CA2890665A1 - Aqueous drilling fluids for dual polymer encapsulation - Google Patents

Abstract

An aqueous drilling fluid is provided for use in steam assisted gravity drainage (SAGD) recovery of bitumen from oil sands. The aqueous drilling fluid consists of at least two oppositely charged water soluble polymers. The drilling fluid causes the encapsulation of bitumen to prevent the accretion thereof on the drill string and other equipment which comes into contact with zones of rock or soil containing bitumen. A method of providing more efficient encapsulation of the bitumen is provided. The method comprises of applying two oppositely charged polymers either sequentially or simultaneously.

Description

AQUEOUS DRILLING FLUIDS FOR DUAL POLYMER ENCAPSULATION
TECHNICAL FIELD
[0001] The present disclosure relates to the extraction of bitumen deposits from oil sands by steam assisted gravity drainage (SAGD). More particularly the disclosure relates to a drilling fluid to prevent the accretion bitumen on the drill string and other equipment which comes into contact with zones of rock or soil containing bitumen.
BACKGROUND

[0002] Bitumens are known to be comprised of an exceedingly large number of organic molecules which, in the case of the Alberta oil sand bitumen (AOSB), range from the simplest organic molecule, methane, to large polymeric molecules having molecular weights in excess of 15,000. In the AOSB hundreds of organic molecules representing paraffinic, olefinic, aromatic and heterocyclic structures with various functional groups have been identified. Most of these molecules are neutral but some have acidic or basic functions and are capable of salt formation. Others, by virtue of their skeletal or functional reactivity, may form n-bonded, hydrogen bonded or charge transfer complexes. While most of the constituent molecules are stable; some are relatively unstable and can undergo thermal decomposition even well below room temperature.

[0003] A major problem with drilling in rock or soil formations containing bitumen is that the heavy tar-like bitumen accretes to drilling equipment including the drill string. Drilling operators must frequently halt the drilling, and take the drilling equipment out of service in order to remove bitumen accretion on the drill string and other equipment which comes into contact with the bitumen.

[0004] Water-based drilling fluids that contain solvents or wetting agents as anti-accretion additives are known and some were disclosed in the Canadian patents 2454312, 2481543, 2451585 and 2437522. These solvent and/or surfactant systems rely on the solvent's ability to dissolve bitumen.

[0005] More recent anti-accretion drilling fluid additives reported in the patent literature consist of polymers such as non-ionic, cationic and hydrophobically associating polymers. These polymer additives are believed to prevent accretion of the bitumen or heavy oil to metal surfaces via an encapsulation mechanism that involves the formation of an ion pair between the cationic functionalities on the encapsulating polymer and the negative charges found in the composition of bitumen. This mechanism is supported by the experimental observation that polymers with increasing cationic charge provide better encapsulating and anti-accretion properties. Encapsulation systems are described in Canadian patents 2508339, 2624834 and 2635300.

[0006] Drilling fluids of the prior art that include a cationic polymer have the disadvantage that they can be incompatible with other drilling fluid additives used as viscosifiers, rheology modifiers and/or fluid loss control agents More specifically, the cationic polymer can coagulate polymers added as viscosifiers and decrease the overall viscosity and carrying capacity of the drilling fluid.
This is particularly problematic in horizontal wells such as those drilled in SAGD
operations.

[0007] The conventional wisdom regarding the formulation of drilling fluids indicates that the use of cationic polymers for the encapsulation of bitumen in drilling fluids) poses a compatibility problem with the conventional anionic drilling fluid additives, such as, polyanionic cellulose (PAC) and xanthan gum, because of the cationic/anionic interaction of the polymers.

[0008] Opposite ion interaction has always been happening in the drilling fluids industry but more often than not it was viewed as an undesirable effect.
Typically, aqueous drilling fluids contain anionic polymers like xanthan gum and carboxymethyl cellulose and the engineers avoid the addition of oppositely charged polymers mainly because of the unpredictability of the effects of the unwanted and undesirable interaction of the oppositely charged polymers on the rheological properties of the drilling fluid. The cationic/anionic interaction makes it very difficult to control the rheology and filtrate loss when using cationic polymers in a drilling fluid.

[0009] The use of cationic polymers for bitumen encapsulation has been reported in the Canadian patent CA 2,508,339, but the inventors attempted to prevent this interaction and its subsequent adverse effects on the rheological properties of the drilling fluid through the addition of salt. "For example, in drilling fluids comprising a viscosifier the addition of a salt, when used at a specific concentration, will prevent the attraction of the cationic polymer to the viscosifier if the viscosifier has an anionic charge (e.g. Xanthan gum). The ability of the salt to prevent this attraction is the result of the natural mobility of the salt cations, which are attracted to anionic sites of the viscosifier. Since the salt cations are smaller and more mobile than the cationic polymer they can move faster and closer to the viscosifier anionic sites, thereby repelling the cationic charge of the polymer, as like charges repel each other. Since the size of salt cations is at least an order of magnitude smaller than the polymer they cannot encapsulate the viscosifier. As such, the viscosifier is not pulled out of solution as it would be if it interacted with the cationic polymer. This salt/viscosifier interaction allows the viscosifier to fully hydrate and provide viscosity" (paragraph [0047]).

