This document relates to methods of treating a subterranean formation containing hydrocarbons.
In the conventional fracturing of wells, producing formations, new wells or low producing wells that have been taken out of production, a formation can be fractured to attempt to achieve higher production rates. Proppant and fracturing fluid are pumped into a well that penetrates an oil or gas bearing formation. High pressure is applied to the well, the formation fractures and proppant carried by the fracturing fluid flows into the fractures. The proppant in the fractures holds the fractures open after the pressure is relaxed and production is resumed. Various fluids have been disclosed for use as the fracturing fluid, including liquefied petroleum gas (LPG). Various chemicals may be added to the fracturing fluid, such as gelling agents, breakers, activators, and surfactants.
A method of treating a subterranean formation containing hydrocarbons is disclosed, the method comprising: modifying the subterranean formation with a surface energy reducing agent; and injecting into the subterranean formation a fracturing fluid containing a base fluid and a gelling agent; in which the surface energy reducing agent is selected to effectively reduce the surface energy of the subterranean formation to at or below the surface tension of the gelling agent.
In various embodiments, there may be included any one or more of the following features: The surface energy reducing agent is selected such that the modified subterranean formation does not bond with the gelling agent. The surface energy reducing agent adheres to the subterranean formation more strongly than the gelling agent adheres to the subterranean formation. The surface energy reducing agent is selected to effectively reduce the net force of adhesion between the subterranean formation and the gelling agent (FFG) from above to below the net force of cohesion of the gelling agent (FGG). The method comprises breaking a gel, formed of the gelling agent, in the subterranean formation, in which the surface energy reducing agent is selected to effectively reduce the surface energy of the subterranean formation to at or below the surface tension of the gelling agent when broken. Modifying is carried out by injecting fracturing fluid comprising the surface energy reducing agent. Modifying comprises coating. The surface energy reducing agent comprises a surfactant. The surfactant comprises one or more of an ionic surfactant and a non-ionic surfactant. The ionic surfactant comprises one or more of an anionic surfactant, a cationic surfactant, and a zwitterionic surfactant. The surface energy reducing agent comprises an alkyne-diol. The surface energy reducing agent comprises one or more of Surfanol MB, Surfanol 104-PG50, Surfanol 2502, Dynol 604, and Dynol 607. The base fluid comprises hydrocarbons and the gelling agent comprises a gelling agent for hydrocarbons. The gelling agent comprises a polyacrylimide. The gelling agent comprises a phosphate. The base fluid comprises liquefied petroleum gas. The gelling agent comprises a gelling agent for liquefied petroleum gas. The gelling agent is selected to have a surface tension of between twenty and forty-six dynes/cm when in the subterranean formation after breaking.
These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.
Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:
Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.
During well treatment, gelling agents or other injected chemicals may stick to the formation on flowback, reducing permeability and potentially plugging the well. Surface science has identified at least five mechanisms of adhesion to explain why one material sticks to another, namely mechanical adhesion, electrostatic adhesion, chemical adhesion, dispersive adhesion, and diffusive adhesion. Regarding the adherence of a liquid to a solid or coated solid in a downhole environment, the latter three appear most relevant. Chemical adhesion occurs when two materials form a compound at the join. Ionic, covalent, and hydrogen bonding are examples of chemical adhesion. Diffusive adhesion occurs when materials merge at the joint by diffusion, for example if the molecules of the liquid are mobile and soluble in the solid or liquid coating the solid. Dispersive adhesion, similar to chemical adhesion, occurs when two materials are held together by van der Waals forces, which involve the attraction between slightly charged molecules, such as polar compounds. Positive and negative poles may be a permanent property of a molecule (Keesom forces) or a transient effect which can occur in any molecule (London forces).
In surface science, adhesion usually refers to dispersive adhesion. In a solid-liquid-gas system (such as a drop of liquid on a solid surrounded by air) contact angle may quantify adhesiveness. In general, where the contact angle 45 is low (ex.
Referring to
A generic example treatment of subterranean formation 24 goes as follows. The fracturing fluid may be pumped from reservoir 10 down line 12, where various components may be added to the fluid, for example via one or more component addition systems 14, 16, 18. For example, components such as gelling agent and proppant may be added from addition systems 16 and 18, respectively. The addition systems may be, for example, hoppers. Once the fracturing fluid is prepared and ready, a frac pressure pump 20 injects the frac fluid down a well 22 and into subterranean formation 24. In some cases, one or more component or fluid may be added to the frac fluid after the pump 20. The concept of reservoir treatment is well known, and the details need not be described here. In fracturing treatments, pressure may be applied to the frac fluid injected into the subterranean formation 24. The pressure may be sufficient to cause fracturing of the subterranean formation.
