Patent Application
20240010907
This invention relates to a multifunctional coating applied on the proppant's surface for reducing the friction of fracturing fluid with the coiled tubing and channels as proppants are transported from the oil application fields to the downhole wellbore fracture zones in the hydraulic fracturing operation. The mixed chemicals can also be added into the fracturing fluid directly as a viscosity enhancer that stabilizes the pumping pressure at a high flow rate, and functionally, as dust suppression agents to mitigate the worker's risks of exposure toward the microcrystalline silica dust. The advantage of the developed recipes over other fracturing fluid and additive chemicals is that the disclosed chemical compositions could be applied by simple blend of proppants with these disclosed chemicals without a need for drying operation in the manufacturing plant, during the transportation, and at the terminals and oil application fields.
Recently, concerns over fracture conductivity damage by viscous fluids such as guar gums in ultra-tight formations found in the unconventional reservoirs have been promoting the industry to develop alternative fracturing fluid such as slick water and viscoelastic surfactants to booster the hydrocarbon production, however, there have been various technical challenges and practical application issues to be addressed in the operation. Easy wear-out of fracturing operation tools and equipment; dustiness of respirable microcrystalline silica triggering the disease of micro-silicosis of lung cancers; caking and bridging of the grains to grains of the products in the transportation processes; loss of pumping pressure and high demands for high horsepower at high flow rates in the completion and stimulation operation; high costs of newly developed additive chemicals are often mentioned in literature. For examples, resin coated sands and/or self-suspending proppants were described in the U.S. patent applications (20120190593, 20150252253, 20150252252, 20180155614, 20180119006, 20190093000, 20190002756), and U.S. Pat. Nos. 9,868,896, 10,144,865, and 10,316,244. Hydrogel coating was used to coat on the proppant surface for enhancing the oil well productivity in U.S. patent application 20180340117. self-healing, self-cleaning, and self-lubrication multifunction surfaces were claimed by U.S. Pat. Nos. 9,963,597 and 10,011,860, 10,221,321, 10,233,334.
Reduced dust in the product's transportation terminals or oil fields was disclosed in U.S. Pat. No. 10,066,139 that the mineral oil could be used to treat the frac sand surface. U.S. Pat. No. 10,023,790 disclosed a water-soluble electrolyte solution recipe that can be applied on the frac sand surface with spraying to achieve the long-term dust suppression. U.S. Pat. No. 5,595,782, granted to Cole Robert on January of the 21st, 1997, disclosed a suspending sugar/oil emulsion that was used to mitigate the dusty particles. Sugar alcohol ester and its mixture of glycerol chemical components were used to suppress the dust in U.S. patent application of 20190010387. Guar and polysaccharides were also reported to achieve the dust suppression in U.S. Pat. No. 10,208,233.
In other instances, a fracturing treatment involves pumping a proppant mixed with the injected fracturing fluid into a subterraneous formation. During the pumping of the fracturing fluid into the well-bore, a considerable amount of energy may be lost due to the friction between the turbulent flow and the formation and/or tubular goods (e.g. pipes and coiled tubing, etc.). An additional horsepower may be necessary to achieve the desirable treatment. In general, a friction-reducing agent can be used to overcome the drawback from fracturing operation. The friction reducer is a chemical additive that alters the fluid characters so that the fluid can carry the suspended proppants downhole along the pipelines and channels easily with reduced energy losses. Chemical additives used as friction reducers include guar gum, its derivatives, polyacrylamide and polyethylene oxide, and other hydratable materials. For examples, U.S. Pat. No. 3,943,060, disclosed friction reducer chemicals useful in water treatment for viscosity reduction. U.S. Pat. No. 5,948,733, disclosed recipes for controlling fluid loss.
These hydratable additives of friction reducer solution are often sensitive to divalent cations such as calcium and magnesium chloride, and trivalent compounds such as ferric chloride and aluminum trihydrate. Most of these cation's chemical additives are widely contained in the ground water and special treatments of these water might be required to resolve the high dose of total dissolved solids (TDS) issues in the hydraulic fracking operation. Technically, special wastewater treatment technologies such as distillation and reverse osmosis might be used to reduce the water hardness issues. Decreased friction reducer performance in a high TDS brine has been a major challenge for reusing production water in hydraulic fracturing operation. Furthermore, the proppant is abrasive when it is moving along the downhole pipeline at high shearing rates. The abrasiveness of the proppants can cause erosion on the surfaces inside pumps, connected pipes, downhole tubules, and equipment. The lower friction reducer performance in the field causes a spike in pumping pressure for a given flow rate and if sustained, it could ruin the pumping operation.