[00010] In addition, certain drilling fluids of the prior art that contain a non-ionic polymer do not perform well in certain geological formations and may not prevent accretion on drilling equipment to a satisfactory degree.

[00011] It is an object of the present invention to provide a drilling fluid having superior anti-accretion properties for bitumen.

[00012] It is a further object to provide a drilling fluid which does not suffer from the practical compatibility issues with other drilling fluid additives.

[00013] It is a further object to provide a drilling fluid which will perform well in most geological formations and which can be modified during the drilling process as different geological conditions are encountered.

SUMMARY OF THE INVENTION

[00014] An aqueous drilling fluid to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, said drilling fluid comprises an anionically charged water soluble polymer and a cationically charged water soluble polymer. The ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is 1:99 to 99:1 on dry weight of total applied polymer basis. A preferred ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is from 10:90 to 90:10. The most preferred ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is from 70:30 to 30:70 on dry weight of total applied polymer basis.

[00015] In accordance with an embodiment of the present invention one of the anionically charged water soluble polymer and the cationically charged water soluble polymer is a high MW polymer and its counter ion polymer is a lower MW

polymer. More particularly, one of the anionically charged water soluble polymer and cationically charged water soluble polymer has a weight-average molecular weight equal to or greater than 5,000,000 and its counter ion polymer has a weight-average molecular weight equal to or less than 4,000,000.

[00016] In accordance with an embodiment of the present invention, one of the anionically charged water soluble polymer and cationically charged water soluble polymer has a charge density greater than 50% while its counter ion polymer has a charge density lower than 20%.

[00017] In accordance with an embodiment of the present invention, each of the anionically charged water soluble polymer and the cationically charged water soluble polymer has a weight-average molecular weight of between 5,000,000 -15,000,000, and charge density of between 10-30%, and is present in a ratio of between 30:70 and 70:30.

[00018] In accordance with an alternate embodiment of the present invention, an aqueous drilling fluid to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, said drilling fluid comprises an anionically charged water soluble polymer and a cationically charged water soluble polymer. Each of the anionically charged water soluble polymer and the cationically charged water soluble polymer has a weight-average molecular weight of between 5,000,000 15,000,000 and charge density of between 10-30% and is present in an addition mixture in the ratio of between 30:70 and 70:30. The addition mixture comprises a fast soluble and a regular grade polymer.

[00019] In accordance with a further embodiment of the present invention, an addition mixture for adding to an aqueous drilling fluid to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, comprise an anionically charged water soluble polymer and a cationically charged water soluble polymer, each of which has a weight-average molecular weight of between 5,000,000 -15,000,000, and charge density of between 10-30%, and is present in the addition mixture in the ratio of between 30:70 and 70:30.

[00020] In accordance an embodiment of the present invention a method of encapsulating bitumen during drilling in subterranean wells having a bituminous formation comprises adding to a drilling fluid used in drilling into said wells an anionically charged water soluble copolymer and a cationically charged water soluble copolymer.

[00021] In accordance with another embodiment of the present invention, a method of encapsulating bitumen during drilling in subterranean wells having a bituminous formation comprising the steps of adding a water soluble polymer or group of polymers carrying the same charge to a drilling fluid, and once the drilling is commenced or the bituminous formation is penetrated, slowly adding a counter ion water soluble polymer or polymeric group to the drilling fluid. The steps of the method may be repeated cyclically.
BRIEF DESCRIPTION OF THE DRAWINGS

[00022] FIG. 1 shows a photograph of a section of carbon steel pipe after treatment with Anionic polymer-of approximate Mwt. Of 15,000,000 and anionic charge density of 10% according to the method in Example 1.

[00023] FIG. 2 shows a photograph of a section of carbon steel pipe after treatment with Cationic polymer of approximate Mwt. Of 8,000,000 and Charge density of 60% according to the method in Example 1.

[00024] FIG. 3 shows a photograph of a section of carbon steel pipe after treatment with nonionic Polymer -Mwt. 10,000,000 and Charge density of 1-3%
according to the method in Example 1.

[00025] FIG. 4 shows a photograph of a section of carbon steel pipe after treatment with 70% of Anionic (No.1) + 30% of Cationic (No.2) according to the method in Example 1.

[00026] FIG. 5 shows a photograph of a section of carbon steel pipe after treatment with 30% of Anionic (No.1) + 70% of Cationic (No.2) according to the method in Example 1.

[00027] FIG. 6 shows a photograph of a section of carbon steel pipe with no polymeric additives-blank- according to the method in Example 1.

[00028] FIG. 7 shows a photograph of a section of carbon steel pipe with AN
905 VHM according to the method in Example 2.

[00029] FIG. 8 shows a photograph of a section of carbon steel pipe with 20% FO 4490 Standard and 80% AN 905 VHM aaccording to the method in Example 2.

[00030] FIG. 9 shows a photograph of a section of carbon steel pipe with 20% FO 4490 Standard and 80% AN 905 VHM aaccording to the method in Example 2.

[00031] FIG. 10 shows a photograph of a section of carbon steel pipe with FO 4490 Standard aaccording to the method in Example 2.

[00032] FIG. 11 shows a photograph of the section of carbon steel pipe of FIG. 10 from a slightly different angle.

