group consisting of water soluble electrolytes/salts, oxygen scavengers, scale inhibitors, corrosion inhibitors, fluid-loss additives, bactericides, clay stabilizers, and surfactants.

4. The dry polymer powder of claim 3, wherein the surfactant comprises a block polymer nonionic surfactant.

5. The dry polymer powder of claim 3, wherein the water soluble electrolytes/salts comprise alkaline and alkaline earth metals and ammonia salts or salts of water-soluble amines, sodium, potassium, and ammonium salts of chlorides, sulfates, phosphates, acetates, formates, and methanesulfonates.

6. The dry polymer powder of claim 1, wherein the dry polymer powder comprises at least one of a polyacrylamide, a copolymer of acrylamide and acrylic acid, a functionalized derivative thereof, a galactomannan, or a cellulosic polymer or derivatives thereof, wherein the polymer can be crosslinked or not crosslinked, provided that if they are homo- or co-polymers of acrylic acid, they are not crosslinked.

7. The dry polymer powder of claim 1, wherein the proportion of polymer particles smaller than 100-mesh (˜150 microns) is between 10% and 50% of the total polymer particles.

8. The dry polymer powder of claim 1, wherein the proportion of polymer particles between 60-mesh and 100-mesh (˜205 to ˜150 microns) is between 10% and 30% of the total polymer particles.

9. The dry polymer powder of claim 6, the dry polymer powder has a particle size distribution of <40 mesh=about 50.3%, 40 to 100 mesh=about 38.2%, 100 to 140 mesh=about 10.9%, 140 to 200 mesh=about 0.2%; 200 to 325 mesh=about 0.2%, and >325 mesh=about 0.2%.

10. A dry polymer powder for use in the petroleum industry for enhanced petroleum recovery, comprising a dry polymer powder selected from the group consisting of at least one of a polyacrylamide, a copolymer of acrylamide and acrylic acid, a functionalized derivative thereof, a galactomannan, or a cellulosic polymer or derivatives thereof, wherein the polymer can be crosslinked or not crosslinked, provided that if they are homo- or co-polymers of acrylic acid, they are not crosslinked, wherein the dry polymer powder is sized between two size limits, namely at least about 85 wt % of particles of a size smaller than about 40-mesh, and at least 75 wt % of particles of a size greater than 200-mesh, and wherein the polymer size range ensures that the dry polymer powder will efficiently hydrate in the water or brine within about one minute without forming fisheyes.

11. The dry polymer powder of claim 10, further comprising at least one additive selected from the group consisting of water soluble electrolytes/salts, oxygen scavengers, scale inhibitors, corrosion inhibitors, fluid-loss additives, bactericides, clay stabilizers, and surfactant.

12. The dry polymer powder of claim 11, wherein the surfactant comprises a block polymer nonionic surfactant.

13. The dry polymer powder of claim 11, wherein the water soluble electrolytes/salts comprise alkaline and alkaline earth metals and ammonia salts or salts of water-soluble amines, sodium, potassium, and ammonium salts of chlorides, sulfates, phosphates, acetates, formates, and methanesulfonates.

14. A method for using the dry polymer powder of claim 1 as a friction reducer in fracking water, comprising adding the dry polymer powder of claim 1 directly to a stream of fresh water or brine without pre-hydrating the dry power before introducing it to fresh water or brine.

15. The method for using the dry polymer powder of claim 14, wherein the dry polymer powder comprises at least one of a polyacrylamide, a copolymer of acrylamide and acrylic acid, a functionalized derivatives thereof, a galactomannan, or cellulosic polymer or derivatives thereof, wherein the polymer can be crosslinked or not crosslinked, provided that if they are homo- or co-polymers of acrylic acid, they are not crosslinked, and wherein the polymer size range ensures that the dry polymer powder will efficiently hydrate in the water or brine within about one minute without forming fisheyes.

