Carbon dioxide viscosity enhancement with polyolefins

Abstract

The disclosed technology relates to compositions and methods for increasing the viscosity of carbon dioxide compositions, and methods for employing viscosified carbon dioxide compositions to increase the production and recovery of hydrocarbons from subterranean formations.

Description

[Background technology]

[0001] The disclosed technology relates to compositions and methods for increasing the viscosity of carbon dioxide compositions, as well as methods for enhancing the production and recovery of sequestered carbon dioxide and hydrocarbons from subterranean formations that employ the viscosified carbon dioxide compositions.

[0002] Many efforts exist to capture atmospheric carbon dioxide and store it underground, commonly in geological formations, a process known as geological carbon sequestration. Geological carbon sequestration faces certain challenges, including the potential for pressurized supercritical carbon dioxide to escape from geological formations. The process of sequestration of carbon dioxide from oil and gas production, fossil-fuel-based power plants, and other stationary sources is part of humanity's key efforts to reduce greenhouse gas emissions. In the near future, government policies may mandate carbon dioxide sequestration in geological repositories. These repositories include active and depleted oil and gas wells, saline aquifers, salt domes, and deep, unminable coal deposits. Continuous supercritical carbon dioxide injection, especially in the presence of reservoir heterogeneity, tends to be problematic due to unfavorable mobility, viscous fingering / channeling, and premature breakthrough of carbon dioxide. Reservoir modeling of supercritical carbon dioxide has shown that uneven distribution of carbon dioxide injection into geological formations negatively impacts the utilization of the overall storage capacity. Furthermore, unfavorable mobility can lead to unwanted leakage of carbon dioxide back to the surface, thus negating the reason for sequestration. Without thickening of supercritical carbon dioxide for more effective mobility control, and ultimately higher carbon dioxide storage capacity in geological formations, large-scale sequestration of carbon dioxide will be significantly limited.

[0003] In the recovery of hydrocarbons, such as oil or natural gas, from underground hydrocarbon-bearing formations or reservoirs, primary recovery methods, which typically utilize natural formation pressure to produce hydrocarbons through suitable production wells, typically recover only a limited percentage of the original hydrocarbons present in the reservoir. Therefore, various supplemental recovery techniques have been developed to maintain formation pressure or improve hydrocarbon displacement. Water flooding, often enhanced with polymers and surfactants, is one method, but can have environmental costs. "Miscible flooding" is another common supplemental recovery technique to improve hydrocarbon displacement.

[0004] In the production of hydrocarbons, such as oil or natural gas, from underground hydrocarbon-bearing formations or reservoirs, a fluid, often water, is injected into the formation to fracture the formation and release hydrocarbons therein. However, much of the fluid remains trapped within the formation, resulting in a significant consumption of fluid resources, among other environmental risks. The use of carbon dioxide as a fracturing fluid can help reduce the use and impacts of other fluids, namely water, and can also provide a convenient disposal site for excess carbon dioxide.

[0005] Miscible flooding involves introducing into the formation a fluid that is miscible with the hydrocarbons to be displaced. One such fluid is carbon dioxide. Carbon dioxide is considered a miscible-type flooding agent because, typically under high-pressure supercritical conditions, carbon dioxide acts as a solvent. However, the low viscosity of supercritical carbon dioxide can limit (or affect or reduce) the ability to sweep oil into a production well (or zone) for enhanced recovery. Thus, without significant viscosity enhancement for more effective mobility control and ultimately higher production rates, the applications of carbon dioxide are limited.

[0006] The idea of ​​thickening carbon dioxide using a polymer is known in the art, for example, from Heller, JP et al., "Direct Thickeners for Mobility of CO2 Floods." (Soc. Pet. Eng. J., 1985, 25, 679-686).

[0007] Furthermore, Zhang, S. et al. (2013) in their paper "Effects of polymers as direct CO2 thickener on a light crude oil and CO2" (J. Polym. Res., 20(61). pp. 1-13) teach the use of poly(vinyl ethyl ether) ("PVEE") and low molecular weight (-900 Mw) poly(1-decene) ("P1D") as effective thickeners for carbon dioxide. The ability to increase the viscosity of carbon dioxide by several fold to an order of magnitude using an environmentally friendly and cost-effective thickening system is important to the use of carbon dioxide for hydrocarbon production, recovery and sequestration and the pursuit of oil and gas companies worldwide. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Heller, J.P. et al., "Direct Thickeners for Mobility of CO2 Floods," Soc. Pet. Eng. J., 1985, 25, 679-686 [Non-patent document 2] Zhang, S. et al. (2013) "Effects of polymers as direct CO2 thickener on a light crude oil and CO2" J. Polym. Res., 20(61). pp. 1-13 Summary of the Invention [Means for solving the problem]

[0009] The disclosed technology solves the problem of thickening of carbon dioxide compositions in an efficient and environmentally friendly manner by adding to the composition a branched polyolefin polymer that increases the viscosity of supercritical carbon dioxide.

[0010] Thus, the disclosed technology provides carbon dioxide compositions comprising a large amount of carbon dioxide and at least one branched polyolefin polymer that can increase the viscosity of supercritical carbon dioxide.

[0011] Branched polyolefin polymers are C2 to C 24 For example, the branched polyolefin polymer may be a polyisobutylene polymer.

[0012] Branched polyolefin polymers are also C3 to C 24 For example, the branched polyolefin polymer may be a polydecene polymer.

[0013] Preferably, the polyolefin polymer may have a number average molecular weight of 140 to 5000 as measured by gel permeation chromatography using polystyrene standards.

