WO2019149580A1

WO2019149580A1 - Diurea compound based thickeners for liquid and supercritical hydrocarbons

Info

Publication number: WO2019149580A1
Application number: PCT/EP2019/051550
Authority: WO
Inventors: Markus Hansch; Meik Ranft; Christian Bittner
Original assignee: Basf Se
Priority date: 2018-01-30
Filing date: 2019-01-23
Publication date: 2019-08-08

Abstract

The present invention relates to a composition comprising at least one compound of general formula (I) and at least one liquid or supercritical C₂-C₅ hydrocarbon. The present invention further relates to the use of the at least one compound of general formula (I) as thickener for the at least one liquid C₂ -C₅ hydrocarbon. The invention also relates to a method of fracturing a subterranean formation penetrated by a wellbore with the composition of the present invention. The invention further relates to a method of enhanced oil recovery using the composition of the present invention.

Description

Diurea compound based thickeners for liquid and supercritical hydrocarbons Field of the Invention

The present invention relates to a composition comprising at least one compound of general formula (I) and at least one liquid or supercritical C₂-C₅ hydrocarbon. The present invention further relates to the use of the at least one compound of general formula (I) as thickener for the at least one liquid C₂-C₅ hydrocarbon. The invention also relates to a method of fracturing a subterranean formation penetrated by a wellbore with the composition of the present in vention. The invention further relates to a method of enhanced oil recovery using the compo sition of the present invention.

Background of the Invention

Hydraulic fracturing is a widely used oil and gas production stimulation technique. It is a well- known process used to recover hydrocarbon fluids such as gases (e.g., natural gas) or liquids (e.g., oil or petroleum) that are otherwise trapped or present in the pores of underground formations. At its most basic level, hydraulic fracturing involves the creation of fractures (e.g., cracks, fissures, etc.) in rocks or underground formations which will allow hydrocarbon fluids to flow toward a production well. Hydraulic fracturing of subterranean formations (also re ferred to as fracking), provides a pathway for hydrocarbon fluids to move more easily through tight low permeability (micro Darcy) formations (e.g., shale, certain clay sandstones, lime stones, etc.) to a production well.

Fracturing fluids are designed to enable the initiation or extension of fractures and the simul taneous transport of suspended proppant (for example, naturally-occurring sand grains, res in-coated sand, sintered bauxite, glass beads, ultra-lightweight polymer beads and the like) into the fracture to keep the fracture open when the pressure is released.

Water based fracturing (hydrofracturing) is the most common one, in which the fracturing fluid comprising at least water, water-soluble thickeners and proppants are used. Although widely distributed, said technology has some drawbacks: when releasing the pressure after fracturing, a huge amount of water is returned to the surface through the injection well. Said wastewater produced from the formation typically is a mixture of used fracturing fluid and formation water. Formation water usually comprises a very high amount of salts. Consequent ly, the wastewater produced also comprises salts and furthermore chemicals of the fracturing fluid or decompositions products thereof. Disposal of such a wastewater mixture may be ex pensive. Furthermore, by using water, the surfaces of the subterranean formation become wetted which may impair the production of crude oil from the formation. Intensified concerns by the public regarding water pollution (requires ~3-6 million gallons of water per well) for hydrofracturing have prompted many companies to search for alternatives to hydrofracturing, especially in water-sensitive formations. Petroleum fluids have been used for fracturing purpose since 1950. Because of its volatility, liquified petroleum gas (LPG) leaves no residue behind. The benefits of using high pressure volatile light alkanes for fracturing include the elimination of the formation damage associated with conventional aqueous fluids, and the ease of removal of the hydrocarbons via depressur ization, the absence of waste water, and the ability to recapture the alkanes at the wellhead after the proppant is placed. Liquid hydrocarbons (mixtures of propane, butane) and natural gas liquid (unfractionated hydrocarbon mixture comprising ethane, propane, butane, isobu tane, and pentane plus) have been used as fracturing fluids for waterless fracking. However, the disadvantage of these liquified alkane based fracturing fluids is the low viscosity. This re quires the use of certain gelling chemicals for the“gelation” or“thickening” of the light liquid alkanes to enable them to generate larger fractures and to carry higher concentrations of larger sand proppant particles.

US 3,368,627 describes a fracturing method that uses a combination of a liquid C₂-C₆ hydro carbon and C0₂ mix as the fracturing fluid.

US 9187996 B1 discloses a fracturing fluid mixture which is used to hydraulically fracture un derground formations in a reservoir, by mixing at least natural gas comprising methane and a base fluid comprising an aqueous or hydrocarbon well servicing fluid to form the fracturing fluid mixture, and injecting the fracturing fluid mixture into a well.

For oil formations, in order to obtain the desired fracture width, higher viscosity fracturing fluids are employed. Consequently, higher loading of proppants is used to suitably prop open the relatively wide fractures. Fluids with low viscosity typically lack sufficient viscosity to carry such amounts of proppants, especially at high temperatures. A variety of chemicals/molecules are used to increase the viscosity of the fracturing fluid. With any viscosity increase, some type of gelling chemical (thickener) must be used first. Viscosity is used to carry proppant into the formation, but when a well is being flowed back or produced, it is undesirable to have the fluid pull the proppant out of the formation. For this reason, a chemical known as a breaker is almost always pumped with all gel or crosslinked fluids to reduce the viscosity. This chemical is usually an oxidizer or an enzyme. The oxidizer reacts with the gel to break it down, reducing the fluid's viscosity and ensuring that no proppant is pulled from the formation. An enzyme acts as a catalyst for the breaking down of the gel. Sometimes pH modifiers are used to break down the crosslink at the end of a hydraulic fracture job, since many require a pH buffer sys tem to stay viscous. The rate of viscosity increase for several gelling agents is pH-dependent, so that occasionally pH modifiers must be added to ensure viscosity of the gel.