16. The method for using the dry polymer powder of claim 15, wherein the dry polymer powder further includes at least one additive selected from the group consisting of water soluble electrolytes/salts, oxygen scavengers, scale inhibitors, corrosion inhibitors, fluid-loss additives, bactericides, clay stabilizers, and surfactants.

17. The method for using the dry polymer powder of claim 16, wherein the at least one additive comprises a block polymer nonionic surfactant.

18. The method for using the dry polymer powder of claim 16, wherein the at least one additive is a water soluble electrolytes/salt selected from the group consisting of alkaline and alkaline earth metals and ammonia salts or salts of water-soluble amines, sodium, potassium, and ammonium salts of chlorides, sulfates, phosphates, acetates, formates, and methanesulfonates.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a diagrammatic sketch of the added on-the-fly operation mode to directly introduce dry friction reducer powder into main hydraulic fracturing fluids just prior to be pumped by high pressure pumps to a well's borehead.

[0020] FIG. 2 is a plot of friction reduction performance versus time of the ground MAX-165 and its precursor MAX 165.

[0021] FIG. 3 is a plot of friction reduction performance versus time of the dry polymer powder at specifically selected particle size zones.

[0022] FIG. 4 is a plot of friction reduction performance versus time of the ground MAX-165 at various concentrations mixing with 2% KCl.

[0023] FIG. 5 is a plot of friction reduction performance versus time of the ground MAX-165 and salt mixture in the presence of different concentrations of selected surfactant.

[0024] FIG. 6 is a plot of friction reduction performance versus time of the ground MAX-165 under various pre-hydration conditions.

DETAILED DESCRIPTION

[0025] In certain embodiments, the polymer powder is sized between two size limits, namely at least 86, 90, or 95 wt %, or any wt % between any two of these values, of particles of a size smaller than 40-mesh (˜425 microns), and at least 76, 80, 85, 90, or 95 wt %, or any wt % between any two of these values, of particles of a size greater than 200-mesh (˜75 microns). All references used herein for mesh sizes of the invention are in ASTM/U.S. Standard sizes.

[0026] In one embodiment, the polymer powder having at least 85 wt % of particles of a size smaller than 40-mesh (˜425 microns) and at least 75 wt % of particles of a size greater than 200-mesh (˜75 microns) have particles selected from −40+60 mesh (˜425 to ˜250 microns), −60+100 mesh (˜205 to ˜150 microns), −100+140 mesh (˜150 to ˜106 microns), or −140+200 mesh (˜106 to ˜75 microns). In some embodiments, the proportion of polymer particles smaller than 100 mesh (˜150 microns) is greater than 10%, 20%, 30%, 40%, or 50% by weight of the total polymer particles or a percentage between any two of these. In some embodiments, the proportion of polymer particles between 60-mesh and 100-mesh (˜205 to ˜150 microns) is greater than 10%, 20%, or 30% by weight of the total polymer particles or a percentage between any two of these.

[0027] In some embodiments, inversion time is less than about 60 s, 50 s, 40 s, 30 s, 20 s, or 15 s, or a value between any two of these. In some embodiments, maximum friction reduction efficiency achieved is greater than 40%, 42%, 44%, 46%, 48%, or 50%, or a percentage between any two of these. In some embodiments, friction reduction efficiency at 20 min is greater than 25%, 26%, 27%, 28%, 29%, or 30%, or a percentage between any two of these.

[0028] The dry polymer can be polymerized by any suitable method known in the art. In certain embodiments, the polymer is polyacrylamide or a copolymer of acrylamide and acrylic acid, or functionalized derivatives thereof. The functionalization consists in incorporating charged (anionic, cationic, amphoteric) or pendant hydrophilic or hydrophobic groups onto the polymer backbone. This can be achieved by adding specialty monomers during polymerization or carrying out further reactions post polymerization. In one embodiment, the polymer is polyethylene oxide or derivatives thereof. In another embodiment, the polymer is a galactomannan or cellulosic polymer or derivatives thereof. The polymers can be crosslinked or not crosslinked, provided that if they are homo- or co-polymers of acrylic acid, they are not crosslinked. Particles of mesh −40, +100 (between ˜425 and ˜150 microns) may comprise greater than about 25% by weight of the total polymer in dry form in certain embodiments.