[0014] The branches of the branched polyolefin polymer may comprise at least one of aromatic hydrocarbyl groups, aliphatic hydrocarbyl groups, cyclic hydrocarbyl groups, and mixtures thereof. In particular, the branches of the branched polyolefin polymer may comprise hydroxyl-containing aromatic groups. The branches of the branched polyolefin polymer may also comprise amine-containing aromatic groups.

[0015] The carbon dioxide composition may comprise from 0.01 to 5 wt % of the branched polyolefin polymer, based on the weight of the composition.

[0016] The disclosed technology also includes a method for increasing hydrocarbon production from a subterranean hydrocarbon-bearing formation, the method comprising injecting a carbon dioxide composition as described above into the formation and recovering the released hydrocarbons from the hydrocarbon-bearing formation.

[0017] The disclosed technology also includes a method of sequestering carbon dioxide, which method includes injecting a carbon dioxide composition as described above into a geological formation.

[0018] The disclosed technology also includes a method for increasing the viscosity of supercritical carbon dioxide, which method includes adding a thickening agent to the carbon dioxide, wherein the thickening agent is at least one branched polyolefin polymer that increases the viscosity of the supercritical carbon dioxide. DETAILED DESCRIPTION OF THE INVENTION

[0019] Various preferred features and embodiments are described below by way of example and not by way of limitation.

[0020] composition The compositions herein comprise carbon dioxide. Carbon dioxide consists of two oxygen atoms covalently bonded to a single carbon atom. Carbon dioxide can exist as a solid, liquid, gas, or, at temperatures above its critical point, as a supercritical fluid. A supercritical fluid is a fluid that exhibits both the properties of a liquid, such as the ability to dissolve other substances, and the properties of a gas, such as the ability to diffuse through solids. When in a supercritical state, carbon dioxide has the ability to mix uniformly with, or is miscible with, hydrocarbons such as crude oil, and therefore may improve the recovery of such hydrocarbons.

[0021] The carbon dioxide composition will also include at least one branched polyolefin polymer. Polyolefins are well known in the art. In one embodiment, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 2 to 24 carbon atoms.

[0022] As used herein, the term "olefin" refers to an unsaturated hydrocarbon compound having a hydrocarbon chain containing at least one carbon-carbon double bond in its structure, where the carbon-carbon double bond is not part of an aromatic ring. Olefins may be linear, branched, or cyclic. "Olefin" is defined as meaning a single isomer or is intended to encompass all structural isomers of olefins, unless the context clearly dictates otherwise.

[0023] Derivable or derived means that the polyolefin is polymerized from an initial polymerizable olefin monomer or mixtures thereof having the indicated number of carbon atoms. In embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 3 to 24 carbon atoms. In some embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 4 to 24 carbon atoms. In further embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 5 to 20 carbon atoms. In yet further embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 6 to 18 carbon atoms. In yet further embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 8 to 14 carbon atoms. In alternative embodiments, the polyolefin employed in the carbon dioxide composition may be derivable (or derived) from an olefin having from 8 to 12 carbon atoms.

[0024] As used herein, the term "carbon backbone" of a polyolefin is defined as the linear carbon chain therein having the greatest number of carbon atoms.

[0025] As used herein, the term "branch group" with respect to polyolefins refers to a group other than hydrogen attached to the carbon backbone of the polyolefin other than that attached to the carbon atom at the extreme end of the carbon backbone.

[0026] Often, the polymerizable olefin monomer comprises one or more of propylene, isobutene, 1-butene, isoprene, 1,3-butadiene, or mixtures thereof.

[0027] An example of a useful polyolefin is polyisobutylene.

[0028] Polyolefins also include poly-α-olefins derivable (or derived) from α-olefins. As used herein, the term "alpha-olefin" refers to a polymer having a terminal carbon-carbon double bond (R 1 R 2 )-C=CH2). As used herein, "polyalphaolefin" ("PAO") includes any oligomer and polymer of one or more alpha-olefin monomers. PAOs are oligomeric or polymeric molecules produced from the polymerization reaction of alpha-olefin monomer molecules in the presence of a catalyst system, optionally further hydrogenated to remove any residual carbon-carbon double bonds therein. Thus, PAOs may be dimers, trimers, tetramers, or any other oligomer or polymer containing two or more structural units derived from one or more alpha-olefin monomers. PAO molecules are 13 The PAO molecule may be highly regioregular, such that the bulk material exhibits isotacticity or syndiotacticity as measured by C NMR. 13The poly-α-olefins may be highly regiodisordered, such that the bulk material is substantially atactic, as determined by C NMR. PAO materials made using metallocene-based catalyst systems are typically referred to as metallocene PAOs ("mPAOs"), while PAO materials made using traditional non-metallocene catalysts (e.g., Lewis acids, supported chromium oxides, etc.) are typically referred to as conventional PAOs ("cPAOs"). The poly-α-olefins used herein may be mPAOs. The poly-α-olefins used herein may also be cPAOs.