Referring to
In a stage 42, a fracturing fluid containing a base fluid, for example from tank 10, and a gelling agent, for example from addition unit 16, is injected into the subterranean formation 24. The treatment, which may be a fracturing treatment, may then be completed, for example by pressuring up the fluid in well 22 to frac, and delivering proppant from addition unit 16 into the fractures formed in the subterranean formation.
Referring to
The surface energy reducing agent 44 may be selected such that the modified subterranean formation shown in
The gelling agent 46 selected may have a surface tension of between twenty and forty-six dynes/cm when in the subterranean formation after breaking. In some cases the method includes the stage of breaking a gel, formed of the gelling agent 46, in the subterranean formation 24, in which the surface energy reducing agent 44 is selected to effectively reduce the surface energy of the subterranean formation 24 to at or below the surface tension of the gelling agent 46 when broken. Thus, the broken gelling agent is targeted by the surface energy reducing agent 44, as it is broken gel that may be left in formation 24. This may be a consideration if the gelling agent changes surface tension upon breaking due to a chemical change in the gelling agent. The surface energy reducing agent may make the formation 24 omniphobic, in order to allow easy removal of the base fluid as well as the fracturing chemicals.
Referring to
The base fluid may comprise hydrocarbons, such as C6-C20 hydrocarbons, and the gelling agent may comprise a gelling agent for hydrocarbons. The gelling agent may comprise a phosphate based chemical. In other cases the base fluid may be water, and the gelling agent may be a gelling agent for water. The base fluid may comprise liquefied petroleum gas, and the gelling agent may comprise a gelling agent for liquefied petroleum gas. LPG has been advantageously used as a fracturing fluid to simplify the recovery and clean-up of frac fluids after a frac. Exemplary LPG frac systems are disclosed in WO2007098606, incorporated herein by reference. One example of a suitable gelling agent for LPG is created by first reacting diphosphorous pentoxide with triethyl phosphate and an alcohol having hydrocarbon chains of 3-7 carbons long, or in a further for example alcohols having hydrocarbon chains 4-6 carbons long. The orthophosphate acid ester formed is then reacted with aluminum sulphate to create the desired gelling agent. The gelling agent created will have hydrocarbon chains from 3-7 carbons long or, as in the further example, 4-6 carbons long. The hydrocarbon chains of the gelling agent are thus commensurate in length with the hydrocarbon chains of liquid petroleum gas used for the frac fluid. This gelling agent is more effective at gelling a propane or butane fluid than a gelling agent with longer hydrocarbon chains. The proportion of gelling agent in the frac fluid is adjusted to obtain a suitable viscosity in the gelled frac fluid.
In some embodiments, a volatile-phosphorus free gelling agent may be used, for example for gelling hydrocarbons. Such a gelling agent may have the general formula of:
where X is an OR1, NR1R2, or SR1 group, R1 is an organic group having 2-24 carbon atoms, and R2 is an organic group or a hydrogen. Y is an NR3R4 or SR3 group, R3 is an organic group having 2-24 carbon atoms, and R4 is an organic group or a hydrogen. Such gelling agent may be made as follows. Phosphorus oxyhalide is reacted with a chemical reagent to produce substantially only diester phosphorus oxyhalide, the chemical reagent comprising at least one of an organic alcohol having 2-24 carbon atoms, an organic amine with an organic group having 2-24 carbon atoms, and an organic sulfide having 2-24 carbon atoms. The diester phosphorus oxyhalide is then hydrolyzed to produce diester phosphoric acid. Further examples are given in WO/2010/022496, incorporated herein by reference.
LPG may include a variety of petroleum and natural gases existing in a liquid state at ambient temperatures and moderate pressures. In some cases, LPG refers to a mixture of such fluids. These mixes are generally more affordable and easier to obtain than any one individual LPG, since they are hard to separate and purify individually. Unlike conventional hydrocarbon based fracturing fluids, common LPGs are tightly fractionated products resulting in a high degree of purity and very predictable performance. Exemplary LPGs include ethane, propane, butane, or various mixtures thereof. As well, exemplary LPGs also include isomers of propane and butane, such as iso-butane. Further LPG examples include HD-5 propane, commercial butane, and n-butane. The LPG mixture may be controlled to gain the desired hydraulic fracturing and clean-up performance. LPG fluids used may also include minor amounts of pentane (such as i-pentane or n-pentane), and higher weight hydrocarbons.
LPGs tend to produce excellent fracturing fluids. LPG is readily available, cost effective and is easily and safely handled on surface as a liquid under moderate pressure. LPG is completely compatible with formations and formation fluids, is highly soluble in formation hydrocarbons and eliminates phase trapping—resulting in increased well production. LPG may be readily and predictably viscosified to generate a fluid capable of efficient fracture creation and excellent proppant transport. After fracturing, LPG may be recovered very rapidly, allowing savings on clean up costs. In some embodiments, LPG may be predominantly propane, butane, or a mixture of propane and butane. In some embodiments, LPG may comprise more than 80%, 90%, or 95% propane, butane, or a mixture of propane and butane.
Exemplary gelling agents that may be used are disclosed by Whitney in U.S. Pat. Nos. 3,775,069 and 3,846,310, the specifications of which are incorporated by reference. Such gelling agents may create water-sensitive gels. An example of a suitable gelling agent comprises a combination of an alkoxide of a group IIIA element and an alkoxide of an alkali metal. When combined, the alkoxide of the group IIIA element and the alkoxide of the alkali metal react to form a polymer gel. The group IIIA element may comprise one or more of boron and aluminum for example. In some embodiments, the alkoxide of a group IIIA element comprises M1(OR1)(OR2)(OR3), in which M1=the group IIIA element, and R1, R2, and R3 are organic groups. Each of the organic groups of R1, R2, and R3 may have 2-10 carbon atoms, and may comprise an alkyl group. In one embodiment, M1=boron, and R1, R2, and R3 comprise 2-10 carbon atoms. The alkali metal may comprise one or more of lithium, sodium, and potassium for example. In some embodiments, the alkoxide of an alkali metal further comprises M2(OR4), in which M2=the alkali metal, and R4 comprises an organic group. The organic group of R4 may comprise 2-24 carbon atoms, for further example 12 carbon atoms, and may comprise an alkyl group. In one embodiment, M2=lithium and the organic group of R4 comprises 2-24 carbon atoms. In some embodiments, R4 may further comprise: (AQ)n(R5)x(R6)y. in which A is an organic group, Q is O or N, n is 1-10, R5 and R6 are organic groups, x is either 1 or 2 depending on the valence of Q, and y is 0 or 1 depending on the valence of Q. Thus, the alkoxide of an alkali metal formed would have the formula of M2O(AQ)n(R5)x(R)y. A may have 2-4 carbon atoms. The organic groups of R5 and R6 may each have 1-16 carbons. Where y=1, R6 is bonded to the Q atom. Organic groups as disclosed herein may refer to groups with at least one carbon atom, as long the resulting gelling agent is suitable for its purpose. Examples of organic groups include phenyl, aryl, alkenyl, alkynyl, cyclo, and ether groups. A suitable amount of gelling agent may be used, for example 0.25-5% by weight of the fracturing fluid. In addition, the a suitable ration of the alkoxide of a group IIIA element and the alkoxide of an alkali metal may be used, for example 3:1 to 1:3, with 1:1 being a preferable ratio.
The following exemplary procedure may be used to form a fracturing fluid containing a water sensitive gel as discussed in the preceding paragraph. Butyl lithium (3.53 mL of a 1.7 M solution in pentane, 6 mmol) was added dropwise to a stirring solution of dodecanol (1.12 g, 6 mmol) in pentane (125.00 g, 1% by wt gelling agents in pentane). This mixture was then stirred for a further 1 h at room temperature. A separate solution of tributyl borate (1.62 mL, 6 mmol) in pentane (125.00 g) was prepared in a blender at 17% variance with a rheostat for 5 min. To this solution was added the lithium alkoxide solution and a hydrated breaker, for example CaSO4(2H2O) (2.91 g, 0.15% by vol. H2O, 60 mesh) Blending was continued for 1 min at 30% variance. Over this time cloudy white gels formed. These were tested on a Brookfield viscometer-60° C., 4 h, 110 psi.
Exemplary breakers for use with water-sensitive gels include hydrated breakers. For example, the hydrated breaker may comprise one or more hydrates, wherein water of the one or more hydrates is releasable so as to act with the water-sensitive carrier to reduce the viscosity of the fracturing fluid. A hydrated breaker may have a crystalline framework containing water that is bound within the crystalline framework and releasable into the fracturing fluid to act on the water-sensitive gel to reduce the viscosity of the fracturing fluid. Hydrated breakers are disclosed for example in U.S. application Ser. No. 12/609,893 and CA Application No. 2685298 the content of which is incorporated here by reference where permitted by law.
In some embodiments, a gelling agent need not be specifically targeted by the surface energy reducing agent. For example, the surface energy reducing agent may be selected to effectively reduce the surface energy of the subterranean formation to at or below the surface tension of one or more of the base fluid, breaker, activator, gelling agent, or other treating chemical. Thus, the targeted injected chemicals may be easily removed after treatment is complete, and potential for well damage by tacky chemicals is reduced or eliminated.
Various surfactants may be used as the surface energy reducing agent. For example, the surfactant may comprise one or more of an ionic surfactant and a non-ionic surfactant. For further example, if used the ionic surfactant may comprise one or more of an anionic surfactant, a cationic surfactant, and a zwitterionic surfactant.
Anionic surfactants may be based on permanent anions such as sulfate, sulfonate, and phosphate, or pH-dependent anions such as carboxylate. Example anionic surfactants based on sulfates include alkyl sulfates such as ammonium lauryl sulfate and sodium lauryl sulfate (SDS), alkyl ether sulfates such as sodium laureth sulfate (also known as sodium lauryl ether sulfate or SLES), and sodium myreth sulfate. Example anionic surfactants based on sulfonates include docusates such as dioctyl sodium sulfosuccinate. Example anionic surfactants based on sulfonates also include sulfonate fluorosurfactants such as perfluorooctanesulfonate (PFOS), and perfluorobutanesulfonate. Example anionic surfactants based on sulfonates also include alkyl benzene sulfonates. Example anionic surfactants based on phosphates include alkyl aryl ether phosphate and alkyl ether phosphate. Example anionic surfactants based on carboxylates include alkyl carboxylates such as fatty acid salts (soaps) and sodium stearate. Example anionic surfactants based on carboxylates also include sodium lauroyl sarcosinate. Example anionic surfactants based on carboxylates also include carboxylate fluorosurfactants such as perfluorononanoate, and perfluorooctanoate (PFOA or PFO).
Cationic surfactants may be based on pH-dependent amines or permanently charged quaternary ammonium cations. Example cationic surfactants based on pH-dependent amines include primary, secondary or tertiary amines. For example, primary amines may be used that become positively charged at pH<10, and secondary amines may be used that become charged at pH<4. One example of a pH-dependent amine is octenidine dihydrochloride. Example cationic surfactants based on permanently charged quaternary ammonium cations include alkyltrimethylammonium salts such as cetyl trimethylammonium bromide (CTAB a.k.a. hexadecyl trimethyl ammonium bromide), and cetyl trimethylammonium chloride (CTAC). Example cationic surfactants based on permanently charged quaternary ammonium cations also include cetylpyridinium chloride (CPC), polyethoxylated tallow amine (POEA), benzalkonium chloride (BAC), benzethonium chloride (BZT), 5-bromo-5-nitro-1,3-dioxane, dimethyldioctadecylammonium chloride, and dioctadecyldimethylammonium bromide (DODAB).
Zwitterionic surfactants, which may be amphoteric, may be based on primary, secondary or tertiary amines or quaternary ammonium cations with sulfonate, carboxylate, or phosphate anions. Example zwitterionic surfactants with sulfonates include CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate), and sultaines such as cocamidopropyl hydroxysultaine. Example zwitterionic surfactants with carboxylates include amino acids, imino acids, and betaines such as cocamidopropyl betaine. Example zwitterionic surfactants with phosphates include lecithin.
Nonionic surfactants may include fatty alcohols such as cetyl alcohol, stearyl alcohol, cetostearyl alcohol (for example comprising predominantly of cetyl and stearyl alcohols), and oleyl alcohol. Nonionic surfactants may also include polyoxyethylene glycol alkyl ethers (Brij or CH3—(CH2)10-16—(O—C2H4)1-25—OH) such as octaethylene glycol monododecyl ether, and pentaethylene glycol monododecyl ether. Nonionic surfactants may also include polyoxypropylene glycol alkyl ethers (CH3—(CH2)10-16—(O—C3H6)1-25—OH). Nonionic surfactants may also include glucoside alkyl ethers (CH3—(CH2)10-16—(O-Glucoside)1-3-OH) such as decyl glucoside, lauryl glucoside, and octyl glucoside. Nonionic surfactants may also include polyoxyethylene glycol octylphenol ethers (C8H17—(C6H4)—(O—C2H4)1-25—OH) such as Triton X-100. Nonionic surfactants may also include polyoxyethylene glycol alkylphenol ethers (C9H19—(C6H4)—(O—C2H4)1-25—OH) such as nonoxynol-9. Nonionic surfactants may also include glycerol alkyl esters such as glyceryl laurate. Nonionic surfactants may also include polyoxyethylene glycol sorbitan alkyl esters such as polysorbates. Nonionic surfactants may also include sorbitan alkyl esters such as spans. Nonionic surfactants may also include cocamide MEA, and cocamide DEA. Nonionic surfactants may also include dodecyl dimethylamine oxide, and block copolymers of polyethylene glycol and polypropylene glycol such as poloxamers.
LP10 is a broken dialkyl phosphate LPG gel.
In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.
This application claims the benefit under 35 U.S.C. §119(e) of Provisional Application No. 61/433,076, filed Jan. 14, 2012.
Number | Date | Country | |
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61433076 | Jan 2011 | US |