Patent Application
20080011476
The present invention relates to methods and compositions useful in treating subterranean formations, and more particularly, to improved methods for coating particulates with tackifying compounds for use in downhole applications, such as for consolidating relatively unconsolidated portions of subterranean formations and minimizing the flow back of unconsolidated particulate material (referred to collectively herein as “particulate migration”).
In the production of hydrocarbons from a subterranean formation, the subterranean formation preferably should be sufficiently conductive to permit desirable fluids, such as oil and gas, to flow to a well bore that penetrates the formation. One type of treatment that may be used to increase the conductivity of a subterranean formation is hydraulic fracturing. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid or a “pad” fluid) into a well bore that penetrates a subterranean formation at a sufficient pressure to create or enhance one or more fractures in the subterranean formation. The fluid used in the treatment may comprise particulates, often referred to as “proppant particulates” or “proppant,” that are deposited in the resultant fractures. These proppant particulates are thought to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to a well bore. The term “propped fracture” as used herein refers to a fracture (naturally-occurring or otherwise) in a portion of a subterranean formation that contains at least a plurality of proppant particulates. The term “proppant pack” refers to a collection of proppant particulates within a fracture.
A type of particulate migration that may affect fluid conductivity in the formation is the flow back of unconsolidated particulate material (e.g., formation fines, proppant particulates, etc.) through the conductive channels in the subterranean formation, which can, for example, clog the conductive channels and/or damage the interior of the formation or equipment. There are several known techniques used to control particulate migration, some of which may involve the use of consolidating agents. The term “consolidating agent” as used herein includes any compound that is capable of minimizing particulate migration in a subterranean formation and/or modifying the stress-activated reactivity of subterranean fracture faces and other surfaces in subterranean formations.
One well-known technique used to control particulate migration in subterranean formations is commonly referred to as “gravel packing,” which involves the placement of a filtration bed of gravel particulates in the subterranean formation, which acts as a barrier to prevent particulates from flowing into the well bore. These gravel packing operations may involve the use of consolidating agents to bind the gravel particulates together in order to form a porous matrix through which formation fluids can pass.
Another technique that may be used to control particulate migration involves coating proppant particulates with a consolidating agent (such as a tackifying compound) to facilitate their consolidation within the formation and to prevent their subsequent flow-back through the conductive channels in the subterranean formation. The term “consolidating agent” as used herein implies no particular mechanism or mode of consolidation or stabilization. Consolidating agents may provide adhesive bonding between formation particulates to alter the distribution of the particulates within the formation in an effort to reduce their potential negative impact on permeability and/or fracture conductivity. Consolidating agents also may cause formation particulates to become involved in collective stabilized masses and/or stabilize the formation particulates in place to prevent their migration that might negatively impact permeability and/or fracture conductivity. The term “tackifying compound” as used herein refers to a chemical compound capable of developing or enhancing the capability/strength of adhesion of particulates in a subterranean formation, and refers to both aqueous and nonaqueous tackifying compounds.
Although tackifying compounds are used frequently, they may be difficult to handle, transport and clean-up due to their inherent tendency to stick to equipment or anything else with which they may come into contact. Therefore, it would be desirable to provide compositions and methods that would, among other things, help ease the handling, transport and clean up operations associated with using consolidating agents.
The present invention relates to methods and compositions useful in treating subterranean formations, and more particularly, to improved methods for coating particulates with tackifying compounds for use in downhole applications, such as for combating particulate migration.
In one embodiment, the present invention provides a method comprising: providing a tackifying compound and at least one surfactant; mixing the surfactant with the tackifying compound to form a tackifying compound surfactant mixture; coating the tackifying compound surfactant mixture onto particulates to form coated particulates; mixing the coated particulates into a treatment fluid; and placing the treatment fluid into a subterranean formation.
In one embodiment, the present invention provides a method comprising: providing a tackifying compound surfactant mixture; and coating at least a plurality of particulates with the tackifying compound surfactant mixture to produce a plurality of coated particulates.