Another drawback of the friction reducer chemical additives applied to the oil fields is that if the well's bottom hole static temperature is high, a regular polyacrylate sodium acrylamide (PAM) polymer might be subject to a degradation, specially, a modified hydrolyzed (HPAM) hydrogel polymer is required to deliver the desirable transportation performance for proppants with the viscous gel materials. In general, 30% or more polyacrylate sodium sulfonate in components is required to resist the decomposition of the HPAM under the regular well bottom hole static temperature. Improvement of HPAM performance with different emulsion reaction mechanisms was reported. For instance, U.S. Pat. No. 9,783,628 disclosed a synthesized method for preparing a high viscosity emulsion chemical additive that can be used to enhance the hydrate viscosity of fracturing fluid. In another developed additive technologies, U.S. Pat. No. 9,701,883 demonstrated that an addition of silicon polyether could potentially enhance the hydration viscosity when silicon polyether components are mixed with polyacrylate sodium acrylamide polymers. A high TDS tolerance toward the ionic frictional reducer recipes could be realized by an addition of special silicon polyether components. Special cross-linking agents were added in the fluid to reduce the shearing damage created. U.S. Pat. No. 8,661,729 disclosed a hydraulic fracture composition and method in which hydrolyzed polyacrylate sodium acrylamide (HPAM) is imbedded in the resin matrix. U.S. patent application of 2012/0190593 described a self-suspending coating that expands more than 100% of its volume to enhance the transportation capabilities of the suspended proppants in the downhole conditions.
Although many coatings and chemical additive technologies are available, multi-functionalized coatings delivering synergistic effects are still needed. So far, the research has been focused on mimicking one system at a time. In fact, a complex approach with mimicking of natural bio-inspired chemical and microstructure is needed, in which multiple functional coatings to come up with non-trivial designs for highly effective materials with unique properties are conceived and developed. The developed new fracturing fluids, proppant's coating, or additive products should meet the following criteria: 1) it should be slippery, no sticking, and bridging issues in the processes of handling and shipping; 2) if the coating is applied in any processing step, it can mitigate the risk of dust due to the respirable microcrystalline silica; 3) it has enough hydrated viscosity to fracture; 4) it has enhanced hydrophobicity that allows the frac fluid flowed with least pumping pressure and kinetic energy.
Coatings and chemical additives disclosed in this application provide solid answers in a response to the above issues.
In the disclosed invention of the developed coatings, it was found that chemical compositions and coating additives could deliver the desirable synergistic effects with a hydro-dual-phobic feature: 1) the disclosed chemical composition and coating can be applied in wet condition without a need for drying; none of arching or bridging during storage and transportation will occur; 2) the coated proppant surface is more slippery and anti-blocking than without the surface treatment of proppants and have enhanced drag/friction reducing capabilities for the fracturing fluid to transport the proppants moving toward the down hole of the wellbore at a high flow rate; 3) alternatively, the coatings can be added into fracturing fluid as a viscosity enhancer at the oil application fields.
By weight percentage (wt.), the chemical composition and coatings are comprising of:
The procedures for formulating the chemical additives are comprising of an addition of lubricants into a container, then, the granular particles or microparticles, micro/nanotextured particles are added into the lubricant solution and the mixed components are heated over 140° F. under stirring conditions until (b) is partially or totally dissolved in the container, then, an emulsifier, and/or a hydrogel polymeric material, or their mixture, are added into the pre-mixed components to create an emulsified shell/core micelle. Alternatively, hydrogel polymers can be added into mixer before emulsifiers. Phase transition materials such as wax and bio-derivative materials are preferred to serve as core layer or bumpy materials. The emulsifiers are served as a shell layer of the emulsion. Alternatively, the hydrogel polymers are served as both the inner and core layers or intermediate layer in the emulsified micelles.
After the combined components of (a)+(b)+(c)+(d) are fully mixed, (e) can be added into the container and continuously blended for an extended time, then, water a polar solvent (f) can be charged into the container to make an adjustment on the viscosity of the final recipes. The mixture is cooled down slowly, then, the mixed solution will create an emulsion complex, packed in a container, and stored for late use.
To a separately mixed container, the proppants, are first added, then, coatings, obtained from the above processes, are mixed into the container without a need for drying the blended components. The formulated chemical compositions and additives can be used as a coating directly applied to the proppant's surface. Alternatively, it can be added into the fracturing fluid as a friction reducer agent directly with or without a friction reducer in liquid or in powder. A spraying operation can be applied to the coating at the terminal or manufacturing facilities. The coating materials can be sprayed on the surface of proppants served as dust suppression agent, anti-blocking agent, friction reducer agent, and scale-inhibition agent that benefit the completion and well stimulation. The details in the recipe preparation and processing disclosure for preparing the coatings and additive emulsion are illustrated in the subsequent section in the examples 1 to 40 in detail.
Of the materials used for hydraulic fracking operation in the oil and gas energy exploration, two most important key materials are granular materials such as frac sand and fracturing fluid added with friction reducer additives included. Fracturing sand materials are used for propping and opening the downhole rocks and creating fracture in the formation, fracturing fluid for transporting the frac sand and/or proppants delivered into the desirable destination of targeted fracture opening. Technically, it requires that the proppants have defined shape, crush strength under the special downhole closure stress, appropriate particle size, and competitive price. Preferred proppant's materials should meet API standards or meet specified customer on-demand request per mutual agreements. Typical proppant's materials include the North White Sand, Brady brown sand, local basin sand, ceramics, and bauxite spherical materials.
Hydrogel Polymers: More specifically, since the proppant product has a higher density than water, any proppant suspended in the water will tend to separate quickly and settle out from the water very rapidly. To help its suspension in the transportation to the wellbore destination, it is common to use a viscosity-increasing agent for increasing the viscosities of used fracking water. Common practices in current manufacturing technologies disclosed are to use hydrogel polymers such as polyethylene glycol, polyacrylate and polyacrylamide polymers and/or their copolymers either added into the fracturing fluid, in which, the use of additional surfactants is involved. Powder polymers are conventionally used in these applications due to the high polymer concentration available in the form as compared to the solution polymers with reduced shipping cost.