[0029] While dry polymer in the size ranges noted above will provide exceptional functionality as a friction reducer without additives, the addition of water soluble electrolytes/salts and block polymers can be beneficial in the formulations of the invention.

[0030] Accordingly, one or more water-soluble electrolytes/salts in finely divided form include without limitation salts of alkaline and alkaline earth metals and ammonia salts or salts of water-soluble amines can optionally be added to the formulation. In some embodiments the salts are the sodium, potassium, and ammonium salts of anions such as chlorides, sulfates, phosphates, acetates, formates, and methanesulfonates. Salts should be in finely divided form. In one aspect, salts in finely divided form have a particle size less than about 500 microns.

[0031] The optional block polymer is a block polymer nonionic surfactant that is, however, not a silicone surfactant. The block polymer should not be confused with the polymer in dry form, the latter being generally a high molecular weight polymer. In some embodiments, the block polymer is a triblock copolymer composed of both ethylene oxide and propylene oxide units, and variously known or branded as Poloxamer, Pluronic® (BASF), Antarox® (Solvay), Synperonic (Croda), Epan (DKS), and by other names from other suppliers. Certain embodiments of the invention can further comprise surface active agents other than block polymer nonionic surfactants.

[0032] Friction reduction efficiency is determined by a loop test well known in the art using inventive compositions with a polymer concentration at for example around 1 pound per thousand gallons (pptg) or around 0.012 wt %. Persons skilled in the art would understand that friction reduction can be achieved at other dilute polymer concentrations.

[0033] Embodiments of the invention may further contain other solid additives and chemicals known to be commonly used in oilfield applications by those skilled in the art, in sufficient amounts as to be useful for a treatment fluid in such applications. These include, but are not necessarily limited to, materials such as oxygen scavengers, scale inhibitors, corrosion inhibitors, fluid-loss additives, bactericides, clay stabilizers, surfactants (in dry form, possibly absorbed or adsorbed onto an inactive support material) to reduce capillary pressures or surface tension, and the like. Non-limiting examples of some suitable scale inhibitor include phosphonate, phosphate esters, and the like. Any suitable biocides may be used in embodiments of the invention.

[0034] The polymers of the present embodiments should have a molecular weight (MW) sufficient to provide a desired degree of friction reduction or ability to increase viscosity of the aqueous-based hydraulic fracturing fluid. They may have a weight average MW in the range from about 500,000 g/mol to about 60,000,000 g/mol, as determined by intrinsic viscosity methods. The one or more block polymer surfactants may have a hydrophilic-lipophilic balance (HLB) of at least 6, at least 12, or at least 20 (or values between these), and may be added as a mixture of surfactants having different HLB values.

[0035] In some embodiments of the invention the acrylamide monomer accounts for 10 mole % to 95 mole % of the polymer in the polymerization reaction, or 10 mole % to 70 mole % in some embodiments, and the one or more other monomers, including for example, (meth)acrylic acid or various acrylic sulfonic acids and salts thereof, account for 1 mole % to 60 mole % of the polymerization reaction, or 5 mole % to 40 mole % in some embodiments. In other embodiments, the one or more specialty monomers used for functionalization, including hydrophobic monomers, account for 0.5 mole % to 20 mole % of the polymer in the polymerization reaction, or 1 mole % to 10 mole % in certain embodiments. Acrylates can result from acrylamides by caustic hydrolysis, and quaternary ammonium groups can result from quaternization of tertiary amines. The mole percentages of polymer units in a polymerized product of the present invention can be described by the same mole percentages provided herein to characterize monomer incorporation. The polymerization reaction can be carried out by methods known in the art, for example free radical chain polymerization, employing suitable initiators and redox initiation systems.

