CA2888866C

CA2888866C - Polymeric encapsulant for aqueous drilling fluid

Info

Publication number: CA2888866C
Application number: CA2888866A
Authority: CA
Inventors: Amir A. Mirzaei; Hirbod Rad
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-04-24
Filing date: 2015-04-24
Publication date: 2022-03-22
Anticipated expiration: 2035-04-24
Also published as: CA2888866A1; CA2927781A1

Abstract

A use of a family of terpolymers in a drilling fluid for steam assisted gravity drainage is disclosed.
More specifically, a drilling fluid, comprising a polymer dissolved in an aqueous phase, wherein the polymer is a terpolymer based on repeating units of a first type of hydrophobic moiety, a second type of hydrophobic moiety and of an anionic charged group.

Description

POLYMERIC ENCAPSULANT FOR AQUEOUS DRILLING FLUID
FIELD OF THE INVENTION
The present invention is directed to the use of a polymer in an aqueous drilling fluid for steam assisted gravity drainage operations. More specifically, it is directed to the use of a terpolymer in SAGD.
BACKGROUND
Oil sand deposits are found predominantly in the Middle East, Venezuela, and Western Canada. The Canadian bitumen deposits, being the largest in the world, are estimated to contain between 1.6 and 2.5 trillion barrels of oil, so the potential economic benefit of this invention carries significance within this resource class. The term "oil sands" refers to large subterranean land formations composed of reservoir rock, water and heavy oil and/or bitumen.
Bitumen is a heavy, black oil which, due to its high viscosity, cannot readily be pumped from the ground like other crude oils. 'Therefore, alternate processing techniques must be used to extract the bitumen deposits from the oil sands. The basic principle of known extraction processes is to lower the viscosity of the bitumen by applying heat, injecting chemical solvents, or a combination thereof, to a deposit layer, thereby promoting flow of the material throughout the treated reservoir area, in order to allow for recovery of bitumen from that layer.
At present there are two main methods that are used to recover bitumen from the oil sands in Alberta, Canada. The two methods are truck and shovel surface mining for subsequent extraction and steam assisted gravity drainage (SAGD). SAGD is used when the depth of the bitumen formation, such as in the Fort McMurray formation in Canada, is too deep to access and retrieve via the truck and shovel method. Two horizontal wells are drilled, one on top of the other with approximately 5 meters spacing there between. The shallower horizontal well is the injector well and is used to pump steam into the formation in order to treat and soften the bitumen and allow it to flow. The deeper horizontal well is the production well which collects the heated bitumen for pumping to surface. SAGD, as with most recovery strategies, is focused on increasing bitumen temperature within a limited region around a steam injection well. The reduced-viscosity oil is then allowed t flow by gravity drainage to an underlying point of the reservoir and to be collected by a horizontal production well. The heavy oil/bitumen is then brought to the surface for further processing.
In the course of SAGD drilling operations, the drillstring and/or other equipment come into contact with zones of rock and/or soil containing bitumen. However, bitumen is a relatively sticky substance that may readily adhere to any surface that it contacts, including the surfaces of the well-bore and/or any equipment utilized during the drilling operations. If a sufficient amount of bitumen adheres to surfaces in the well-bore or drilling equipment, it may, among other things, prevent the drillstring from rotating, prevent fluid circulation, or otherwise impede the effectiveness of a drilling operation. In some cases, it may become necessary to remove and/or disassemble the drillstring in order to remove accretions of bitumen, a process which may create numerous cost and safety concerns. The accretion of bitumen on drilling equipment and/or in the well-bore also can impede any subsequent operations down hole, including cementing, acidizing, fracturing, sand control, and remedial treatments.
SAGD drilling operations were initially plagued with severe issues due to the sticky nature of bitumen. Drilling fluids used conventionally at the time contained no additives to overcome the problems of drilling in bitumen and, as a result, the bitumen stuck to everything including the drill-string, casing and surface equipment which resulted in rig down-time and significant expenditure by the operator.
As a result of the earlier experiences with drilling in bitumen-containing formations, it became known to use additives within the fluid systems to attempt to inhibit bitumen accretion and, as a result, improve ROP. In the last ten years there have been a number of patents filed for drilling fluid systems or additives to overcome the problems associated with drilling SAGD
wells.
Water-based drilling fluids that contain solvents or wetting agents as anti-accretion additives and were intended to limit bitumen accretion to metal surfaces are described in