[00033] FIG. 12 shows a photograph of a section of carbon steel pipe with no anti-accretion additives-blank- according to the method in Example 2.

[00034] FIG. 13 shows a photograph of the section of carbon steel pipe of FIG. 12 from a slightly different angle.
DETAILED DESCRIPTION OF EMBODIMENTS

[00035] Coacervation encapsulation is a technology which has been used commercially since the 1950s in the pharmaceutical, fragrance and specialty products industries. The relatively limited number of polymeric agents which can be used in food preparations and the difficulty in dealing with encapsulates having both aqueous and lipid solubility properties have drastically limited the application of coacervation for flavor encapsulation in the food industry. A general discussion of these issues is provided by R. Versic in Flavor Encapsulation. American Chemical Society Symposium Series #370, S. Risch and G. Reneccius, Eds., 1988, Chapter 14, "Coacervation for Flavor Encapsulation,". Coacervation microcapsule systems can be generated in the form of simple coacervates and/or complex coacervates.

[00036] Simple coacervation includes a process wherein a single kind of hydrophilic polymeric material is caused to emerge from aqueous solution as a part of a separated liquid phase, by addition to the system, of some non-connplexing phase-separation-inducing material. The emergent phase contains a relatively high concentration of the hydrophilic polymeric material and that hydrophilic polymeric material does not rely solely on electrical charge or on complexing to sustain the phase separation.

[00037] Complex coacervation includes a process wherein at least two oppositely electrically-charged hydrophilic polymeric materials are caused to emerge from aqueous solution by being mutually attracted to and complexed with one another and by, thereby, having their solubility in the aqueous manufacturing vehicle decreased. In the instance of complex coacervation, the emergent phase contains substantially all of the electrically-charged hydrophilic polymeric material utilized in forming the complex.

[00038] While coacervation encapsulation has been widely used for the encapsulation of micron sized droplets of oily liquids inside of a polymer containing aqueous phase, it has rarely been practiced for encapsulation of larger particle size solids inside of an aqueous phase and in some case it was found that the ensuing encapsulation was mainly the result of the direct interaction of oppositely charged polymers on the surface of the particles.

[00039] In accordance with the present invention, at least two oppositely charged polymers added to a drilling fluid have been determined to provide improved encapsulation efficiency of bitumen by comparison with the use of either of the oppositely charged polymers alone. It should be understood that the number and type of polymers that can be incorporated in the drilling fluid is not limited as long as the charge interaction concept is followed. One can add as many polymers as practically feasible and mix them simultaneously or sequentially to achieve a net charge balance of anionic, cationic or nonionic. Nonionic homo and copolymers of polyacrylic and polyacrylamide type are among the polymers covered since they carry a residual anionicity which can be effectively used in the interaction process.

[00040] It should be further understood that drilling fluid may typically contain numerous additional components. In accordance with the present invention the aqueous drilling fluid, to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, comprises an anionically charged water soluble polymer and a cationically charged water soluble polymer; and further comprises one or more other components selected from the group consisting of fluid-loss control additives, weighting materials, rheology control additives, clay swelling control additives, anti-foaming agents, biocides, bridging agents, wetting agents, emulsifiers, lost circulation additives, water soluble lubricants, oil soluble lubricants, salts, buffering agents, corrosion inhibitors, acids, alkalis and mixtures thereof.

[00041] The Interaction Process

[00042] Without being bounded by any theory, the interaction of a cationic polymer and an anionic polymer typically forms an entanglement in the form of =
(A+B-M:B) rather than a chemical reaction of the type (A+B.- C)

[00043] The following drawing provides a useful visual representation of a complex coacervation system:
= r'gr) =
+
= 1;, =
40) = _ L_) Anionic polymef Cationic polymer Complex =Ku' yaks polpon complex hydrogtel ("Hydrogels: Methods of Preparation, Characterisation and Applications", Syed K.
H. Gulrez, Saphwan Al-Assaf and Glyn 0 Phillips Hydrocolloids Research Centre Glyndwr University, Wrexham United Kingdom)

[00044] The resulting complex coacervate is capable of efficiently encapsulating bitumen particles (not shown). The focus of the present invention is the selection of preferred combinations and ratios of cationic polymers and anionic polymers to form a complex coacervate to most efficiently encapsulate bitumen particles. The combinations and ratios are more important in the present invention than the presence or absence of any particular cationic or anionic polymer.

[00045] In a preferred embodiment, when one charged polymer or group of charged polymers are selected from higher molecular weight polymers, the counter ion polymer or group of polymers are selected from the lower molecular weight polymers. Without being bounded by any theory, it is believed that the higher molecular weight polymer(s) provides an incomplete encapsulation and the lower molecular weight polymer(s) complements the encapsulation by a bridging action.

[00046] In accordance with the present invention, it is preferred that the anionic polymers to be added to the drilling fluid will have a charge density ranging from 1% to 100%. The preferable range is between 5 to 70%; while the most preferable range is between 10 to 30%.

[00047] It is preferred that the cationic polymers to be added to the drilling fluid will have a charge density of 1% to 100% while the preferable range is between 5 to 70% and the most preferable range is between 10 to 30%.

