Patent Application
20160200965
This application claims the benefit of Canadian Patent Application 2,877,025, filed Jan. 9, 2015.
Embodiments taught herein relate to methods and apparatus for treating particulate materials and, more particularly, for treating proppants used for fracturing operations to hydrophobically modify the surfaces thereof.
Sand slurries are used in a variety of industries, including but not limited to, petroleum, pipeline, construction and cleaning industries. One example where large amounts of sand slurry are used is hydraulic fracturing. Hydraulic fracturing of subterranean formations is used for increasing oil and gas production. In a hydraulic fracturing process, a fracturing fluid is injected into a wellbore for introduction into the subterranean formation at a pressure sufficient to initiate a fracture. Increased volumes of oil and gas flow through the fracture to the wellbore for enhancing production.
Fracturing fluid is flowed back to surface, generally at a last stage of a fracturing treatment. At least a portion of the proppant is left in the created fracture to prevent closure of the fracture after pressure is released. The proppant-filled fracture provides a highly conductive channel allowing oil and/or gas in the formation reach the wellbore more efficiently.
Frequently particulates, generally referred to as proppants, are suspended in the fracturing fluid, forming a slurry which is transported into the fracture. Proppants include, but are not limited to, sand, ceramic particles, glass spheres, bauxite (aluminum oxide), and the like. Sand has been the most commonly used proppant to date. Fracturing fluids in common use include various aqueous and hydrocarbon gels. Liquid carbon dioxide and nitrogen gas are also used in fracturing treatments. The most commonly used fracturing fluids are aqueous fluids containing cross-linked polymers or linear polymers to effectively transport proppants into formation.
The conductivity of the proppant in the fracture, referred to as the proppant-pack, plays a dominant role in increased transport of the oil and gas to the wellbore. It is well known however that the conductivity can be adversely affected, such as by polymer residues in the fracturing fluid, which greatly reduce the conductivity of the proppant-pack.
The density of sand is about 2.6 g/cm3 while the density of water is 1 g/cm3. The large density difference between sand and water causes sand to settle quickly in water, even under conditions of relatively high water turbulence. Once settled, sand is not easily lifted by the flow of the aqueous liquid from which it has settled.
Conventionally, sand has been suspended in a viscoelastic fluid to make a relatively stable slurry under static and/or dynamic conditions. In viscoelastic fluids, yield stress, which is the minimum shear stress required to initiate flow in a viscoelastic fluid, plays a dominant role in suspending the sand particles. The viscosity of the fluid acts to slow down the rate of particle settling, while the yield stress helps to suspend the particles. Under dynamic conditions, agitation or turbulence further helps to stabilize the slurry. Therefore, to cost-effectively prepare stable sand slurries, conventional methods have focused on manipulating the rheological properties of the fluid by adding sufficient amounts of viscosifier, for example, a natural or synthetic polymer, into the slurry. It is not unusual that a polymer is used together with a foaming agent to manipulate the rheology and reduce water usage, thereby reducing formation damage.
Flotation has been used in minerals engineering for the separation of finely ground valuable minerals from other solids, such as other minerals. Crude ore is ground to fine powder and mixed with water, collecting reagents and, optionally, frothing reagents. When air is blown through the mixture, hydrophobic mineral particles cling to the bubbles, which rise to form froth on the surface. The waste material (gangue) settles to the bottom. The froth is skimmed off. Water and chemicals are then removed from the froth, leaving a clean concentrate. The process, generally called froth flotation, is used for a variety of minerals.
The primary mechanism in froth flotation is the selective aggregation of micro-bubbles with hydrophobic particles under dynamic conditions to lift the particles to the liquid surface. The minerals and their associated gangue usually do not have sufficient hydrophobicity to allow bubbles to attach thereto. Hydrophobicizing agents, often referred to in the prior art as collecting agents, or collectors, are chemical agents that are able to selectively adsorb to desired minerals surfaces and make them hydrophobic to permit the aggregation of the particles and micro-bubbles and thus promote separation.
Frothers are chemical agents added to a slurry mixture to promote the generation of semi-stable froth. In a so-called “reverse flotation process”, the undesired minerals, such as silica sand in the froth are floated away from the valuable minerals which remain in the tailings. The reverse flotation of silica is widely used in processing iron as well as phosphate ores.
A wide variety of chemical agents are useful as hydrophobicizing agents and frothers for flotation of silica particles. Amines such as simple primary and secondary amines, primary ether amine and ether diamines, tallow amines and tall oil fatty acid/amine condensates are known to be useful for hydrophobicizing silica particles. It is well established that these chemical compounds strongly adsorb to sand surface and change the sand surface from hydrophilic to hydrophobic. In fact, the reason that these compounds are used is because of the ability to hydrophobicize the sand surface to allow the formation of stable sand/bubble aggregations. Preferred conventional hydrophobicizing agents are amine collectors having at least about twelve carbon atoms. Such hydrophobicizing agents are commercially available from, for example, Akzo Nobel of Amsterdam, Netherlands or Tomah Products Inc. of Milton. Wis. USA. Other possible hydrophobicizing agents are oleate salts which typically require the presence of multivalent cations such as Ca++ or Mg++ to work effectively.
