PROPPANT AND METHOD OF MANUFACTURING A PROPPANT

Abstract

The present invention concerns a method for manufacturing a proppant for a particular stimulation fluid, or for manufacturing a stimulation fluid for a particular proppant. The present invention also concerns a proppant for hydrocarbon stimulation, wherein the proppant comprises a plurality of amorphous spherical glass particles which have not undergone any further chemical or thermal treatment, a method of preparing the proppant, and uses of the proppant in hydrocarbon stimulation.

Claims

1. A proppant for fracture stimulation, wherein the proppant comprises a plurality of amorphous spherical glass particles which have not undergone any further chemical or thermal treatment.

2. The proppant of claim 1, wherein the density and average diameter of the glass particles are chosen such that the proppant can be transported in a stimulation fluid at velocities in the range of 0.04 m s.sup.−1-0.25 m s.sup.−1.

3. The proppant of claim 1, wherein the density and average diameter of the glass particles are chosen such that the proppant can be transported in a stimulation fluid at velocities in the range of 0.01 m s.sup.−1-0.16 m s.sup.−1.

4. The proppant of claim 1, wherein the proppant has a particle diameter in the range 40 μm-500 μm.

5. The proppant of claim 1, wherein the proppant has a density in the range 0.9-2.5 g cm.sup.−3.

6. The proppant of claim 1, wherein the glass is selected from a soda-lime silicate glass, a borosilicate glass or a phosphate glass.

7. The proppant of claim 6, wherein the glass is a soda-lime silicate glass.

8. The proppant of claim 1, wherein the particle size distribution of the glass particles is in the range of 50 μm-125 μm.

9. The proppant of claim 1, wherein the glass particles have a crush strength of 0.01 MPa-55 MPa at 2000 psi-8000 psi.

10. The proppant of claim 1, wherein the glass particles have a sphericity of ≥0.70, preferably ≥0.85.

11. The proppant of claim 1, wherein the glass particles have a roundness of ≥0.70, preferably ≥0.85.

12. The proppant of claim 1, wherein the crystallinity of the glass particles is less than about 5 vol %, preferably less than about 3 vol %, more preferably less than about 1 vol %.

13. The proppant of claim 1, wherein the conductivity of the proppant, in use, is in the range 5 mDa-100 mDa.

14. The proppant of claim 1, wherein the glass particles contain bubbles, pores or voids.

15. The proppant of claim 1, wherein the glass particles are solid glass particles.

16. The proppant according to claim 1, wherein the glass particles have a particle size and density falling between the upper and lower boundaries shown in either of FIG. 3 or 4.

17-41. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] In order that the invention may be more readily understood, it will be described further with reference to the following Figures and to the specific examples hereinafter.

[0085] FIG. 1 shows a plot of the suspension velocity of sand in water as a function of the diameter of the sand particles.

[0086] FIG. 2 shows a plot of suspension velocity as a function of proppant particle diameter for soda-lime silicate glass (SLS) in a propane stimulation fluid, alongside the suspension velocity of sand in water as a function of the size of the sand particles.

[0087] FIG. 3 is a graph illustrating the upper and lower limits of proppant diameters that will be transported effectively in propane for a given proppant density.

[0088] FIG. 4 is a graph illustrating the upper and lower limits of proppant diameters that will be transported effectively in liquid petroleum gas (LPG) having the composition shown in Table 2 for a given proppant density.

[0089] FIG. 5 is a graph comparing the crush strength of a range of proppants according to the invention with sand and carbo (i.e. Carbolite, aluminosilicate proppant) as a function of pressure. The proppants are labelled “GTS” with a composition as identified in Example 1 and numerical values indicating the average diameter of the particles. “Retention %” indicates the percentage of the volume of proppant that is not crushed to fines.

[0090] FIG. 6 is a graph comparing the crush strength of a 100 μm diameter proppant according to the invention with 100 μm diameter sand as a function of pressure. “Retention %” indicates the percentage of the volume of proppant that is not crushed to fines.

[0091] FIG. 7 is a graph comparing the crush strength of a proppant according to the invention with carbo (i.e. Carbolite, aluminosilicate proppant) as a function of pressure. “Retention %” indicates the percentage of the volume of proppant that is not crushed to fines. It shows that the glass particles of the invention have improved crush strength compared to carbo up to approximately 7000 psi.