2 Canadian patents 2,454,312; 2,481,543; 2,451,585 and 2,437,522. These solvent and/or surfactant systems rely on the solvent's ability to dissolve bitumen. This approach limits the number of wells that can be drilled before the drilling fluid must be stripped of the built-up bitumen.
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 2,508,339; 2,624,834 and 2,635,300.
Hydrophobically associating polymers have been used in some oilfield applications, for example, as viscosifiers in enhanced oil recovery (polymer flooding), in drilling/completion fluids, as acid stimulations and as drag reducing agent as described in Han et al. Soc. of Petroleum Engineers, 104432, pp. 1-6, 2006 and in Taylor K. C. et al. Canadian International Petroleum Conference, Jun. 12-14, 2007, and in oily water cleanup as described in U.S. Pat. No.
4,734,205.
It has been theorized in US 7,879,768 (CA 2,635,300) to An Ming Wu that the hydrophobic group of hydrophobically associating polymers strongly adsorbs on the bitumen surfaces through its oil affinity force, and the hydrophilic groups of the hydrophobically associating polymers make the bitumen surface water wet and provides less sticking. Further, the hydrophobically associating polymers can effectively prevent the bitumen from dispersing.
Accordingly, these hydrophobically associating polymers are excellent bitumen and/or tar, flocculent and sticking inhibitors.
While this application is not bound by any theory regarding the bitumen encapsulation and anti-accretion properties of hydrophobically modified polymers, it has been found that the

3 dual hydrophobicity of the polymers -ubject to this application remarkably increase the anti-accretion and encapsulation performance of these polymers. Moreover, since the hydrophobically associating polymers subject of this application are anionic, they are compatible with conventional drilling fluid additives.
Amphiphilic polymers are increasingly used to control the rheology in aqueous formulations. These polymers typically include a hydrophilic backbone with grafted hydrophobic units or in another type, grafted amphiphilic units that are surfactant-like and therefore are often referred to as polysoaps.
In Journal of molecular structure, 2000, vol.554, p.99-108, Chassenieux, Fundin, Ducouret and Iliopoulos have reported that it was possible to prepare a new type of amphiphilic water soluble polymer based on repeating units of two water insoluble polymers, poly(dimethylhexadecyl(vinylbenzyl)ammonium chloride) and polystyrene. At relatively low concentration, the solutions behave as viscous fluids whereas for higher concentration, viscoelastic properties appear. Though these polymers could be used in SAGD
specific drilling fluids to prevent bitumen sticking, they are cationic and therefore, are likely to raise compatibility issues with anionic components of drilling fluid.
Certain 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 viscosiflers.
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. In addition, certain drilling fluids of the prior art that contain a non-ionic polymer do not perform well in certain formations and may not prevent accretion on drilling equipment to a satisfactory degree.
SUMMARY OF THE PRESENT INVENTION
The present invention relates to the application of anionic amphiphilic polymers in SAGD operations. The polymers used according to the present invention are terpolymers based on repeating units of two different types of hydrophobic moieties modified with anionic charged