[0036] The polymers of the present embodiments should be included in the solution or dispersion in an amount sufficient to provide the desired friction reduction or other functions. In some embodiments, polymers comprise at least 0.005% by weight of the solution or dispersion. In some embodiments, polymers account for a percentage by weight of the solution or dispersion total that is 0.006%, 0.008%, 0.01%, 0.012%, 0.014%, 0.016%, 0.018%, 0.02%, 0.022%, 0.024%, 0.026%, 0.028%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any percentage by weight in a range delimited by any two of these. Different relative amounts, or ratios, of the polymer in dry from to the water-soluble salt or block polymer surfactant are effective. In one embodiment, the ratio by weight of the polymer to the optional water-soluble salt is in the range of about 4:1 to about 1:4.

[0037] In other embodiments, the composition comprising polymer powder, water soluble salts, and block polymer surfactants may be combined with an aqueous diluent to form a treatment fluid. Examples of the aqueous diluent include, but are not limited to, DI water, fresh water, brine, seawater, flowback water, produced water, and recycled water. Present embodiments of both the composition and method can be practiced at a temperature ranging from about 10° C. to about 120° C., and especially from about 20° C. to about 95° C.

EXAMPLES

[0038] Detailed friction reduction performance evaluation procedure has been published in our recent presentation to the Society of Petroleum Engineers (SPE-171025). Specifically, friction reduction was evaluated using a recirculating flow loop. A constant high rate of flow is maintained for a testing fluid in the loop, which in Applicant's apparatus comprises two tubing sizes, 1 inch (˜2.54 cm) and ¾ (˜1.9 cm). Two different sets of pressure transducers on the loop measure pressure differentials across a 10 foot (˜3 m) test section of the ¾ inch (˜1.9 cm) tubing. Other than the loop itself, the loop assembly consists of one 6.9 U.S. gallon (˜26 L) reservoir with an overhead mixer, a progressive cavity pump usually operated to supply 65 psi of pressure, a flow meter, and a data acquisition unit. Fluids were pumped at 25 U.S. gallons per min (˜94.6 L/min). All tests were performed at ambient temperature. In this procedure, the reservoir was first filled with tap water, then KCl slowly added to 2% by weight and recirculation allowed to continue for 5 min for complete salt dissolution. Thereafter the Applicant started to collect pressure difference across the test section versus time. Data for the untreated brine served as a baseline. A sample was then loaded into the reservoir at 120 ppm, or other concentrations as specified in each case, and pressure difference data again collected.

[0039] Three performance parameters are calculated from the percentage friction reduction (% FR) versus time, which is determined using the following equation: % FR=(dP untreated fluid−dP treated fluid)/dP untreated fluid*100 (Equation 1), where dP means the pressure difference across the loop's test section. These three parameters are (i) the maximum friction reduction (Max FR), which is the maximum % FR that can be attained; (ii) inversion/hydration time (T_inv), which is defined as the time it takes to reach 90% of Max FR; and (iii) the friction reduction after 20 minutes (FR20), which is the % FR still maintained after 20 minutes.

[0040] In the field of fracking, the so-called base fluid/carrier is almost never fresh water alone, but typically is a brine solution—indeed the formation water is a brine. 2% KCl is a simple way in laboratory studies to mimic this reality, and is represented in Examples 1-5. Thus, this small percentage should be considered as a “base” or “background” level of salt, not extra salt. In some studies a more complex mixture of salts or total dissolved solids (TDS) are made or obtained, up to 7 or 10%. However, 20%˜25% total added salt NaCl (see Examples 4 and 5) would be considered extra salt, going above and beyond a “base” or “background” level.