[00048] The ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is 1:99 to 99:1 on dry weight of total applied polymer basis. Preferably said ratio is from 10:90 to 90:10 on dry weight of total applied polymer basis. Most preferably the ratio is from 70:30 to 30:70 on dry weight of total applied polymer basis. In the most preferable embodiment, a high molecular weight, low charge density (typically a charge density of less than 20%) polymer or group of polymers are accompanied by counter ion polymer or polymer group having a lower molecular weight and higher charge density (typically a charge density of greater than 50%).

[00049] The ratio of the quantities of cationically charged polymer to anionically charged polymer to be applied to the drilling fluid may be from 1 to 99 to 99 to 1 The preferred range is from 10to 90 to 90 to 10The optimal range is from 30 to 70 to 70 to 30.
Example 1:

[00050] Example 1 illustrates the efficacy of adding a high molecular weight anionic polymer with anionic charge density of 10% when it is followed by a cationic polymer of lower molecular weight of 7,000,000 and a cationic charge density of 60%.

[00051] Six (6) cylinders were filled with 300m1 of water, 0.5 grams of xanthan gum, and 0.5 grams of selected water soluble oppositely charged polymers to be tested. The anionic polymer was Alcomer TM 338 available from BASF with 10% anionic charge and molecular weight of approximately 15,000,000. The cationic polymer was Zeta TM 7557 (also available from BASF) with 60% cationic charge and molecular weight of approximately 7,000,000.

[00052] Six 1/4" carbon steel pipe sections 10 cm in length were placed one in each cylinder. 100 grams of bitumen was then added to each of the cylinders.
The cylinders were rolled for 24 hours and then the pipes were removed for visual examination of bitumen accretion. The following Table 1 summarizes the results of the visual examination of the six pipes.

[00053] Table 1 Sample Polymer Appearance No. After 24 Hours Of Rolling 1 Anionic-approx. Mwt. Of Some sticking 15,000,000 Charge density of 10%
2 Cationic-approx. Mwt. Of clean 7,000,000 Charge density of 60%
3 Nonionic-Mwt. Of 10,000,000 Fairly clean Charge density of 1-3%
4 70% of Anionic (No.1) and Very clean 30% of Cationic (No.2) 70% of Cationic (No.2) and Very clean 30% of Anionic (No.1) 6 Blank Sever bitumen accretion

[00054] Anionic polymers:

[00055] In the present application, "anionic polymers" refers to polymers which have one or more anionic or negatively charged groups attached to the polymer. Examples of anionic groups include, without limitation, carboxylate, sulfonate and phosphonate. Anionic polymers contain units of "anionic monomers". A "monomer" is a polymerizable moiety such as, but not limited to an allylic, vinylic or acrylic compound. An "Anionic monomer" means a monomer which possesses a net negative charge.

[00056] The weight-average molecular weight of anionic polymers for use in the present invention may be from as low as 1000 to as high as 50,000,000, so long as the polymer remains water soluble. A preferred weight-average molecular weight range is from 1,000,000 to 25,000,000, with the weight-average molecular weight range of from 5,000,000 to 15,000,000 being the most preferred. For the purposes of the present invention, an anionic polymer having a molecular weight in excess of 5,000,000 is considered to be a high molecular weight polymer, while an anionic polymer having a molecular weight below 4,000,000 is considered to be a low molecular weight polymer.

[00057] The anionic polymer may be wholly anionic or it may contain both anionic and non-ionic repeating units. The anionic polymer must always exhibit higher anionic charge density than the completely non-ionic polymers.
Generally the polymer comprises greater than 10 mole % anionic repeating units. In some applications the anionic polymer may comprise 50 to 100 mole % anionic repeating units whereas in other applications it may be desirable for the polymer to comprise at least 15 mole % and up to 50 mole % anionic repeating units.The anionic polymer has a water solubility of at least 0.01g/100 ml of water.

[00058] The anionic polymer is desirably prepared from at least one anionic water soluble ethylenically unsaturated monomer, optionally with at least one non-ionic monomer. By water soluble we mean that the monomer has a solubility of at least 0.01g/100 ml of water at 25 C. Such polymers may be prepared by any of the standard industrial processes for making polymers, for instance by solution polymerization, reverse phase suspension polymerisation or reverse phase emulsion polymerization. The anionic polymer thus may be provided in the form of beads, powder or emulsions.

[00059] Typically the anionic polymer is selected from the group consisting of polymers of ethylenically unsaturated carboxylic acid or sulphonic acid, for instance acrylic acid, maleic acid, itaconic acid or alkali metal salts thereof.
Alternatively the polymer may be formed from potentially monomers, for instance maleic anhydride. Typically the anionic polymer is selected from copolymers comprising acrylamide with monomers selected from methacrylic acid or 2-acrylamido-2-methylpropane sulphonic acid and salts thereof.

[00060] Preferably the anionic polymer is selected from copolymers comprising acrylamide with monomers selected from methacrylic acid or 2-acrylamido-2-methylpropane sulphonic acid and salts thereof.

[00061] Representative anionic monomers include but are not limited to acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-l-propanesulfonic acid, acrylamidomethylbutanoic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, allyl sulfonic acid, ally' phosphonic acid, sulfomethylated acrylamide, phosphonomethylated acrylamide and the water soluble alkali metal, alkaline earth metal, and ammonium salts thereof.