Typical gelling chemicals include: (1) Conventional linear gels - These gels are cellulose deriva tives (carboxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, hydroxypropyl cellulose, methyl hydroxyl ethyl cellulose), guar or its derivatives (hydroxypro- pyl guar, carboxymethyl hydroxypropyl guar), (2) Borate-crosslinked gels - These are guar- based fluids cross-linked with boron ions (from aqueous borax/boric acid solution). These gels have higher viscosity at pH 9 onwards and are used to carry proppants. After the fracturing job, the pH is reduced to 3-4 so that the cross-links are broken and the gel is less viscous and can be pumped out. Organometallic-crosslinked fluids zirconium, chromium, antimony, titani um salts are known to crosslink the guar based gels. The crosslinking mechanism is not re versible. So once the proppant is pumped down along with the cross-linked gel, the fracturing part is done. The gels are broken down with appropriate breakers; (3) Aluminum phosphate- ester oil gels - Aluminum phosphate and ester oils are slurried to form cross-linked gel. These are one of the first known gelling systems.

WO 2007/098606 A1 discloses a fracturing system for a well, in which a mixture of propane and butane is injected into the well along with an inert gas such as nitrogen. The mixture of propane and butane is thickened with a gelling agent created by reacting diphosphorus pentoxide with triethyl phosphate and C₃-C₇ alcohol which is further reacted with aluminum sulfate.

US 2011/0284230 A1 discloses waterless fracturing method in which liguified petroleum gas (LPG) is used as a fracturing fluid. A gelling agent created by reacting diphosphorus pentoxide with triethyl phosphate and C₃-C₇ alcohol which is further reacted with aluminum sulfate.

WO2014036498 A2 relates to multi-arm star macromolecules which are used as thickening agents or rheology modifiers, for use in hydraulic fracturing fluid compositions.

WO 2016/064645 A1 describes a Y-Grade Natural gas liguid (NGL) stimulation fluid, compris ing about 30% to 80% of ethane; about 15% to 50% of propane; about 15% to 45% of butane; about 15% to 40% of isobutane; about 5% to 25% of pentane plus, proppant, carbon dioxide, nitrogen and a gelling agent which includes at least one of phosphate esters and organo- metallic complex cross-linkers.

Aluminum phosphate-ester oil gels are very limited in use currently, because of formation damage and difficulty in cleanup. Due to the costs associated with guar, it is not economical to obtain the desired high viscosity by simply increasing the concentration of the guar poly mer. Overly concentrated guar fracturing fluids lead to adverse effects for the formation and proppant pack, i.e., formation or proppant pack damage, offsetting the benefit brought by the fracturing process.

Use of the gelling agent based on guar gums, borate-crosslinked gels or aluminum phos phate-ester oil gels reguires a gel breaker which is added to break the gel, after the fractur ing.

In addition to the disadvantages of using the gelling agents as described above, their solubili ty in liguid hydrocarbon is another challenge, this being the reason that very few gelling agents are reported for the liguid hydrocarbons. Additionally, gelling agents/thickeners are also employed in enhanced oil recovery(EOR) or tertiary recovery process. In the domestic oil production, enhanced oil recovery is used for recovering the residual oil trapped in the formation. For this, the known techniques are high pressure carbon dioxide flooding and flooding with natural gas liquids (NGL), which is primari ly a mixture of ethane, propane, butane and a small amount of pentanes and higher alkanes. High pressure carbon dioxide or NGL has the ability to mix with oil to swell it, make it less vis cous, detach it from the rock surface and cause the oil to flow more freely within the reservoir towards the production well. NGL flooding is more efficient than C0₂ flooding because the amount of oil recovered per amount of solvent injected is more. However, NGL has low den sity and viscosity relative to crude oil and thus it tends to exhibit gravity override as it flows through the formation, reducing oil recovery in the lower portions of reservoir. The NGL flow can be tailored by adding thickeners/gelling agents. Thickeners/gelling agents for ethane, propane, butane and pentane are intended to dissolve completely in these high-pressure flu id, forming a transparent, thermodynamically stable, single-phase solution capable of flowing through the porous media in a controlled manner. However, the thickeners/gelling agents being used for the thickening of the NGL for EOR are similar to those as described above for the waterless fracking, hence they exhibit the same drawbacks as indicated above.

Accordingly, it is an object of the presently claimed invention to provide a gelling agent (thickener) which overcomes the problems associated with the gelling agents of the prior art.

It is also an object to provide a gelling agent which is soluble in liquid hydrocarbons and su percritical hydrocarbons and whose viscosity can be easily lowered, without use of additional oxidative molecules or additional operations, after fracturing or recovery of oil is done.

Summary of the Invention

Surprisingly it was found that certain diurea compounds show improved thickening properties of liquid or supercritical hydrocarbons and lead to fracturing fluids with the desired viscosity. The diurea compounds of the present invention do not require a breaker molecule or an oxi dizer to decrease the viscosity after the fracturing or after the recovery of oil.

Thus, in an aspect the presently claimed invention relates to a composition comprising

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon;

(ii) at least one compound of general formula (I)

wherein R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^_Ci alkyl.

In another aspect, the presently claimed invention relates to the use of the at least one com- pound of general formula (I) as thickener for the at least one liquid or supercritical C2-C5 hy drocarbon.

In another aspect, the presently claimed invention relates to the use of the at least one com- pound of general formula (I)

wherein R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^_Ci alkyl;

as thickener for the at least one liquid or supercritical C₂-C₅ hydrocarbon.

In another aspect, the presently claimed invention relates to the use of the composition com- prising

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon;

(ii) at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^~Ci alkyl;

for fracturing.

In another aspect, the present invention is directed to use of the composition comprising

(i) at least one liquid or supercritical C₂-Cs hydrocarbon; and

(ii) at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubsti tuted C₁-C₁₄ alkyl. for enhanced oil recovery (EOR).