In general, the use of copolymers of acrylamide with aqueous cationic and anionic monomers could prevent frictional loss in well completion and stimulation as disclosed in various U.S. patents. The dose level of frictional reducer agents added into the fracturing fluid is typically added as a fraction reducer additive that allows maximum fluid to flow with a minimized pumping pressure and energy by using a dose range of from 0.20 to 2.0 gallons of friction reducer polymer per 1000 gallons of water (gpt). The friction reducer solution has a low hydrated viscosity of 3 to 100 (cps).
Hydrogel polymers are commercially available in the market. For examples, there are several brands of SNF products, such as FLOPAM DR 6000 and DR 7000, that can be incorporated directly into fracturing fluid1. Both polymers are anionic polyacrylamide. Alternatively, FTZ620, FTZ610, and LX641 polyacrylate acrylamide polymers, manufactured by Shenyang JiuFang Technology Ltd., are also useful polymers as alternative HPAM as friction reducer and coating ingredients2. Other polyacrylate and acrylamide polymers with cationic and nonionic molecular structure, are also potential candidates as hydrogel polymers. The structure of hydrolyzed polyacrylate sodium acrylamide can be linear or branched with dendrimers having hyperbranched polyester amide structure, other water-soluble polymers, such as polyvinyl alcohol (PVOH) and polyethylene glycol, are also potential candidates as substitute polymers of HPAM. 1https//www.snf.us/wp_contest/cploads/2004/08/Floppam_Drag.reducer.pdf.2 https//www.if_chinapolymer.com.
A further benefit of coating the proppants with the hydrogel polymers is that the fine particles such as crystalline silica dust can be mitigated to reduce the risk of workers exposed toward the respirable microcrystalline silica dust for chronic diseases and reducing contamination of the working environments. The percentage dose level of hydrogel polymers in the recipes will be in a range of within 0.01 to 35.0%, preferred 0.001 to 15.0%, more preferred 0.001%, 5.0%.
Lubricant: The synthesis processes of the HPAM polymers are involved in an inverted emulsion. Mineral oil or saturated hydrocarbon (kerosene) is, in general, used as a key solvent for preparing the HPAM friction reducer emulsion. As a result, HPAM hydrogel polymer is dispersible in the lubricant. Lubricants or oils are comprising of the derivatives from petroleum crude oil, containing saturated hydrocarbon and alkyl group from C6 to C25. Alternatively, the lubricants can also be originated from the bio-derivative resource such as corn, soy bean, sunflower, linseed oil containing the long chain alkyl components. The lubricants can also be synthetic oil chemicals made of reactive ester or hydroxyl functional alkyl chains or saturated hydrocarbons coupled with silane coupling agent or having silicon functional groups.
A broad definition of lubricants could be found in an URL link3. It is defined as a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. The dose applied in the chemical compositions for lubricants is added in a range from 1.0 to 90%. A typical mineral oil that can be used is a white mineral oil labelled as 70 Crystal Plus white mineral oils, manufactured by STE Oil Company, TX, USA. It is a series of derivatives of petroleum crude oils. Alternatively, soybean oil and linseed oil, or synthesis silicon oil can be used as lubricants. Other examples of lubricants include ethylene bisstearic acid, amide, oxy stearic acid, amide, stearic acid, stearic acid coupling agents, such as an amino-silane type, an epoxy-silane type and a vinyl-silane type and a titanate coupling agent. 3https/en.wiki.pedia.org/wiki/lubricant.
Micro/Nanotextured Domains: Of the disclosed chemical composition and emulsion coatings as shown in
Another benefit with waxy materials is that wax is cost-effective as hydrophobic domain materials and easy to be emulsified into coatings. It has a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures, including higher alkanes and lipids, melting to give low viscosity liquids. Waxes are insoluble in water but soluble in organic and nonpolar solvents. Natural waxes of different types are produced by environmentally friendly plants. For example, Carnauba wax, also called Brazil wax and Palm wax, originally from the leaves of the palm, is consisting mostly of aliphatic esters (40 wt. %), diesters of 4-hydroxycinnamic acid (21.0 wt. %), ω-hydroxycarboxylic acids (13.0 wt. %), and fatty alcohols (12 wt. %). The compounds are predominantly derived from acids and alcohols in the C26-C30 range. Distinctive for carnauba wax is the high content of diesters as well as methoxy-cinnamic acid4. 4https://en.wikipedia.org/wiki/Carnauba_wax.
Paraffin waxes are hydrocarbons, mixtures of alkanes usually in a homologous series of chain lengths. They are mixtures of saturated n- and iso-alkanes, naphthene, and alkyl- and naphthene-substituted aromatic compounds. A typical alkane paraffin wax chemical composition comprises hydrocarbons with the general formula CnH2n+2 and C31H64. The degree of branching has an important influence on the properties. Microcrystalline wax is a lesser produced petroleum-based wax that contains higher percentage of iso-paraffinic (branched) hydrocarbons and naphthenic hydrocarbons. The candle and paraffin wax are commercially available in the commodity market.