[00062] A typical, widely used, anionic polyacrylamide-acrylic acid copolymer is usually produced as follows:
- I
Na011 Acry !amide Acrylic acid --:C142¨CH C142¨CH-N112 ONa in Sodium Acry late Acrylatmde copolymer

[00063] NaOH can be replaced with other alkali metal bases or salts which would replace Na with the corresponding alkali metal.

[00064] Anionic polymers can be hydrophobically modified with hydrophobic moieties including but not limited to alkyl halides, sulfonates, sulfates, and organic acid derivatives. Examples of suitable organic acid derivatives include, but are not limited to, octenyl succinic acid, dodecenyl succinic acid and anhydrides, esters and amides of octenyl succinic acid or dodecenyl succinic acid. In certain exemplary embodiments, the hydrophobic compounds may have an alkyl chain length of about 4 to about 30 carbon atoms.

[00065] For example, anionic polymers include: hydrophobically modified sulfonated polyacrylamide, hydrophobically modified polymers derived from acrylic acid, methaacrylic acid, homopolymer of acrylic acid, acenaphthylene, 1 -vinylnaphthalene, acenphthylene, polyacrylic acid, methyl methacrylate, styrene, methyl methacrylate-acrylic acid copolymer, hydrophobically modified polyacrylates (HM-PA), Hydrophobically modified anionic cellulose derivatives, hydrophobically modified anionic starch derivatives, hydrophobically modified anionic guar derivatives as long as the water soluble polymer carries anionic charges.

[00066] Anionic, hydrophobic polysaccharides can have general structure:
R' R"
--- (G)-(G)-(G)-(G)- - -I
wherein R can be a hydrophobic vinyl polymer, G is a monosaccharide or substituted monosaccharide, R' and R", which may or may not be the same, can be selected from ¨R3¨COOH and ¨R3¨000-M', wherein R3 is a Ci to 04 alkylene group and M is an alkali or alkaline earth metal. The amount of the hydrophobic vinyl polymer can vary as much as necessary as long as the polymer remains water soluble. Hydrophobic vinyl polymer in the range from 0.1-10.0%
by weight of the polysaccharide is preferred.

[00067] Cationic Polymers

[00068] In accordance with the present invention, the cationic water-soluble polymer includes any water-soluble polymer which carries or is capable of carrying a cationic (positive) charge when dissolved in water, whether or not that charge-carrying capacity is dependent upon pH. The cationic polymer is a water soluble polymer containing a net positively-charged atom/s or associated group/s of atoms covalently linked to its polymer molecule or containing groups reasonably anticipated to become cationic. The polymer has a water solubility of at least 0.01g/100 ml of water.

[00069] Molecular weight of cationic polymers incorporated can be from as low as weight average molecular weight of 1000 to as high as 50,000,000 or as long as the polymer remains water soluble. Preferably from 1,000,000 to 25,000,000 and most preferably from 5,000,000 to 15,000,000. For the purposes of the present invention, a cationic polymer having a molecular weight in excess of 5,000,000 is considered to be a high molecular weight polymer, while a cationic polymer having a molecular weight below 4,000,000 is considered to be a low molecular weight polymer.

[00070] Examples of suitable cationic water-soluble polymer include poly(diallyldimethyl ammonium chloride), copolymers containing diallyldimethyl ammonium chloride and another monomer, poly(epichlorohydrin/dimethylamine), cationized starch, chitosan or copolymers of vinyl monomers having cationic amine or quaternary ammonium functionalities with water soluble spacer monomers such as acryl- amide, ethacrylamide, alkyl and dialkyl acrylamides, alkyl and dialkyl methacrylamides, alkyl acrylate, alkyl methacrylate, vinyl caprolactone, and vinyl pyrrolidone. The alkyl and dialkyl substituted monomers may have 01-07 alkyl groups. Other suitable spacer monomers include vinyl esters, vinyl alcohol (made by hydrolysis of poly- vinyl acetate), maleic anhydride, propylene glycol, and ethylene glycol.

[00071] The cationic amines can be primary, secondary, or tertiary amines.

[00072] Amine-substituted vinyl monomers can be polymerized in the amine form, and then optionally can be converted to ammonium by a quaternization reaction. Amines can also be similarly quaternized subsequent to formation of the polymer. For example, tertiary amine functionalities can be quaternized by reaction with a salt of the formula R'X wherein R' is a short chain alkyl, preferably a Ci-Cy alkyl, more preferably a 01-03 alkyl, and X is an anion which forms a water soluble salt with the quaternized ammonium.

[00073] Cationic amino and quaternary ammonium monomers may include, for example, vinyl compounds substituted with dialkyl- aminoalkyl acrylate, diallylaminoalkyl methacrylate, monoalkyl- aminoalkyl acrylate, monoalkylaminoalkyl methacrylate, trialkyl methacryloxyalkyl ammonium salt, trialkyl acryloxyalkyl ammonium salt, diallyl quaternary ammonium salts, and vinyl quaternary ammonium monomers having cyclic cationic nitrogen-containing rings such as pyridinium, imidazolium , and quaternized pyrrolidone, e.g., alkyl vinyl imidazolium, alkyl vinyl pyridinium, alkyl vinyl pyrrolidone salts. Suitable amine-substituted vinyl monomers for use herein include dialkylaminoalkyl acrylate, dia lkylaminoalkyl methacrylate, dialkylaminoalkyl acrylamide, and dialkylaminoalkyl methacrylamide.