4 groups. In a preferred embodiment, the first hydrophobic moiety is an aromatic compound such as styrene and the second hydrophobi:- moiety is a fatty acid. Depending on the modification rate, and on the neutralization degree, these polymers behave as highly hydrophobic but nevertheless soluble in aqueous solution. The invention also relates to aqueous drilling fluids containing the subject polymers that exhibit remarkable bitumen encapsulation and anti-accretion properties.
According to one aspect of the present invention, there is provided a drilling fluid, comprising a polymer dissolved in an aqueous phase, wherein the polymer is a terpolymer based on repeating units of a first type of hydrophobic moiety, a second type of hydrophobic moiety and of an anionic charged group. Preferably, the first and second type of hydrophobic moieties have different hydrophobic nature. Preferably, the first hydrophobic moieties type contains an aromatic group. More preferably, the aromatic hydrophobic moiety is a styrene derivative.
According to a preferred embodiment, the second hydrophobic moieties type contains a fatty acid including an alkyl side chain CnH2n+1, with n being an integer greater or equal to 6.
Preferably, n is selected from the group consisting of 8, 10, 12, 14 and 16.
More preferably, the alkyl side chain is grafted to the backbone of the polymer through hetero-functional groups.
More preferably, hetero-functional group is selected from the list consisting of amide, ester and urethane.
According to a preferred embodiment, the anionic charged group is a phosphate.
More preferably, the anionic charged group is a sulfonate.
According to a preferred embodiment, the polymer is represented by the general chemical , formula:
.., ...
rii, ___________________________ -c-P _ _c-V - C _______ H, SON.

5 where x is the substitution degree and y is between 0.1 and 0.4.
Preferably, the anionic charged group is a carboxylic group.
According to a preferred embodiment, the polymer is represented by the general chemical formula:
Ila ____________________________ I I _______ COI12,,,I _ where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5, z varies from 0.5 to 0.75 and R
is a monovalent cation or a proton. Preferably, the modification rate, defined as 200x, is 60 and n is 8, 10, 12, 14 or 16. More preferably, the modification rate, defined as 200x, is 50 and n is 12, 14 or 16. Even more preferably, the modification rate, defined as 200x, is 10 and n is 12. Most preferably, the modification rate, defined as 200x, is 20 and n is 12, 14 or 16.
According to a preferred embodiment, the polymer concentration is less than 3%
by weight. Preferably, the polymer concentration is less than 2% by weight, more preferably, the polymer concentration is less than 1.5% by weight.
According to another aspect of the present invention, there is provided a use of a terpolymer based on repeating units of a first and second type of hydrophobic moieties and of an anionic charged group in a SAGD drilling fluid.
BRIEF DESCRIPTION OF THE FIGURES
The invention may be more completely understood in consideration of the following description of various embodiments of the invention in connection with the accompanying figures, in which:
Figure 1 is a photograph of a carbon steel pipe treated with a solution according to the present invention and which was exposed to 100 grams of bitumen and rolled for 24 hours.

6 Figure 2 is a photograph of a carbon steel pipe untreated and exposed to 100 grams of bitumen and rolled for 24 hours.
DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION
The present invention is directed to the novel use of polymers for bitumen encapsulation in aqueous drilling fluids. The present invention thus relates to aqueous solutions of polymers based on three kinds of repeating units: two moieties preferably of different hydrophobic nature and anionic charged groups.
Preferably, the first and second types of hydrophobic moieties show clearly distinct hydrophobic properties as exhibited by their limited solubility in water or their polarity. This can be achieved, for instance, by selecting for the first moiety an aromatic and for the second moiety a fatty acid with a long aliphatic chain (preferably an alkyl chain with at least 7 carbon atoms).
The alkyl chain may be hydrogenated or perfluorated and is preferably grafted to the backbone chain through a hetero-functional group such as an amido, an ester or a urethane.
The anionic amphiphilic polymers of the present invention may be designed with various hydrophobic modification rates while remaining water-soluble. The anionic group may, for instance, can be selected from the group consisting of: a carboxylic, a sulfonate or a phosphate group. The polymers according to the present invention are terpolymers based on combination of a first and second type of hydrophobic groups and of anionic charged groups.
Two types of anionic charged groups have been studied: carboxylates and sulfonates groups.
In a further embodiment, the invention relates to drilling fluids for drilling SAGD wells containing the polymers of the invention as bitumen encapsulator and anti-accretion additive.
These drilling fluids typically contain less than 30 kg of polymer per cubic meter of the drilling fluid.