Synthetic waxes are primarily derived by polymerizing ethylene. Alpha olefins are chemically reactive because they contain a double bond which is on the first carbon. The newest synthetic paraffins are hydro-treated alpha olefins which removes the double bonds, making a high melt, narrow cut and hard paraffin wax. The wax is a very hydrophobic material. It has melting points in general above 35° C. or more. More specifically, the melt points of the wax are above 55° C. It has a measured water contact angle between 108 and 116(°) (Mdsalih, et al. 2012). The percent wax quantities added into the mixture of designated recipes should be in a range from 0.01% to 15.0%, more preferred less than 5.0%. Other typical synthesis waxes include reactive wax such as ethylene stearamide, bis-ethylene stearamide, and their blends with other wax or solid lubricant materials that have lubricants and slippery characters. Besides wax, other nano-particles, such as polylactic polymers, SPI, nanofillers, lipids, sweet rice, and other bio-derivatives, might be used as macro/nanotextured materials mixed together with wax to achieve desirable hydrophobicity and hydrophilicity. Hydro-dual phobic domain materials are referred to the materials that can be described as a material that behaves as hydrophilic, also hydrophobic with a dual-phoblicity. It can be a two system by a synergistic blend or one system chemically modifying a solid surface with multifunctional attributes. For example, a silane coupling surface treatment will allow the surface of modification to become either hydrophilic or hydrophobic, leading to be a hydro-dual-phobic. As such, as the modifying surface is contact with water, it will tend to expose itself with hydrophilic attributes. As it is attached with non-polar solvent, it will tend to expose its wax or alkyl functional groups on the surrounding environments. As such, the coated molecular components can be adapted to the solvents or air with appropriate fitness to the systems.
Emulsifier: An emulsifier is a surfactant chemical. It can be cationic, anionic, nonionic, zwitterionic, amphiphilic having linear long chain, branched with di-functional, tri- or multi-functional star's structures, consisting of a water-loving hydrophilic head and an oil-loving hydrophobic tail. The hydrophilic head is directed to the aqueous phase and the hydrophobic tail to the oil phase. The emulsifier positions itself at the oil/water or air/water interface and, by reducing the surface tension, has a stabilizing effect on the emulsion. In addition to their ability to form an emulsion, it can interact with other components and ingredients. In this way, various functionalities can be obtained, for examples, interaction with proteins or carbohydrates to generate connected clusters both chemically and physically.
Typical emulsifiers include stearic acid oxide ethylene ester, sorbitol fatty acid ester, glyceryl stearate acid ester, octadecanoic acid ester, combination of these esters, fatty amine, acid chemical additives and compounds, alkylphenol ethoxylates such as Tergitol NP series and Triton x-100 from Dow chemicals, glycol-mono-dodecyl ether, ethylated amines and fatty acid amides. For example, SPAN 60: polysorbitan 60 (MS) and PEG100 glyceryl stearate MS are two typical emulsifiers used for emulsion coatings in cosmetics industries. Typical emulsifier is branched as polyoxide-ethylene parts, groups found in the molecules such as monolaurate 20, monopaimitate 40, monostearate 60, monooleate 80, et al. with HLB from 4.0 to 20.0, preferred around 10.0 to 17.0.
Dose levels of added emulsifiers in the emulsion can be within a range of 0.01% to 5.0%, more specially less than 3.0%. The emulsifiers are water insoluble and only dispersible. It is only dissolved in hot water. Wax and SPI or polyhydroxy sugar compounds can be included as core materials in the micelle structure by being added as emulsifiers. Here, the emulsifiers serve as the shell components in the micelle structure.
The emulsifiers used in this coating are critical components. As shown in
Cross-linking Agent: To enhance the stiffness or strength of the hydrogel polymers, cross-linking agents can be added in the mixed components. Typical cross-linking agents added can be polymers with reactive functionalities. A typical polymer, such as polyurethane dispersive agents, containing the un-saturated UV curable cross-linker agents, could be added into the chemical component's system. Reaction of cross-linking agents can be chemically cross-linked with non-reversable connections in nature or reversable with hydrogen bonding, pending upon the blended component's condition. Alternatively, chemicals, containing epoxy, amine, amine or reactive aldehyde, glutaraldehyde, hexamine, and hydroxy-amine functional groups and compounds, could be added into the coatings or/and solutions. Isocyanate and silane coupling reactive cross-linked polymers can also be used. The preferred dose level of cross-linking chemicals is less than 10.0% by total wt., more preferred less than 5.0%.
Antimicrobial Agent: As biomaterials or its derivatives are incorporated in the recipes, antimicrobial agent, preservatives, preventing the bio-materials from bacteria or micro-fermentation, can be added in the recipes, common additives, including glutaraldehyde, formaldehyde, benzyl-C12-16-dimethylbenzyl ammonium chloride, fatty amine, alternatively, inorganic antimicrobial materials, such as copper sulfates, copper oxide nano powder, can be used.
Water: Water is assumed to be a key component for preparing the emulsion as media and dilute agent to hydrate and adjust the coating into appropriate viscosity. Preferred viscosity of the final coatings will be in a range of 5 to 50 (cps) at the ambient temperature, the dose level of the water added will be in a range of within from 80.0% to 97.0% in total, preferred larger than 85.0%.