[00074] The cationic polymers can also comprise mixtures of monomer units derived from amine- and/or quaternary ammonium-substituted monomer and/or compatible spacer monomers.

[00075] Some representative cationic monomers include dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, including, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethyaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts such as acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldiethylammonium chloride and diallyldimethyl ammonium chloride. Alkyl groups are .generally 01_4 alkyl.

[00076] In a non-limiting, preferable embodiment, the cationic polymer can be a cationic polyacrylamide.The cationic polyacrylamide is generally prepared by copolymerizing acrylamide with an ethylenically unsaturated cationic monomer.
In one embodiment, the cationic polyacrylamide generally have the structure:

-CH2 _________________________________ CH2 - x - 1 I

[00077] wherein x is a molar fraction of acrylamide or methacrylamide in the copolymer, y is a molar fraction of cationic comonomer in the copolymer, x and y are within the range of from 0 to 1 and (x+y)_-_-1, R1 is hydrogen or methyl, R2 is hydrogen or methyl, A1 is ¨0¨ or ¨NH¨, R3 is alkylene having from 1 to 3 carbon atoms or hydroxypropylene, R4, R5 and R6 are independently methyl or ethyl and X1 is an anionic counter ion, such as, for example, chloride, bromide, methyl sulfate, ethyl sulfate or the like.

[00078] In a preferred embodiment, R1 is hydrogen and the cationic monomer is selected from the group consisting of 2-acryloyloxyethyltrimethyl ammonium chloride (also known as AETAC or 2-((1-oxo-2-propenyl)oxy)-N,N,N-trimethyl-ethanaminium chloride), 2-methacryloyloxyethyltrimethyl ammonium chloride (also known as METAC or N,N,N-trimethy1-2-[(1-oxo-2-propenyl)oxy]-ethanaminium chloride,), 3-acrylamidopropyltrimethyl ammonium chloride (also known as APTAC

or N,N,N-trimethy1-3-[(1-oxo-2-propenyl)amino]-1-propanaminium chloride), 3-methacrylamidopropyltrimethyl ammonium chloride (also known as MAPTAC or N,N,N-trimethy1-3-[(2-methyl-1-oxo-2-propenyl)amino]-1-propanaminium chloride), and the like, including combinations. When a polymer is referred to as comprising a monomer or comonomer, it is understood that the monomer is present in the polymer in the polymerized form of the monomer or in the derivative from the monomer. However, for ease of reference the phrase comprising the (respective) monomer or the like may be used as shorthand.

[00079] The molar ratio of acrylamide (x) to cationic monomer (y) in one typically in the range of 0:1 to 0.95:0.05 with the proviso that the sum of the molar ratios of x and y adds up to 1. The cationic polyacrylamide can be random or block copolymers.

[00080] Cationic polymers may also be hydrophobically modified in accordance with the present invention, so long as they remain water soluble after modification and remain cationically charged. Non-limiting examples of water soluble hydrophobically modified cationic polymers include but not limited to hydrophobically modified cationic polyacrylamide, hydrophobically modified cationic cellulose, hydrophobically modified cationic starch, hydrophobically modified chitosan and so on.

[00081] In a non-limiting embodiment, the water soluble cationic polymer is a copolymer comprising acrylamide or substituted acrylamide such as methacrylamide, and cationic monomers that are acrylates or, quaternary or acid salt of an acrylate.

[00082] Sequential Application Of Oppositely Charged Polymers In the sequential addition method, one polymer or group of polymers carrying the same charge is added to the drilling fluid and once the drilling is commenced or the bituminous formation is penetrated, the counter ion polymer or polymeric group is then slowly added to the drilling fluid. The one or more particular anionically charged water soluble polymers and one or more particular cationically charged water soluble polymers are selected from the polymers discussed above.
Selection criteria and pairing of polymers is made from in accordance criteria relating to the ratios of charge density, molecular weight and ionic charge as discussed above. It should be understood that this process may occur cyclically or in a onetime manner, as necessitated by the particular drilling conditions.
Example 2 discussed below illustrates the results of sequential application of the anionically charged water soluble polymer and the cationically charged water soluble polymer.
Example 2

[00083] Five (5) cylinders were filled with 300m1 of water, 0.5 grams of xanthan gum, and 0.5 grams in total of selected water soluble oppositely charged polymers to be tested. The anionic polymer was AN 905 VHM, available from SNF Canada with 5% anionic charge and molecular weight of approximately 15,000,000 Dalton.
The cationic polymers were also sourced from SNF Canada. FO-4490 VHM
having a charge density of about 40% and approximate molecular weight of 10,000,000 Dalton and FO-4490 Standard with the same charge density of around 40% and approximate molecular weight of 4,000,000 Dalton.