In one embodiment, the present invention provides a method comprising: providing at least a plurality of particulates that have been coated with a tackifying compound surfactant mixture to produce a plurality of coated particulates; suspending the coated particulates in a fracturing fluid or a gravel pack fluid; placing the fracturing fluid or the gravel pack fluid in a subterranean formation; and performing a fracturing or a gravel packing operation.
The features and advantages of the present invention will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.
The present invention relates to methods and compositions useful in treating subterranean formations, and more particularly, to improved methods for coating particulates with tackifying compounds for use in downhole applications, such as for combating particulate migration. The methods of the present invention may be used in conjunction with the use of a tackifying compound in any suitable well treatment in which it is desirable to control particulate migration and/or modify the stress-activated reactivity of subterranean fracture faces and other surfaces in subterranean formations. These methods can be performed at any time during the life of the well.
One of the many advantages of the methods of the present invention is that they may enhance the efficiency and ease of using tackifying compounds by allowing for, inter alia, relatively easy clean up of equipment and reduced job failure due to the buildup of the tackifying compounds on the equipment. The methods of the invention provide for treating proppant particulates with tackifying compounds with their tackiness temporarily “switched off” during coating to help minimize potential handling problems, such as proppant bridging and lock-up of coating equipment. The term “switched off” as used herein refers to the relative tackiness of the tackifying compound. When “switched off,” the tackifying compound has a lesser degree of tackiness.
In some embodiments, the present invention provides methods comprising the steps of: providing a tackifying compound and at least one surfactant; mixing the surfactant with the tackifying compound to form a tackifying compound surfactant mixture; coating the tackifying compound surfactant mixture onto particulates to form coated particulates; mixing the coated particulates into a treatment fluid; and placing the treatment fluid into a subterranean formation. The treatment fluid may be used in fracturing, gravel packing, and frac-packing applications.
It is believed that the surfactant binds with sites of the tackifying compound to make those sites unavailable, causing the tackiness of the tackifying compound to reduce and perhaps disappear. It is possible that a charged species of the surfactant participates in this phenomenon, possibly by saturating these binding sites with water molecules. This appears reversible, however, and once the surfactant is removed (or its concentration is sufficiently reduced, e.g., as the water molecules are removed from the binding sites), that the tackiness of the tackifying compound may be restored and beneficially used as contemplated.
1. Suitable Non-aqueous Tackifying Compounds
In some embodiments of the present invention, non-aqueous tackifying compounds may be used. A particularly preferred group of non-aqueous tackifying compounds comprises polyamides that are liquids or in solution at the temperature of the subterranean formation such that they are, by themselves, non-hardening when introduced into the subterranean formation. A particularly preferred product is a condensation reaction product comprised of commercially available polyacids and a polyamine. Such commercial products include compounds such as mixtures of C36 dibasic acids containing some trimer and higher oligomers and also small amounts of monomer acids that are reacted with polyamines. Other polyacids include trimer acids, synthetic acids produced from fatty acids, maleic anhydride, acrylic acid, and the like. Such acid compounds are commercially available from companies such as Witco Corporation, Union Camp, Chemtall, and Emery Industries. The reaction products are available from, for example, Champion Technologies, Inc. and Witco Corporation.
Additional compounds which may be used as non-aqueous tackifying compounds include liquids and solutions of, for example, polyesters, polycarbonates and polycarbamates, natural resins such as shellac and the like.
Other suitable non-aqueous tackifying compounds are described in U.S. Pat. No. 5,853,048 issued to Weaver, et al. and U.S. Pat. No. 5,833,000 issued to Weaver, et al., the relevant disclosures of which are herein incorporated by reference.
Non-aqueous tackifying compounds suitable for use in the present invention may either be used such that they form a non-hardening coating or they may be combined with a multifunctional material capable of reacting with the non-aqueous tackifying compound to form a hardened coating. A “hardened coating” as used herein means that the reaction of the tackifying compound with the multifunctional material will result in a substantially non-flowable reaction product that exhibits a higher compressive strength in a consolidated agglomerate than the tackifying compound alone with the particulates. In this instance, the non-aqueous tackifying compound may function similarly to a hardenable resin.