Procedures for preparing the chemical composition and additives disclosed herein relate to the recipes for a multi-functional coating, comprising a multi-layered or hybrid shell and core structure having a desirable synergistic effect to the fracturing fluid. It is not wishing to be limited by theory, applicants believe that the added components following a special procedure form a mixed unknown and undefined multi-layer and a micro-micelle emulsion structure that can deliver special multi-functional performance in a response to the product's performance request. The coating chemical components can be described as that a phase transition material, such as petroleum wax, biomaterials, and/or granular materials, organic or inorganic derivative particle materials (labelled 102), sized in diameters from 0.000001 (micron) to 1000 (micron), could be dissolved or dispersed in the mineral oil (101) by heating and re-condensed and crystalized back into solid bump and particles as the mixed component's temperature is below the melting temperature of mixed components.
The non-polar lubricant solvents such as mineral oil and alkyl group are saturated carbon and unsaturated hydrocarbons in the range of from C6 to C18 (101), also, included in the recipes are saturated carbons in the range of C12 to C26 in the range and mostly alkanes, cycloalkanes, and various aromatic hydrocarbons (102). It can be classified as paraffin, naphthenic, and aromatic. The preferred heating temperature for the mixed chemicals can be as high as 140° F., then, the surfactants or emulsifiers (103) can be added into the mixed solution, resulting in a uniform emulsion with multi-layered shell/core structure.
Finally, a hydrogel polymer (106) and cross-linking agents (105) are added into the solution. The micelle structure disclosed here is just for demonstration only. The actual micelle structure might be a hybrid one with an ambiguous intermediate layer or interface instead of a clear shell and core's structure. The wax particles as the core of the micelles are encapsulated within the emulsifier molecules. The emulsifier molecules are hybridized with hydrogel HPAM polymers extended toward the water phases. The emulsifier molecules play essential roles in dispersing the wax or other micro-nanotextured particles and fiber materials in the hydrogel polymers and solvents temporally. Meanwhile, it also allows the wax or other textured particles to migrate and suspended on the top of the coating layers. As a result, the hydrophobic coating domains and bump dots can be generated.
After being blended for 5 (minutes), the mixed components can be charged with polar solvents such as water (104) into the mixture, Brookfield viscosity of the mixed materials can be determined at a spindle rotation speed of 6,12, 30, and 60 (RPM), then, the coating materials are sealed in the package for late use. A schematic of emulsion in shell/coremicelle structure is illustrated in
Alternatively, the multifunctional coating materials of micelles can be added into a fracturing fluid such as frictional reducer solution incorporated with certain percentage of brine solutions such as 2.0% sodium chloride or positum chloride (NaCl-108), in which a frictional reducer agent (107
If the coating is sprayed or blended with proppants, the surface of the coatings could be conceptually simplified with a patch of typical domains: a) hydrophobic and b) hydrophilic domains originally from the mixed ratio of different chemical compositions and their relative polarities of hydrophobicity and hydrophilicity in
As shown in
The proppants used in the disclosed invention are referred to as these materials such as North white frac sand, brown sand, local basin sand, ceramics, bauxite, glass sphere, ceramic sphere, and hollow spheres, saw dust, walnut shell particle materials. These materials can be made with organic or inorganic or their hybrids. The particle size can be 100 mesh, 40/70, 30/50, 20/40 per API specification or 40/70, others pending upon the customer specification. Regular and common available equipment can be used for mixing the proppants with the emulsion such as rotary mixer and nozzle spraying.
As shown in
These island areas, comprising of the waxy or/and SPI components as the top layer, are surrounded by hydrogel polymers prepared with free radical polymerization through an inverted emulsion process. The hydrogel polymers are compatible with the lubricants and make the coating top layer of the coating surface smooth. Therefore, the lubricant and mineral oil can penetrate itself or sink itself in the hydrogel polymer matrices to grant the coated surface flexible to each other between adjacent grains of proppants. Since the lubricant/mineral oil has a low surface tension (22 dynes/cm), it is believed that the coating disclosed here potentially grants its self with anti-sticking and anti-blocking attribute important during the products handling and transportation.
Brine solution and total dissolved solids (TDS) of brine is referred as to the water solution containing salt cationic particles or elements. In the available water resource of oil field, the water, in general, contains quite bit of cationic salts such as calcium and magnesium ion. 2.0% to 10.0% sodium chloride or potassium chloride are prepared in hydraulic fracturing operation to reduce the percentage swelling created by clays. Since the cationic salts are positively charged, interaction of cationic salts such as calcium cations with friction reducer of the fracturing fluid has always been a challenging issue. Potential drawbacks of cationic ions are that it precipitates the polyacrylate acrylamide polymers and makes the polymers coiled together and dramatically reduce the hydrated viscosity of fracturing fluid. As a result, more HPAM chemicals are needed to overcome the drawbacks of the precipitation of cationic ion before the viscosity of the fracturing fluid can be regained.
Total dissolved solids (TDS) is one critical parameter used to define the qualities of water for the cationic strength. Alternatively, another parameter is the electronic conductivity. Both are positively related to each other. In addition, solution pH value is also an important parameter that controls the rheology of fracturing fluid. In general, the preferred pH value of HPAM is slightly higher than 7.0. The chemical composition and coatings with high salt tolerance capabilities are preferred. Various advantages of disclosed recipes and formulation will be further illustrated in the explanatory examples 1 to 40.
A summary of the recipes described in examples 1 to 7 is listed in table 1.