Compounds generally useful as frothers in flotation include, but may not be limited to, low molecular weight alcohols including methyl isobutyl carbinol (MIBC) and glycol ethers.
By way of example only, U.S. Pat. Nos. 7,723,274 and 8,105,986 to Applicant, incorporated herein by reference in their entirety, have recognized that enhancing the transporting capability of particulates within a slurry is possible by rendering the particulate surfaces sufficiently hydrophobic to attach gas bubbles to particulate surfaces. Thus, the particulates are buoyed within the slurry and settling is minimized therein. Consequently, particulates such as proppants can be transported into the formation effectively without requiring the addition of viscosifiers to the fluid. Thus, the so-formed aqueous slurry can be used in various oilfield services, particularly in slickwater fracturing operations.
Different hydrophobicizing agents, including silicone compounds or hydrocarbon amines, as well as methods of preparing and using the slurry, are disclosed in U.S. Pat. No. 8,236,738; US Published Application 2014-0243245; U.S. Pat. No. 7,723,274; US Published Application 2010-0197526; U.S. Pat. No. 8,105,986; US Published Application 2012-0071371; US Published Application 2015-0252254 and Published Application US 2015-0307772.
Further, frothers, which act to stabilize bubbles can be added into the slurry. The most commonly used frothers are aliphatic alcohols, including particularly, methyl isobutyl carbinol (MIBC), 2-ethyl hexanol, n-pentanol, n-butyl, n-hexanol, 2-butanol, n-heptanol, n-octanol, isoamyl alcohol, polyethylene glycol, polypropyl glycol, as well as cyclic alcohols including pine oil, terpineol, fenchyl alcohol, alkoxy paraffins such as 1, 1, 3,-triethoxybutane (TEB) and polypropyl glycol ethers, such as commercial product DOWFROTH® available from Dow Chemical Company. It is understood that mixtures of the frothers, for example mixtures of the alcohols, are often used. As well, oils, including hydrocarbon oils such as mineral oils or paraffin oils and natural oils, can be used alone or in combination with, for example, an alcohol frother, to stabilize the bubbles on the particulate surfaces and enhance particulate agglomeration to improve proppant pack conductivity and oil/gas production. In all cases, a gas, such as nitrogen or carbon dioxide, is also typically added into the slurry.
In the prior art, where hydrophobicizing agents have been added to fracturing fluids for the purposes of hydrophobically modifying the proppants to enhance transport of the proppants within the fracturing fluids, the hydrophobicizing agents have been added into water, upstream of the blender tub and prior to the addition of the proppants and any other conventional frac fluid chemicals or to the slurry downstream of the blender tub. Thereafter, the gas, such as nitrogen, is normally added to the slurry and the slurry is pumped downhole.
These prior art methods may be limited as the efficacy of the hydrophobicizing agent to treat the proppant is compromised when added to the water stream or to the slurry as the hydrophobicizing agent may not efficiently contact the proppant surfaces. Conventionally, for this reason, the slurries have been over-treated with the hydrophobicizing agent to try to address the issue resulting in overusage of the hydrophobicizing agent. In this case, the relatively large residual portion of hydrophobicizing agent, which does not contact the poppant surface, remains in the water and may build up on flow meters and the like following use in fracturing operations.
Alternatively, proppants can be pre-treated, such as at a proppant or sand mining facility. The pre-treated proppant is then delivered to sand storage. There are some issues with this approach as well, including but not limited to, obtaining supply of product on time, holding and storing inventory of the product, shipping the product over large distances and/or being required to have facilities near operating areas to obtain product. Further, in order to obtain proppants coated with specific additives, a supply of additive would also have to be shipped to the supplier for custom-treatment of the proppant.
There is interest in the various industries, and particularly in the oil and gas industry, for apparatus and methods for treating of particulates, such as proppants, that are more efficient and cost effective.
Embodiments taught herein are used for the preparation of a proppant slurry wherein the proppants are treated on-the-fly with an additive, prior to the proppants coming into contact with other components of the slurry. In the case of a fracturing fluid, the proppant, such as sand, is treated with hydrophobicizing agent to hydrophobically modify the sand to render surfaces of the sand hydrophobic while the sand is substantially dry. The modified proppant is thereafter blended with a fluid component, such as water, for forming the proppant slurry to be used, for example, in a fracturing operation. The addition of the hydrophobicizing agent directly to the dry proppant on-the-fly allows for the optimization of the interaction between the proppant and hydrophobicizing agent. The optimization results in lower hydrophobicizing agent utilization, lower cost and reduced environmental impact such as dust suppression on site.