[0029] The α-olefins may be linear or branched, or may be a mixture thereof. Examples include monoolefins such as propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, etc. Other examples of α-olefins include 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and mixtures thereof. Other examples of α-olefins, in yet another embodiment, include 1-nonadecene, 1-eicosene, 1-heneicosene, 1-docosene, 1-tricosene, and 1-tetracosene. Preferred LAO feeds are 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene. Examples of preferred α-olefin mixtures as monomers for making poly-α-olefins include, but are not limited to, C6 / C8; C6 / C10; C6 / C12; C6 / C14; C6 / C16; C6 / C8 / C10; C6 / C8 / C12; C6 / C8 / C14; C6 / C8 / C16; C8 / C10; C8 / C12; C8 / C14; C8 / C16; C8 / C10 / C12; C8 / C10 / C14; C8 / C10 / C16; C10 / C12; C10 / C14; C10 / C16; C10 / C12; C10 / C14; C10 / C16; C10 / C12 / C14; C10 / C12 / C16, etc. One example of a useful α-olefin is 1-decene.

[0030] An example of a useful poly-α-olefin is poly-decene.

[0031] Polyolefins may also be copolymers of at least two different olefins, also known as olefin copolymers (OCPs). These copolymers are preferably copolymers of α-olefins having from 2 to about 28 carbon atoms, preferably copolymers of ethylene and at least one α-olefin having from 3 to about 28 carbon atoms, typically of the formula CH2=CHR1, where R1 is a straight or branched chain alkyl radical containing from 1 to 22 carbon atoms. Preferably, R1 in the above formula may be an alkyl of 1 to 8 carbon atoms, more preferably an alkyl of 1 to 2 carbon atoms.

[0032] The composition may be substantially free of ethylene and its polymers. The composition may be completely free of ethylene and its polymers. By substantially free, it is meant that the composition contains less than 0.01% by weight of a given substance. In some embodiments, substantially free means less than 0.005% by weight of a given substance. Substantially free may also mean less than 1000 ppm of a given substance. In some embodiments, substantially free may mean less than 500 ppm of a given substance. Substantially free may also mean less than 250 ppm of a given substance. In some embodiments, substantially free may mean less than 100 ppm of a given substance. Substantially free may also mean less than 50 ppm of a given substance. In some embodiments, substantially free may mean less than 30 ppm of a given substance. Substantially free may also mean less than 10 ppm, less than 5 ppm, or even less than 1 ppm of a given substance. The composition may be substantially free of propylene and its polymers. The composition may be completely free of propylene and its polymers.

[0033] The polyolefin polymers prepared from the aforementioned olefin monomers may have a number average molecular weight of 140 to 5000. The polyolefin polymers prepared from the aforementioned olefin monomers may also have a number average molecular weight of 200 to 4750. The polyolefin polymers prepared from the aforementioned olefin monomers may also have a number average molecular weight of 250 to 4500. The polyolefin polymers prepared from the aforementioned olefin monomers may also have a number average molecular weight of 500 to 4500. The polyolefin polymers prepared from the aforementioned olefin monomers may also have a number average molecular weight of 750 to 4000 as measured by gel permeation chromatography using polystyrene standards.

[0034] Some polyolefins contain branches due to the structure of the polymer. For example, polymerization of α-olefins along the α-bonds results in the tails of these monomers branching along the polymerized α-olefin. The longer the α-olefin, the longer the branches in the resulting polyolefin. For example, polydecene can result in a polymer with branches of 8 carbon atoms.

[0035] A typical hydrogenated PAO molecule can be represented by Formula I below: [ka] where R 1 , R 2 , R 3 , R 4 and R 5 Each of R 6 , and R 7 is the same or different in each occurrence and independently represents hydrogen or a substituted or unsubstituted hydrocarbyl (preferably alkyl) group, and n is a non-negative integer corresponding to the degree of polymerization.

[0036] Thus, when n=0, Formula I represents a dimer formed from the reaction of two monomer molecules after a single addition reaction between the two carbon-carbon double bonds.

[0037] When n=m, where m is a positive integer, Formula I represents the molecule produced from the reaction of m+2 monomer molecules after m+1 steps of addition reactions between two carbon-carbon double bonds.

[0038] Thus, when n=1, Formula I represents a trimer formed from the reaction of three monomer molecules after a two-step addition reaction between two carbon-carbon double bonds.

[0039] R 1 Starting with R 7 Assuming that the linear carbon chain ending in has the maximum number of carbon atoms among all linear carbon chains present in Formula I, then the R 1 Starting with R 7 A linear carbon chain ending in R constitutes the carbon backbone of poly-α-olefins of Formula I. 2 , R 3 , R 4 and R 5 Each of the above and R 6 may be a substituted or unsubstituted hydrocarbyl (preferably alkyl) group, and (if not hydrogen) is a branched group.

[0040] If only α-olefin monomers are used in the polymerization process and no isomerization of monomers and oligomers occurs in the reaction system during polymerization, R 1 , R 2 , R 3 , all R 4 and R 5 , R 6 , and R 7 Approximately half of the R 1 , R 2 , R 6 , and R 7 one of which is methyl and the group R 1 , R 2 , R 3 , all R 4 and R 5 , R 6 , and R 7In this case, about half of the R 2 is methyl and R 3 , all R 5 , and R 6 is hydrogen and R 1 , all R 4 , and R 7 Assuming that the longest carbon chain contained therein has 8 carbon atoms, and n=8, the carbon backbone of the PAO molecule of Formula I contains 35 carbon atoms, and the branching groups (R 2 , all R 4 ) can have an average branch group length of 7.22 (i.e., (1+8*8) / 9). This PAO molecule can be produced by polymerizing 1-decene using a specific metallocene catalyst system, described in more detail below, and can be represented by Formula II below: [ka]

[0041] However, depending on the polymerization catalyst system used, varying degrees of isomerization of the monomers and / or oligomers may occur in the reaction system during the polymerization process, resulting in varying degrees of substitution on the carbon backbone. 2 , R 3 , all R 5 is methyl and R 6 is hydrogen and R 1 has 8 carbon atoms in the longest linear carbon chain contained therein, and all R 4 and R 7 Assuming that R has 7 carbon atoms in the longest linear carbon chain therein and n=8, the carbon backbone of the PAO molecule of Formula I contains 34 carbon atoms, and the branching groups (R 2 , all R 4 , and R 5) can have an average branch length of 3.67 (i.e., (1+1+7*8+1*8) / 18). This PAO molecule can be produced by polymerizing 1-decene using a specific nonmetallocene catalyst system, described in more detail below, and can be represented by Formula III below: [ka]

[0042] PAO basestocks useful in this invention can be homopolymers made from a single alpha-olefin monomer or copolymers made from a combination of two or more alpha-olefin monomers.