In another aspect, the present invention relates to a method of fracturing a subterranean for mation penetrated by a wellbore, comprising the steps of

(a) formulating the composition comprising the at least one liguid or supercritical C₂-C₅ hydro

-carbon, and

at least one compound of general formula (I) with the at least one proppant to obtain a fracturing fluid, and

(b) pumping the fracturing fluid of step (a) down the wellbore.

Detailed description of the Invention

Before the present compositions and formulations of the invention are described, it is to be understood that this invention is not limited to particular compositions and formulations de scribed, since such compositions and formulation may, of course, vary. It is also to be under stood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

If hereinafter a group is defined to comprise at least a certain number of embodiments, this is meant to also encompass a group which preferably consists of these embodiments only. Fur thermore, the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)" etc. and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a seguential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodi ments of the invention described herein are capable of operation in other seguences than described or illustrated herein. In case the terms "first", "second", "third" or“(A)”,“(B)” and “(C)” or "(a)", "(b)", "(c)", "(d)", "i", "ii" etc. relate to steps of a method or use or assay there is no time or time interval coherence between the steps, that is, the steps may be carried out simultaneously or there may be time intervals of seconds, minutes, hours, days, weeks, months or even years between such steps, unless otherwise indicated in the application as set forth herein above or below. In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advanta geous.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodi ment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more em bodiments. Further-more, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodi ments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the claimed embodiments can be used in any combination.

In one aspect, the presently claimed invention relates to a composition comprising

(i) at least one liquid or supercritical C₂-Cs hydrocarbon;

(ii) at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci Ci₄ alkyl.

(i) Liquid or supercritical hydrocarbon

In an embodiment, the hydrocarbon is at least one liquid or supercritical C₂-C₅ hydrocarbon.

The at least one liquid or supercritical C₂-C₅ hydrocarbon is selected from the group consist ing of ethane, n-propane, n-butane, n-pentane, isopropane, isobutane, isopentane, isomers and mixtures thereof. The at least one liguid or supercritical C₂-C₅ hydrocarbon is selected from the group consist ing of n-propane, n-butane, n-pentane and mixtures thereof. The term‘liguid’ refers to the C₂-C₅ hydrocarbon in a liguid state. C₂-C₅ hydrocarbon such as ethane, n-propane, isobutane are present in gas phase at ambient conditions and suitable pressure and temperature for liguefying them is well known to the person skilled in the art and the present invention is not limited by the choice of the same. However, hydrocarbon such as n-propane and isopropane exist as liguid at ambient conditions.

In an embodiment, the at least one liguified C₂-C₅ hydrocarbon (i) can be such as, but not limited to, a liguified petroleum gas (LPG) or a natural gas liguid (NGL). As is known to the person skilled in the art, LPG is a mixture of propane and butane, while NGL is a mixture of ethane, propane, butane and pentane. LPG is liguid under low pressure of 5-10 atmospheres but without the need to cool it. NGL is separated from the gas state in the form of liguids, in a field facility or in a gas processing plant through absorption or condensation.

A supercritical fluid is defined as any substance at a temperature and pressure above its criti cal point, where distinct liguid and gas phases do not exist. The term‘supercritical C₂-C₅ hy drocarbon’ refers to C₂-C₅ hydrocarbon at a temperature and pressure above their respective critical point, where distinct liguid and gas phases do not exist. For instance, for supercritical propane, critical pressure = 42.5 bar and critical temperature = 97°C.

(ii) Compound of general formula (I)

In a preferred embodiment, the composition of the present invention comprises the at least one compound of general formula (I)

wherein

In connection with“alkyl”, the term“substituted” within the scope of this invention is under stood as meaning the substitution of hydrogen by 1, 2, 3, 4 or 5 substituents selected from the group consisting of F, Cl, Br, I, CN, NH₂, NH-Ci-₆-alkyl, NH-Ci-₆-alkylene-OH, N(Ci-₆-alkyl)₂, N(Gi-₆-alkylene-OH)₂, N0₂, SH, S-Ci-₆-alkyl, S-benzyl, 0-Ci-₆-alkyl, 0-Ci-₆-alkylene-OH, =0, O- benzyl, C (=0) Ci_₆- alkyl, C0₂H, C(=0)-0-Ci-₆-alkyi, phenyl and benzyl. The substitution of hy drogen occurs either on different atoms or on the same atom, for example trisubstituted on the same carbon atom, as in the case of CF₃ or CH₂CF₃, or at different positions, as in the case of CH(CI)-CH=CH-CHCI₂. Polysubstitution can be carried out with the same or with different substituents, such as, for example, in the case of CH(OH)-CH=CH-CHCI₂.

Preferably, the substituents are selected from the group consisting of F, Cl, I, N(Ci-₆-alkyl)₂, N(Gi-₆-alkylene-OH)₂, N0₂, S-Ci-₆-alkyl, S-benzyl, O-Ci-₆-alkyl, O-Ci-₆-alkylene-OH, =0, O- benzyl, C (=0) Ci_₆- alkyl, C0₂H, C(=0)-0-Ci-₆-alkyi, phenyl and benzyl.

As used herein,“branched” denotes a chain of atoms with one or more side chains attached to it. Branching occurs by the replacement of a substituent, e.g., a hydrogen atom, with a co valently bonded aliphatic moiety.

Preferably, R¹ and R² are, independently of one another, selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n- undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, 2-ethylhexyl, 1,5-dimethyl hexyl, isopropyl, isobu tyl, isopentyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 1-ethyl-1-propyl, 1-phenyl-1-ethyl, tert-butyl, isohexyl, isoheptyl, 2-pro pylheptyl, 1,1,3,3-tetramethyM-butyl, isononyl, isodecyl, isoundecyl, isododecyl, isotridecyl, isotetradecyl, and isomers thereof.