)
Mineral Oil
10
20
)
Mineral Oil
99
10
20
4.26
indicates data missing or illegible when filed
The test results of rheology and solution properties based upon examples 8 to 13 are summarized in table 2. It was discovered that an incorporation of the disclosed recipes listed in examples 3 to 6 could potentially boost the hydrated viscosity of the standard fracturing fluid solution while maintain other performance properties of the products as the same. Also, in the case of the fracturing fluid containing large TDS of hard water with cationic ions such as Ca+2 and Mg+2, the added emulsion coatings could still maintain the hydrated viscosity of the fracking fluid.
)
CP)
indicates data missing or illegible when filed
As listed in table 2, the Brookfield viscosity of example 9 showed a 20% increase at a rod spindle rotary speed of 60 (RPM) over that of example 8 of the standard fracturing fluid solution. The shear rate at the rod spindle rotary speed of 60 (RPM) is equivalent to 1020 (1/s) shear rate, which is attributed to the added 5.0% emulsion coating prepared with the recipe of PMSI_1_115_1 recipe listed in table 1. Also, at the shear rate of 525 (1/s), the viscosity of example 9 was 16 (cps). In contrast, the viscosity of example 8 is only 13.6 (cps).
One well-known issue with regular fracturing fluid solution is that high concentration brine is detrimental to the fracturing fluid performance as illustrated in example 11, in which 10% of cationic solutions of PMSI_2_89_1 with calcium and magnesium cationic ions blended with standard fracturing fluid solution of example 1 reduced the mixed solution viscosity to 5.0 (cps) at the rod spindle rotary speed of 60 (RPM). The data result listed in example 10 demonstrates that a 5.0% addition of emulsion coatings with recipe of example 3f (table 1) into the standard FR solution increased its viscosity from 5.0 (cps) to 6.6 (cps) at the rod spindle rotation speed of 60 (RPM), 30% more than the viscosity in example 11.
An increase of dose level incorporated the example 3f coatings at 15.0% will increase the hydrated viscosity of mixed fracturing fluid solution by 70.0% from 5.0 (cps) to 8.5 (cps) in example 11. In the example 12, 10% of emulsion coated proppants (PMSI_2_81_2) blended with the standard solution of example 8 for 3 minutes did not alter the viscosity of the example 11. Salt and cationic water tolerance will be enhanced if certain emulsion coatings are blended into the fracturing fluid.
About 220-235 (gram) (m) of tested liquid was used to fill up the top container connected to the vertical plastic pipeline (Lv). Quantity of the liquid (Q) flowing through the tubing pipeline in the vertical direction was measured by collecting the total quantities of liquid in the container located in the bottom by the end of the test. The total interval, at which the whole liquid flowed through the whole length (Lh) of pipeline in the horizontal direction, was determined by a digital timer (t). The viscosity of the flow liquid was calculated by the following Poiseuille's equation (1):
Where μa is the apparent viscosity of the tested liquid; r is the radius of the testing tube; ΔPm is the hydraulic pressure of the tested liquid, which can be calculated by subsequent equation (2); m is the total mass of tested liquid; t the total time for the liquid flowing through the whole pipeline in vertical direction; Q(t) is the total liquid through the pipeline in volume; g is the gravity; Lh is the pipeline length in the horizontal direction.
ΔPm=Hvρg (2)
where Lv is the height of vertical testing tube; ρ is the density of the tested liquid.
The velocity (v) of liquid through testing tube was calculated with equation (3):
The Reynolds number was calculated with equation (4):
Special fracturing fluid empirical formula was used to calculate the coefficient of friction (COF) for calculating the pressure difference (ΔP). Here, a Morrison correction factor was used to determine the COF as described in equation (5) (Assefa & Kansha, 2015):
Pressure difference in the test tubing could be calculated as described in equation (6), once Cf was obtained.
The drag reduction (DR) percentage was calculated using equation (7):
It was assumed that the Reynolds number for tap water and others was 15000 (turbulent flow), the calculated dynamic viscosity was 0.00052 (mPa·s). The velocity of tap water through the test tube was 0.491 (m/s), ΔP (tap water)=203 (pascal). The calculated test results are listed in table 4.
A comparative study on exam 15 vs. exam 16 as listed in table 4 shows that more pumping pressure is needed if 2.0% NaCl and 0.20% friction reducer (FR) are used in exam 16 than in exam 15. Both chemical additives and samples coated with multi-functional coatings will significantly reduce the drag force (pumping pressure) significantly. For instance, a 5.0% addition of chemical composition of the sample in exam 17 and a blend of 1/10 addition of proppant coated with multifunctional coatings of the sample in exam. 18 could reduce the pumping pressure of DR % 45.8% and 47.2% over the sample in exam 16, based upon equation (7). The DR % of these two samples in exam 17 and 18 are 54% and 55% less than exam. 23 (Ctrl.).
All the data in the examples from 15 to 23 is summarized in the table 4. Of the tested samples from examples 15 to 23, if the proppant is coated with PMSI_81_1 at a dose level of 1.5% (example 20), its drag reduction % will reduce by 72% over the control condition of the untreated sands at a NaCl 2.0% and friction reducer of 0.20% fracturing fluid solution (example 23). Clearly, the DR % originally from multifunctional coatings are exceptional in exam 20 over the exam 23 even in case that there are a lot of cationic ions containing in the solution.