[0041] The procedure for the dissolution and fisheyes tests are as follows: 2000 ppm active selected polymer was poured into 250 mL distilled water at 500 rpm and stirred for 1 minute; then the resulting solution was poured through a screen (about 20 mesh), then rinsed with 2000 mL tap water; the residual solid contents (if any) on the screen were collected and transferred onto a clean foil pan; the foil pan was dried for 2.5 hours in an 80° C. oven to observe the formation and the size or quantity of solid gel (if any).

Example 1

[0042] A commercial polyacrylamide-based dry polymer powder, MAX-165, offered by the Applicant ChemEOR, Inc. was used as the baseline. Particulars on the particle size distribution of the batch/lot of MAX-165 tested are as follows: Mesh <40 mesh=50.3%; 40 to 100 mesh=38.2%; 100 to 140 mesh=10.9%; 140 to 200 mesh=0.2%; 200 to 325 mesh=0.2%; and >325 mesh=0.2%. Friction reduction performances of polymer powders with selected range of particle sizes were summarized as follows. All tests were conducted with 120 ppm active polymer in 2% KCl solution (to mimic a typical background level of salinity.)

TABLE-US-00001 Range of Particle Size Max FR T_inv FR20 MAX 165 as is 41.51 70 29.13  <40 mesh 46.18 120 27.61  40-100 mesh 47.01 55 28.24 100-140 mesh 49.9 26 27.67 140-200 mesh 47.56 21 27.41 200-325 mesh 41.94 15 27.74 >325 mesh 41.51 15 26.49

[0043] The dissolution and fisheyes testing results as summarized as follow:

TABLE-US-00002 Range of Particle Undissolved Dry Weight of Size Fisheye Particle Fisheyes (g)  <40 mesh No Yes 0  40-60 mesh No Yes 0  60-100 mesh No No 0 100-140 mesh Yes No 0.068 140-200 mesh Yes No 0.221 200-325 mesh Yes No 0.180 >325 mesh Yes No 0.235

[0044] These data show that shorter hydration time can be attained by reducing the particle sizes of polymers; and the smaller the particle sizes are, the shorter the hydration time can be attained. In particular, the hydration time is less than 1 minute when the particle size of polymers is smaller than 40 mesh (420 microns). However, the dissolution rate and the tendency of the fisheyes formation are in conflict. When the particle sizes become smaller, the tendency to form fisheyes increases. These data also show that there exists a narrow range of the particle size, within which the hydration time is less than 1 minute and there will not be formation of fisheyes. The range is within 60-100 mesh, or 150˜250 microns.

Example 2

[0045] A polymer composition was tested for friction reduction performance having particles 93.4% by weight of a size smaller than 40 mesh (420 microns), and 92% by weight of a size greater than 200 mesh (74 microns), wherein particles of sizes from 40 to 200 mesh comprise 85.4% by weight of the total. A hydration time of less than 1 min was attained, and no fisheyes formation observed. The test was conducted with 120 ppm active polymer in 2% KCl solution.

TABLE-US-00003 Range of Particle Size Max FR T_inv FR20 Ground MAX-165 (93.4% −40 mesh; 45.71 48 28.58 92% +200 mesh; 85.4% −40 +200 mesh

[0046] These data show that by eliminating larger particle sizes, that is, in particular, those of particle sizes greater than 40 mesh, in the dry polymer composition, a sufficiently short hydration time of less than 1 minute is achievable. By simultaneously also eliminating those very fine particle, in particular of sizes smaller than 200 mesh, the formation of fisheyes can be avoided. Thus, a dry polymer composition having a great majority of polymer particles sized between about 40 to 200 mesh results in a composition that has exceedingly fast inversion times without formation of fisheyes.

Example 3

[0047] The polymer composition of EXAMPLE 2, herein denoted as “Ground MAX-165”, is blended with various concentrations of the NaCl salt. All percentages are by weight, and all tests were conducted at 120 ppm active polymer in 2% KCl solution. No fisheye formation was observed in any of these tests. These data show that the addition of salt substantially improves polymer hydration.