[0043] The branching groups on the PAO molecule can be linear alkyl groups having at least 6 carbon atoms. The branching groups on the PAO molecule can be linear alkyl groups having at least 8 carbon atoms.

[0044] In one embodiment, a branched PAO polymer, such as a polydecene polymer, is provided having a molecular weight of 1000 to 5000. The branched PAO polymer, such as a polydecene, may also have a number average molecular weight of 1250 to 4750. The branched PAO polymer, such as a polydecene, may also have a number average molecular weight of 1500 to 4500. The branched PAO polymer, such as a polydecene, may also have a number average molecular weight of 2000 to 4250. The branched PAO polymer, such as a polydecene, may also have a number average molecular weight of 2500 to 4000 as measured by gel permeation chromatography using polystyrene standards.

[0045] Polyolefins may also be functionalized with substituents to add branches along the polyolefin backbone, for example, the polyolefin may be functionalized with at least one of an aromatic hydrocarbyl group, an aliphatic hydrocarbyl group, a cyclic hydrocarbyl group, and mixtures thereof, such that the branches of the branched polyolefin polymer comprise at least one of an aromatic hydrocarbyl group, an aliphatic hydrocarbyl group, a cyclic hydrocarbyl group, and mixtures thereof.

[0046] In some embodiments, the polyolefin may be functionalized with at least one aromatic hydrocarbyl group so that each branch of the branched polyolefin polymer contains at least one aromatic hydrocarbyl group. The aromatic hydrocarbyl group may be, for example, a hydroxyl-containing aromatic group such as a phenol group, an amine-containing aromatic group such as aniline, or a mixture thereof. Other aromatic groups may include, for example, phenylmethylene; o-heptyl-phenylmethylene; and p-heptylphenylmethylene; aniline and alkylaniline; indole and alkylindole; quinoline and alkylquinoline; isoquinoline and alkylisoquinoline; pyrazine and alkylpyrazine; quinoxaline and alkylquinoxaline; acridine and alkylacridine; pyrimidine and alkylpyrimidine; quinazoline and alkylquinazoline. The aromatic group may also be a polycyclic aromatic group, for example, naphthalene, naphthol, or other fused aromatic ring phenolic analogs, naphthylamine, or other aniline analogs.

[0047] In one embodiment, the aromatic group is a hydroxyl-containing aromatic group. In one embodiment, the aromatic group is a phenol group. In one embodiment, the aromatic group is an amine-containing aromatic group. In one embodiment, the aromatic group is a hydroxyl- and amine-containing aromatic group. In one embodiment, the aromatic group is a 2-((dimethylamino)methyl)phenol group.

[0048] In some embodiments, the polyolefin may be functionalized with at least one aliphatic hydrocarbyl group, such that the branches of the branched polyolefin polymer contain at least one aliphatic hydrocarbyl group.

[0049] In some embodiments, the polyolefin may be functionalized with at least one cyclic hydrocarbyl group so that the branches of the branched polyolefin polymer contain at least one cyclic hydrocarbyl group. Exemplary cyclic groups include, for example, cyclohexylmethylene. Other cyclic groups may include heterocyclic groups such as, for example, pyridine and alkylpyridines, pyrrole and alkylpyrrole, piperidine and alkylpiperidine, pyrrolidine and alkylpyrrolidine, imidazole and alkylimidazole. Other cyclic groups may include, in particular, vinylpyridine and / or vinylimidazole, as well as styrene.

[0050] In some embodiments, the polyolefin may be a polyisobutylene polymer having a number average molecular weight of 140 to 5000. The polyisobutylene polymer may also have a number average molecular weight of 200 to 4500. The polyisobutylene polymer may also have a number average molecular weight of 250 to 4000. The polyisobutylene polymer may also have a number average molecular weight of 300 to 3500. The polyisobutylene polymer may also have a number average molecular weight of 350 to 3000. The polyisobutylene polymer may also have a number average molecular weight of 400 to 2500 as measured by gel permeation chromatography using polystyrene standards.

[0051] The carbon dioxide composition may comprise 0.01 to 5 wt. % of the branched polyolefin polymer, based on the weight of the composition. The carbon dioxide composition may comprise 0.05 to 4.5 wt. % of the branched polyolefin polymer, based on the weight of the composition. The carbon dioxide composition may also comprise 0.1 to 4 wt. % of the branched polyolefin polymer, based on the weight of the composition. The carbon dioxide composition may also comprise 0.5 to 3.5 wt. % of the branched polyolefin polymer, based on the weight of the composition.