In a broad aspect, apparatus, adapted for use with one or more inclined augers supplying proppant to a blender tub for mixing the proppant with a liquid for preparing a proppant slurry, comprises: one or more main spray nozzles mounted above a discharge end of each of the one or more inclined augers so as to distribute an additive to substantially dry proppant discharging to fall from the discharge end of the auger into the blender tub. The one or more main spray nozzles distribute the additive generally in a direction of fall of the discharging proppant.
In embodiments one or more auxiliary spray nozzles are mounted adjacent the discharge end of the auger and protrude into the discharging proppant. The one or more auxiliary spray nozzles distribute the additive within and beneath the proppant.
Further, in embodiments, one or more spray orifices are also mounted adjacent the discharge end of the auger. The one or more spray orifices distribute the additive into the proppant substantially perpendicular to the direction of fall of the proppant.
The main and auxiliary nozzles form spray patterns, the nozzles being spaced so as to overlap the spray patterns from adjacent nozzles for optimizing delivery of the additive to the proppant.
In another broad aspect, a method for forming a proppant slurry on-the-fly comprises: lifting a substantially dry proppant above a blender tub for falling therefrom into the blender tub. An additive is distributed onto the falling proppant, generally in a direction of fall of the proppant for distributing the additive onto the proppant surfaces forming a modified proppant. Thereafter liquid is introduced into the modified proppant for mixing therewith for forming the slurry.
In embodiments, the additive is distributed by spraying onto the proppant. The spraying is generally in the direction of fall of the proppant and is from above the falling proppant. The spraying can also be from within and beneath the falling proppant.
Where the slurry is used for fracturing, the additive is distributed in an amount relative to loading of the proppant and a pumping rate of the slurry into a wellbore. Further, the additives are selected to be compatible with the liquid and any additional additives added to the slurry.
In embodiments wherein the slurry is used for fracturing and the additive is a hydrophobicizing agent, the hydrophobicizing agent is distributed from about 0.1 L to about 40 L per metric tonne of proppant. In embodiments, the hydrophobicizing agent is distributed from about 2 L to about 20 L per metric tonne of proppant.
In embodiments wherein the slurry is used for fracturing, the additive is a hydrophobicizing agent and the proppant loading is from about 0.01 kg/m3 to about 2200 kg/m3, the hydrophobicizing agent is distributed to the proppant at about 0.1 L/min to about 300 L/min.
While Applicant is aware that pre-treating of proppant can be achieved off-site, such as at mining facilities, pre-treatment may present issues, including but not limited to, obtaining supply of product on time, holding and storing inventory of the product, shipping the product over large distances and/or being required to have facilities near operating areas to obtain product. Further, in order to obtain proppants treated with specific additives, a supply of additive would also have to be shipped to the supplier for custom-treatment of the proppant. Where different additives may be selected for each operation based upon a variety of factors, such as the water in which the fracturing fluid is prepared, the chemicals required in the fracturing fluid, the well conditions and the like, a service company may have to purchase and store many different pre-coated proppants.
Historically, as previously noted, preparing a proppant slurry for fracturing operations and treatment of proppants therein, on-the-fly, has been performed by adding the additive, a hydrophobicizing agent, directly to the liquid, typically water, either at the upstream, suction side of the blender or at the downstream, discharge side of the blender. The slurry was then allowed to mix in the plumbing of the surface pumping equipment. Often, the additive was over-delivered to compensate for the fact that a certain portion of the additive would remain in the water and was unable to adsorb to the surface of the proppant.
Unlike the historical approach described above, embodiments taught herein spray the additive directly onto substantially dry proppant, on-the-fly, before the proppant is added to the liquid, which typically contains any additional, conventional frac fluid additives. Thus, the interaction between the proppant and additive is optimized, resulting in lower additive utilization, lower cost, reduced environmental impact and lowered operational costs.
Embodiments taught herein are particularly suitable for on-the-fly treatment of proppant particles with hydrophobicizing agents for hydrophobically modifying surfaces of the proppant and for forming aqueous fracturing fluid slurries. Substantially dry proppant particles are contacted with the hydrophobicizing agent, prepared in water, prior to contact with any other chemicals, fluids or the like. The hydrophobicizing agent is selected for its ability to hydrophobically modify the proppant as well as its compatibility with other chemicals or fluids in the fracturing fluid and/or with specific wellbore and formation characteristics. Treatment on-the-fly thereby eliminates the need to prepare and store a variety of proppants coated with different hydrophobicizing agents and to transport a specific proppant to a specific well site.
In embodiments, the proppant is contacted with the additive when the proppant, typically sand, is substantially dry. “Substantially dry” is intended to mean having amounts of water or other liquid associated therewith that permit an economically significant reduction in the amount of additive necessary to ensure sufficient hydrophobic modification of the surfaces of the proppant to achieve stable sand/bubble aggregations for forming the proppant packs within the fractures. Further, the substantially dry proppant is flowable, so as to be stored in silos, sand hogs and the like and conveyable for delivery to hoppers and to be lifted by augers.