Sine less drag force is needed in the coated frac sand, an application of the disclosed coatings will use less pumping energy to drive the proppants down further under the downhole condition. The tool and equipment wear-out cost could also potentially be reduced due to the reduced friction of coatings. Besides a comparison between example 20 and 23, drag-force reductions, to certain degree, are also demonstrated in other samples.
The swelling percentage of the above samples was measured following the procedures described here. 1) pre-dry the sample in the oven-overnight, then; charge the sample with a reusable home-made cloth container to hold 50.0 (gram) of samples in each bag; 2) determine the bag's original weight and after being pre-soaked weight with a digital balance prior to packing the 50 (gram) of the tested sample; 3) immerse the samples with tap water at the ambient temperature and 4) start to count the time; and take the samples weight at a regular time interval among 1, 2, 3, 5, 10, 20, 30 (minutes), then, place the soaked sample back to the same bathes. The percentage of mass swelling was determined by equation (8):
where M is the weight of samples at time (t); Mo is the weight of samples before being immersed in the tested solvent/water.
The % swelling following the above procedure for example 24 is listed in table 5. The average % Swelling rate=43.47% after being immersed in water for 300 (second); 46.00% after 600 (second). All experimental data reported is an average value of 3 individual measurements of samples. A caking phenomenon was observed after the wet sample was dried under the sun with a 5 (lbs) of weight placed on the top of the sandwiched aluminum foils on the inspected sample from the example 24 as shown in
Following the same procedures as example 24 of setting up the caking and blocking test, 50.0 (gam) of coated samples from example 25 were soaked with tap water and sandwiched between two sheet of aluminum foils, then, 5 (lbs) of weight on the aluminum foil was placed on the samples sandwiched between two aluminum films. The samples were left at ambient temperature under outdoor environment under the sun in a parallel order as example 24. After the samples were exposed under the sun more than 72 hours with the 5 (lbs) of weights, the samples from both examples of 24 and 25 were inspected. No caking and blocking occurred in the example of 25. Individual grains could move independently from each other without caking and sticking together.
The applicants believe that the addition of the disclosed coating blended into the powder FR or liquid FR is a unique feature of this invented technologies from previous art and literature. The proppant grains coated with the disclosed coatings did not encounter the issues of grain to grain sticking together. It is conceivable that in the actual production, there is no need to dry the products when the coating is mixed or blended with FR chemical additives in both liquid and powder form. The products can be transported and handled without an issue of arching and bridging from manufacturing plant to terminal, from the onsite oil field to the downhole bottom well-bore, and from bottom wellbore to target destination of fracturing crack of the formation. Experimental test setting on the two samples from example 24 and 25 is shown in
In addition, samples from exam 25 and 26 might be potential candidates for preventing the excessive leak-off of processing water after the wells are closed since both are swollen extensively that can hold processing water from flowing.
For a shear thinning materials such as described here, the rheological properties of the decanted solutions were described with Bingham's model with equation (9):
μ=k(y)n (9)
where r is the shear rate of tested solution; k consistency index; n fracturing fluid flow index in the Bingham model.
The Reynolds number used for characterizing the flow behavior were calculated with a more general equation shown in equation (10):
Based upon the equations (9) and (10), the Reynolds number for each tested solution was calculated and the efficient of friction (EOF) was calculated and plotted in
The rheological property data measured in examples 29 to 33 was fitted with equations 9 and 10 to obtain the Reynolds number, then, coefficient of friction in a response to the tested sample at specific blending time was calculated based upon the equation 5. A plot of frictional coefficient vs. sample's blending time is shown in
In example 30, the friction coefficient of the tested sample has the similar cycle variation pattern as example 29 with a reduced value of frictional coefficient since the fracturing fluid used in this case was standard fracturing fluid instead of water. In addition, the added emulsion coatings made the coatings more slippery, protecting the fracturing fluid from further degradation and shearing loss.
In example 31, the friction coefficient was kept consistent during the whole blending period without a variation. In this case, the slippery coatings, in fact, blocked the proppants from strong interaction with standard fracturing fluid polymers. Potentially, less shearing and polymer degradation occurred during the blending and transportation of proppants into wellbore. Potentially, the dose of frac fluid (FR) can be reduced while keep the performance of mixed solution the same.
In example 32, the frictional coefficient of the decant solution presented consistent value around 0.0077-0.0078 until 30 (minutes). Shearing and cut-off of polymer molecules occurred more extensively after a blending time of 30 (minutes).
To get a better comparison, the dust concentration (Dexample 34) from untreated sand (example 34) was used as base. The reduction % for other treated samples was calculated with the following equation 11.
where % DR is the sum of % dust reduction, Dx(i) is the measured dust concentration at the time interval of i.
A comparison of dust concentration among the tested examples 34 to 39 is shown in
It is well-known that for a lotus leaf observed under the scanning electronic microscopy (SEM) on the very distinctive surface of its tips, a hydrophilic second layer is formed by thin nanometric wires. This structure is covered with a waxy layer that increases the hydrophobic effect, which makes the water droplets maintain its spherical shape. The waxy layer favors the rolling of the droplets by forming a thin layer of air on the top of the waxy layer. Self-cleaning functionality is granted with the water microdroplet carrying the dust particles away from the lotus leaf.