Multifunctional materials suitable for use in the present invention include, but are not limited to, aldehydes, dialdehydes such as glutaraldehyde, hemiacetals or aldehyde releasing compounds, diacid halides, dihalides such as dichlorides and dibromides, polyacid anhydrides such as citric acid, epoxides, furfuraldehyde, glutaraldehyde, aldehyde condensates, and silyl-modified polyamide compounds and the like, and combinations thereof. Suitable silyl-modified polyamide compounds that may be used in the present invention are those that are substantially self-hardening compositions capable of at least partially adhering to particulates in the unhardened state, and that are further capable of self-hardening themselves to a substantially non-tacky state to which individual particulates such as formation fines will not adhere to, for example, in formation or proppant pack pore throats. Such silyl-modified polyamides may be based, for example, on the reaction product of a silating compound with a polyamide or a mixture of polyamides. The polyamide or mixture of polyamides may be one or more polyamide intermediate compounds obtained, for example, from the reaction of a polyacid (e.g., diacid or higher) with a polyamine (e.g., diamine or higher) to form a polyamide polymer with the elimination of water.
In some embodiments of the present invention, the multifunctional material may be mixed with the tackifying compound in an amount of from about 0.01% to about 50% by weight of the tackifying compound to effect formation of the reaction product. In other embodiments, the compound is present in an amount of from about 0.5% to about 1% by weight of the tackifying compound. Suitable multifunctional materials are described in U.S. Pat. No. 5,839,510 issued to Weaver, et al., the relevant disclosure of which is herein incorporated by reference.
2. Suitable Types of Surfactants
Surfactants suitable for use in the present invention are those capable of binding the active sites in the tackifying compound so as to reduce the tackiness of the tackifying compound. In some embodiments, the surfactant may comprise an ethyoxylated lauryl alcohol, an ethoxylated nonylphenol, an ethoxylated nonylphenol phosphate ester, a cationic surfactant, a nonionic surfactant, an alkyl phosphonate surfactant, or a combination thereof.
In some embodiments, the surfactant may comprise a cationic surfactant. Examples of suitable cationic surfactants include, but are not limited to, alkylamidobetaines such as cocoamidopropyl betaine, alpha-olefin sulfonate, trimethyltallowammonium chloride, C8 to C22 alkylethoxylate sulfate and trimethylcocoammonium chloride. Cocoamidopropyl betaine is especially preferred. Other suitable surfactants available from Halliburton Energy Services include: “19NTM,” “G-Sperse Dispersant,” “Morflo III®” surfactant, “Hyflo® IV M” surfactant, “Pen-88MTM” surfactant, “HC-2TM Agent,” “Pen-88 HTTM” surfactant, “SEM-7 TM” emulsifier, “Howco-Suds TM” foaming agent, “Howco Sticks TM” surfactant, “A-Sperse TM” Dispersing aid for acid additives, “SSO-21E” surfactant, and “SSO-21MW TM” surfactant.