In a preferred embodiment, R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted C₆-Ci₃ alkyl.

More preferably, R¹ and R² are, independently of one another, selected from the group con sisting of n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, 2-ethylhexyl, 1,5- dimethyl hexyl, isopropyl, isobutyl, isopentyl, isohexyl, isoheptyl, 2-propylheptyl, 1,1,3,3- tetramethyM-butyl, isononyl, isodecyl, isoundecyl, isododecyl, isotridecyl and isomers thereof.

Most preferably, R¹ and R² are, independently of one another, selected from the group con sisting of 2-ethylhexyl, 1,5-dimethyl hexyl, isotridecyl and isomers thereof.

The at least one compound of general formula (I) can be obtained by reacting diisocyanates with monoamines.

For the present invention, the diisocyanate is toluene diisocyanate (TDI). Toluene diisocyanate exists in 6 isomeric forms, of which toluene 2,4-diisocyanate and toluene 2,6-diisocyanate are commercially available. For the present invention, the preferred diisocyanates are toluene 2,6- diisocyanate (CAS 91-08-7) and toluene 2,4-diisocyanate (CAS 584-84-9) or mixtures thereof. A preferred diisocyanate is a mixture of the 2,4 and 2,6 isomers of toluene diisocyanate, pref erably the mixture comprises 2,4 toluene diisocyanate in the range of > 80 % to < 98 %, more preferably in the range of > 80 % to < 95 %.

When toluene 2,4-diisocyanate is used as a diisocyanate, the at least one compound of gen eral formula (la)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci-Ci alkyl;

is obtained.

When toluene 2,6-diisocyanate is used as a diisocyanate, compounds of general formula (lb)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^_Ci alkyl;

is obtained.

In case a mixture of diisocyanate, toluene 2,4-diisocyanate and toluene 2,6-diisocyanate is used, a mixture of compounds of general formula (la) and compounds of general formula (lb) is obtained.

Accordingly, in a preferred embodiment, the composition comprises

(i) at least one liguid or supercritical C₂-C₅ hydrocarbon, and

(ii) at least one compound of general formula (la)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci Ci alkyl.

In another preferred embodiment, the presently claimed invention is directed to the composi tion comprising

(i) at least one liguid or supercritical C₂-C₅ hydrocarbon;

(ii) at least one compound of general formula (lb)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci-Ci4 alkyl.

Preferably, the compounds of general formula (I) are prepared by reacting a mixture of tolu ene 2,4-diisocyanate and toluene 2,6-diisocyanate with a monoamine.

The monoamine is selected from the group consisting of methylamine, ethylamine, n- propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, n- nonylamine, n-decylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, n- tetradecylamine, 2-ethylhexylamine, 1,5-dimethyl hexylamine, isopropylamine, isobutylamine, isopentylamine, 3-methyl-1-butylamine, 2-methyl-1-butylamine, 1-Ethyl-1-propylamine, 1- phenyl-1-ethylamine, tert-butylamine, isohexylamine, isoheptylamine, 2-propylheptylamine, , 1,1,3,3-tetramethyM-butylamine, isononylamine, isodecylamine, isoundecylamine, isododecyl- amine, isotridecylamine, isotetradecylamine, and isomers thereof.

In a preferred embodiment, the monoamine is selected from the group consisting of n- hexylamine, n-heptylamine, n-octylamine, n-nonylamine, n-decylamine, n-undecylamine, n- dodecylamine, 2-ethylhexylamine, 1,5-dimethyl hexylamine, isopropylamine, isobutylamine, isopentylamine, isohexylamine, isoheptylamine, 2-propylheptylamine, 1,1,3,3-tetramethyM- butylamine, isononylamine, isodecylamine, isoundecylamine, isododecylamine, isotridecyla mine and isomers thereof.

In a more preferred embodiment, the monoamine is selected from the group consisting of 2- ethylhexylamine, 1,5-dimethyl hexylamine, isotridecylamine and isomers thereof.

The monoamines are reacted with the diisocyanates in an organic solvent (F. Lortie, Langmuir 2002, 18, 7218). The resulting product is separated from the organic solvent and then dis solved in liguid or supercritical hydrocarbon to prepare inventive compositions.

In a preferred embodiment, the at least one compound of general formula (I) has molecular weight in the range of > 200 g/mol to < 2000 g/mol, more preferably in the range of > 200 g/mol to < 1500 g/mol, even more preferably in the range of > 200 g/mol to < 1400 g/mol or > 300 g/mol to < 1400 g/mol and most preferably in the range of > 400 g/mol to < 1400 g/mol. In another embodiment, the presently claimed invention is directed to a composition com prising the at least one compound of general formula (I) in an amount in the range of > 0.01 to < 10.0 % by weight of the final weight of the composition, more preferably in the range of > 0.01 to < 10.0 % by weight or > 0.01 to < 9.0 % by weight or > 0.01 to < 8.0 % by weight or > 0.01 to < 7.0 % by weight or > 0.01 to < 6.0 % by weight or > 0.01 to < 5.0 % by weight, > 0.01 to < 4.0 % by weight or > 0.01 to < 3.0 % by weight or > 0.01 to < 2.0 % by weight or even more preferably in the range of > 0.05 to < 10.0 % by weight or > 0.05 to < 9.0 % by weight or

> 0.05 to < 8.0 % by weight or > 0.05 to < 7.0 % by weight or > 0.05 to < 6.0 % by weight or > 0.05 to < 5.0 % by weight or > 0.05 to < 4.0 % by weight or > 0.05 to < 3.0 % by weight or > 0.05 to < 2.0 % by weight and most preferably in the range of > 0.01 to < 10.0 % by weight or

> 0.01 to < 9.0 % by weight or > 0.01 to < 8.0 % by weight or > 0.01 to < 7.0 % by weight or > 0.01 to < 6.0 % by weight or > 0.01 to < 5.0 % by weight or > 0.01 to < 4.0 % by weight or >

0.01 to < 3.0 % by weight or > 0.01 to < 2.0 % by weight; in each case by weight of the final weight of the composition.

