Patent Application
20150307773
1) Field of the Invention
The present invention relates to proppant for use with fracking fluid having improved sedimentary properties and voids.
2) Background of the Invention
Natural gas production from shale gas reservoirs has shown a rapidly growing trend over the past decade and has become a significant source of U.S. domestic gas supply. In recent times, the combination of fracking with horizontal drilling technology as greatly improved the ability to extract natural gas form subterranean layers such as shale.
Fracking, sometimes called hydraulic fracturing, is a process that is used to extract natural gas from shale, particularly from relatively deep wells. With the improvements in horizontal drilling, used in conjunction with vertical drilling, highly pressurized fracking fluids can be injected into the shale layer of subterranean areas. This pressure can open or create fissures in the shale providing for a channel to allow for natural gas to flow into the wellbore as greater rates. When the pressure of the fracking fluid exceeds the fracture gradient of the rock or shale, the fracture is opened and/or extended.
When the pressure is removed from the fracture the fracture, due to the ambient pressures, tends to close of reseal. This reduces the amount or rate in which gas can escape into the wellbore. The productivity of a hydraulically fractured well depends on having a fracture which is effectively propped open over its length and height. Proppant is added to the fracking fluid so that the proppant can prop open these fissures. To achieve desired results, good or adequate proppant transport is a central issue in slickwater fracture treatments because of the low viscosity of the fracturing fluid. Proppant transport within a fracture is influenced by a number of factors including: fracture width, injection rate, fluid leak-off, fluid rheology, density difference between the fluid, friction, drag, and the physical properties of the proppant itself. It is also advantageous that the proppant have a sufficiently high crush strength so that the ambient forces of a fissure do not cause the proppant to crush thereby reducing the effectiveness of the proppant.
On attempt to reduce or eliminate the fracture closing is shown in U.S. Pat. No. 8,298,667 which is directed to a composition and method for making a proppant and utilizes a sphere. A significant disadvantage of using the sphere shape for a proppant is sedimentation. As the proppant travel through the fluid, the sphere tends to “settle” limited the distance that the proppant travels into the well and fissure. This sedimentation of proppant has historically been a limited factor in performance.
Further, the state of the art currently is to use sand, resin coated sand, lightweight ceramic, intermediate density ceramic or highly dense ceramic in an attempt to make a more desirable proppant and ultimately improve the production of a well. In several tests, ceramic offers superior performance to that of sand. Further, irregular shaped proppant seem to provide improved performance, however, these shapes are a product of irregularities in the proppant themselves and not a designed structured controlled proppant shape. Further, sand has the additional disadvantage of a lower crush strength making it less desirable as a proppant. Additionally, when proppant does crush, it breaks into smaller particles which can result in clogging the fracture, reducing the void in the proppant and reducing well production.
Recently, there has also been an attempt to improve proppant by using material that have a specific gravity from 1.7 to buoyant to reduce sedimentation and increase distribution of proppant throughout the well and its fissures. In PCT Patent Application PCT/2012/061329 at attempt at an improved proppant is disclosed as a ceramic ultra-lightweight porous proppant that can be used in fracking. This application states that silicon carbide and silicon nitride can advantageously provide a high degree of strength while having sufficient porosity to remain lightweight and facilitate fluid transport. Again, however, this reference discloses a spherical shape for the proppant.
U.S. Pat. No. 7,836,952 is directed to a proppant for use in a subterranean formation and is concerned with bridging of proppant and preventing proppant flow back. Flow back is when the proppant “flows back” into the wellbore during production, contaminates and clogs the wellbore and reduces oil production. Proppant that flows back also has to be separated from the oil before the oil is commercially useful. This reference is directed to the wellbore injection and designed to bridge the opening at the wellbore. Further, the designs of this reference include many edges which focus ambient forces and disadvantageously reduces the crush and compression resistance of the disclosed shapes.
In designing an optimal proppant, the time that the proppant remains suspended in the fluid is important so that the proppant does not settle out of the fluid preventing an advantageous amount of proppant from entering the fissure to a sufficient depth. The longer the proppant remains in the fluid and does not settle out, the deeper into the fissure the proppant can travel to prop open the fissure for gas and oil extraction. Therefore, the less sedimentation that occurs the more production the fissure can be for oil and gas production.