In some embodiments, the surfactant may comprise a nonionic surfactant. Such preferred nonionic surfactants include, but are not limited to, alcohol oxyalkylates, alkyl phenol oxyalkylates, nonionic esters such as sorbitan esters and alkoxylates of sorbitan esters. Examples of suitable surfactants include but are not limited to, castor oil alkoxylates, fatty acid alkoxylates, lauryl alcohol alkoxylates, nonylphenol alkoxylates, octylphenol alkoxylates, tridecyl alcohol alkoxylates, such as POE-10 nonylphenol ethoxylate, POE-100 nonylphenol ethoxylate, POE-12 nonylphenol ethoxylate, POE-12 octylphenol ethoxylate, POE-12 tridecyl alcohol ethoxylate, POE-14 nonylphenol ethoxylate, POE-15 nonylphenol ethoxylate, POE-18 tridecyl alcohol ethoxylate, POE-20 nonylphenol ethoxylate, POE-20 oleyl alcohol ethoxylate, POE-20 stearic acid ethoxylate, POE-3 tridecyl alcohol ethoxylate, POE-30 nonylphenol ethoxylate, POE-30 octylphenol ethoxylate, POE-34 nonylphenol ethoxylate, POE-4 nonylphenol ethoxylate, POE-40 castor oil ethoxylate, POE-40 nonylphenol ethoxylate, POE-40 octylphenol ethoxylate, POE-50 nonylphenol ethoxylate, POE-50 tridecyl alcohol ethoxylate, POE-6 nonylphenol ethoxylate, POE-6 tridecyl alcohol ethoxylate, POE-8 nonylphenol ethoxylate, POE-9 octylphenol ethoxylate, mannide monooleate, sorbitan isostearate, sorbitan laurate, sorbitan monoisostearate, sorbitan monolaurate, sorbitan monooleate, sorbitan monopalmitate, sorbitan monostearate, sorbitan oleate, sorbitan palmitate, sorbitan sesquioleate, sorbitan stearate, sorbitan trioleate, sorbitan tristearate, POE-20 sorbitan monoisostearate ethoxylate, POE-20 sorbitan monolaurate ethoxylate, POE-20 sorbitan monooleate ethoxylate, POE-20 sorbitan monopalmitate ethoxylate, POE-20 sorbitan monostearate ethoxylate, POE-20 sorbitan trioleate ethoxylate, POE-20 sorbitan tristearate ethoxylate, POE-30 sorbitan tetraoleate ethoxylate, POE-40 sorbitan tetraoleate ethoxylate, POE-6 sorbitan hexastearate ethoxylate, POE-6 sorbitan monstearate ethoxylate, POE-6 sorbitan tetraoleate ethoxylate, and/or POE-60 sorbitan tetrastearate ethoxylate. Preferred nonionic surfactants include alcohol oxyalkyalates such as POE-23 lauryl alcohol and alkyl phenol ethoxylates such as POE (20) nonyl phenyl ether. Other applicable nonionic surfactants are esters such as sorbitan monooleate.
The surfactant may be used in an amount sufficient to counterattack the tackiness of the tackifying compound to the desired degree. The surfactant is preferably present in the tackifying compound surfactant mixture in an amount in the range from about 0.1% to 10% by weight.
3. Suitable Particulates
A wide variety of particulate materials may be used (e.g., as proppant or gravel) in accordance with the present invention, including, but not limited to, sand; bauxite; ceramic materials; glass materials; resin pre-coated proppant (e.g., commercially available from Borden Chemicals and Santrol, for example, both from Houston, Tex.); polymer materials; “TEFLON”™ (tetrafluoroethylene) materials; nut shells; ground or crushed nut shells; seed shells; ground or crushed seed shells; fruit pit pieces; ground or crushed fruit pits; processed wood; composite particulates prepared from a binder with filler particulate including silica, alumina, fumed carbon, carbon black, graphite, mica, titanium dioxide, meta-silicate, calcium silicate, kaolin, talc, zirconia, boron, fly ash, hollow glass microspheres, and solid glass; or mixtures thereof. The particulates used may have a particle size in the range of from about 2 to about 400 mesh, U.S. Sieve Series. Preferably, the particulates are graded sand having a particle size in the range of from about 10 to about 70 mesh, U.S. Sieve Series. Preferred sand particle size distribution ranges are one or more of 10-20 mesh, 20-40 mesh, 40-60 mesh or 50-70 mesh, depending on the particle size and distribution of the formation particulates to be screened out by the proppant. For high stress applications (e.g., those involving about 6000 psi or more), preferred particulates are likely ceramic particles and sintered bauxite since these materials have relatively high crush resistance.
B. Description of Some Methods of the Present Invention
In some embodiments, the present invention provides methods comprising the steps of: providing a tackifying compound and at least one surfactant; mixing the surfactant with the tackifying compound to form a tackifying compound surfactant mixture; coating the tackifying compound surfactant mixture onto particulates to form coated particulates; mixing the coated particulates into a treatment fluid; and placing the treatment fluid into a subterranean formation. Preferably the treatment fluids used in the present invention are aqueous-based fluids. Suitable aqueous-based fluids that may be used in the present invention include fresh water, salt water, brine, seawater, or any other aqueous fluid that, preferably, does not adversely react with the other components used in accordance with this invention or with the subterranean formation. The aqueous fluid preferably is present in the treatment fluids of the present invention in an amount in the range from about 40% to 80% by weight of the tackifying compound surfactant mixture.
The treatment fluid may be used in fracturing, gravel packing, and frac-packing applications. The term “coated particulate” as used herein means particulates that have been at least partially coated with a process comprising a tackifying compound surfactant mixture of the present invention. The particulates may be coated by any suitable method as recognized by one skilled in the art with the benefit of this disclosure, e.g., using a method comprising a sand screw. The term “coated” does not imply any particular degree of coverage of the particulates with the tackifying compound surfactant mixture.
One example of a method of the present invention comprises the steps of: providing a tackifying compound surfactant mixture; and coating at least a plurality of particulates with the tackifying compound surfactant mixture to produce a plurality of coated particulates. These coated particulates may then be used downhole, for example, in a fracturing or a gravel packing operation.
In some embodiments, the methods of the present invention may be used, inter alia, in primary, remedial, or proactive methods. Whether a particular method of this invention is “primary,” “remedial,” or “proactive” is determined relative to the timing of a fracturing treatment or a gravel packing treatment. A primary method of the present invention may involve using the methods of the present invention in conjunction with a fracturing fluid or a gravel pack fluid. The remedial methods may be used in wells wherein a portion of the well has been fractured and propped. The remedial methods also may be used in a gravel packing situation, for example where there has been a screen problem or failure. The proactive methods may be used in wells that have not yet been fractured or gravel packed. The proactive methods can be performed in conjunction with a fracturing treatment, for example, as a pre-pad to the fracturing treatment or in any diagnostic pumping stage performed before a fracturing, gravel packing, or acidizing procedure.
In accordance with the methods and compositions of the present invention, all or part of the particulate transported into the fractures is coated (preferably on-the-fly) with a tackifying compound surfactant mixture and may then be suspended in a fracturing fluid or used as part of a gravel packing process. The amount of tackifying compound surfactant mixture coated on the particulates is in the range from about 0.1% to about 20% by weight of the particulate, with about 1 to about 5% being preferred. The term “on-the-fly” is used herein to mean that a flowing stream is continuously introduced into another flowing stream so that the streams are combined and mixed while continuing to flow as a single stream. The coating of the dry particulates with the tackifying compound surfactant mixtures and any mixing of the coated particulates with a fracturing fluid or treatment fluid are all preferably accomplished on-the-fly. Preferably the particulates are coated using a sand screw. The methods of the present invention should allow less torque to be used in conjunction with the sand screw, which may be beneficial.
As is well understood by those skilled in the art, such mixing can also be accomplished by batch mixing or partial batch mixing.
To facilitate a better understanding of the present invention, the following examples of certain aspects of some embodiments are given. In no way should the following examples be read to limit, or define, the entire scope of the invention.
First, a mixture of a tackifying compound was prepared by mixing 10 cc of “SANDWEDGE NT” (available from Halliburton Energy Services in Duncan, Okla.) with 0.1 cc of “SSO-21” (a cationic surfactant also available from Halliburton Energy Services). From this mixture, 1.5 cc was obtained to dry coat onto 100 gram of 20/40 mesh Brady sand in a 4 ounce cup. It was observed that there was a lack of tackiness between sand grains as compared to a normal coating with “SANDWEDGE NT,” although the mixture was coated well on the sand. After coating thoroughly with a spatula, the coated sand was mixed with warm tap water and rinsed off. After rinsing the coated sand twice with water, about 100 cc each time, the tackiness began to come back.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, and set forth every range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.