[0052] One purpose of the polyolefin polymer is to increase the viscosity of supercritical carbon dioxide. The absolute viscosity of supercritical carbon dioxide varies depending on the temperature and pressure at which the viscosity is measured, but has been found to be approximately 0.07 cP at 2000 psi and 0.09 cP at 2900 psi as measured by a viscometer. When the polyolefin polymer is dosed into the supercritical carbon dioxide, it can increase the viscosity of the composition compared to the initial supercritical carbon dioxide viscosity, up to the point where the supercritical carbon dioxide becomes unable to flow.

[0053] In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by at least 100%, which increase may also be referred to as 2-fold or "2x," meaning that the absolute viscosity of the carbon dioxide composition is 100% greater than the absolute viscosity of its own supercritical carbon dioxide. For example, if the absolute viscosity of supercritical carbon dioxide is 0.05, then a 100% greater relative viscosity would be 0.05 + (0.05) * 100% = 0.01, or 2 times greater. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by about 100% to near the point where the composition does not flow freely, for example, by about 1, 2, 3, 3.5, 4, 4.5, or 5 orders of magnitude or more. As used herein, "orders of magnitude" means approximately a factor of 10. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by at least 150%, which may also be referred to as 2.5 times or "2.5x." In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by about 150% to near the point where the composition does not flow freely, e.g., by about 1, 2, 3, 3.5, 4, 4.5, or 5 orders of magnitude or more. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by at least 200%, which may also be referred to as 3 times or "3x." In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by about 200% to near the point where the composition does not flow freely, e.g., by about 1, 2, 3, 3.5, 4, 4.5, or 5 orders of magnitude or more. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by at least 250%, or 3.5 times.In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by about 250% to about the point where the composition does not flow freely, e.g., by about 1, 2, 3, 3.5, 4, 4.5, or 5 orders of magnitude or more. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by at least 300%, i.e., by a factor of 4. In some embodiments, the polyolefin polymer can be dosed into the carbon dioxide composition to increase the relative viscosity of the composition by about 300% to about the point where the composition does not flow freely, e.g., by about 1, 2, 3, 3.5, 4, 4.5, or 5 orders of magnitude or more.

[0054] Given the temperatures and pressures involved in obtaining supercritical carbon dioxide, measuring absolute viscosity is difficult and may yield slightly different results from well to well. However, when comparing the viscosities of two samples from the same well using the same measurement method (i.e., comparing the viscosity of supercritical carbon dioxide with the viscosity of a carbon dioxide composition containing a polyolefin polymer), the trend in relative viscosity should be the same or similar between methods. Therefore, the relative viscosity values ​​herein can be arrived at by measuring the absolute viscosity of the comparison samples using any reasonable test method. One method can be to employ a viscometer.

[0055] One useful means for screening polyolefin polymers can be to determine their solubility in supercritical carbon dioxide. Generally, the more soluble a second substance is in a first substance, the more available the second substance is for reaction with the first substance. While complete solubility is desirable, even partially soluble polymers can result in improved viscosity. Polymer solubility can be measured by methods known in the art, such as visual inspection or cloud point. In one embodiment, the solubility of a polyolefin polymer in a carbon dioxide composition can be measured using a sapphire rocking cell test. The sapphire rocking cell test employs an instrument with two rocking cells, typically about 20 mL in volume, each equipped with a stainless steel ball to aid in stirring. Each cell is filled with a specified volume of a selected branched polyolefin polymer and then infused with carbon dioxide to the desired supercritical carbon dioxide pressure. The cells are then immersed in a constant temperature water bath. The cell is rocked in a water bath from a 45° angle to a -45° angle at a predetermined rocking frequency, such as 15 times per minute. The water bath is brought to the desired temperature, and the sapphire cell is observed for the solubility of the polyolefin polymer in supercritical carbon dioxide. If the polyolefin is completely soluble in supercritical carbon dioxide at a given pressure and temperature, the supercritical mixture will appear homogeneous; otherwise, separate phases will be observed in the cell.

[0056] In some cases, the actual pressure required for hydrocarbon solubility in supercritical carbon dioxide may depend on the minimum miscible pressure (MMP) of the hydrocarbons present, which can be found by simple experimentation with hydrocarbon samples from the reservoir and carbon dioxide composition, which can be easily performed by one skilled in the art.

[0057] method One aspect of the disclosed technology is the use of a branched polyolefin polymer to thicken carbon dioxide. Thus, the technology provides a method for increasing the viscosity of supercritical carbon dioxide. The method may include adding a thickening agent to the carbon dioxide. The thickening agent is at least one branched polyolefin polymer that increases the viscosity of the supercritical carbon dioxide. The method may further include pressurizing the carbon dioxide composition at a temperature to cause the formation of supercritical carbon dioxide.

[0058] The carbon dioxide compositions described herein may be employed to sequester carbon dioxide in subterranean geological formations and to recover hydrocarbons from subterranean hydrocarbon-bearing formations.

[0059] Hydrocarbons can be recovered from underground hydrocarbon-bearing formations or reservoirs by injecting a solvent (in this case, carbon dioxide) into the reservoir through an injection well and recovering hydrocarbon-bearing fluids from a production well that is some horizontal distance or offset from the injection well. In practice, more than one injection well and more than one production well may be used, and these may be arranged in several different patterns suitable for this type of solvent-driven operation. However, for simplicity, the invention will be described below with reference to only a single injection well and a single production well.