The at least one compound of general formula (I) may be solid or sticky, wax-like compound at ambient conditions.

In an embodiment, the at least one compound of general formula (I) may be dissolved in a solvent in which they do not self-assemble, but rather are molecularly dissolved, prior to their addition to the liguid or supercritical hydrocarbons. This may result in concentrated solutions with low viscosities facilitating handling and mixing with the liguid or supercritical hydrocar bons which are to be thickened according to the invention.

In a preferred embodiment, the suitable solvents are C1-C30 alcohols. C1-C30 alcohols are se lected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, 2-ethylhexanol, 2-propylhepanol, isononanol, decanol, dodecanol. Suitable solvents may include (poly)alkylene glycols or alkyl (poly)alkylene glycols like polypropylene glycol, polyethylene glycol, polybutylene glycol, butylene glycol, propylene glycol, ethylene glycol, methyl propylene glycol, methyl dipropylene glycol, methyl tripropylene glycol, butyl propyl ene glycol, butyl dipropylene glycol, butyl tripropylene glycol, methyl ethylene glycol, methyl diethylene glycol, methyl triethylene glycol, butyl ethylene glycol, butyl diethylene glycol, butyl triethylene glycol. Further suitable solvents include water, tetrahydrofuran, 1,4-butanediol, 1,3- propylenglycol, and aromatic solvents like toluene, xylene, solvent naphtha, alkylated aromat ics like Wibarcan^®. The addition of chlorides may further decrease the viscosity of concentrat ed solution of the diurea compounds, for example NaCI, LiCI, KCI, NMe₄CI and NBu₄CI.

Proppants

The fracturing fluid further comprises at least one proppant which is suspended in the fractur ing fluid. Proppants are small hard particles which remains in place in the fractures once the high pressure is removed, and thereby props open the fractures to enhance the flow of oil into the wellbore. Consequently, the proppant increases the procurement of oil by creating a high-permeability, supported channel through which the oil can flow.

Suitable proppants are known to the skilled artisan. Examples of proppants include naturally- occurring proppants such as sand grains, nut shells, minerals, gravels, mine tailings, coal ash es, rocks, smelter slag, diatomaceous earth, crushed charcoal, micas, sawdust, wood chips, and synthetically produced proppants such as silica proppants, ceramic proppants, metallic proppants, synthetic organic proppants, and mixtures thereof. Proppant comprising a particle and a polycarbodiimide coating disposed on the particle as described in WO 2010/049467 A1 can also be used.

Resin coated versions of sand grains is also a suitable proppant.

Typical resin coatings include bisphenols, bisphenol homopolymers, blends of bisphenol ho mopolymers with phenol-aldehyde polymer, bisphenol-aldehyde resins and polymers, phe nol-aldehyde polymers and homopolymers, modified and unmodified resoles, phenolic mate rials including arylphenols, alkylphenols, alkoxyphenols, and aryloxyphenols, resorcinol resins, epoxy resins, novolak polymer resins, novolak bisphenol-aldehyde polymers and waxes, as well as precured or curable versions of such resin coatings.

Silica proppants suitable for use, but are not limited to, glass spheres and glass microspheres, glass beads, silica quartz sand, and sands of all types such as white or brown sand. In case of silica fibers being used, the fibers can be straight, curved, crimped or spiral shaped, and can be of any grade, such as E-grade, S-grade and AR-grade. Examples of suitable resin-coated silica proppants are for example FlexSand™ LS, FlexSand™ M, available from BJ services, U.S., TX and Tempered HS^®, Tempered LC^®, Tempered DC^® and Tempered TF^® from Santrol, Fresno, TX.

Examples of suitable ceramic proppants suitable for use are ceramic beads, ultra-lightweight porous ceramics, economy lightweight ceramics such as‘Econoprop™, lightweight ceramics such as Carbolite^®, intermediate strength ceramics such as Carboprop^®, high strength ceram ics such as Carbohsp^®, sintered bauxite, encapsulated ceramic proppants as well as any resin coated or resin impregnated version of these.

Metallic proppants suitable for use include, but are not limited to, aluminium shot, aluminium pellets, aluminium needles, aluminium wire, iron shot, steel shot, and the like, as well as any resin coated versions of these metallic proppants.

Examples of synthetic organic proppants are plastic particles, plastic beads, nylon beads, ny lon pellets, styrene divinyl benzene beads, carbon fibers such as Panex^® carbon fibers from Zoltek Corporation, ultra-lightweight polymer beads and resin agglomerate particles as well as resin coated versions thereof. In a preferred embodiment, the amount of proppant in the fracturing fluid is in the range of > 50 kg to < 3500 kg per m³ of the fracturing fluid, preferably in the range of > 50 kg to < 1200 kg per m³ of the fracturing fluid.

Additives

Depending upon the type of subterranean formation being treated and the intended type of treatment operation being conducted, other components may be optionally included in one or both of the proppant slurry and non-proppant injection liguid. A person having ordinary skill in the art, with the benefit of this disclosure, will recognize when such optional additives should be included, as well as the appropriate amounts to include.