It is known that not all falling objects travel in a straight line in a fluid. Objects falling in a fluid can flutter, tumble or both based upon many factors. An object that has a shape to promote fluttering and/or tumbling will be suspended in a fluid longer thereby reducing sedimentation rates.
Accordingly, it is an object of the present invention to provide for a proppant with improved sedimentation rates and suspension in fluid.
It is another object of the present invention to provide for a proppant with a shape that promotes fluttering, tumbling or both.
The above objection are addressed by providing a proppant for use with fracking fluid comprising a plurality of three dimensional structures wherein each structure has a longitudinal axis, center of mass and center of pressure wherein the center of pressure and the center of mass do not align in a stable manner when settling in a fluid due to drag caused by frictional forces on the structure regardless of the orientation of the structure. The proppant can include at least one three dimensional structure is a cylinder having a bore. Each structure can have a width in the range of 100 μm to 3000 μm, wall thickness in the range of 100 μm to 400 μm, inner diameter in the range of 100 μm to 200 μm and length in the range of 100 μm to 3000 μm.
A plurality of structures can be included in a mixture of structures having a width in the range of 100 μm to 3000 μm, wall thickness in the range of 100 μm to 400 μm, inner diameter in the range of 100 μm to 200 μm and length in the range of 100 μm to 3000 μm. A first end of the structure can have a first plane having an angle of incident θ1 offset from perpendicular to the longitudinal axis; and, a second end of the structure can have a second plane having an angle of incident θ2 offset from perpendicular to the longitudinal axis.
The θ1 can be substantially equal to θ2 and the difference can be equal to or less than 30°. The difference between θ1 and θ2 for two structures can vary in a range of 25° to 65°. At least one structure can have a cross section selected from the group consisting of: an asymmetrical circle, a semi-circle, an asymmetrical semi-circle, a cross, a shape having an elongated center bar, I-beam and T. The drag coefficient can be greater than 2.3. The void defined by a plurality of structures can be greater than 30%. The structures can be manufactured by extrusion and selected from the group consisting of bauxite, bauxite compounds, alumina and mulite. The sedimentation rate in water can be at least 15% slower than the sedimentation rate of a cube made from the same material as the structures and with the same width of the structures. The sedimentation rate in water can be at least 45% slower than the sedimentation rate of a cube made from the same material as the structures and with the same width of the structures.
The following drawings and used to better explain and understand the invention and are part herein of the specification:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
When the structure is in fracking fluid, it is desirable for the structure to engage in two motions to keep the structure suspended for as long as possible in the fluid to reduce sedimentation. The first motion that is desired is a side-to-side oscillation (flutter) and the second motion is an end-over-end rotation (tumble). When these two motions occur while the structure is traveling in a fluid stream, it is referred to as a flutter-tumble motion.
Referring to
Additionally, when the shape is rotated, the center of mass can be moved out of equilibrium in relation to the center of pressure there is a desire of the shape to return to equilibrium which can assist in rotating the shape as shown in direction 28. The competing forces on the structure as it moves through the fracking fluid causes the structure to flutter thereby reducing sedimentation. In one embodiment, the outer wall and inner wall of the structure include microstructures.
In one embodiment, a three dimensional structure shown as a slanted cylinder proppant 10 having a longitudinal axis 12, an outer diameter 14, wall thickness 16, length 18, first side 20 and second side 22. The first and second sides can have a planar cross section. The first sidewall includes an angle θ1 and the second sidewall includes an angle θ1. In one embodiment, a first end of the structure has a first plane that has an angle of incident of θ1 in offset from perpendicular to the longitudinal axis. The second end of the stricture, opposite the first end in one embodiment, has a second plane that has an angle of incident of θ1 offer from perpendicular to the longitudinal axis. In one embodiments, θ1 is substantially equal to θ2 providing for a symmetry between the first sidewall and second sidewall. The angle θ1 and θ2 can be in the range of 25° and 65° and in one embodiment, equal to or less than 30°.
In one embodiment, the cylinder does not include a bore. This structure can include physical dimensions of width in the range of 100 μm to 3000 μm, wall thickness in the range of 100 μm to 400 μm, inner diameter in the range of 100 μm to 200 μm and length in the range of 100 μm to 3000 μm.