Embodiments taught herein provide a simple operational and cost effective apparatus and process for hydrophobically modifying proppant surfaces for making aqueous slurries for hydraulic fracturing operations. Over-treatment to ensure adequate surface modification is thereby minimized or eliminated, reducing the amount of additive required.
Embodiments taught herein are described in the context wherein the proppant is sand P, the liquid is water W and the additive A is a hydrophobicizing agent. This is in no way intended to limit embodiments taught herein to use this specific context. As one of skill will appreciate, embodiments taught herein are applicable to a variety of proppants whose surfaces can be treated or modified prior to use as well as to a variety of additives which may be used to treat proppant and to a variety of liquid in which a proppant slurry can be prepared.
Having reference to
Having reference to
In an embodiment, as shown in
In another embodiment, as shown in
In yet another embodiment, as shown in
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In embodiments, wherein two or more main nozzles 30 are used, the two or more main nozzles 30 are spaced such that the spray from one main nozzle 30 typically overlaps the spray from the adjacent main nozzles 30 for optimizing distribution of the hydrophobicizing agent A to the sand P. As will be appreciated, spacing between the nozzles 30 can be adjusted for overlapping of the spray therefrom dependent upon at least the size and/or the shape of the spray pattern to extend across substantially all of the transverse extent of the sand P as it exits the auger 12.
Having reference to
In embodiments, the spray pattern is the flat fan pattern for even distribution (
Having reference to
The auxiliary nozzles 40 have a first portion 44 which extends outwardly from the spray bar 42 and have a second portion 46 which extends therefrom. The spray can be directed at an angle θ2 from about 0° to about 180° relative to the spray bar 42 to distribute the hydrophobicizing agent A onto the sand P and generally in the direction of fall of the sand P. The auxiliary nozzles 40 generally protrude upwardly into the sand P as the sand P begins to fall from the discharge end 16 of the auger 12 into the blender tub 18. In embodiments the hydrophobicizing agent A is sprayed generally parallel to the direction of the fall of the sand P. In embodiments the spray from the auxiliary nozzles 40 is directed at about a 90° angle relative to the hydrophobicizing agent A being sprayed from the one or more main nozzles 30.
Having reference to
In embodiments, as shown in
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In embodiments, having reference to
In cases, where some of the one or more main or auxiliary spray nozzles 30, 40 or spray orifices 42 are not required, certain of the nozzles 30,40 or orifices 48 can be taken out of service by plugging. Additional nozzles 30,40 or orifices 48 can also be added, depending upon the system requirements.
In embodiments, the hydrophobicizing agent A is added at a rate in the range from about 0.1 L/metric tonne of sand P to about 40 L/metric tonne of sand P. In embodiments of on-the-fly applications, the rate generally varies from about 2 L/metric tonne of sand P to about 20 L/metric tonne of sand P. Applicant believes that embodiments taught herein result in a significant reduction in the amount of hydrophobicizing agent A used compared to prior art processes wherein the hydrophobicizing agent A was added to the water W upstream of the blender tub 18 or was added to the slurry S downstream of the blender tub 18. Reductions by as much as about ⅓ of the amounts used in the prior art have been observed, as shown in testing data provided below.
Further, in embodiments, the system is typically operable from about 0.1 psi to about 2000 psi to create the spray from the main and auxiliary nozzles 30,40 suitable to coat the falling sand P with the hydrophobicizing agent A. The system however has been designed such that operating pressures are not limiting. Exemplary pressures are generally from about 10 psi to about 200 psi.
In embodiments, application rates of hydrophobicizing agent A for on-the-fly operations are typically from about 0.1 L/min to about 300 L/min using sand slurry concentrations from about 0.01 kg/m3 to about 2200 kg/m3.
Performance of Hydrophobicization
Slick water systems comprising 250 kg/m3 to 1000 kg/m3 of sand for each of 40/70, 30/50 and 20/40 mesh sand were prepared according to conventional methodology and according to embodiments taught herein. Each of the systems also contained 2 L/m3 of a clay control additive and 1 L/m3 of a friction reducer.
The systems prepared using conventional on-the-fly methodologies were prepared as follows:
The systems prepared according to embodiments taught herein were prepared as follows:
The results demonstrate that the slurry, prepared according to embodiments taught herein, using the pretreated sand performs better than the slurry prepared using the conventional on-the-fly method, particularly for the coarser, less easily suspended sand (20/40 and 30/50 sand). The concentration of the sand appears to have a significant effect on sand floating, wherein when sand concentration is low the sands tend to float on top of the water, whereas with increasing sand concentration, the sand mass tends to suspend within the water rather than floating on top. Although sand in both the pre-treated and conventional on-the-fly slurries agglomerate having significantly larger volume than untreated sand, the embodiments taught herein generally result in a larger agglomeration volume than the conventional methodology.