Such components may include, for example, salts, pH control additives, surfactants, foaming agents, antifoaming agents, breakers, biocides, crosslinkers, additional fluid loss control agents, stabilizers, chelating agents, scale inhibitors, gases, mutual solvents, particulates, cor rosion inhibitors, oxidizing agents, reducing agents, antioxidants, relative permeability modifi ers, viscosifying agents, scale inhibitors, emulsifying agents, de-emulsifying agents, iron con trol agents, clay control agents, flocculants, scavengers, lubricants, friction reducers, viscosifi- ers, weighting agents, hydrate inhibitors, consolidating agents, delay agents, any combination thereof, and the like. Such components may include gelling/thickening agents reported in the state-of-the art such as tributyltin fluoride (TBTF), hydroxyl aluminum bis(2-ethylhexanoate) (HADEH), crosslinked phosphate ester (HGA70 C6 + HGA 65), silanol and ultra-high molecular weight poly-a-olefin drag reducer (DRA), gelling agent created by reacting diphosphorus pentoxide with triethyl phosphate and C3-C7 alcohol which is further reacted with aluminium sulfate, cellulose and cellulose derivatives, multi-arm star macromolecules.

However, in a more preferred embodiment, the at least one compound of general formula (I) are by themselves efficient thickening agents for the at least one C2-C5 liguid or supercritical hydrocarbon and do not reguire additional gelling/thickening agents as additives.

In an aspect, the present invention is directed to use of the at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci-Ci4 alkyl;

as thickener for the at least one liguid or supercritical C₂-C₅ hydrocarbon. In another embodiment, the present invention is directed to use of the at least one com pound of general formula (la)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^~Ci₄ alkyl;

In an embodiment, the present invention is directed to use of the at least one compound of general formula (lb)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^_Ci₄ alkyl;

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon; and

(ii) at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^~Ci₄ alkyl. for fracturing. In another embodiment, the present invention is directed to use of the composition compris ing

(0 at least one liquid or supercritical C₂-C₅ hydrocarbon; and

(ii) at least one compound of general formula (la)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^~Ci₄ alkyl. for fracturing.

In another embodiment, the present invention is directed to use of the composition compris ing

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon; and

(ii) at least one compound of general formula (lb)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted Ci^_Ci₄ alkyl. for fracturing.

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon; and

(ii) at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted C₁-C₁₄ alkyl. for enhanced oil recovery (EOR).

In another aspect, the present invention relates to a method for fracturing a subterranean formation.

In an embodiment, the method of fracturing a subterranean formation according to the pre sent invention may be applied to any subterranean formation, preferably hydrocarbon con taining subterranean formations. The hydrocarbons may be oil and/or gas. Besides oil and/or gas the formations may contain water which usually comprises salts. The salinity of the for mation water may be in the range of > 10,000 ppm to < 230,000 ppm.

The formations may be sandstone, carbonate or shale formations and the formation tempera ture may be up to 175°C.

In a preferred embodiment, inert gas such as nitrogen may be used as a gas blanket. When nitrogen is added to the fracturing fluid, the method has a particular utility for fracturing coal or shale formations.

According to an embodiment, a foam may be created by the mixing of composition accord ing to the present invention with inert gases such as nitrogen or carbon dioxide, where said nitrogen concentration is greater than 50% or where said carbon dioxide concentration is greater than 35%, or by a combination of nitrogen and carbon dioxide where said combined concentration of nitrogen and carbon dioxide in greater than 50% causes the resulting gase ous mixture to be outside the flammability limit.

For applying the method according to the present invention to the formation, the formation is penetrated by at least one wellbore. The wellbore may be a“fresh” wellbore drilled into the formation which needs to become prepared for oil and/or gas production.

In another embodiment, the wellbore may be a production well which already has been used for producing oil and/or gas but the production rate decreased and it is necessary to fracture the formation (again) in order to increase production. The method according to the present invention comprises at least two process steps (a) and (b). The method may optionally comprise further process steps.

In a preferred embodiment, the method of fracturing a subterranean formation penetrated by a wellbore, comprises the steps of

(a) formulating the composition comprising at least one liguid or supercritical C₂-C₅ hydro car

-bon and at least one compound of general formula (I) with the at

least one proppant to obtain a fracturing fluid, and

(b) pumping the fracturing fluid of step (a) down the wellbore.

In course of process step (a) a fracturing fluid comprising at least one liguid or supercritical C₂-C₅ hydrocarbon, at least one compound of general formula (I) and at least one proppant is formulated. The fracturing fluid may contain optionally further components/additives.

In an alternate process step (a), a fracturing fluid comprising at least one liguid C₂-C₅ hydro carbon, at least one compound of general formula (I), at least one proppant, an inert gas se lected from nitrogen and carbon dioxide or mixtures thereof and at least one emulsifying agent is formulated.

In course of process step (b) the fracturing fluid is pumped into a wellbore. In a preferred em bodiment, the fracturing fluid is pumped in to the wellbore at a rate and pressure sufficient to flow into the formation and to initiate or extend a fracture in the formation. In order to initiate or to extend fractures in the formation, a bottom hole pressure sufficient to open a fracture in the formation is necessary. The bottom hole pressure is determined by the surface pressure produced by the surface pumping eguipment and the hydrostatic pressure of the fluid col umn in the wellbore, less any pressure loss caused by friction. The minimum bottom hole pressure reguired to initiate and/or to extend fractures is determined by formation properties and therefore will vary from application to application. Methods and eguipment for fracturing procedures are known to the skilled artisan. The fluid simultaneously transports suspended proppants and the proppant becomes deposited into the fractures and holds fractures open after the pressure exerted on the fracturing fluid has been released.

In course of further process steps, such as step (c), the applied pressure is reduced thereby allowing at least a portion of the injected hydrocarbons to become recovered from the for mation. Upon reducing the applied pressure, the pressurized hydrocarbons stream, by virtue of their own pressure, back to the surface. Reducing the pressure allows the fractures to close. Proppant“props” fractures open and fracturing fluid is shut in or allowed to flow back. At the surface, chokes may be used to generate a pressure differential to allow fluid to begin to flow from the formation into the well bore.

Advantages compared to thickeners known in the state-of-the-art: 1. Diurea compounds of general formula (I) are more shear stable compared to high mo lecular weight polymers

2. The thickening efficiency of the diurea compounds of general formula (I) is higher than state-of-the-art thickeners for propane and butane.