7 While preparation methods for these polymers are not within the scope of this application and one skilled in the art may find other suitable synthesis method, the described method is to be understood as a reference only.
Example 1 Synthesis of Carboxylated Terpolymer First, a copolymer styrene and maleic anhydride acid (SMA) is obtained. The synthesis was performed with an SMA copolymer in which each monomer unit consist of exactly one styrene unit and one maleic anhydride unit (in other words, z=0.5), so that the molecular mass of the repeated unit is 102 g/mol. Other commercially available SMA copolymers have higher styrene content with z varying from 0.5 to 0.75. The tested SMA copolymer had a molecular weight Mw of 150 kg/mol as measured in the laboratory.
In the second step, the SMA polymer is hydrophobically modified with an amine CnH2n4-11=1H2. Different amines having a purity of 99% were tested with n being an even number between 8 and 18.
In a three-necked bottle, 6 g of SMA were dissolved in 150 ml THF
(tetrahydrofuran), under N2 atmosphere, at 60 C. After two hours, 3.3 g of amine, in 50 ml THF
were added drop wise. The reaction was allowed to occur for 24h at 60 C. The terpolymer was recovered by precipitation in diethylether and drying over vacuum.
The general chemical formula ef the synthetized polymer is thus:
Fl ________________________________ II H ___ Et __ ( .02H CO
101 _ 0"rL.0 _I
CI ti n with n being either 8, 10, 12 or 16. For a modification rate of 100%, x equals 0.5. Therefore x varies between 0 and 0.5 (0.5 corresponding to a modification rate equal to 100%, the modification rate is defined as 200x).

8 The last step is the hydrolysis of the polymer allowing its solubilization in water under basic conditions (addition of NaOH), at 60 C., over 6 hours under stirring.
Note that sodium hydroxide can be substituted with other hydroxide of monovalent cation such as lithium hydroxide or potassium hydroxide for instance.
Depending on the neutralizatiu-n rate, the polymer formula can be thus expressed by where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5 and R is a monovalent cation or a proton:
H __ H
¨C¨C¨(¨C ________________ Hz I I
c-o2R co,ll CU
-' -1,ra Example 2 Sulfonated Terpolymers Equivalent sulfonated terpolymers, with sulfonate groups replacing the carboxylate groups were prepared to improve the thermal stability and the compatibility with calcium ions.
The main steps of a first synthesis route includes first, the synthesis of a copolymer based on styrene and dodecylmethacrylate, using toluene as solvent, at 70 C for a duration of 30 minutes. This step is followed by a sulfonation at 50 C, using dichloroethane as solvent in presence of H2SO4-The sulfonation reaction is controlled by adjusting the reaction time. The resulting polymer is obtained through evaporation and dissolution in DMSO.
Starting with a mixture of 80% styrene and 20% dodecylmethacrylate, a 74%
styrene/26% dodecylmethacrylate copolymer was prepared in the first step, leading after sulfonation to the following general chemical formula where x is the sulfonation degree.

9 _______________ C C __________ C C ________________ H2 H2 H2 ___________ 11101 _ C12 _ - 0.74(1-x) SO3Na Another synthesis route is based on terpolymerization of styrene, styrene sulfonate and alkylacrylamide. The solvent is DMSO. The polymerization was allowed to proceed for 24 hours at 65 C. The resulting polymer is obtained by precipitation in ether.
The terpolymer having the following formulae was obtained:

_______________ C C ____________ C C _______________ _ C12H25 OO
- 0.3 - 0.16 - 0.54 S 03Na Example 3 A polymer synthesized using a Styrene-Maleic anhydride resin of 1:1 styrene to maleic anhydride ratio. This polymer was hydrophobically modified with dodecylamine and the degree of modification was approximately 15%. The molecular weight was estimated to be approximately 11000.
Example 4 Two cylinders were filled with 300 ml of water and 0.5 grams of xanthan gum was added to each.
To one cylinder 0.5 grams of the above polymer was added and the other one was kept as blank. To each cylinder a 3/4 " carbon steel pipe of 10 cm in length was placed and 100 grams of bitumen was added. The cylinders were rolled for 24 hours and the pipes were removed for visual examination.