[0060] The carbon dioxide compositions described herein should be injected under sufficient pressure such that, under conditions prevailing in the reservoir, the carbon dioxide in the composition exists as a dense phase, i.e., it exists neither as a liquid nor as a dense vapor under supercritical conditions. Generally, this means that the carbon dioxide is injected under the required dense phase condition, i.e., at a pressure of about 0.468 g cm. -3This is accomplished by maintaining a pressure in the reservoir high enough to maintain a density greater than 1000 psia. This pressure, itself, increases with increasing reservoir temperature, and therefore should be selected according to the reservoir temperature. The viscosity-increasing methods discussed herein can be employed at pressures of 500 psia or greater, e.g., up to 10,000 psia, or e.g., 750-6000 psia. Typical minimum pressures to maintain a dense phase state are 900 psia at 85°F, 1200 psia at 100°F, 1800 psia at 150°F, 2500 psia at 200°F, and 3100 psia at 250°F (6205 kPa at 30°C, 8275 kPa at 38°C, 12410 kPa at 65°C, 17235 kPa at 93°C, and 21375 kPa at 120°C).

[0061] Thus, a method for recovering hydrocarbons from a subsurface hydrocarbon-bearing formation may include at least some, if not all, of the following steps, although not necessarily in the following order: Determining the temperature and pressure of hydrocarbon formations; Optionally, screening for suitable branched polyolefin polymers, for example by either determining the solubility of the at least one branched polyolefin polymer at the temperatures and pressures encountered in the formation, which can be done, for example, by performing a sapphire rocking cell test, or by determining the MMP of the hydrocarbons present; selecting at least one branched polyolefin polymer; injecting a carbon dioxide composition comprising carbon dioxide and at least one branched polyolefin polymer into a hydrocarbon formation; and ·Recovering hydrocarbons released from hydrocarbon-bearing formations.

[0062] The amount of each chemical component described is expressed exclusive of any solvent or diluent oil that may be customarily present in commercially available materials, i.e., on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be construed as being a commercially available material that may contain isomers, by-products, derivatives, and other materials normally understood to be present in commercially available products.

[0063] As used herein, the term "hydrocarbyl substituent" or "hydrocarbyl group" is used in its ordinary sense, as is well known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include:

[0064] Hydrocarbon substituents, i.e., aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic, aliphatic, and alicyclic-substituted aromatic substituents, as well as cyclic substituents in which a ring is completed through another portion of the molecule (e.g., two substituents together form a ring).

[0065] Substituted hydrocarbon substituents, that is, in the context of this invention, substituents containing non-hydrocarbon groups which do not alter the predominantly hydrocarbon character of the substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, amino, and sulfoxy).

[0066] Hetero substituents, i.e., substituents that are predominantly hydrocarbon in nature but, in the context of this invention, contain atoms other than carbon in a ring or chain otherwise composed of carbon atoms, encompassing substituents such as pyridyl, furyl, thienyl, and imidazolyl. Heteroatoms include sulfur, oxygen, and nitrogen. Generally, no more than two, or no more than one non-hydrocarbon substituent will be present for every 10 carbon atoms in the hydrocarbyl group, although alternatively, there can be no non-hydrocarbon substituents in the hydrocarbyl group.

[0067] It is known that some of the materials described above may interact in the final formulation, resulting in components of the final formulation that are different from those initially added. For example, metal ions (e.g., those in detergents) may migrate to other acidic or anionic sites on other molecules. The products formed thereby, including products formed upon employing the compositions of the present invention in their intended use, may not be easily explained. Nevertheless, all such modifications and reaction products are included within the scope of the present invention, which includes compositions prepared by combining the components described above. [Example]

[0068] Sample 1 - Unhydrogenated decene dimer with a number average molecular weight of 280

[0069] Sample 2 - Unhydrogenated metallocene polydecene with a number average molecular weight of 2300

[0070] Sample 3 - Unhydrogenated metallocene polydecene with a number average molecular weight of 2900

[0071] Sample 4 - Polyolefin phenol derived from polyisobutylene with a number average molecular weight of 590

[0072] Sample 5 - Polyolefin phenol derived from polyisobutylene with a number average molecular weight of 950

[0073] Sample 6 - Mannich reaction product of Sample 5 with dimethylamine

[0074] Sample 7 - Polyisobutylene succinic anhydride reaction products with aromatic amines

[0075] Sample 8 - Polyisobutylene succinic anhydride, maleated ethylene / propylene copolymer, reaction products with aromatic amines

[0076] Sample 9 - Reaction products of maleated ethylene / propylene copolymer with aromatic amines

[0077] Sample 10 - Maleated product of Sample 2

[0078] Sample 11 - Reaction product of Sample 10 with polyethylene polyamine

[0079] Sample 12 - Polyisobutylene with a number average molecular weight of 2700

[0080] Sample 13 - Polyisobutylene with a number average molecular weight of 2060

[0081] Sample 14 - Polyisobutylene with a number average molecular weight of 1000

[0082] Sample 15 - Polyisobutylene with a number average molecular weight of 1,000,000

[0083] Each of Samples 1-15 was tested for solubility in carbon dioxide in a sapphire rocking cell test. A designated weight of sample polymer was loaded into two separate rocking cells containing 20 mL of carbon dioxide, each containing a stainless steel ball to aid in stirring. The cells were filled to 2500 psi and then immersed in a 35°C thermostatic water bath. The cells were rocked in the water bath from a 45° angle to a -45° angle at a rocking frequency of 15 times per minute to observe the solubility of the sample polymer in supercritical carbon dioxide. If the sample was soluble, the supercritical mixture appeared homogeneous; if not, separate phases were observed within the cells. [Table 1]