3. No additional reguirement of adding gel breakers or oxidizing molecules.

Compounds

Toluene 2,4-diisocyanate (TDI) 95%,

1,5-Dimethylhexylamine 99%, are available from Aldrich.

2-Ethylhexylamine (2-EHNH₂) 99%,

Tridecylamine isomer mixture (iCi3H₂₇NH₂), CAS 86089-17-0.

Kerocom^® PIBA (65% by weight solution of polyisobutylene amine based on high-reactivity polyisobutene, M_n=1000, in an aliphatic hydrocarbon mixture) are available from BASF SE, Ludwigshafen, Germany.

Heptadecylamine isomer mixture (iCi₇H3₅NH₂) was obtained by alcohol amination of heptade- canol M (isomer mixture of primary heptadecanols, branched and linear, CAS no. 90388-00-4, from BASF SE) as described in W02011101303. n-Pentane, 98% from Aldrich

Propane, 99.99% from Matheson

TBTF: Tributyltin fluoride

HADEH: Hydroxyl aluminum bis(2-ethylhexanoate)

HGA70 C6 + HGA 65: Crosslinked phosphate ester by Lubrizol Oilfield Solutions

Silanol: Polydimethylsiloxane Silanol SE 30 (Mw 972540) from Momentive.

DRA: Ultra-high molecular weight poly-a-olefine drag reducer (Liguid-Power™ Flow Improv er) from Lubrizol Specialty Products, M >2*10⁷ g/mol.

Methods

Amine number

The total amine number (titration with perchloric acid) was determined according to

DIN EN ISO 9702.

Preparation of diurea compounds of general formula (I)

Example 1 was prepared as described in F. Lortie et al., Langmuir 2002, 18, 7218-7222.

Example 4 was prepared as described in V. Simic et al., J. Am. Chem. Soc. 2003, 125, 13148- 13154.

General procedure for the preparation of examples 2, 3, and 5:

A solution of the toluene 2,4-diisocyanate in dichloromethane (1.0 eguivalent, 3.4 ml sol vent/mmol diisocyanate) was admixed with a solution of the amine in dichloromethane (2.0 eguivalents according to total amine number, 0.67 ml solvent/mmol amine) at room tempera- ture. The exothermic reaction was cooled. After the addition was complete, stirring was con tinued at room temperature for 2 hours. The precipitated product was filtered and recrystal lized from ethyl acetate.

Table 1

* = not within the scope of the invention

Determination of the rheology-modifying properties in n-pentane

0.1 g of the compound under test was stirred in 99.9 g n-pentane at room temperature until complete dissolution. The rheological data were determined by using a low shear rheometer LS 300 from proRheo (Germany). The rheometer is designed to measure low viscous fluids. The geometry used was a concentric cylinder device of Couette type with rotating cup. The diameters of cup and bob are 6 mm and 5.5 mm, respectively. The bob is of DIN type (with conical end) and has a length of 8 mm. Evaporation of the volatile components was retarded by measuring at 20°C.

All viscosities have been measured as a function of the shear rate at a constant concentration of 0.1% (w/w). Significant shear thinning behavior was found for the samples 2 and 4. Never theless, even when the other samples show a less pronounced shear thinning, there is still an indication of a shear induced structural orientation with the shear thinning behavior in the viscosity regime of 1-2 mPas.

In order to better compare the viscosifying efficiency a relative viscosity value was calculated from the values at 5 s ¹ for samples 2 and 4. For the other samples the plateau value from the zero-shear viscosity plateau was taken. The relative viscosity is the ratio of the viscosity of the fluid with the dissolved thickener to the viscosity of the pure fluid.

The following results were obtained:

Table 2

* = not within the scope of the invention

The above Table 2 indicates that by adding the inventive compounds even in small quantities, a huge increase in the viscosity can be achieved.

Determination of solubility and cloud point pressures in propane:

The solubility of example 4 in propane was assessed using an invertible, variable volume cell as described in A. Dhuwe et al., Journal of Petroleum Science and Engineering, 145, 2016, 266 and A. Dhuwe et al., J. of Supercritical Fluids 2016, 114, 9. The samples required heating to 110- 115°C and stirring at 5000 psi in propane to attain dissolution. Stable, transparent solutions were obtained at these conditions. The solutions were then cooled to the desired T and then slowly expanded to get the cloud point pressures, which are summarized in table 3. Table 3

The above Table indicates that the compound of inventive example 4 is quite soluble in pro pane. The resultant solution is transparent and stable above the cloud point pressure. Cloud point pressures range between -1000 - 4000 psi over the 0.5 - 2.0wt% of the compound of inventive example 4 and at temperature range of 25 °C-100 °C, with the highest cloud point pressure being associated with the highest concentration and temperature. Determination of relative viscosities in propane

Falling ball viscometry was employed via measuring the terminal velocity of a close-clearance glass that falls through the solution after the cell is rapidly inverted as described in A. Dhuwe et al., Journal of Petroleum Science and Engineering, 145, 2016, 266 and A. Dhuwe et al., J. of Supercritical Fluids 2016, 114, 9. Relative viscosity (solution viscosity/viscosity of the pure pro pane) was obtained as a function of concentration, pressure and temperature. All measure ments were taken at pressures greater than the cloud point pressure (i.e. in the single-phase region). In all cases the surface-average shear rate on the falling ball is about 7000/(relative viscosity) sA

Table 4

The ball was able to fall for compound of inventive example 4 at a concentration of 0.5 wt.%, 1.0 wt.%, 1.5 wt.% and 2.0wt% and temperature of 80 °C and 100 °C. The ball was not able to fall through the extremely viscous transparent solutions at 40 °C and 60 °C and concentrations of 1.0, 1.50 and 2.0 wt%. The ball was not able to fall through the extremely viscous transpar ent solutions at 25°C and concentrations of 0.50, 0.75, 1.00, 1.25, 1.50 and 2.00wt%.

The above table indicates that the compound of inventive example 4 is a remarkable thicken- er for propane. There is an increase of viscosity with higher concentrations and a decrease with increasing temperature. As the fracturing fluid goes down into the subterranean bore- well, the temperature rises and with the rise in the temperature, the viscosity of the inventive compound of the present invention decreases, thereby obviating the need of any oxidizers which are usually employed for decreasing the viscosity of the polymers after the fracturing fluid has reached the desired region. Thus, the inventive compounds of the present invention are suitable thickening agents for the fracturing process. It is believed that the inventive com pounds of general formula (I) form tube-like structures (“supramolecular polymers”) via hy drogen-bonding as described for example 1 in liguid hydrocarbons like dodecane and toluene in V. Simic et al., J. Am. Chem Soc. 2003, 125, 13148.

Comparison of the rheology modifying properties with state-of-the-art thickeners

As comparative examples, the rheology-modifying properties of the state of the art thicken ers, namely, tributyltin fluoride (TBTF), hydroxyl aluminum bis(2-ethylhexanoate) (HADEH), crosslinked phosphate ester (HGA70 C6 + HGA 65), silanol and ultra-high molecular weight poly-a-olefin drag reducer (DRA) are summarized in table 5. The data was obtained from Aman Kishorji Dhuwe, Thickeners for Natural Gas Liguids to improve the Performance in En hanced Oil Recovery and Dry Hydraulic Fracturing, M.S. Thesis, University of Pittsburgh, 2016 (available online: http://d-scholarship.pitt.edu/26533/). Parts of the thesis have been pub lished in A. Dhuwe et al., Journal of Supercritical Fluids, 114, 2016, 9; A. Dhuwe et al., Journal of Petroleum Science and Engineering, 145, 2016, 266. The results from table 5 were obtained using the same procedure as the results for inventive example 4 in table 4. Table 5

The comparison shows that inventive compound of example 4 has a superior thickening effi ciency for propane compared to the state-of-the-art thickeners. The thickening efficiency of the inventive compound of example 4 is more than ten times higher than those of the thick eners of the state-of-the-art.

Claims

1 A composition comprising

(i) at least one liquid or supercritical C₂-C₅ hydrocarbon; and

(ii) at least one compound of the general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubsti tuted C₁-C₁₄ alkyl.

2. The composition according to claim 1, wherein the at least one liquid or supercritical C₂- C₅ hydrocarbon (i) is selected from the group consisting of ethane, n-propane, n- butane, n-pentane, isopropane, isobutane, isopentane, isomers and mixtures thereof.

3. The composition according to claim 1 or 2, wherein the at least one liquid or supercriti cal C₂-C₅ hydrocarbon (i) is selected from n-propane, n-butane, n-pentane, isomers and mixtures thereof.

4. The composition according to claim 1, wherein R¹ and R² are, independently of one an other, selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n- tetradecyl, 2-ethylhexyl, 1,5-dimethyl hexyl, isopropyl, isobutyl, isopentyl, 3-methyl-1- butyl, 2-methyl-1-butyl, 1-ethyl-1-propyl, 1-phenyl-1-ethyl, tert-butyl, isohexyl, isoheptyl, 2-pro pylheptyl, 1,1,3,3-tetramethyl-1-butyl, isononyl, isodecyl, isoundecyl, isododecyl, isotridecyl, isotetradecyl, and isomers thereof.

5. The composition according to claim 1, wherein R¹ and R², independently of one another, are linear or branched, substituted or unsubstituted C₆-Ci₃ alkyl.

6. The composition according to claim 5, wherein R¹ and R² are, independently of one an other, selected from the group consisting of n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, 2-ethylhexyl, 1,5-dimethyl hexyl, isopropyl, isobutyl, isopentyl, iso hexyl, isoheptyl, 2-propylheptyl, 1,1,3,3-tetramethyM-butyl, isononyl, isodecyl, isound ecyl, isododecyl, and isomers thereof.

7. The composition according to one or more of claims 1 to 6, further comprising at least one proppant.

8. The composition according to claim 7, wherein the at least one proppant is selected from the group consisting of sand grains, resin-coated sand, sintered bauxite, glass beads, glass spheres, glass microspheres, silica guartz sand, ultra-lightweight polymer beads, minerals, ceramic beads, nut shells, gravels, mine tailings, coal ashes, rocks, smel ter slag, diatomaceous earth, crushed charcoals, micas, sawdust, wood chips, resinous particles, polymeric particles, plastic particles, plastic beads, nylon pellets, styrene divinyl benzene beads, carbon fibers and combinations thereof.

9. The composition according to one or more of claims 1 to 8, further comprising at least one inert gas selected from nitrogen, carbon dioxide and mixtures thereof.

10. The composition according to one or more of claims 1 to 9, wherein the at least one compound of general formula (I) is present in an amount in the range of > 0.01 wt.% to < 5.0 wt.%, with respect to the total weight of the composition.

11 Use of the at least one compound of general formula (I)

wherein

R¹ and R², independently of one another, are linear or branched, substituted or unsubsti tuted C_rCi4 alkyl;

as thickener for the at least one liguid or supercritical C₂-C₅ hydrocarbon.

12. Use of the composition according to claim 1 for fracturing.

13. A method of fracturing a subterranean formation penetrated by a wellbore, comprising the steps of

(a) formulating the composition according to one or more of claims 1 to 10 with the at least one proppant to obtain a fracturing fluid, and

(b) pumping the fracturing fluid of step (a) down the wellbore.

14. Use of the composition according to claim 1 for enhanced oil recovery.

15. A method for enhanced oil recovery from a well bored into an oil reservoir comprising the steps of

(a) injecting the composition according to one or more of claims 1 to 10 into the well bore; and

(b) recovering oil from the well bore.