TABLE-US-00004 Range of Particle Size Max FR T_inv FR20 25% Ground MAX-165 + 75% NaCl 43.92 35 26.67 50% Ground MAX-165 + 50% NaCl 44.81 46 28.69 75% Ground MAX-165 + 25% NaCl 45.22 44 28.56

Example 4

[0048] Various concentrations of a surfactant, Pluronic® F-68, a nonionic oligomeric surfactant powder (offered by BASF Corporation), are added to a polymer-salt mixture composition. The positive effect of the surfactant additive on polymer hydration as exhibited by shortened T_inv's is surfactant concentration dependent. Adverse effect seen in terms of Max FR decrease is relatively small. A small amount of this type of surfactant, up to 3% at least, can substantially improve polymer hydration.

TABLE-US-00005 Range of Particle Size Max FR T_inv FR20 Ground MAX-165 + 25% NaCl + 1% F68 48.68 57 30.32 Ground MAX-165 + 25% NaCl + 2% F68 45.93 49 33.75 Ground MAX-165 + 25% NaCl + 3% F68 46.68 40 34.46

Example 5

[0049] Conventional dry polymer products are also subject to conventional handling, which requires pre-hydration. In this example, an 80% Ground MAX-165+20% NaCl mixture is either added on the fly (inventive—first line in table below) or pre-hydrated (and as part of the standard pre-hydration practice first sheared for various times). Their performance is compared. Under fresh water condition, higher polymer concentrations (240-300 ppm) are used. Runs lasted 400 seconds (˜6.6 minutes) to test the effect of pre-hydration under shearing on Max FR and T_inv. FR20 was not tested.

TABLE-US-00006 Polymer Pre- Concen- hydration tration shear rate Max Condition (ppm) (RPM) FR T_inv RF20 Unhydrated “on-the-fly” 240 — 76 30 — polymer powder  1 minute pre-hydration 240 3000 78 27 —  1 minute pre-hydration 240 9000 70 22 —  5 minute pre-hydration 240 3000 75 21 —  5 minute pre-hydration 240 9000 44 20 — 300 minute pre-hydration 240 1000 66 20 — 300 minute pre-hydration 300 1000 68 19 —

[0050] Under low shearing conditions (1000˜3000 RPM), the negative effect of hydration on decreased Max FR is relatively small. Even after 5 hours of hydration at 1000 RPM shearing, only about 10% in Max FR reduction was observed. However, high shearing had more significant adverse effects on Max FR. At 9000 RPM shearing, even 5 minute of pre-hydration significantly reduces MAX FR, by more than 40%. Polymer powders begin to dissolve during the pre-hydration process and are subject to shear degradation.

Example 6

[0051] The dry polymer powders (80% Ground MAX-165+20% NaCl) is pre-hydrated at 1000 RPM for 300 minute (5 hours), then friction reduction performance tests are carried out in API (American Petroleum Industry) brine (which is water with 8% NaCl+2% CaCl.sub.2 to mimic heavy brine) and compared with the performance of the same polymer powder added on-the-fly. The main focus of this example is to compare initial friction reduction performance, only 400 seconds (˜6.6 minutes) runs were conducted in these tests, so there are not FR20 data given. Under the API (American Petroleum Industry) brine condition, the added on-the-fly mode has better friction reduction performance than the long-time pre-hydration mode. After long-time exposure to various cationic compounds in the API brine, polymers degrade even under relatively slow shearing. Therefore, under heavy brine conditions, such as those recycling the flowback water or produced water, the added on-the-fly mode of the dry friction reducer will perform better than the pre-hydration mode.

TABLE-US-00007 Polymer Pre-hydration Concentration shear rate Max Condition (ppm) (RPM) FR T_inv RF20 on-the-fly 240 — 42 37 — 300 minute 240 1000 9 44 — pre-hydration

[0052] Accordingly, as can be appreciated from the Example above. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention.