Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/60—Compositions for stimulating production by acting on the underground formation
  • C09K8/62—Compositions for forming crevices or fractures
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/60—Compositions for stimulating production by acting on the underground formation
  • C09K8/80—Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
  • C09K8/805—Coated proppants

Definitions

• the invention relates to a method for the production of coated proppants, and also to the proppants obtained according to this method, to the uses thereof and to methods which use the proppants.
• Well fracturing is an often used technique to increase the efficiency and productivity of oil and gas wells. Overly simplified, the process involves the introduction of a fracturing fluid into the well and the use of fluid pressure to fracture and crack the well strata. The cracks allow the oil and gas to flow more freely from the strata and thereby increase production rates in an efficient manner.
• Proppants can be made of virtually any generally solid particle that has a sufficiently high crush strength to prop open cracks in a rock strata at great depths and temperatures of about 35° C and higher. Sand and ceramic proppants have proved to be especially suitable for commercial use.
• a proppant that is flushed from the well is said to have a high "flow back." Flow back is undesirable.
• the flushed proppants are abrasive and can damage or clog the tubular goods used to complete the well, valves and pipelines in downstream processing facilities.
• One type of synthetic resin coatings can be used to impart a degree of adhesion to the proppant so that flow back is substantially reduced or eliminated.
• Such resins can include phenol resin, epoxy resin, polyurethane-phenol resin, furane resin, etc. See published US Patent Application Nos. 2002/0048676, 2003/0131998, 2003/0224165, 2005/0019574, 2007/0161515 and 2008/0230223 as well as US Patent Nos. 4,920,192; 5,048,608; 5,199,491; 6,406,789;
• the synthetic coating is not completely cured when the proppant is introduced into the well.
• the coated, partially-cured proppants are free flowing, but the coating resin is still slightly reactive.
• the final cure is intended to occur in situ in the strata fracture at the elevated closure pressures and temperatures found "down hole.”
• Such partially cured coatings can also exhibit a number of performance issues ranging from:
• a second type of synthetic coating is described as being pre-cured or tempered.
• the coating is essentially cured during the manufacturing process.
• This type of coating will strengthen the substrate particle so that it can withstand a higher stress level before grain failure.
• Such a pre-cured coating with also exhibit the following traits: (1) Excellent storage stability; (2) Minimal chemicals that can be leached out of the coating to interfere with carrier fluid viscosity or breaker systems; and (3) A coating that is resilient to the abrasion of pneumatic handling.
• pre-cured coating The main limitation of a pre-cured coating is that it cannot create significant particle to particle bonding when placed in the fracture and temperature and closure pressure are applied. This means that a pre-cured coated particle can do little to prevent proppant flowback after the well is opened up to start the clean-up process or to produce the well. Such pre-cured products can also exhibit reductions in bonding capability and/or strength if exposed to elevated temperatures during handling or storage.
• polyurethane coatings are generally faster than phenol resins, cure at lower temperatures and do not have gaseous emissions that require specialized recovery equipment.
• the coating step with polyurethanes can be carried out at temperatures of about 10° C to about 250° C although temperatures of less than about 110° C are preferred to minimize emissions during the coating process as well as energy use.
• Polyurethane coatings can also be performed without the use of solvents, whereas many of the known methods, as a rule, require organic solvents for the resinous coating.
• the components in polyurethane systems are also generally easier to use and pose lower environmental issues. These factors could reduce the cost to make coated proppants. [13]
• the phenolic coating cured too slowly to generate sufficient bond strength in a reasonable amount of time.
• the activator plasticizer softens the coating so that the coating can gain some adhesion properties when the coated proppant solids are pushed into contact due to the closure stress from the closing of the fractured strata cracks. This adhesion will never result in a substantial measurable unconfined compressive strength but can result in a somewhat consolidated sample.
• the activator would be used at concentrations ranging from 5-20 gallons/ 1000 gallons of fracturing fluid (known as "frac" fluid). While the activator can help the phenolic coated proppant to function (to some degree) in low temperature applications it does have the following issues:
• the activator chemistry can create problems with frac fluid rheology and breakers systems.
• the activator is another factor in trying to quantify the effects of a fracturing treatment on the environment.
• the phenolic coating also has environmental issues because of the components that can be leached out of the coating (formaldehyde, phenol and
• a proppant could be substantially covered with a fast cure coating that could be produced to a free flowing state in a short period, e.g., less than about four minutes, while also exhibiting good crush resistance, resistance to hot water coating loss and low dust generation during pneumatic conveyance.
• a coating and coating process that comprises the step of: coating a proppant solid with a substantially homogeneous coating mixture that comprises (i) at least one isocyanate-functional component having at least 2 isocyanate groups, and (ii) at least one curing agent comprising a monofunctional alcohol, amine or amide, in an amount sufficient and under conditions sufficient to substantially cure said proppant coating and form free flowing, coated proppants in a period of time of less than about four minutes to form a free-flowing, substantially cured, coated proppant.
• a coated, free flowing proppant according to the invention comprises a solid proppant core particle that is substantially covered with a coating that comprises the reaction product of a coating mixture that comprises at least one isocyanate component and a curing agent to form a substantially fully cured proppant coating that is capable of forming particle-to-particle bonds at elevated temperature and pressure, such as those found downhole in an oil or gas well.
• the coating process of the present invention results one or more layers of cured polyurethane around a solid proppant core that is substantially cured and crosslinked quickly to produce a coated proppant product that acts like it has a hybrid coating, i.e., one that acts like a pre-cured coating in its resists dissolution of the coating under the rigorous combination of high heat, agitation, abrasion and water found downhole in an oil or gas well; exhibits good crush resistance and fracture conductivity; and has a tough coating that exhibits low levels of dust or fines generation during pneumatic conveyance as well as in use downhole but also exhibits traits of a partially cured coating in its ability to form particle-particle bonds with similarly coated proppants at downhole conditions.
• the coating process has a high production rate due to its low cycle time for the coating/curing process, low emission level and a low overall production cost and does not lose bonding capability if exposed to elevated temperatures during handling or storage.
• Figure 1 is a TMA plot of Dimension Change at various Temperatures in a TMA test of pre-cured, partially cured Phenolic A, partially cured Phenolic B that is more curable than Phenolic A, and the coating of the present invention as discussed in Example 6.
• Figure 2 is a bar chart of crush test results of various coated proppants tested in
• Figure 3 is a chart of Unconfined Compressive Strength for the coated proppants of Example 6.
• FIG. 1 Figure 4 charts the fracture conductivity of three coated proppants used in
• Figure 5 depicts the results of coating loss tests in simulated well down-hole conditions.
• Figures 6 and 7 illustrate the results of comparative conductivity tests in a simulated low temperature well using a proppant according to the present invention and a prior art proppant coated with a phenolic resin.
• Figure 8 shows the results of high temperature tests for unconfined compressive strength under high temperature well conditions and either with or without a three hour preheat exposure.
• the coating formulation of the present invention includes a substantially homogeneous mixture of a curable coating formulation that comprises: (a) at least one isocyanate-functional reactant having at least 2 isocyanate groups, and (ii) at least one curing agent comprising a monofunctional alcohol, amine or amide.
• the coating formulation may further comprise one or more curing agents in the form of amine reactants, metal catalysts, and/or polyol-functional reactants.
• the components are used in an amount sufficient and under conditions that are also sufficient to substantially cure the proppant coating and form free flowing, coated proppants in a fairly short period of time.
• the coated proppant thus exhibits the good handling and low dust characteristics of a pre-cured product but also exhibits in-strata consolidation characteristics and flow-back resistance that are like a partially cured product.
• the coating process of the present invention applies one or more layers of a curable coating formulation around a solid proppant core that is quickly and substantially cured to resist dissolution of the coating under the rigorous combination of high heat, agitation, abrasion and water that are found downhole in a well.
• the cured coating exhibits a sufficient resistance to a 10 day autoclave test or 10 day conductivity test so that the coating resists loss by dissolution in hot water of less than 25 wt , more preferably less than 15 wt , and even more preferably a loss of less than 5 wt .
• the substantially cured coating of the invention thus resists dissolution in the fractured stratum while also exhibiting sufficient particle- to-particle reaction bond strength to resist flow back and sufficiently high crush strength to maintain conductivity of the fractures.
• ISO 13503-5 :2006(E) "Procedures for measuring the long term conductivity of proppants", the disclosure of which is herein incorporated by reference.
• ISO 13503-5:2006 provides standard testing procedures for evaluating proppants used in hydraulic fracturing and gravel packing operations.
• ISO 13503-5:2006 provides a consistent methodology for testing performed on hydraulic fracturing and/or gravel packing proppants.
• the "proppants” mentioned henceforth in this part of ISO 13503-5:2006 refer to sand, ceramic media, resin-coated proppants, gravel packing media, and other materials used for hydraulic fracturing and gravel-packing operations.
• ISO 13503-5:2006 is not applicable for use in obtaining absolute values of proppant pack conductivities under downhole reservoir conditions, but it does serve as a consistent method by which such downhole conditions can be simulated and compared in a laboratory setting.
• the present invention is particularly directed to a proppant coating technology that exhibits decidedly different traits when kept dry (as in a storage bin) as opposed to when the coated proppant is added to the fracturing fluid and pumped into the fracture.
• One way to characterize this difference is by analyzing the test results from a TMA (thermal mechanical analyzer).
• TMA thermo mechanical analyzer
• the preferred coating will show a Tg softening point that is well above any possible storage temperature (> 75 °C). This assures that the coated product can be safely stored as long as it is kept relatively dry.
• the resulting Tg is now measured at a level that is ⁇ 50 °C.
• the coated sand will have the necessary properties to promote adhesion at low temperature applications once the fracture has closed and the resulting differential stress is placed on the proppants. Since the coating's ability to bond is not related to a chemical reaction rate, once the fracture has closed thereby exerting a closure stress on the proppant pack, there is no need for an extended shut-in period, e.g., 18 - 24 hours, before opening the well up to cleanup and production.
• the isocyanate-functional component for the present invention comprises an isocyanate-functional component with at least 2 reactive isocyanate groups.
• Other isocyanate- containing compounds may be used, if desired.
• suitable isocyanate with at least 2 isocyanate groups an aliphatic or an aromatic isocyanate with at least 2 isocyanate groups (e.g. a diisocyanate, triisocyanate or tetraisocyanate), or an oligomer or a polymer thereof can preferably be used.
• These isocyanates with at least 2 isocyanate groups can also be carbocyclic or heterocyclic and/or contain one or more heterocyclic groups.
• the isocyanate-functional component with at least 2 isocyanate groups is preferably a compound or oligomer of compounds of the formula (III) or a compound of the formula (IV):
• A is each, independently, an aryl, heteroaryl, cycloalkyl or heterocycloalkyl.
• A is each, independently, an aryl or cycloalkyl. More preferably A is each, independently, an aryl which is preferably phenyl, naphthyl or anthracenyl, and most preferably phenyl. Still more preferably A is a phenyl.
• heteroaryl is preferably a heteroaryl with 5 or 6 ring atoms, of which 1, 2 or 3 ring atoms are each, independently, an oxygen, sulfur or nitrogen atom and the other ring atoms are carbon atoms. More preferably the heteroaryl is selected among pyridinyl, thienyl, furyl, pyrrolyl, imidazolyl, pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl, oxazolyl, isoxazolyl or furazanyl.
• cycloalkyl is preferably a C3 io-cycloalkyl, more preferably a C5-7-cycloalkyl.
• heterocycloalkyl is preferably a heterocycloalkyl with 3 to
• ring atoms (more preferably with 5 to 7 ring atoms), of which one or more (e.g. 1, 2 or 3) ring atoms are each, independently, an oxygen, sulfur or nitrogen atom and the other ring atoms are carbon atoms.
• heterocycloalkyl is selected from among tetrahydrofuranyl, piperidinyl, piperazinyl, aziridinyl, acetidinyl, pyrrolidinyl, imidazolidinyl, morpholinyl, pyrazolidinyl, tetrahydrothienyl, octahydroquinolinyl, octahydroisoquinolinyl, oxazolidinyl or isoxazolidinyl.
• the heterocycloalkyl is selected from among tetrahydrofuranyl, piperidinyl, piperazinyl, pyrrolidinyl, imidazolidinyl, morpholinyl, pyrazolidinyl, tetrahydrothienyl, oxazolidinyl or isoxazolidinyl.
• each R 1 is, independently, a covalent bond or Ci- 4 - alkylene (e.g. methylene, ethylene, propylene or butylene).
• each R is hydrogen or a covalent bond.
• each R 2 is each, independently, hydrogen, a halogen (e.g. F, CI, Br or ⁇ ), a Ci- 4 -alkyl (e.g. methyl, ethyl, propyl or butyl) or Ci ⁇ -alkyoxy (e.g. methoxy, ethoxy, propoxy or butoxy).
• a halogen e.g. F, CI, Br or ⁇
• a Ci- 4 -alkyl e.g. methyl, ethyl, propyl or butyl
• Ci ⁇ -alkyoxy e.g. methoxy, ethoxy, propoxy or butoxy
• each R is, independently, hydrogen or a Ci- 4 - alkyl. More preferably each R is hydrogen or methyl.
• R 3 is a covalent bond, a Ci- 4 -alkylene (e.g. methylene, ethylene, propylene or butylene) or a group -(CH2)R31-0-(CH2)R32-, wherein R31 and R32 are each, independently, 0, 1, 2 or 3.
• R is a -CH2- group or an -O- group.
• each q is, independently, an integer from 0 to 4, preferably 0, 1 or 2.
• the corresponding group A has no substituent R , but has hydrogen atoms instead of R .
• each r and s are, independently, 0, 1, 2, 3 or 4, wherein the sum of r and s is equal to 2, 3 or 4.
• each r and s are, independently, 0, 1 or 2, wherein the sum of r and s is equal to 2. More preferably, r is equal to 1 and s is equal to 1.
• Examples of the isocyanate with at least 2 isocyanate groups are: toluol-2,4- diisocyanate; toluol-2,6-diisocyanate; 1,5-naphthalindiisocyanate; cumol-2,4-diisocyanate; 4- methoxy- 1 ,3-phenyldiisocyanate; 4-chloro- 1 ,3-phenyldiisocyanate; diphenylmethane-4,4- diisocyanate; diphenylmethane-2,4-diisocyanate; diphenylmethane-2,2-diisocyanate; 4-bromo- 1,3-phenyldiisocyanate; 4-ethoxy-l,3-phenyl-diisocyanate; 2,4'-diisocyanate diphenylether; 5,6- dimethyl-l,3-phenyl-diisocyanate; methylenediphenyl diisocyanate
• Particularly preferred isocyanates with at least 2 isocyanate groups are toluol diisocyanate, methylenediphenyl diisocyanate, diphenylmethane diisocyanate, an oligomer based on toluol diisocyanate, an oligomer based on methylenediphenyl diisocyanate (poly-MDI) or an oligomer based on diphenylmethane diisocyanate and polymers thereof.
• the coatings of the invention can be cured with at least one of a variety of curing agents, including reactive, non-reactive (e.g., "catalysts”) and partially reactive agents.
• curing agents including reactive, non-reactive (e.g., "catalysts") and partially reactive agents.
• preferred curing agents are selected from amine-based curing agents, hydroxyl- functional curing agents, polyols, and/or metal-based catalysts. Particularly preferred curing agents are one or more monofunctional alcohols, amines and/or amides.
• the amine-based curing agents may also be used as a mixture of a fast-acting first curing agent and a second, latent curing agent. Either of these first and/or second amine-based curing agents may be reactive, nonreactive or partially reactive.
• Suitable single amine-based curing agent or a mixture of amine-based curing agents can include, but are not limited to, ethylene diamine; hexamethylene diamine; 1-methyl- 2,6-cyclohexyl diamine; 2,2,4- and 2,4,4-trimethyl-l,6-hexanediamine; 4,4'-bis-(sec- butylamino)-dicyclohexylmethane and derivatives thereof; l,4-bis-(sec-butylamino)- cyclohexane; l,2-bis-(sec-butylamino)-cyclohexane; 4,4'-dicyclohexylmethane diamine; 1,4- cyclohexane-bis-(methylamine); l,3-cyclohexane-bis-(methylamine), isomers, and mixtures thereof; diethylene glycol bis- (aminopropyl)ether; 2-methylpentamethylene-diamine;
• diaminocyclohexane isomers, and mixtures thereof; diethylene triamine; triethylene tetramine; tetraethylene pentamine; propylene diamine; 1,3-diaminopropane; dimethylamino propylamine; diethylamino propylamine; imido-bis- (propylamine); monoethanolamine, diethanolamine; triethanolamine; monoisopropanolamine, diisopropanolamine; isophoronediamine; 4,4'- methylenebis-(2-chloroaniline) ; 3 ,5-dimethylthio-2,4-toluenediamine; 3 ,5-dimethylthio-2,6- toluenediamine; 3,5-diethylthio-2,4-toluenediamine; 3,5-diethylthio-2,6-toluenediamine; 4,4'- bis-(sec-butylamino)-benzene; and derivatives thereof; di
• the amine-terminated curing agent is 4,4'-bis-(sec-butylamino)- dicyclohexylmethane.
• Preferred amine-based curing agents for use with the present invention include triethylenediamine; bis(2-dimethylaminoethyl)ether; tetramethylethylenediamine; pentamethyldiethylenetriamine; 1 ,3,5-tris(3-(dimethylamino)propyl)- hexahydro-s-triazine and other tertiary amine products of alkyleneamines.
• catalysts that promote the reaction of isocyanates with hydroxyls and amines that are known by the industry can be used in the present invention, e.g., transition metal co-catalysts of Groups III or IV used for polyurethane foams.
• a particularly preferred metal co-catalyst is a tin complex such as stannous 2-ethylhexanoate or an organotin compound, such as dibutyltin dilaurate and tin-containing salts.
• catalysts that promote isocyanate trimerization over other reaction mechanisms See, e.g., US Patent No. 5,264,572 (cesium fluoride or
• the amine-based curing agent may have a molecular weight of about 64 or greater. In one embodiment, the molecular weight of the amine-curing agent is about 2000 or less. In addition, any of the amine-terminated moieties listed above for use as the isocyanate- reactive component to form the prepolymer may be used as curing agents to react with the prepolymers.
• the saturated amine-based curing agents suitable for use with the present invention include, but are not limited to, ethylene diamine; hexamethylene diamine; 1- methyl-2,6-cyclohexyl diamine; 2,2,4- and 2,4,4-trimethyl-l,6-hexanediamine; 4,4'-bis-(sec- butylamino)-dicyclohexylmethane; l,4-bis-(sec-butylamino)-cyclohexane; l,2-bis-(sec- butylamino-cyclohexane; derivatives of 4,4'-bis-(sec-butylamino)-dicyclohexylmethane; 4,4'- dicyclohexylmethane diamine; l,4-cyclohexane-bis-(methylamine); 1,3-cyclohexane-bis- (methylamine); diethylene glycol bis-(aminopropyl) ether; 2-
• propylene diamine dipropylene triamine; 1,3-diaminopropane; dimethylamino propylamine; diethylamino propylamine; imido-bis- (propylamine); monoethanolamine, diethanolamine;
• triethanolamine monoisopropanolamine, diisopropanolamine; triisopropanolamine;
• isophoronediamine ⁇ , ⁇ '-diisopropylisophorone diamine and mixtures thereof.
• the curative used with the prepolymer include 3,5- dimethylthio-2,4-toluenediamine,3,5-dimethyl-thio-2,6-toluenediamine, 4,4'-bis-(sec- butylamino)-diphenylmethane, ⁇ , ⁇ '-diisopropyl-isophorone diamine; polyoxypropylene diamine; propylene oxide-based triamine; 3,3'-dimethyl-4,4'-diaminocyclohexylmethane; and mixtures thereof.
• a hindered secondary diamine may be more suitable for use in the prepolymer.
• an amine with a high level of stearic hindrance e.g., a tertiary butyl group on the nitrogen atom, has a slower reaction rate than an amine with no hindrance or a low level of hindrance.
• 4,4'-bis-(sec-butylamino)-dicyclohexylmethane (CLEARLINK 1000® from Huntsman Corporation in The Woodlands, Texas) may be suitable for use in combination with an isocyanate to form the polyurea prepolymer.
• CLARLINK 1000® 4,4'-bis-(sec-butylamino)-dicyclohexylmethane
• N,N'-diisopropyl-isophorone diamine also available from Huntsman Corporation, under the tradename JEFFLINK®, may be used as the secondary diamine curing agent.
• a trifunctional curing agent can be used to help improve cross-linking and, thus, to further improve the chemical and/or abrasion resistance of the coating.
• a triol such as trimethylolpropane or a tetraol such as ⁇ , ⁇ , ⁇ ', ⁇ '-tetrakis (2- hydroxylpropyl)ethylenediamine may be added to the formulations.
• the curing agent is mixed with or co-applied to the solid proppant core as the first isocyanate and any other reactants are mixed so that the curing process has begun by the time the coating formulation is applied to the surface of the solid proppant core. It is also possible to premix the isocyanate and polyol together immediately before entry into the mixer. This probably would give a slightly more uniform distribution of the chemicals in the coating. Alternately, it would be possible to premix the polyol and curing agent before they are added to the isocyanate.
• the isocyanate, polyol, combination of (a) polyol and (b) curing agent or each individually are continuously added to solid proppant in a moving mixer at a rate that is not substantially greater than the rate of the crosslinking reaction between and among the ingredients.
• the specific rate will depend on the size of the mixer, the type of mixer, and whether batch or continuous production is desired.
• the goal is to substantially completely coat the proppant solid with a coating that becomes cured in the mixer and is discharged as a free- flowing, discrete particulates.
• the amperage draw rate of the mixer can be used as a guide in tumbling-type mixers because the build-up of an uncured, tacky coating on the proppant solids will increase the load on the mixer motor which can be monitored by a simple amp meter.
• Adding the reaction components at a rate that is consistent with the reaction rate of the curing process avoids substantial increases in amperage allows the coating process, avoids stalling the motor or interrupting the coating process, and maximizes the productivity of the equipment used to perform the coating/curing process.
• the isocyanate is added at a controlled rate over a relatively short period, e.g., about a minute.
• the proppant coating of the invention may also be cured alone or with other curing agents with a single hydroxy-terminated curing agent (i.e., a monol such as C1-C20 alcohols such as ethanol, isopropyl, butanol, or stearyl alcohol ) or a mixture of hydroxy- terminated curing agents.
• a monol such as C1-C20 alcohols such as ethanol, isopropyl, butanol, or stearyl alcohol
• a mixture of hydroxy- terminated curing agents i.e., a monol such as C1-C20 alcohols such as ethanol, isopropyl, butanol, or stearyl alcohol
• the appropriate use of such a monol capping agent or chain terminator can help to control the impact of internal, unreacted -NCO groups that can have adverse properties on the final coating.
• any added polyhydroxy compounds can bring into the coating certain properties that are not related to the original isocyanate or polyhydroxy component, such as enhanced or decreased hydrophobicity, corrosion resistance, viscosity modification in fracturing fluid, reduce the frictional drag of production fluids once in the fracture, ion exchange and antimicrobial effects.
• Suitable hydroxy-terminated curing agents include, but are not limited to, ethanol, ethylene glycol; diethylene glycol; polyethylene glycol; propylene glycol; 2-methyl-l,3- propanediol; 2,-methyl-l,4-butanediol; dipropylene glycol; polypropylene glycol; 1,2- butanediol; 1,3-butanediol; 1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;
• polytetramethylene ether glycol preferably having a molecular weight ranging from about 250 to about 3900
• resorcinol-di-(beta-hydroxyethyl)ether and its derivatives preferably having a molecular weight ranging from about 250 to about 3900
• the hydroxy-terminated curing agent may have a molecular weight of at least about 50.
• the molecular weight of the hydroxy-terminated curing agent is about 2000 or less. In yet another embodiment, the hydroxy-terminated curing agent has a molecular weight of about 250 to about 3900. It should be understood that molecular weight, as used herein, is the absolute weight average molecular weight and would be understood as such by one of ordinary skill in the art.
• saturated hydroxy-terminated curing agents included in the list above, are preferred when making a light stable composition.
• Those saturated hydroxy-terminated curing agents include, but are not limited to, ethylene glycol; diethylene glycol; polyethylene glycol; propylene glycol; 2-methyl-l,3-propanediol; 2,-methyl-l,4-butanediol; dipropylene glycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol; 1,4-butanediol; 2,3-butanediol; 2,3- dimethyl-2,3-butanediol; trimethylolpropane; cyclohexyldimethylol; triisopropanolamine; N,N,N',N'-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycol bis-(aminopropyl)ether; 1,5-pentanedi
• the amount of curing agent that is added to the coating will generally fall within the range from about 0.01 wt to about 95 wt of the complete coating formulation.
• a polyol component can be added to the coating formulation.
• the polyol component may or may not have reactive amine functionality and can comprise oxides, polyesters, polyamides, polyurethane, epoxy, silicone or polysiloxane, or vinyl backbones which react to become an integral part of the resulting coating on the proppant core.
• a useful polyurethane coating is a phenolic polyurethane made with a phenolic polyol according to a patent application that was filed with the German Patent Office under no. DE 10 2010 051 817.4 on November 19, 2010 and entitled "Proppant Coating Technology", the disclosure of which is herein incorporated by reference. This patent is summarized below in the context of the process of the present invention.
• Another polyol component for the present process comprises a phenol resin that comprises a condensation product of a phenol and an aldehyde, such as formaldehyde.
• the phenol resin is preferably a resole or novolak phenol resin and more preferably a benzyl ether resin.
• the resole-type phenol resin can be obtained, for example, by condensation of phenol or of one or more compounds of the following formula (I), with aldehydes, preferably formaldehyde, under basic conditions.
• R is in each case, independently, a hydrogen atom, a halogen atom, Ci-i6-alkyl
• Ci-12-alkyl preferably Ci-6-alkyl, and still more preferably methyl, ethyl, propyl or butyl
• -OH preferably methyl, ethyl, propyl or butyl
• p is an integer from 0 to 4, preferably 0, 1, 2 or 3, and more preferably 1 or 2.
• Novolak-type phenol resin for the present invention comprises the condensation product of phenol or of one or more compounds of the formula (I) defined above, with aldehydes, preferably formaldehyde, under acidic conditions.
• the phenol resin is a benzyl ether resin of the general formula (II):
• A, B and D each are, independently, a hydrogen atom, a halogen atom, a C 1-16 - hydrocarbon residue, -(Ci-i6-alkylene)-OH, -OH, an -0-(Ci-i6-hydrocarbon residue), phenyl, -(Ci-6-alkylene)-phenyl, or -(Ci-6-alkylene)-phenylene-OH;
• the halogen atom is F, CI, Br or I;
• the Ci-i6-hydrocarbon-residue is preferably Ci-i6-alkyl, C 2 -i6-alkenyl or C 2-16 - alkinyl, more preferably Ci-i 2 -alkyl, C 2 -i 2 -alkenyl or C 2 -i 2 -alkinyl, still more preferably Ci-6-alkyl, C 2 -6-alkenyl or C 2 -6-alkinyl, and still more preferably Ci- 4 - alkyl, C 2 - 4 -alkenyl or C 2 - 4 -alkinyl, and still more preferably Ci-i 2 -alkyl, and still more preferably Ci-6-alkyl, and still more preferably methyl, ethyl, propyl or butyl, and most preferably methyl;
• the residue -(Ci-i6-alkylene)-OH is preferably -(Ci-i 2 -alkylene)-OH, more preferably -(Ci-6-alkylene)-OH, and still more preferably -(Ci- 4 -alkylene)-OH, and most preferably a methylol group (-CH 2 -OH);
• the -0-(Ci-i6-hydrocarbon)-residue is preferably Ci-i6-alkoxy, more preferably C 1-12 - alkoxy, and still more preferably Ci-6-alkoxy, and still more preferably Ci- 4 - alkoxy, and still more preferably -O-CH3, -0-CH 2 CH 3 , -0-(CH 2 ) 2 CH 3 or -O- (CH 2 ) 3 CH 3 ;
• the residue -(Ci-6-alkylene)-phenyl is preferably -(Ci- 4 -alkylene)-phenyl, and more preferably -CH 2 -phenyl;
• the residue -(Ci-6-alkylene)-phenylene-OH is preferably -(Ci- 4 -alkylene)- phenylene- OH, and more preferably -CH 2 -phenylene-OH;
• R is a hydrogen atom of a Ci-6-hydrocarbon residue (e.g. linear or branched C 1-6 - alkyl). R is particularly preferred as a hydrogen atom. This is the case, for example, when formaldehyde is used as aldehyde component in a condensation reaction with phenols in order to produce the benzyl ether resin of the formula (II);
• n 1 and m are each, independently, 0 or 1.
• n is an integer from 0 to 100, preferably an integer from 1 to 50, more preferably from 2 to 10, and still more preferably from 2 to 5;
• the polyol component is a phenol resin with monomer units based on cardol and/or cardanol.
• Cardol and cardanol are produced from cashew nut oil which is obtained from the seeds of the cashew nut tree.
• Cashew nut oil consists of about 90% anacardic acid and about 10% cardol.
• By heat treatment in an acid environment a mixture of cardol and cardanol is obtained by decarboxylation of the anacardic acid.
• Cardol and cardanol have the structures shown below:
• Cardol specifically refers to compound CAS-No. 57486-25-6 and cardanol specifically to compound CAS-No. 37330-39-5.
• Cardol and cardanol can each be used alone or at any particular mixing ratio in the phenol resin.
• Decarboxylated cashew nut oil can also be used.
• Cardol and/or cardanol can be condensed into the above described phenol resins, for example, into the resole- or novolak-type phenol resins.
• cardol and/or cardanol can be condensed e.g. with phenol or with one or more of the above defined compounds of the formula (I), and also with aldehydes, preferably formaldehyde.
• the amount of cardol and/or cardanol which is condensed in the phenol resin is not particularly restricted and preferably is from about 1 wt% to about 99 wt%, more preferably about 5 wt% to about 60 wt%, and still more preferably about 10 wt% to about 30 wt%, relative to 100 wt% of the amount of phenolic starting products used in the phenol resin.
• the polyol component is a phenol resin obtained by condensation of cardol and/or cardanol with aldehydes, preferably formaldehyde.
• the polyol component can still contain other compounds containing hydroxyl groups.
• the other compounds containing hydroxyl groups can be selected from the compounds containing hydroxyl groups that are known to be useful for making polyurethanes, e.g., hydroxy-functional polyethers, hydroxy-functional polyesters, alcohols or glycols.
• One preferred compound containing hydroxyl groups is, for instance, castor oil.
• Compounds containing hydroxyl groups such as alcohols or glycols, in particular cardol and/or cardanol, can be used as reactive thinners.
• the amount of the other compounds containing hydroxyl groups depends on the desired properties of the proppant coating and can suitably be selected by the person skilled in the art. Typical amounts of compounds containing hydroxyl groups are in the range of between about 10 wt and about 80 wt , preferably from about 20 wt to about 70 wt , relative to 100 wt of the polyol component.
• step (a) 100 parts by weight of the polyol component is used with about 100 to about 600, preferably about 210 to about 530, more preferably about 220 to about 420, and still more preferably about 230 to about 400 parts by weight of the isocyanate base value.
• Ratios of iso:polyol from about 10:90 to as low as 100:0 are usable depending on the equipment, conditions and production rate provided that the coating and reaction are completed during the coating process.
• the preferred range of iso:polyol is generally within the range from about 10:90 to about 90: 10.
• the isocyanate base value defines the amount of the isocyanate component which is equivalent to 100 parts by weight of the polyol component.
• the NCO-content (%) of the isocyanate component is defined herein according to DIN ISO 53185.
• To determine the OH- content (%) of the polyol component first the so-called OH-number is determined in mg KOH/g according to DIN ISO 53240 and this value is divided by 33, in order to determine the OH- content.
• step (a) an excess of NCO-groups in the isocyanate component of between about 100 and about 500%, preferably about 110 to about 430%, more preferably about 120% to about 320%, and still more preferably about 130% to about 300%, relative to the OH-groups in the polyol component is used.
• one or more additives can be mixed with the proppant, the polyol component and the isocyanate component.
• These additives are not particularly restricted and can be selected from the additives known in the specific field of coated proppants. Provided that one of these additives has hydroxyl, amine or amide functional groups, it should be considered as a different reactive group-containing compound, as described above in connection with the polyol component. If one of the additives has isocyanate groups, it should be considered as a different isocyanate- group-containing compound. Additives with hydroxyl groups and isocyanate groups can be simultaneously considered as different hydroxyl- group- containing compounds and as different isocyanate-group-containing compounds.
• the coating formulation of the present invention also optionally includes a reactive amine or reactive amide component, preferably an amine-terminated compound or an amide.
• a reactive amine or reactive amide component preferably an amine-terminated compound or an amide.
• the coating formulation can, however, be made effectively and with good properties in the absence or substantial absence of a reactive amine component apart from the reactive polyol and isocyanate components.
• the reactive amine component can enhance crosslink density within the coating and, depending on component selection, can provide additional characteristics of benefit to the cured coating.
• Reactive amine components for use in the present invention include C1-C40 amine-terminated, amine-containing, or amide compounds such as monoamines (e.g., butyl amine), amides (e.g., fatty acid amides, stearyl amides), diamines, triamines, amine- terminated glycols such as the amine-terminated polyalkylene glycols sold commercially under the trade name JEFF AMINE from Huntsman Performance Products in The Woodlands, Texas.
• amides can be particularly useful for enhancing flow and hydrophobic properties as well as the antimicrobial properties of the coatings.
• Suitable diamines include primary, secondary and higher polyamines and amine- terminated compounds.
• Suitable compounds include, but are not limited to, ethylene diamine; propylenediamine; butanediamine; hexamethylenediamine; 1,2-diaminopropane; 1,4- diaminobutane; 1,3-diaminopentane; 1,6-diaminohexane; 2,5-diamino-2,5-dimethlhexane; 2,2,4- and/or 2,4,4-trimethyl-l,6-diaminohexane; 1,11-diaminoundecane; 1,12-diaminododecane; 1,3- and/or 1,4-cyclohexane diamine; l-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane; 2,4- and/or 2,6-hexahydrotoluylene diamine; 2,4'
• aspartic esters which is a secondary amine derived from a primary polyamine and a dialkyl maleic or fumaric acid ester, for use in the invention.
• useful maleic acid esters include dimethyl maleate, diethyl maleate, dibutyl maleate, dioctyl maleate, mixtures thereof and homologs thereof.
• Suitable triamines and higher multifunctional polyamines for use in the present coating include diethylene triamine, triethylenetetramine, and higher homologs of this series.
• JEFF AMINE diamines include the D, ED, and EDR series products.
• the D signifies a diamine
• ED signifies a diamine with a predominately polyethylene glycol (PEG) backbone
• EDR designates a highly reactive, PEG based diamine.
• JEFF AMINE D series products are amine terminated polypropylene glycols with the following representative structure:
• JEFFAMINE EDR- 148 (XTJ-504) and JEFFAMINE EDR- 176 (XTJ-590) are much more reactive than the other JEFFAMINE diamines and triamines. They are represented by the following structure:
• JEFF AMINE T series products are triamines prepared by reaction of propylene oxide (PO) with a triol intiator followed by amination of the terminal hydroxyl groups. They are exemplified by the following structure:
• SD Series and ST Series products consist of secondary amine versions of the
• the SD signifies a secondary diamine and ST signifies a secondary trimine.
• the amine end-groups are reacted with a ketone (e.g. acetone) and reduced to create hindered secondary amine end groups represented by the following terminal structure:
• the amine containing compound can be monofunctional as primary amines and amides, each capable of incorporating desireable properties into the coating, e.g., hydrophobic characteristics, better flow properties and antimicrobial properties.
• the proppant coating compositions of the invention may also include various additives.
• the coatings of the invention may also include pigments, tints, dyes, and fillers in an amount to provide visible coloration in the coatings.
• Other materials include, but are not limited to, reaction enhancers or catalysts, crosslinking agents, optical brighteners, propylene carbonates, coloring agents, fluorescent agents, whitening agents, UV absorbers, hindered amine light stabilizers, defoaming agents, processing aids, mica, talc, nano-fillers, silane coupling agents, antislip agents, water affinity or repulsion components, impact modifiers, water-activated catalysts, viscosifiers, flowaids, anticaking agents, wetting agents, toughening agents such as one or more block copolymers, and components that act to remove at least some portion of the heavy metals and/or undesirable solutes found in subterranean groundwater. See, copending US patent application serial number 13/224726 filed on 1 September 2011 entitled "D
• the additives are preferably present in an amount of about 15 weight percent or less. In one embodiment, the additive is present in a non-zero amount of about 5 percent or less by weight of the coating composition.
• amorphous silica e.g., silica flour, fumed silica and silica dispersions
• silica alternatives such as those used in sandblasting as an alternative to silica or organofunctional silane like the DYNASYLAN fluids from Evonik Degussa Corporation in Chester, PA
• Applied amounts of the amorphous silica are generally within the range from about 0.001 wt to about 1 wt based on the dry proppant weight.
• additives can include, for example, solvents, softeners, surface-active agents, molecular sieves for removing the reaction water, thinners and/or adhesion agents can be used.
• Silanes are a particularly preferred type of adhesion agent that improves the affinity of the coating resin for the surface of the proppant.
• Silanes can be mixed in as additives in step (a), but can also be converted chemically with reactive constituents of the polyol component or of the isocyanate component.
• Functional silanes such as amino- silanes, epoxy-, aryl- or vinyl silanes are commercially available and, as described above, can be used as additives or can be converted with the reactive constituents of the polyol component or of the isocyanate component. In particular, amino-silanes and epoxy-silanes can be easily converted with the isocyanate component.
• An optional, additional additive is a contaminant removal component that will remove, sequester, chelate or otherwise clean at least one contaminant, especially dissolved or otherwise ionic forms of heavy metals and naturally occurring radioactive materials (NORMS), from subterranean water or hydrocarbon deposits within a fractured stratum while also propping open cracks in said fractured stratum.
• NORMS radioactive materials
• the contaminant removal component is associated with the proppant solid as a chemically distinct solid that is introduced together with the proppant solid as: (a) an insoluble solid secured to the outer or inner surface of the proppant solid with a coating formulation that binds the solids together, (b) as a solid lodged within pores of the proppant solid or (c) as a chemical compound or moiety that is mixed into or integrated with a coating or the structure of the proppant solid.
• Additional added functionality can also be in the form of fracturing fluid breakers, de-emulsifiers, and bactericides.
• an auxiliary particle to the proppant may also be in the form of an ion exchange resin that is pretreated or which itself constitutes a dissolvable solid for the slow release of corrosion or scale inhibitors. Such slow release materials could prove beneficial and advantageous to the overall operation and maintenance of the well.
• the proppants can be virtually any small solid with an adequate crush strength and lack of chemical reactivity. Suitable examples include sand, ceramic particles (for instance, aluminum oxide, silicon dioxide, titanium dioxide, zinc oxide, zirconium dioxide, cerium dioxide, manganese dioxide, iron oxide, calcium oxide, magnesium oxide, or bauxite), or also other granular materials.
• sand for instance, aluminum oxide, silicon dioxide, titanium dioxide, zinc oxide, zirconium dioxide, cerium dioxide, manganese dioxide, iron oxide, calcium oxide, magnesium oxide, or bauxite
• Proppant sands are a preferred type of proppant for the present invention.
• Sand is mainly used in the hydraulic fracturing process of natural gas and oil wells to increase their productivity of valuable natural resources.
• Proppant sand is monocrystalline with a high silica content of at least 80 wt%, and more typically greater than about 97 wt% silica.
• No more than 0.1% of the material may be coarser than the next largest mesh size [e.g. for 20/40, up to 10% of the proppant may be between 16 and 20 mesh, but no more than 0.1% can exceed 16 mesh], and
• proppant is divided into: low-density, medium density, high-density. According to the anti-crushing strength, proppant is divided into 52Mpa, 69Mpa, 86Mpa and 103Mpa four series. Specifications of proppant sand are generally: 12-18 mesh, 12- 20 mesh, 16-20 mesh, 16-30 mesh, 20-40 mesh between 30-50 mesh, 40-60 mesh, 40-70 mesh and smaller.
• the proppants to be coated preferably have an average particle size within the range from about 50 ⁇ m and about 3000 ⁇ m, and more preferably within the range from about 100 ⁇ m to about 2000 ⁇ .
• the method for the production of coated proppants according to the present invention can be implemented without the use of solvents. Accordingly, the mixture obtained in step (a) in one embodiment of the method is solvent-free, or is essentially solvent-free.
• the mixture is essentially solvent-free, if it contains less than 20 wt , preferably less than 10 wt , more preferably less than 5 wt , and still more preferably less than 3 wt , and most preferably less than 1 wt of solvent, relative to the total mass of components of the mixture.
• the method is implemented without the use of organic solvents.
• the mixture obtained in step (a) is free of organic solvents, or is essentially free of organic solvents.
• the mixture is essentially free of organic solvents, if it contains less than 20 wt , preferably less than 10 wt , more preferably less than 5 wt , and still more preferably less than 3 wt , and most preferably less than 1 wt of solvent, relative to the total mass of components of the mixture.
• step (a) the proppant is preferably heated to an elevated temperature and then contacted with the coating components.
• the proppant is heated to a temperature within the range of about 50° C to about 150° C to accelerate crosslinking reactions in the applied coating.
• the temperature of the coating process is not particularly restricted outside of practical concerns for safety and component integrity.
• the preferred conditions for the coating/curing step of the present invention are generally at conditions within the range of about 50° to about 175° C, more preferably at a temperature within the range from about 75° C to about 150° C, and most preferably at a temperature within the range from about 80° C to about 135° C. This temperature avoids a number of emissions issues, reduces the amount of energy consumed in the coating process and also reduces the cooling time for the coated proppants for further handling and packaging.
• the mixer used for the coating process is not particularly restricted and can be selected from among the mixers known in the specific field.
• a pug mill mixer, agitation mixer, drum mixer, plate-type mixer, tubular mixer, trough mixer or conical mixer can be used.
• the easiest way is mixing in a rotating drum.
• a worm gear can, for example, be used.
• Mixing can be carried out on a continuous or discontinuous basis.
• suitable mixers it is possible, for example, to add adhesion agents, isocyanate, amine and optional ingredients continuously to the heated proppants.
• isocyanate components, amine reactant and optional additives can be mixed with the proppant solids in a continuous mixer (such as a worm gear) in one or more steps to make one or more layers of cured coating.
• the proppant, isocyanate component, curing agent, amine reactant, polyol, and optional additives are mixed homogeneously.
• the isocyanate component and amine reactant are distributed uniformly on the surface of the proppants.
• the coating ingredients are preferably kept in motion throughout the entire mixing process.
• coating/curing process can be combined in proportions that will affect performance
• an isocyanate-containing component is used in an amount within the range from about 100 wt% to about 400 wt% based on a reactive polyol-containing component in the curable coating mixture. Lower proportions of excess isocyanate can be used to move the curing process towards substantially complete reaction of all of the -NCO groups within the applied proppant coating by the time the product is discharged as a free-flowing solid. The lower amount of isocyanate-containing component tend to add more thermoplastic properties to the coating for better performance in low temperature applications.
• the proppant coating is cured to an amount less than about 10 wt% of reactive -NCO groups based on the originally applied weight of the proppant coating.
• the most preferred low temperature proppants according to the invention contain have a weight ratio of isocyanate- functional component that is within the range from about 100-175 wt% of the polyol-functional component with a low coating loss under simulated downhole testing conditions.
• the preferred high temperature product contains about 200-400% by weight of isocyanate-functional component to polyol-functional component and exhibits a coating loss of less than about 2% in simulated downhole testing conditions.
• the coating is preferably performed at the same time as the curing of the coating on the proppant.
• the coated proppant becomes free-flowing at a time of less than 5 minutes, preferably within the range of 1-4 minutes, more preferably within the range of 1-3 minutes, and most preferably within the range of 1-2.5 minutes to form a coated, substantially cured, free-flowing, coated proppant.
• This short cycle time combines with the relatively moderate coating temperatures to form a coating/curing process that provides lower energy costs, smaller equipment, reduced emissions from the process and the associated scrubbing equipment, and overall increased production for the coating facility.
• the coating material may be applied in more than one layer. In this case, the coating process is repeated as necessary (e.g. 1-5 times, 2-4 times or 2-3 times) to obtain the desired coating thickness.
• a typical size range for coated proppant is typically within the range of about 16 to about 100 mesh.
• the amount of coating resin that is, of the polyurethane resin applied to a proppant, is preferably between about 0.5 and about 10 wt , more preferably between about 1% and about 5 wt , resin relative to the mass of the proppant as 100 wt .
• proppants can be coated at temperatures between about 10°C and about 150°C and preferably in a solvent-free manner. The coating process requires a comparatively little equipment and if necessary can also be carried out near the sand or ceramic substrate source, near the geographically location of the producing field or at/near the well itself.
• the coated proppants can additionally be treated with surface-active agents, anticaking agents, or auxiliaries, such as talcum powder or stearate or other processing aids such as fine amorphous silica to improve pourability, wettability (even to the extent that a water wetting surfactant can be eliminated), dispersability, reduced static charge, dusting tendencies and storage properties of the coated product.
• auxiliaries such as talcum powder or stearate or other processing aids such as fine amorphous silica to improve pourability, wettability (even to the extent that a water wetting surfactant can be eliminated), dispersability, reduced static charge, dusting tendencies and storage properties of the coated product.
• the coated proppants can be baked or heated for a period of time sufficient to further enhance the ultimate performance of the coated particles and further react the available isocyanate, hydroxyl and reactive amine groups that might remain in the coated proppant.
• a post-coating cure may occur even if additional contact time with a catalyst is used after a first coating layer or between layers.
• the post-coating cure step is performed like a baking step at a temperature within the range from about 100° - 200° C for a time of about 1 minute to 4 hours, preferably the temperature is about 125° - 200° C for -1-30 minutes.
• the coated proppant is cured for a time and under conditions sufficient to produce a coated proppant that exhibits a loss of coating of less than 25 wt , preferably less than 15 wt , and even more preferably less than 5 wt when tested according to simulated downhole conditions under ISO 13503-5:2006(E). Even more preferably, the coated proppant exhibits the low dust and handling characteristics of a pre-cured proppant (see API RP 60) but also exhibits a crush test result at 10,000 psi of less than 2%, more preferably less than 1.5%, and especially less than 1%.
• coated proppants of the invention preferably also have an unconfined compressive strength of greater than 100 psi and more preferably more than 500 psi with a fracture conductivity at a given closure stress that is substantially equal to, or greater than, the conductivity of a phenolic coating used in the same product application range.
• the invention also includes the use of the coated proppants in conjunction with a fracturing liquid to increase the production of petroleum or natural gas.
• Techniques for fracturing an unconsolidated formation that include injection of consolidating fluids are also well known in the art. See U.S. Patent No. 6,732,800 the disclosure of which is herein incorporated by reference.
• a fluid is injected through the wellbore into the formation at a pressure less than the fracturing pressure of the formation.
• the volume of consolidating fluid to be injected into the formation is a function of the formation pore volume to be treated and the ability of the consolidating fluid to penetrate the formation and can be readily determined by one of ordinary skill in the art.
• the formation volume to be treated relates to the height of the desired treated zone and the desired depth of penetration, and the depth of penetration is preferably at least about 30 cm radially into the formation. Please note that since the
• consolidation fluid is injected through the perforations, the treated zone actually stems from the aligned perforations .
• an acid treatment is performed by injection of an acidic fluid.
• this acidic treatment typically includes several stages such as an acid preflush, one or more stages of acid injection and an overflush.
• the final step is the fracturing step.
• the primary purpose of the fracture treatment is to connect the wellbore to the formation and in doing so by pass any damage and act as a filter allowing the production of hydrocarbons while holding back formation material.
• the high surface area associated with a fracture makes it a very effective filter, for example, a 13.7 m fracture length with 25 cm height has a surface area of 368 m , compared to the open hole flow area for a gravel pack of 3.2 m with the same zone height.
• the fracturing liquid is not particularly restricted and can be selected from among the frac liquids known in the specific field. Suitable fracturing liquids are described, for example, in WC Lyons, GJ Plisga, Standard Handbook Of Petroleum And Natural Gas
• the fracturing liquid can be, for example, water gelled with polymers, an oil-in-water emulsion gelled with polymers, or a water-in-oil emulsion gelled with polymers.
• the fracturing liquid comprises the following constituents in the indicated proportions: 1000 1 water, 20 kg potassium chloride, 0.120 kg sodium acetate, 3.6 kg guar gum (water-soluble polymer), sodium hydroxide (as needed) to adjust a pH- value from 9 to 11, 0.120 kg sodium thiosulfate, 0.180 kg ammonium persulfate and optionally a crosslinker such as sodium borate or a combination of sodium borate and boric acid to enhance viscosity.
• the invention relates to a method for the production of petroleum or natural gas which comprises the injection of the coated proppant into the fractured stratum with the fracturing liquid, i.e., the injection of a fracturing liquid which contains the coated proppant, into a petroleum- or natural gas-bearing rock layer, and/or its introduction into a fracture in the rock layer bearing petroleum or natural gas.
• the method is not particularly restricted and can be implemented in the manner known in the specific field.
• Suitable proppants include, but are not limited to, sand, bauxite, glass beads, and ceramic beads and resin-coated versions of each.
• the proppant will typically exhibit a size within the range from about 8 to about 100 U.S. Standard Mesh in size. Mixtures of suitable proppants can be used.
• the concentration of proppant in the fracturing fluid can be any concentration known in the art, and will typically be in the range of about 0.5 to about 20 pounds of proppant added per gallon of clean fluid.
• the fracturing fluid can contain an added propp ant-retention agent, e.g.
• Fibers in concentration that preferably ranges from about 0.1% to about 5.0% by weight of proppant, for example selected from natural organic fibers, synthetic organic fibers, glass fibers, carbon fibers, ceramic fibers, inorganic fibers, metal fibers and mixtures thereof, in combination with curable resin-coated proppants are particularly preferred.
• the proppant- retention agent is intended to keep proppant solids in the fracture, and the proppant and proppant-retention agent keep formation particles from being produced.
• test fluid is 2 wt% potassium chloride substitute solution filtered to 3 ⁇ absolute.
• the initial conductivity, permeability and width is measured and compared to the final conductivity, permeability and width after each stress period. Stress is applied and maintained using an Isco 260D. Stress is applied at 100 psi/minute.
• Width of the proppant pack is determined by assembling the conductivity cell with the Ohio sandstone wafers and shims without the sample proppants. The distance between the width bars that are attached to each end of the conductivity cells are measured at each of the four corners and recorded. The cells are then assembled with the proppant samples. The measurements are made again at the beginning and ending of each stress period. Width is determined by subtracting the average of the zero from the average of each of the stress width values. Conductivity is calculated using Darcy's equation.
• k is the proppant pack permeability, expressed in Darcy' s ;
• kWf is the proppant pack conductivity, expressed in millidarcy-feet
• ⁇ is the viscosity of the test liquid at test temperature, expressed in centipoises
• Q is the flow rate, expressed in cubic centimeters per minute
• ⁇ is the differential pressure, expressed in psi
• Wf proppant pack width, expressed in inches.
• Standard US mesh screens are used to separate the sample by size. Not more than 0.1% should be greater than the first specified sieve and not more than 1% should be retained in the pan. There should be at least 90% retained in the specified screens.
• samples of the proppant pack are taken, dried in an oven and weighed. They are then subjected to a temperature of 960° C for 2.5 hours. At the end of this period the samples are cooled and weighed again. The difference between the sample weight after drying but before being subjected to the furnace compared to the sample weight after the time in the furnace, equates to the coating weight . Comparing this number to the same test performed on a sample of the coated material before being subjected to the conductivity test, will equate to the coating weight lost due to the long term exposure to the conditions of the conductivity tests.
• the autoclave test utilizes what amounts to a pressure cooker to subject the coated sands to a hot wet environment that is above the boiling temperature of water. Approximately 20 g of sample is placed in ajar along with 150 ml of distilled water. The lids are placed on sample jars but not tightened. The samples are placed in the autoclave and the chamber is sealed. Heat is applied until the autoclave temperature reaches 250-265° F (121°- 129° C). The samples are maintained under these conditions for the ten day period. At the end of the test period the autoclave is cooled down, opened and the sample jars removed. Each sample is washed with distilled water and then placed in an oven to dry.
• the dried samples are then put through a standard test for determination of coating loss. This result is compared to the results of a coating test that was run on the original sample. The difference in coating weight before and after the autoclave test, quantifies the amount of coating that was dissolved by the exposure to a hot water environment.
• Phenolic Polyol comprising 48% phenolic resin, 28% cashew nut oil, 24% castor oil
• TR90 catalyst increased the reaction rate sufficiently that the amperage on the associated mixer was not exceeded as the coating reactants were metered into the proppant solids in the moving mixer. This suggests that the coating became cured at a rate that was consistent with the feed rate so that the liquid viscosity did not increase the electrical load on the mixer.
• This same method of controlled, metered addition would also apply for other formulations and chemistries under the present invention in order to keep the contents reacting at a rate that does not tax the load on the mixing equipment.
• Phenolic Polyol comprised of 48% phenolic resin, 28% cashew nut oil, 24% castor oil
• Phenolic Polyol comprised of 48% phenolic resin, 28% cashew nut oil, 24% castor oil
• ThermoMechanical Analyzer as supplied by TA Instruments is a device that accurately imposes a small force (i.e., a load) onto a sample which is then subjected to a desired temperature ramp over a defined time. During this increasing temperature period, the force is held constant.
• the probe which imposes the force is connected to a sophisticated micrometer that is capable of measuring fractions of a micron change in the position of the probe. Any change in the position of the probe can be interpreted to reflect an expansion or contraction of the sample that is brought about by the temperature change(s). In many applications, the sample merely expands as it is being heated (for instance raw sand) thereby creating a database that refers to the coefficient of thermal expansion.
• the TMA has the ability to run the samples in a variety of environments.
• a pre-cured, phenolic-coated sand will be characterized by a plot that is essential flat (parallel to the X axis) or has a positive slope. This response is indicative of a coating that is essentially reacted in which there is little to no remaining reactivity that remains in the coating.
• the TMA plot will exhibit a negative slope as early as 80° C to 100° C, but more often after about 125° C to about 175° C. This type of plot is characteristic of a coating that has retained a level of reactivity even after completing the manufacturing process. The more negative the slope and the lower the temperature in which the slope turns negative, the more reactivity that has been left in the coating.
• the top curve is labeled "Pre-cured” and is indicative of the response of a phenolic coating that is no longer reactive.
• the two lower curves are labeled “Partially Cured Phenolic A” and “More Curable Phenolic B.” These curves represent the TMA results from two levels of partially cured coatings.
• the second curve labeled "New Technology” shows a response that is similar to the pre-cured coating curve but actually shows properties that fall between a pre-cured coating and the less reactive partially cured coating.
• the shape of the New Technology curve indicates that the New Technology coating would exhibit some properties that are similar to a pre-cured coating and others that may be similar to the partially cured coatings.
• the New Technology coating performed like a superior, pre-cured coated sand.
• the plot entitled "Unconfined Compressive Strength" in Figure 3 represents a strength measurement of the particle to particle bonds of a coated proppant sand. Historically, a pre-cured coated phenolic sand possess little if any ability to form particle to particle bonds of any measureable strength. In this test the coating labeled Phenolic A exhibited a bond strength UCS of 449 psi. The coating labeled Phenolic B had a UCS of 155 psi. Since the TMA indicated that Phenolic B was a more reactive coating than Phenolic A, one would expect that the UCS results should be reversed.
• the pre-cured phenolic coating sand showed only a weak bonding capability with a measurement of 7 psi. This level of bonding would indicate that the pre-cured phenolic coating is not capable of forming particle-to-particle bonds that would consolidate the proppant or be effective in controlling proppant flowback.
• the New Technology coated sand exhibits the thermal properties of a pre-cured phenolic coated sand and crush resistance superior to a pre-cured phenolic coating. It also shows a bonding capability superior to the partially cured phenolic coated sand and a comparable if not superior fracture conductivity (when measured at 4,000 psi in a long term conductivity test). This would seem to indicate that the new technology contains traits and performance properties from both type coating and would best be described as a "hybrid" coating technology.
• a proppant coating formulation for Example 7 was prepared with an Iso:Polyol ratio of 0.65 equivalent weight at a process temperature of 198° F (92° C) and made from the curable coating ingredients shown in Table 11 :
• Dynasylan® AMEO from Evonik Degussa Corporation in Chester, PA is a bifunctional silane possessing a reactive primary amino group and hydrolyzable ethoxysilyl groups.
• the dual nature of its reactivity is represented by its manufacturer to allow Dynasylan® AMEO to bind chemically to both inorganic materials (e.g. glass, metals, fillers) and organic polymers (e.g. thermosets, thermoplastics, elastomers) thus functioning as an adhesion promoter, crosslinker, and/or surface modifier.
• inorganic materials e.g. glass, metals, fillers
• organic polymers e.g. thermosets, thermoplastics, elastomers
• Table 12 shows the timing and duration for the order of addition of the components making up the curable coating mixture of the invention.
• Discharge 180 What results from the above coating and curing process is a substantially cured and coated proppant having handling characteristics like a pre-cured, resin-coated proppant but with the ability to form interparticle bonds under downhole conditions like a curable, resin- coated proppant.
• the resulting product is then further contacted with a finely divided anticaking agent, like an amorphous silica or silica substitute in dry form or as a dispersion.
• the preferred anticaking agents are either a dry form of very small amorphous silica or a dispersion of nanometer- sized fumed silica.
• Table 13 summarizes the differences between the additives:
• 125° F (52°C), 24 hour shut-in, 1000 psi with a 2 wt% KC1 solution and without use of a bond activator plasticizer show that a 16/30 size of coated proppant sand according to the invention exhibits an unconfined compressive strength of 100 psi, and a 20/40 size blend of coated sand exhibits an unconfined compressive strength of 92 psi. Comparative tests against similarly sized proppants that use a partially-cured phenolic resin coating and 1.5 wt of a bond activator plasticizer show no unconfined compressive strength under the same conditions.
• the coated proppant of the invention forms a shaped sample exhibiting interparticle bonding of 92-100 UCS while the phenolic resin proppant remains loose particulates that show no interparticle bond strength even though an activator was added to promote such bonds.
• Figures 6 and 7 show the results of comparative conductivity tests reflected in
• Table 14 below that compare the proppants of Example 7 against two proppants with partially cured phenolic coatings.
• Figures 6 and 7 show that the 16/30 proppant of the invention exhibits a 79% greater conductivity at 2000 psi and a 32% higher conductivity at 4000 psi than the prior art phenolic proppant coating.
• Figure 7 shows similar results with the 20/40 proppant with a 29% higher conductivity at 2000 psi and 13% greater at 4000 psi.
• Hot water leaching tests show that the proppant coatings of the present invention show that the coating is highly resistant to leaching on components and unreacted materials. Indeed, the test water after the test was classifiable as safe to the limits of tap water for drinking. This contrasts with many phenolic coatings that can leach phenols and formaldehyde after prolonged exposure to hot water.
• Discharge 180 [181] The coated sand of Example 8 and two prior art proppants with partially cured phenolic coatings were then subjected to an unconfined compressive strength test using the equipment and materials described in Example 7 but operated at 250° F (121° C). In one set of conditions, the proppants were subjected to a three hour preheating that would be characteristic of the exposure times and temperatures found in a high temperature well. A comparison set of tests was performed without the preheating to gauge the ability of the proppant to resist the effects of extended exposure to heat before closure stress was applied. The results are shown in Figure 8.

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