Further, Applicant believes that the addition of the other chemical additives can be to ether the suction side or the discharge side of the blender tub without significantly altering the performance of slurries prepared using embodiments taught herein.
Salt Tolerance/Compatibility
Floating as a result of hydrophobicization of the sand was evaluated for slurries prepared in salt water according to embodiments taught herein and in conventional on-the-fly slurries. Different salt concentrations were prepared for KCl, CaCl2, and MgCl2. The sand concentration was fixed at 250 kg/m3 for different mesh size sand. The results are shown in Table B below:
According to the bench testing, slurries prepared using sand treated according to embodiments taught herein can be prepared in water having KCl up to about 10% whereas conventional on-the-fly slurries became less efficient when KCL concentration reached about 7%. Both slurries tolerated high concentrations of Ca2+ and Mg2+ however those prepared using embodiments taught herein appear to perform better. Overall therefore, it appears that sand, treated using embodiments taught herein, is more efficient in brackish and salt water than sand treated using conventional on-the-fly methods.
In another bench test, a silicone-based hydrophobicization agent was tested for flotation performance and/or volume increase, salt tolerance and the effect of pH, when slurries were prepared according to embodiments taught herein. The concentration of 20/40 sand was kept constant at 300 kg/m3 and the hydrophobicizing agent was tested at 0.5% and 0.7% v/w based on the sand.
The slurries were prepared as follows:
Applicant observed that in both the 0.5% and 0.7% v/w slurries formed the desired suspensions.
Salt Tolerance/Compatibility
Further, the 0.5% and 0.7% v/w of sand slurries as described above were also prepared in water containing different concentrations of salts as shown in Table C below:
While salinity affects sand flotation, with respect to different salts such as KCl, CaCl2 and MgCl2, the 0.5% v/w slurry generally demonstrated excellent performance.
Applicant is aware that poor quality water, such as from the Marcellus Shale formation demonstrates reduced efficiency of the sand suspension when used to prepare slurries on-the-fly according to conventional methods.
Slurries were prepared using Marcellus water, known for its very poor quality, according to embodiments taught herein as shown in Table D below:
As shown, slurries prepared according to embodiments taught herein have improved tolerance for poor quality water than has previously been found for slurries prepared on-the-fly using conventional methodologies.
Slurries were prepared using 150 g of 20/40 sand, provided by Sil Industrial Minerals of Edmonton, Alberta, Canada and using silicon-based hydrophobicizing agents A and B at different concentrations, diluted in isopropyl alcohol (IPA), as shown in Table E below.
Different amounts of the hydrophobicizing agents were mixed with 18 mL of well water provided by Sil Industrial Minerals, were added to sand and mixed and were thereafter dried at 60°, instead of spraying on-the-fly, to test embodiments taught herein.
Hydrophobicizing agent A, at 20% in IPA performs slightly better than hydrophobicizing agent B. Lower concentrations of hydrophobicizing agent B however provided acceptable results.
Further testing for reduction in chemical usage was performed, using the same set-up as described above, for 20/40, 30/50 and 40/70 sand and hydrophobicizing agent B. Slurries were prepared in clean water however for each grade of sand at least one slurry was prepared in poor quality Marcellus water to determine the effect thereof.
The results are shown in Table F below:
As can be seen, the consumption of hydrophobicizing agent can be optimized to improve the economics without compromising performance.
Having reference to Table G below, 18 stages in a wellbore were fractured from a bottom or toe of the well, at a total measured depth (TMD) of about 3400 m (TMD), at intervals toward surface, to about 2100 m (TMD).
The first three stages were fractured using a proppant slurry prepared according to the prior art, wherein the hydrophobicizing agent was added to the water used to prepare the slurry, at the suction side of the blender tub or to the slurry at the discharge side of the blender tub.
The remaining 15 stages were fractured using a proppant slurry prepared according to embodiments taught herein. The hydrophobicizing agent was sprayed onto the dry proppant prior to addition of the water, which included at least some other chemical additives conventional for fracturing fluids. In all cases nitrogen, in appropriate amounts, was added to the slurry prior to pumping downhole.
As can be seen, there is a significant reduction in the volume of hydrophobicizing additive required per tonne of sand for stages 4-18, using embodiments taught herein, compared to stages 1-3 wherein the slurry was prepared on-the-fly using conventional methods.
Proppant was spray-treated on-the-fly using a hydrophobicizing agent according to embodiments taught herein. The data for preparation of the slurry for each stage of another 18 stage fracturing operation is provided in Table H below. No direct comparisons were made in the wellbore by fracturing stages using conventionally prepared and treated proppant, however Applicant has calculated the amount of hydrophobicizing agent which would have been added to each stage to be about 1500 L, had the slurry been prepared in the conventional manner.