10 Visual examination revealed that the treated carbon steel pipe had resisted the deposition of bitumen solids to a substantial extent in comparison to the untreated carbon steel pipe.
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the invention, which is defined by the claims appended hereto.

11

Claims

We claim:

1. A drilling fluid, comprising a polymer dissolved in an aqueous phase, wherein the polymer is a terpolymer based on repeating units of a first type of hydrophobic moiety, a second type of hydrophobic moiety and of an anionic charged group.

2. The drilling fluid of claim 1, wherein the first and second type of hydrophobic moieties have different hydrophobic nature.

3. The drilling fluid of claim 1, wherein the first hydrophobic moieties type contains an aromatic group.

4. The drilling fluid of claim 3, wherein the aromatic hydrophobic moiety is a styrene derivative.

5. The drilling fluid according to any one of claims 1 to 4, wherein the second hydrophobic moieties type contains a fatty acid including an alkyl side chain C11H211+1, with n being an integer greater or equal to 6.

6. The drilling fluid of claim 5 wherein n is selected from the group consisting of 8, 10, 12, 14 and 16.

7. The drilling fluid of claim 5, wherein the alkyl side chain is grafted to the backbone of the polymer through hetero-functional groups.

8. The drilling fluid of claim 7, wherein said hetero-functional group is selected from the group consisting of amide, ester and urethane.

Date Recue/Date Received 2021-06-25

9. The drilling fluid of claim 1, wherein the anionic charged group is a phosphate.

10. The drilling fluid of claim 1, wherein the anionic charged group is a sulfonate.

1 L The drilling fluid of claim 10, wherein the polymer is represented by the general chemical formula:
rx, ¨.L.( .--/j c ¨!' __ c El, ii_ H2 o 111, Col {20 0 I/
- i IN 41.161 SO$Nit where x is the substitution degree and y is between 0.1 and 0.4.

12. The drilling fluid of claim 1, wherein the anionic charged group is a carboxylic group.

13. The drilling fluid of claim 12, wherein the polymer is represented by the general chemical formula:
.
_ ,,.... __ L.
[
1 1 1.(1.0,,,, ,,,,:it ....
co,H co sni chi i zn = 1 - (WM
where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5, z varies from 0.5 to 0.75 and R
is a monovalent cation or a proton.

14. The drilling fluid of claim 13, wherein the modification rate, defined as 200x, is 60 and n is 8, 10, 12, 14 or 16.

Date Recue/Date Received 2021-06-25

15. The drilling fluid of claim 13, wherein the modification rate, defined as 200x, is 50 and n is 12, 14 or 16.

16. The drilling fluid of claim 13, wherein the modification rate, defined as 200x, is 10 and n is 12.

17. The drilling fluid of claim 13, wherein the modification rate, defined as 200x, is 20 and n is 12, 14 or 16.

18. The drilling fluid according to any one of claims 13 to 17, wherein the polymer concentration is less than 3% by weight.

19. The drilling fluid according to any one of claims 13 to 18, wherein the polymer concentration is less than 2% by weight.

20. The drilling fluid according to any one of claims 13 to 19, wherein the polymer concentration is less than 1.5% by weight.

21. Use of a terpolymer based on repeating units of a first and second type of hydrophobic moieties and of an anionic charged group in a steam assisted gravity drainage (SAGD) drilling fluid.

Date Recue/Date Received 2021-06-25