[00084] Five 3/4" carbon steel pipe sections, of about 10 cm in length, were placed one in each cylinder. 100 grams of bitumen was then added to each of the cylinders. The cylinders were rolled for 24 hours and then the pipes were removed for visual examination of bitumen accretion. The following Table 2 summarizes the results of the visual examination of the five pipes.
Table 2 Sample Anti-accretion Appearance No. additive After 24 Hours Of Rolling 1 AN 905 VHM High Accretion 2 20% FO 4490 Standard and Excellent accretion 80% AN 905 VHM prevention 3 20% FO 4490 VHM and 80% AN 905 Very good accretion VHM prevention 4 FO 4490 Standard High accretion Blank Very high accretion

[00085] Simultaneous Application Of Oppositely Charged Polymers

[00086] In the simultaneous addition method, one polymer or group of polymers can be treated with additives or go through processes during or after polymerization in order to be dissolved faster than the counter ion polymer or group of polymers. For example US Patent No. 3,734,873 teaches a method of rapidly dissolving water-soluble vinyl addition polymers in water.

[00087] Alternatively, fast soluble grades of some water soluble polymers are commercially available and could be selected for use as one of the oppositely charged polymers. "Fast soluble" polymers would typically take less than an hour to dissolve; whereas, the regular polymers usually take a few hours to dissolve.
While the art has been kept proprietary, it is a well-known fact that the particle size plays a major role in the dissolution rate. Finer particles dissolve faster than larger ones. Also, changing the production method can change the dissolution rate of the same polymer. Coating the particles with some additives can also change the dissolution profile

[00088] The use of a fast soluble polymer together with a counter ion polymer which dissolves at a slower rate will allow the higher molecular weight polymer(s) to form the incomplete encapsulation and then the lower molecular weight polymer(s) to complement the encapsulation by a bridging action without the need to add the oppositely charged polymers in a stepwise fashion.

[00089] Fast soluble polymers can be dry blended with relevant amount of selected counter ion polymer, regular grade polymer or group of polymers and packaged as an additive mixture for addition to a drilling fluid. In onsite use in the drilling field the use of an additive mixture to drilling fluid offers multiple advantages. A drilling operator would only need to stock and store a single additive mixture to reduce accretion of bitumen on drilling equipment.
Moreover, the preferred ratio of oppositely charged polymers is already contained in the additive mixture. This eliminates the need for the operator to determine and measure the effective amounts of both of the oppositely charged polymers (or groups of polymers), and then determine the appropriate timing and order of addition to the drilling fluid, and finally carry out the addition of the polymers to the drilling fluid. Instead, the additive mixture comprising an anionically charged water soluble polymer and a cationically charged water soluble polymer, each having charge densities and molecular weights within the ranges identified in the above, and present in the ratios identified above, is added to the drilling fluid as a single simultaneous application. Once in the drilling fluid, the fast soluble polymers dissolve and the counter ion polymer or group of polymers dissolve in a comparatively retarded manner thereby simulating the "sequential addition"
method.

Claims (26)

WE CLAIM:

1. An aqueous drilling fluid to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, said drilling fluid comprising:
(a) an anionically charged water soluble polymer; and, (b) a cationically charged water soluble polymer.

2. The aqueos drilling fluid of claim 1, wherein the anionically charged water soluble polymer and the cationically charged water soluble polymer together comprise between 0.01 and 25 percent by weight of the drilling fluid.

3. The aqueous drilling fluid of claim 1 wherein the ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is 1:99 to 99:1 on dry weight of total applied polymer basis.

4 The aqueous drilling fluid of claim 3, wherein the preferred ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is from 10:90 to 90:10 on dry weight of total applied polymer basis.

5. The aqueous drilling fluid of claim 4, wherein the most preferred ratio of anionically charged water soluble polymer to cationically charged water soluble polymer is from 70:30 to 30:70 on dry weight of total applied polymer basis.

6. The aqueous drilling fluid of claim 1, wherein one of the anionically charged water soluble polymer and the cationically charged water soluble polymer is a high MW polymer and its counter ion polymer is a lower MW polymer.

7. The aqueous drilling fluid of claim6, wherein one of the anionically charged water soluble polymer and cationically charged water soluble polymer has a weight-average molecular weight equal to or greater than 5,000,000 and its counter ion polymer has a weight-average molecular weight equal to or less than 4,000,000

8. The aqueous drilling fluid of claim 1, wherein the anionically charged water soluble polymer has a weight-average molecular weight of between 1000 and 50,000,000 and a charge density between 1 to 100%.

9. The aqueous drilling fluid of claim 8, wherein the anionically charged water soluble polymer has a weight average molecular weight of between 1,000,000 and 25,000,000 and a charge density of between 5 to 70%.

10. The aqueous drilling fluid of claim 9, wherein the anionically charged water soluble polymer has a weight-average molecular weight of between 5,000,000 and 15,000,000, and a charge density between 10 to 30%.

11. The aqueous drilling fluid of claim 1, wherein the cationically charged polymer has a weight-average molecular weight between 1000 and 50,000,000 and charge density of between 1 to 100%.

12. The aqueous drilling fluid of claim 11, wherein the cationically charged polymer has a weight-average molecular weight of between 1,000,000 to 25,000,000 grams per mole and charge density of between 5 to 70%.