When compared to the amount of hydrophobicizing additive which would have been added to the conventionally prepared slurry, embodiments taught herein demonstrate the ability to significantly reduce additive requirements.
While embodiments of apparatus and processes taught herein are suitable for on-the-fly spray treatment of proppant P with any additive A which can be sprayed thereon, and which is safe to do so, embodiments are described herein in the context of hydrophobicizing additives A which are used to hydrophobically modify surfaces of proppant P. The hydrophobicization of the proppant P causes the formation of stable sand/bubble aggregations for fracturing operations resulting in desirable proppant packs within fractures produced in the formation.
In embodiments, exemplary hydrophobicizing additives are those marketed by Applicant under SANDSTILL™ and FLOWRIDER® or MVP FRAC™. Embodiments of such exemplary hydrophobicizing additives are taught in Applicant's following US patents and published applications, all of which are incorporated herein by reference in their entirety; U.S. Pat. No. 8,236,738; US Published Application 2014-0243245; U.S. Pat. No. 7,723,274; US Published Application 2010-0197526; U.S. Pat. No. 8,105,986; US Published Application 2012-0071371; US Published Application 2015-0252254 and Published Application US 2015-0307772.
The exemplary hydrophobicizing additives A comprise active hydrophobicizing agents and are typically prepared in a liquid medium, such as alcohol, esters or oil, including but not limited to C5 to C30 straight chain hydrocarbons, for spraying on the proppant. In embodiments, the oil or alcohols may further act to enhance proppant agglomeration and attachment of bubbles to the proppant P.
In embodiments, the liquid hydrocarbon is mineral oil. The mineral oil is added to the hydrophobicizing agent to enhance sand agglomeration, to reduce sand dust and to increase a crush strength of the proppants. In another embodiment, a frother, such as methyl isobutyl carbinol (MIBC), can be used in place of the mineral oil or in combination with mineral oil.
Advantageously, as seen from standard UEL and LEL testing, mineral oil has relatively low flammability and therefore when used in embodiments taught herein, has a reduced risk of igniting at the intake of pumps and the like. Further, mineral oil has low volatility and when sprayed onto proppant presents a low risk for adverse health effects.
Amounts of hydrophobicizing agent required for treatment of proppant is generally dependent upon sand loading and the pumping rate of the slurry.
In use, sand is delivered to the intake end of the one or more augers, such as to the hopper, and is lifted by the one or more augers from the hopper to the discharge end of the auger. Hydrophobicizing additive is metered and delivered to the main spray nozzles 30, and to the auxiliary nozzles 40 and orifices 42, if used. Sufficient hydrophobicizing additive A is supplied for the rate of sand delivery by the one or more augers 12 and the additive A selected for treatment of the sand P surfaces to result in the desired slurry characteristics and the overall rate of slurry delivery required for the fracturing operation. The spray nozzles 30,40 and orifices 42 distribute the hydrophobicizing additive A to the substantially dry sand P as it is discharged from the discharge end 16 of the one or more augers 12 and falls into the blender tub 18. At the same time, the liquid component of the slurry, typically water W, is pumped through the piping 24 on the blender truck 10 into the blender tub 18 for mixing with the sand P. Any additional frac fluid additives, such as polymers, clay control additives, surfactants, scale control additives, corrosion inhibitors, biocides, pH control, breakers and the like, are either added to the water W upstream of the blender tub 18 or are added to the slurry S downstream of the blender tub 18. Thereafter, the slurry S is delivered to surface pumping equipment (not shown) for pumping downhole during the fracturing operation.
By way of example only, exemplary hydrophobizing agents include amine hydrophobizing agents, as well as silicon or fluorinated hydrophobizing agents, described as follows.
The term “amine hydrophobizing agent” is used herein to mean long carbon chain hydrocarbon amines containing no silicon or fluoro-based groups in the molecules. Such compounds contain at least fourteen and preferably at least sixteen carbon atoms, which render the surface of the particulates hydrophobic. The amine hydrophobizing agents, include simple primary, secondary, tertiary amines, primary ether amines, di-amines, polyamines, ether diamines, stearyl amines, tallow amines, condensates of amine or alkanolamine with fatty acid or fatty acid ester, condensates of hydroxyethylendiamines.
Examples include the condensate of diethylenetetraamine and tallow oil fatty acid, tetradecyloxypropyl amine, octadecyloxypropyl amine, hexadecyloxypropyl amine, hexadecyl-1,3-propanediamine, tallow-1,3-propanediamine, hexadecyl amine, tallow amine, soyaalkylamine, erucyl amine, hydrogenated erucyl amine, ethoxylated erucyl amine, rapeseed amine, hydrogenated rapeseed amine, ethoxylated rapeseed amine, ethoxylated oleylamine, hydrogenated oleylamine, ethoxylated hexadecyl amine, octadecylamine, ethoxylated octadecylamine, ditallowamine, hydrogenated soyaalkylamine, amine, hydrogenated tallow amine, di-octadecylamine, ethoxylated (2) tallowalkylamine, for example Ethomeen T/12 or ethoxylated (2) soyaalkylamine, for example, Ethomeen S/12, or oleyl amine, for example Armenn OL, or di-cocoalkalamine, for example Armeen 2C from Akzo Nobel Inc., and the condensate of an excess of fatty acids with diethanolamine.