In one embodiment, the drag coefficient of the structures can be greater than 2.3. When the three dimensional shapes are deposited in the fissure, the shapes can stack upon each other. When this occurs the configuration of the shapes and the geometry of the shapes defines a void where in fluid in gas or liquid form can pass. In one embodiment, the void defined by a set of the three dimensional shapes disposed in a fissure is greater than 30%.
In manufacturing of the shapes, the extrusion process can be used resulting in solid shapes or shapes with a bore. Once extruded, the shapes can be further processed by laser cutting, scoring, or by passing through rollers or plates to further define the shapes. Material that can be used for the shapes includes bauxite, bauxite compounds, alumina and mulite.
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Using finite element analysis (FEA), the shapes of
The structures can be manufactured by extrusion and can be made from bauxite, bauxite compounds, alumina and mulite.
The following table provides the dimensions of each of the structure in one embodiment:
A sedimentation test was performed on all structures, using equal density material while keeping the overall particle dimensions about the same. The specific structure is soaked in water, dropped three feet into standing water without leaving the liquid medium with the time to fall the three foot distance measured in seconds. The results are shown in the following table:
Following are the test results from structures made from alumina when compared to the tradition proppant sand. The proppant particle sedimentation drag test results show a significant increase in fall time of alumina particles of the above structures of this invention when compared to that of the proppant sand, which had similar size and weight. The structures of fully dense alumina proppant particles were made to tumble and flutter during sedimentation in water. This movement reduces sedimentation rates greater than 40% compared to proppant sand particles of similar overall size and weight with ranges of the best three designs between 57% to 81%.
In one test, the structures, made from ceramic filled plastic having about a 1.65 g/cm3 material density were tested by soaking the particle in water for at least ten minutes, dropping the particle into a three inch diameter plastic tube filled with water with the time for the particle to fall to the bottom timed providing the following results:
The Slanted C structure performed better than that of sand. Despite being 5 times heavier than sand, this structure, this design performed well with average fall times 13% to 23% faster than that of sand. The slanted hollow cylinder performed better than a cylinder without the slanted sidewalls. This demonstrates the effectiveness of adding slanted features to cause the particles to tumble. In one embodiment, the dimensions of the “C” structure are shown
Referring to
In one embodiment, a conventional mixture of fracking fluid and a conventional proppant can be created at 86. The conventional mixture can be pumped into the fissure under pressure at 88. In one embodiment, the conventional fracking fluid and proppant can be pumped into the fissure until at least 70% of the total volume of the fissure is filled prior to pumping in the fracking mixture with three dimensional structures. In one embodiment, pumping the conventional fracking mixture into the fissure can occur prior to pumping in the conventional mixture. In one embodiment, the ratio of three dimensional structures to conventional proppants in taken from the group consisting of: 0.5:10, 1:9, 2:8, 3:7, 4:6, and 5:5 parts per million.
When used as a proppant, the particles described herein may be pumped in a combination of stages with conventional proppants to achieve an optimum economical approach. For example, reducing the settling velocity may be possible while achieving, for example, taller propped fractures by first pumping 90% of the total volume of conventional proppant to fill the bottom of the fracture and followed with 10% volume of particles described herein at the end to bridge to the fracture and fill the top of the fracture. Various other ratios and methods may be employed depending on various factors such as well landing depths, location of the perforations, fracture thickness and type of fluid used. For example, one application may use 80% conventional proppant and 20% particles described herein or vice versa. Other combinations may have a 70%-30% split, a 60%-40% split, or a 50%-50% split. In some geologies it may be favorable to first pump particles described herein to achieve better propped heights if there are natural fractures thus reversing the order of the pumping. In other circumstances this pairings of particles described herein and conventional proppants may be pumped in more than a single series, such as 3, 7 or 10 series depending on the design and in concentrations ranging 0.5 ppg to 10 ppg, 1 to 9 ppg, 2 to 8 ppg or 3 to 7 ppg. Depending on the application, particles described herein may be separated by size, weight, or otherwise. Larger size distributions may be pumped in the beginning of a job at low concentrations.
It is understood that the above descriptions and illustrations are intended to be illustrative and not restrictive. Other embodiments as well as many applications besides the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The omission in the following claims of any aspect of subject matter that is disclosed herein is not a disclaimer of such subject matter, nor should it be regarded that the inventor did not consider such subject matter to be part of the disclosed inventive subject matter.
| Number | Date | Country | |
|---|---|---|---|
| 61983311 | Apr 2014 | US |