[0084] A ViscoPro2100 moving piston viscometer unit was used to measure the viscosity of each sample mixture with carbon dioxide. The viscometer unit was connected in line with a swinging cell setup. There were two cells with valves, and when both valves were opened, the mixture of CO2 and sample polymer passed from the swinging cell setup to the viscometer. The ViscoPro2100 viscometer consisted of a sensor in which a piston was moved from one end of the sensor to the other with the assistance of an electromagnetic coil. The sensor also consisted of a temperature probe. Once solubility of the sample polymer in CO2 was achieved within the swinging cell, the valve connecting the swinging cell to the viscometer was opened, allowing the fluid to pass to the viscometer sensor. Temperature control was achieved with the assistance of a heating band in the line connecting the viscometer and the swinging cell. Real-time measurements of the viscosity and temperature of the fluid within the sensor were provided. The results of the measurements and the pressure at which each measurement was taken are shown in the table below. [Table 2]

[0085] Each of the documents mentioned above, including any prior application to which priority is claimed, whether or not specifically listed above, is incorporated herein by reference. The citation of any document is not an admission that such document qualifies as prior art in any jurisdiction or constitutes general knowledge of one of ordinary skill in the art. Except in the examples or where otherwise expressly indicated, all numerical quantities specifying amounts of materials, reaction conditions, molecular weights, numbers of carbon atoms, and the like, in this specification should be understood as modified by the word "about." It should be understood that the upper and lower limits of quantities, ranges, and ratios set forth herein may be independently combined. Similarly, the ranges and amounts of each element of the invention may be used together with any ranges or amounts of the other elements.

[0086] As used herein, the transitional term "comprising," which is synonymous with "including," "containing," or "characterized by," is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. However, within each "comprising" recitation herein, the term is intended to encompass, as alternative embodiments, the phrases "consisting essentially of" and "consisting of," where "consisting of" excludes any unspecified elements or steps, and "consisting essentially of" permits the inclusion of additional, unrecited elements or steps that do not materially affect the essential or basic novel characteristics of the subject composition or method.

[0087] A carbon dioxide composition is provided that includes a majority of carbon dioxide and at least one branched polyolefin polymer.

[0088] The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity that is at least 100% greater than that of supercritical carbon dioxide. The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity that is at least 150% greater than that of supercritical carbon dioxide. The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity that is at least 200% greater than that of supercritical carbon dioxide. The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity that is at least 300% greater than that of supercritical carbon dioxide.

[0089] The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 1 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 2 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 3 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 3.5 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 4 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 100% to about 5 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 150% to about 5 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 150% to about 4 order of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 150% to about 3 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 200% to about 5 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 200% to about 4 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 200% to about 3 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 250% to about 5 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 250% to about 4 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 250% to about 3 orders of magnitude. The composition described in any sentence in any preceding paragraph has a relative viscosity of about 300% to about 5 orders of magnitude.The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity of from about 300% to about 4 orders of magnitude. The composition of any sentence in any preceding paragraph, wherein the composition has a relative viscosity of from about 300% to about 3 orders of magnitude.

[0090] The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 140 to 5,000 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 200 to 4,750 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 250 to 4,500 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 500 to 4,500 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 750 to 4,000 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the polyolefin polymer has a number average molecular weight of 1,000 to 5,000 as measured by gel permeation chromatography using a polystyrene standard.

[0091] The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C2 to C24 olefin or a mixture thereof. The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C3 to C24 olefin or a mixture thereof. The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C4 to C24 olefin or a mixture thereof. The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C5 to C20 olefin or a mixture thereof. The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C6 to C18 olefin or a mixture thereof. The composition according to any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C8 to C14 olefin or a mixture thereof. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C8 to C12 olefin or mixtures thereof.

[0092] The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a propylene polymer. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises an isobutene polymer. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a 1-butene polymer. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises an isoprene polymer. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a 1,3-butadiene polymer. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer.

[0093] The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 140 to 5000. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 200 to 4500. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 250 to 4000. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 300 to 3500. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 350 to 3000. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polyisobutylene polymer having a number average molecular weight of 400 to 2500 as measured by gel permeation chromatography using polystyrene standards.

[0094] The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from a C4 to C24 α-olefin or a mixture thereof. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-pentene. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-hexene. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-heptene. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-octene. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-nonene. The composition of any sentence in any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-decene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-decene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-undecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-dodecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-tridecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-tetradecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-pentadecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-hexadecene. The composition of any sentence of any preceding paragraph, wherein the at least one branched polyolefin polymer is polymerized from 1-heptadecene.The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-octadecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-nonadecene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-eicosene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-heneicosene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-docosene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-tricosene. The composition of any sentence in any preceding paragraph, wherein at least one branched polyolefin polymer is polymerized from 1-tetracosene.

[0095] The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 1000 to 5000 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 1250 to 4750 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 1500 to 4500 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 2000 to 4250 as measured by gel permeation chromatography using a polystyrene standard. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 2500 to 4000 as measured by gel permeation chromatography using a polystyrene standard.

[0096] The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of any of the polymers described in the preceding sentence. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6 and C8 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6 and C10 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6 and C12 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6 and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6 and C16 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6, C8, and C10 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6, C8, and C12 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6, C8, and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C6, C8, and C16 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8 and C10 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8 and C12 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8 and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8 and C16 α-olefins. The composition of any sentence of any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8, C10 and C12 α-olefins.The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8, C10, and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C8, C10, and C16 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10 and C12 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10 and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10 and C16 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10, C12, and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10, C12, and C14 α-olefins. The composition of any sentence in any preceding paragraph, wherein the branched polyolefin polymer comprises a mixture of C10, C12, and C16 α-olefins.