The term “silicon or fluorinated hydrophobizing agents” is used herein to mean the hydrophobizing agents disclosed, for example, in U.S. Pat. No. 7,723,274, which include different organosilanes, organosiloxanes, polysiloxanes modified with different functional groups, including cationic, amphoteric as well as anionic groups, fluorinated silanes, fluorinated siloxanes and fluorinated hydrocarbon compounds. In general, organosilanes are compounds containing silicon to carbon bonds. Organosiloxanes are compounds containing Si—O—Si bonds. Polysiloxanes are compounds in which the elements silicon and oxygen alternate in the molecular skeleton, i.e., Si—O—Si bonds are repeated. The simplest polysiloxanes are polydimethylsiloxanes. Polysiloxane compounds can be modified by various organic substitutes having different numbers of carbons, which may contain N, S, or P moieties that impart desired characteristics. For example, cationic polysiloxanes are compounds in which one or more organic cationic groups are attached to the polysiloxane chain, either at the middle or the end or both at the same time. The most common organic cationic groups are organic amine derivatives including primary, secondary, tertiary and quaternary amines (for example, quaternary polysiloxanes including, quaternary polysiloxanes including mono- as well as di-quaternary polysiloxanes, amido quaternary polysiloxanes, imidazoline quaternary polysiloxanes and carboxy quaternary polysiloxanes). Similarly, the polysiloxane can be modified by organic amphoteric groups, where one or more organic amphoteric groups are attached to the polysiloxane chain, either at the middle or the end or both, and include betaine polysiloxanes and phosphobetaine polysiloxanes. Among different organosiloxane compounds which are useful for the present invention, polysiloxanes modified with organic amphoteric or cationic groups including organic betaine polysiloxanes and organic quaternary polysiloxanes are examples. One type of betaine polysiloxane or quaternary polysiloxane is represented by the formula
wherein each of the groups R1 to R6, and R8 to R10 represents an alkyl containing 1-6 carbon atoms, typically a methyl group, R7 represents an organic betaine group for betaine polysiloxane, or an organic quaternary group for quaternary polysiloxane, and have different numbers of carbon atoms, and may contain a hydroxyl group or other functional groups containing N, P or S, and m and n are from 1 to 200. For example, one type of quaternary polysiloxanes is when R7 is represented by the group
wherein R1, R2, R3 are alkyl groups with 1 to 22 carbon atoms or alkenyl groups with 2 to 22 carbon atoms. R4, R5, R7 are alkyl groups with 1 to 22 carbon atoms or alkenyl groups with 2 to 22 carbon atoms; R6 is —O— or the NR8 group, R8 being an alkyl or hydroxyalkyl group with 1 to 4 carbon atoms or a hydrogen group; Z is a bivalent hydrocarbon group, which may have a hydroxyl group and may be interrupted by an oxygen atom, an amino group or an amide group; x is 2 to 4; The R1, R2, R3, R4, R5, R7 may be the same or different, and X− is an inorganic or organic anion including Cl− and CH3COO−.
Examples of organic quaternary groups include [R—N+(CH3)2—CH2CH(OH)CH2—O—(CH2)3—](CH3COO−), wherein R is an alkyl group containing from 1-22 carbons or an benzyl radical and CH3COO− an anion. Examples of organic betaine include —(CH2)3—O—CH2CH(OH)(CH2)—N+(CH3)2CH2COO−. Such compounds are commercial available. It should be understood that cationic polysiloxanes include compounds represented by formula (II), wherein R7 represents other organic amine derivatives including organic primary, secondary and tertiary amines. Other example of organo-modified polysiloxanes include di-betaine polysiloxanes and di-quaternary polysiloxanes, which can be represented by the formula
wherein the groups R12 to R17 each represents an alkyl containing 1-6 carbon atoms, typically a methyl group, both R11 and R18 group represent an organic betaine group for di-betaine polysiloxanes or an organic quaternary group for di-quaternary, and have different numbers of carbon atoms and may contain a hydroxyl group or other functional groups containing N, P or S, and m is from 1 to 200. For example, one type of di-quaternary polysiloxanes is when R11 and R18 are represented by the group
wherein R1, R2, R3, R4, R5, R6, R7, Z, X− and x are the same as defined above. Such compounds are commercially available. Quaternium 80 (INCI) is one of the commercial examples.
Similarly, the polysiloxane can be modified by organic anionic groups, where one or more organic anionic groups are attached to the polysiloxane chain, either at the middle or the end or both, including sulfate polysiloxanes, phosphate polysiloxanes, carboxylate polysiloxanes, sulfonate polysiloxanes, thiosulfate polysiloxanes.