Different from the lotus leaf, if the disclosed multi-functional coating is applied on the proppant surface, it tends to have hydrophobic domain's tips comprised of waxy or other hydrophobic particles directly protruded on the surface of the coatings surrounded with hydrogel polymers immersed in the mineral oil and/or lubricant domains. Since the thin film of mineral or hydrocarbon chemical compositions allows the water dispersed into the coating matrix easily, the water droplet tends to have better wetting capability toward the mineral oil. If the water droplet is small, it can pin self on the surface of coated materials instead of rolling down the surface of coatings. As a result, the drag-force or friction between the probe liquid and coating surface is very small. The consumption of energy for fracturing fluid or oil through the coated proppants is minimized.
Quantitatively, the contact angle of the coated coatings can be expressed with Cassie and Baxter equation (12).
Cos(θY)=f1 cos(θ1)+f2 cos(θ2) (12)
where θY is the measured static contact angle of composite materials for a smooth surface, f1 is the percentage of surface covered by component 1 such as wax; f2 by component 2 such as lubricant or mineral oil or hydrogel coatings; θ1 contact angle of wax under static condition; θ2 the contact angle of lubricant and/or mineral oil/hydrogel polymer layer to the probe liquid.
Fundamentally, the measurement of contact angle and sliding angle is a complex research topic. Publications on how the measured contact angles are related with surface chemistry and topo-graphics of composite materials are widely available in the internet website and literature (Miwa, et al. 2000). Besides, static contact angle, advancing contact angle, and receding contact angles are measurable parameters for characterizing the microdroplets. The hysteresis of material's surface with different chemical composition and roughness is considered as a major reason that causes the variation of advancing and receding contact angles. The sliding angle (SA)−α can be correlated with the advancing contact angle (θadv.) and receding contact angle (θred.). Previous experiment demonstrates that the static contact angle (θstat.) on a smooth surface can be related with advancing contact angle as θadv.=θstat.+Δθ and receding θrec.=θstat.+Δ←. Here, Δθ is equivalent to (θred.−θads.)/2 and ΔG was calculated with equation 13
sin(Δθ)=a*sin(α)*sin(θstat.)/{2−3 cos(θstat)+cos(θstat)3}1/3 (13)
where
Table 7 lists the summary of measured sliding angle (α), static contact angle (θstat.), the hysteresis angle (Δθ) and microdroplet weight of the tested samples with selected coating surfaces.
As the coated proppants are packed together in the downhole fracture and formation, the channels among adjacent grains to grains can be considered as two-phase porous media. The driving forces that dominate the two-phase flow are capillary and viscous forces. Their relative magnitudes govern the two-phase distribution and flow regions. Based upon the two-phase flow regime model proposed by Lenormand, et al. (1990, 1998). For a non-wetting solid substrate surface, the capillary force can be calculated with equation (15).
where σlv is the surface tension of probe liquid, ΔPcapillary is the difference of capillary tube pressure.
Based upon the fitted equations in
where θ exam. 40a is the contact angle of sample coated with the coating of PMSI_2_81_1 and exam. 40c PMSI_2_54_1.
To determine the hysteresis kinetic Energy, the expression of equation 17 were used:
ΔE=σlv{ cos(θ−Δθ)−cos(θ+Δθ)} (17)
where σlv is the surface tension of probe liquid, ΔE is the hysteresis energy difference for the specific solid and liquid interface (HED).
The calculated % DR is 38% of less pressure needed for the proppants coated with disclosed coating of PMSI_2_81-1 than using standard fracturing fluid recipes to effectively flow through the pumped fracturing fluid for water fracturing operation. For crude oil production (assume that corn oil is a representative oil to Crude oil), the % DR is 17% less demand on pumping pressure. Clearly, the coating made the surface of coated proppants hydrophobic and less frictional. It has a sliding angle of 116° as its hysteresis contact angle equivalent to zero at microdroplet wt.=0.0246 (g). It is more compatible with corn oil than water. The applicants believe that the coated proppants provide an excellent shielding effect on the potential scaling and skinning to the flow media with its no-wetting and anti-fouling surface. The Hysteresis contact energy difference predicted by sliding angle (SA) listed in table 8 demonstrated that minimum of 9.56 (dynes/cm) of interface kinetic energy (H_ΔE) was needed for PMSI_2_54_1 recipe coated on the proppant surface. In contrast, the hysteresis kinetic energy for PMSI_2_81_1 was zero.
The cradle and micro-pinhole texture of the coatings are clearly shown in
As shown in
An interesting phenomenon as shown in
Based upon the disclosure present here, it is therefore demonstrated that the objects of the present invention are accomplished by the chemical composition and specified multi-functional coatings and compositions of matter and methods of preparations, its applications, and identified benefits for the hydraulic fracturing operation in oil and gas industries disclosed herein, it showed to be understood that the selection of the specified lubricant, micro-nano-textured particles and phase transition materials, emulsifiers, hydrogel polymers, and cross-linking agent, and made-up water/polar solvent percentage by wt. can be determined by one having ordinary skill in the art without departing from the spirit of the invention herein disclosed and described. It should therefore be appreciated that the present invention is not limited to the specific embodiments described above, but includes variation, modification, and equivalent embodiments defined by the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/027426 | 4/15/2021 | WO |