[0097] The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise aromatic hydrocarbyl groups. The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise hydroxyl-containing aromatic groups. The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise amine-containing aromatic groups. The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise aliphatic hydrocarbyl groups. The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise cyclic hydrocarbyl groups. The composition of any sentence in any preceding paragraph, wherein the branches of the branched polyolefin polymer comprise a mixture of any of the foregoing hydrocarbyl groups.

[0098] The composition of any sentence of any preceding paragraph, wherein the branches of the branched polyolefin polymer are substantially free of or free of succinimide or succinic anhydride functionality.

[0099] The composition of any preceding paragraph, comprising 0.01 to 5 wt. % of a branched polyolefin polymer, based on the weight of the composition. The composition of any preceding paragraph, comprising 0.05 to 4.5 wt. % of a branched polyolefin polymer, based on the weight of the composition. The composition of any preceding paragraph, comprising 0.1 to 4 wt. % of a branched polyolefin polymer, based on the weight of the composition. The composition of any preceding paragraph, comprising 0.5 to 3.5 wt. % of a branched polyolefin polymer, based on the weight of the composition.

[0100] 10. A method for increasing hydrocarbon production from a subterranean hydrocarbon-bearing formation, the method comprising injecting a composition described in any sentence of the preceding paragraph into the formation; and recovering the released hydrocarbons from the hydrocarbon-bearing formation.

[0101] 1. A method for increasing the viscosity of supercritical carbon dioxide, comprising adding to carbon dioxide a thickening agent, the thickening agent comprising at least one branched polyolefin polymer, which thickens the combination of carbon dioxide and thickening agent by at least 100% compared to supercritical carbon dioxide.

[0102] The method of the preceding paragraph, wherein the viscosity is increased at a pressure of 500 to 10,000 psi and a temperature of 30 C to 120 C. The method of the preceding paragraph, wherein the viscosity is increased at a pressure of 750 to 6,000 psi and a temperature of 30 C to 120 C.

[0103] While certain representative embodiments and details have been set forth for the purpose of illustrating the subject invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the present invention is to be limited only by the claims that follow. The present invention provides, for example, the following items. (Item 1) A carbon dioxide composition comprising a majority of carbon dioxide and at least one branched polyolefin polymer. (Item 2) 2. The carbon dioxide composition of claim 1, wherein the composition has a relative viscosity that is at least 100% greater than supercritical carbon dioxide. (Item 3) Item 10. The composition of any one of the preceding items, wherein the polyolefin polymer has a number average molecular weight of 140 to 5000 as measured by gel permeation chromatography using polystyrene standards. (Item 4) Item 10. The composition of any one of the preceding items, wherein the at least one branched polyolefin polymer is polymerized from a C2 to C24 olefin or mixtures thereof. (Item 5) Item 10. The composition of any one of the preceding items, wherein the branched polyolefin polymer comprises a polyisobutylene polymer. (Item 6) 2. The composition according to item 1, wherein the at least one branched polyolefin polymer is polymerized from a C4 to C24 α-olefin or a mixture thereof. (Item 7) 6. The composition according to item 5, wherein the branched polyolefin polymer comprises a polydecene polymer having an Mn of 1000 to 5000. (Item 8) Item 10. The composition of any one of the preceding items, wherein the branches of the branched polyolefin polymer comprise at least one of aromatic hydrocarbyl groups, aliphatic hydrocarbyl groups, cyclic hydrocarbyl groups, and mixtures thereof. (Item 9) Item 10. The composition of any one of the preceding items, wherein the branches of the branched polyolefin polymer comprise hydroxyl-containing aromatic groups. (Item 10) Item 10. The composition of any one of the preceding items, wherein the branches of the branched polyolefin polymer comprise amine-containing aromatic groups. (Item 11) Item 10. The composition of any one of the preceding items, wherein the branches of the branched polyolefin polymer are substantially free of, or free of, succinimide or succinic anhydride functionality. (Item 12) 10. The composition of any one of the preceding items, comprising 0.01 to 5 wt. % of the branched polyolefin polymer, based on the weight of the composition. (Item 13) 10. A method for increasing hydrocarbon production from a subterranean hydrocarbon-bearing formation, the method comprising injecting a composition of any one of the preceding items into the formation and recovering hydrocarbons released from the hydrocarbon-bearing formation. (Item 14) 1. A method for increasing the viscosity of supercritical carbon dioxide, comprising adding to the carbon dioxide a thickening agent, the thickening agent comprising at least one branched polyolefin polymer, that increases the relative viscosity of a combination of the carbon dioxide and the thickening agent by at least 100% compared to the supercritical carbon dioxide. (Item 15) Item 14. The method according to item 13, wherein the viscosity is increased at a pressure of 500 to 10,000 psi and a temperature of 30°C to 120°C.

Claims

1. A carbon dioxide composition comprising a majority of carbon dioxide and a polydecene polymer having a number average molecular weight of 1500 to 5000 as determined by gel permeation chromatography using a polystyrene standard.

2. 10. The carbon dioxide composition of claim 1 comprising 0.01 to 5 wt. % of said polydecene polymer, based on the weight of said composition.

3. 3. The carbon dioxide composition of claim 2, wherein the composition has a relative viscosity at least 100% greater than supercritical carbon dioxide.

4. A carbon dioxide composition according to any one of claims 1 to 3, comprising 0.5 to 5 weight percent of the polydecene polymer based on the weight of the composition.

Images