The organosiloxane compounds also include alkylsiloxanes including hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, hexaethyldisiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane. The organosilane compounds include alkylchlorosilane, for example methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, octadecyltrichlorosilane; alkyl-alkoxysilane compounds, for example methyl-, propyl-, isobutyl- and octyltrialkoxysilanes, and fluoro-organosilane compounds, for example, 2-(n-perfluoro-octyl)-ethyltriethoxysilane, and perfluoro-octyldimethyl chlorosilane. Other types of chemical compounds, which are not organosilicone compounds and which can be used to render proppant surfaces hydrophobic are certain fluoro-substituted compounds, for example certain fluoro-organic compounds including cationic fluoro-organic compounds.
Further information regarding organosilicon compounds can be found in U.S. Pat. No. 7,723,274, in Silicone Surfactants (Randal M. Hill, 1999) and the references therein, and in U.S. Pat. Nos. 4,046,795; 4,537,595; 4,564,456; 4,689,085; 4,960,845; 5,098,979; 5,149,765; 5,209,775; 5,240,760; 5,256,805; 5,359,104; 6,132,638 and 6,830,811 and Canadian Patent No. 2,213,168. Organosilanes can be represented by the formula
RnSiX(4-n) (I)
wherein R is an organic radical having 1-50 carbon atoms that may possess functionality containing N, S, or P moieties that imparts desired characteristics, X is a halogen, alkoxy, acyloxy or amine and n has a value of 1-3. Examples of suitable organosilanes include:
Si(OCH3)4, CH3Si(OCH3)3, CH3Si(OCH2CH3)3, CH3Si(OCH2CH2CH3)3, CH3Si[O(CH2)3CH3]3, CH3CH2Si(OCH2CH3)3, C6H5Si(OCH3)3, C6H5CH2Si(OCH3)3, C6H5Si(OCH2CH3)3, CH2═CHCH2Si(OCH3)3, (CH3)2Si(OCH3)2, (CH2═CH)Si(CH3)2Cl, (CH3)2Si(OCH2CH3)2, (CH3)2Si(OCH2CH2CH3)2, (CH3)2Si[O(CH2)3CH3]2, (CH3CH2)2Si(OCH2CH3)2, (C6H5)2Si(OCH3)2, (C6H5CH2)2Si(OCH3)2, (C6H5)2Si(OCH2CH3)2, (CH2═CH)Si(OCH3)2, (CH2═CHCH2)2Si(OCH3)2, (CH3)3SiOCH3, CH3HSi(OCH3)2, (CH3)2HSi(OCH3), CH3Si(OCH2CH2CH3)3, CH2═CHCH2Si(OCH2CH2OCH3)3, (C6H5)2Si(OCH2CH2OCH3)2, (CH3)2Si(OCH2CH2OCH3)2, (CH2═CH2)2Si(OCH2CH2OCH3)2, (CH2═CHCH2)2Si(OCH2CH2OCH3)2, (C6H5)2Si(OCH2CH2OCH3)2, CH3Si(CH3COO)3, 3-aminotriethoxysilane, methyldiethylchlorosilane, butyltrichlorosilane, diphenyldichlorosilane, vinyltrichlorosilane, methyltrimethoxysilane, vinyltriethoxysilane, vinyltris(methoxyethoxy)silane, methacryloxypropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, aminopropyltriethoxysilane, divinyldi-2-methoxysilane, ethyltributoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, n-octyltriethoxysilane, dihexyldimethoxysilane, octadecyltrichlorosilane, octadecyltrimethoxysilane, octadecyldimethylchlorosilane, octadecyldimethylmethoxysilane and quaternary ammonium silanes including 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride, 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium bromide, 3-(trimethylethoxysilylpropyl)didecylmethyl ammonium chloride, triethoxysilyl soyapropyl dimonium chloride, 3-(trimethylethoxysilylpropyl)didecylmethyl ammonium bromide, 3-(trimethylethoxysilylpropyl)didecylmethyl ammonium bromide, triethoxysilyl soyapropyl dimonium bromide, (CH3O)3Si(CH2)3P+(C6H5)3Cl, (CH3O)3Si(CH2)3P+(C6H5)3Br−, (CH3O)3Si(CH2)3P+(CH3)3Cl−, (CH3O)3Si(CH2)3P+(C6H13)3Cl−, (CH3O)3Si(CH2)3N+(CH3)2C4H9Cl, (CH3O)3Si(CH2)3N+(CH3)2CH2C6H5Cl−, (CH3O)3Si(CH2)3N+(CH3)2CH2CH2OHCl−, (CH3O)3Si(CH2)3N+(C2H5)3Cl−, (C2H5O)3Si(CH2)3N+(CH3)2C18H37Cl−.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2877025 | Jan 2015 | CA | national |