13. The aqueous drilling fluid of claim 12, wherein the cationically charged polymer has a weight-average molecular weight of between 5,000,000 to 15,000,000 and charge density of between 10-30%.

14. The aqueous drilling fluid of claim 13, wherein one of the anionically charged water soluble polymer and cationically charged water soluble polymer has a charge density of greater than 50% and its counter ion polymer has a charge density of lower than 20%.

15. The aqueous drilling fluid of claim 1, wherein each of the anionically charged water soluble polymer and the cationically charged water soluble polymer has a weight-average molecular weight of between 5,000,000 to 15,000,000 and charge density of between 10-30% and is present in a ratio of between 30:70 and 70:30.

16. The aqueous drilling fluid of claim8 wherein the anionically charged water soluble polymer is hydrophobically modified, sulfonated, copolymerized, terpolymerized, tetrapolymerized or grafted with other monomeric or polymeric moieties and the resultant polymer is water soluble and has an anionic charge.

17. The aqueous drilling fluid of claim 16, wherein the anionically charged water soluble polymer is selected from the group consisting of: polyacrylamide-acrylic acid copolymers, sulfonated polystyrene, sulfonated polyvinyl alcohol, hydrophobically modified polyacrylamides and sulfonated polyacrylamide, hydrophobically modified polymers derived from acrylic acid, methaacrylic acid, homopolymer of acrylic acid, acenaphthylene, 1 -vinylnaphthalene, acenphthylene, polyacrylic acid, methyl methacrylate, styrene, methyl methacrylate-acrylic acid copolymer, hydrophobically modified polyacrylates (HM-PA), hydrophobically modified anionic cellulose derivatives, hydrophobically modified anionic starch derivatives, hydrophobically modified anionic guar derivatives, anionic hydrophobically modified polysaccharides, hydrophobically modified vinyl polymers, ethylenically unsaturated carboxylic acid and/or ethylenically unsaturated sulphonic acid.

18. The aqueous drilling fluid of claim 11, wherein the cationically charged polymer is a cationic polyacrylamide having the structure:
wherein x is a molar fraction of acrylamide or methacrylamide in the copolymer, y is a molar fraction of cationic co-monomer in the copolymer, x and y are within the range of from 0 to 1 and (x+y) ~ 1, R1 is hydrogen or methyl, R2 is hydrogen or methyl, A1 is -O- or -NH-, R3 is alkylene having from 1 to 3 carbon atoms or hydroxypropylene, R4, R5 and R6 are independently methyl or ethyl and X1 is an anionic counter ion chloride, bromide, methyl sulfate, ethyl sulfate or the like.

19. The aqueous drilling fluid of claim 17, wherein the cationically charged polymer is selected from the group consisting of: poly(diallyldimethyl ammonium chloride), copolymers containing diallyldimethyl ammonium chloride and another monomer, poly(epichlorohydrin/dimethylamine), cationized starch, chitosan, copolymers of vinyl monomers having cationic amine or quaternary ammonium functionalities with water soluble spacer monomers, acryl- amide, ethacrylamide, alkyl and dialkyl acrylamides, alkyl and dialkyl methacrylamides, alkyl acrylate, alkyl methacrylate, vinyl caprolactone, and vinyl pyrrolidone, include dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, including, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethyaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts such as acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldiethylammonium chloride and diallyldimethyl ammonium chloride.

20. The aqueous drilling fluid of claim 1, wherein each of the anionically charged water soluble polymer and the cationically charged water soluble polymer has a weight-average molecular weight of between 5,000,000 to 15,000,000 and charge density of between 10-30% and are present in an addition mixture in the ratio of between 30:70 and 70:30.

21. The aqueous drilling fluid of claim 20, wherein the addition mixture comprises a fast soluble and a regular grade polymer.

22. The aqueous drilling fluid of claim 1, further comprising one or more components selected from the group consisting of: fluid-loss control additives, weighting materials, rheology control additives, clay swelling control additives, anti-foaming agents, biocides, bridging agents, wetting agents, emulsifiers, lost circulation additives, water soluble lubricants,,oil soluble lubricants, salts, buffering agents, corrosion inhibitors, acids, alkalis and mixtures thereof.

23. An addition mixture for adding to an aqueous drilling fluid to reduce accretion of bitumen on drilling equipment during bitumen recovery from oil sands, said addition mixture comprising anionically charged water soluble polymer and a cationically charged water soluble polymer, each of which has a weight-average molecular weight of between 5,000,000 -15,000,000 and charge density of between 10-30% and is present in the addition mixture in the ratio of between 30:70 and 70:30.

24. A method of encapsulating bitumen during drilling in subterranean wells having a bituminous formation comprising adding to a drilling fluid used in drilling into said wells an anionically charged water soluble copolymer and a cationically charged water soluble copolymer.

25. A method of encapsulating bitumen during drilling in subterranean wells having a bituminous formation comprising the steps of:
(a) adding a water soluble polymer or group of polymers carrying the same charge to a drilling fluid;
(b) once the drilling is commenced or the bituminous formation is penetrated, slowly adding a counter ion water soluble polymer or polymeric group to the drilling fluid.

26. The method of claim 24 wherein the method steps are repeated cyclically.