[0092] FIG. 8 is a graph comparing the crush strengths of a number of proppants according to the invention with bauxite and sand at 6000 psi. “Crush fines %” indicates the percentage of the volume of proppant that is crushed to fines. The graph shows that proppants according to the invention have a greater crush strength and thus produce less fines.

[0093] FIG. 9 is a graph comparing the crush strengths of a number of proppants according to the invention with bauxite and sand at 8000 psi. “Crush fines %” indicates the percentage of the volume of proppant that is crushed to fines. The graph shows that certain proppants have a greater crush strength and thus produce less fines.

DETAILED DESCRIPTION

[0094] For a proppant to be suitable for use in a particular stimulation fluid, it is important that the proppant is transportable in the particular fluid, that is, it is important that the proppant does not settle or float. For a particular combination of stimulation fluid and proppant, there will be a suspension velocity, or range of suspension velocities, for which the proppant is transportable in the fluid, without settling or floating.

[0095] It has been well established, through experiments, that certain proppants may be transported in particular stimulation fluids, and empirical data is available which can be used to derive a link between the suspension velocity and properties of the proppant (specifically density of the proppant and diameter of a proppant particle) and properties of the stimulation fluid (namely the density of the fluid).

[0096] A proppant which has been studied in detail is sand. It is known that sand particles of particular densities and diameters can be successfully transported in stimulation fluids of particular densities. For example, high viscosity “gel” stimulation fluid (containing cross-linked polymers, such as, guar gum) may be used to transport 20/30 mesh sand proppant; high viscosity stimulation fluids (containing other additives) in general may be used to transport 30/50 mesh sand proppant; and slick water (that is, water without viscosity modifiers) may be used to transport 40/70 mesh sand proppant.

[0097] A relationship between suspension velocity, the diameter and density of sand particles, and the density of the stimulation fluid can be derived by fitting Newton's equation to empirical sand data, leading to the following relationship:

[00003]$\begin{array}{cc}{V}_s={1.74\left[g.Math.d.Math.\left(\frac{{\rho }_p-{\rho }_f}{{\rho }_f}\right)\right]}^{\frac{1}{2}},& \left(1\right)\end{array}$

where, V.sub.s is the suspension velocity, p.sub.p is the density of the proppant, p.sub.f is the density of the stimulation fluid, g is the acceleration due to gravity, and d is the diameter of the proppant.

[0098] FIG. 1 shows a plot of suspension velocity as a function of a particle size (measured according to the commonly used mesh size criterion) for sand in slick water which has been generated using equation 1.

[0099] 40-70 mesh sand, which corresponds with sand having particle diameters in the range of about 200 μm to 400 μm, represents a range of sand particle diameters which are readily transported in slick water stimulation fluid using current pumping technology. Sand diameters which are bigger than 40 mesh (approximately 400 μm) are not transported effectively into a fracture because the particles tend to settle. Sand particle having diameters which are smaller than 70 mesh (approximately 200 μm) are difficult to transport because they tend to float on the surface of the water.

[0100] The relationship in equation 1 can be used to determine the suspension velocity required to transport 40 mesh sand. As shown in FIG. 1, the suspension velocity for 40 mesh sand would be 0.143 m s<−1>0 and this value can then be used as a guide to the maximum suspension velocity capable of successfully transporting any proppant in any fluid. Suspension velocities above 0.143 m s<−1> are likely to lead to the proppant settling rather than being transported.

[0101] The suspension velocity for the 70 mesh sand, determined according to equation 1, is 0.108 m s.sup.−1 and this value can then be used as a guide to the minimum suspension velocity capable of successfully transporting any proppant in any fluid. Suspension velocities below 0.108 m s.sup.−1 are likely to lead to the proppant floating on the surface of the stimulation fluid rather than being transported.

[0102] There may be other criteria which are used to select the lower limit of particle diameters other than the smallest particle diameter which remains pumpable. For example, the lower particle diameter limit may be governed by other considerations, such as, the conductivity of the proppant which may reduce to an unacceptable level should the proppant diameter be too small.

[0103] Soda-lime-silicate (SLS) glass materials is a promising material for use as a proppant because SLS can be prepared with a narrow range of particle diameters in a highly spherical form, which is ideal for a proppant for both transport and conductivity. Equation 1 can be used to determine the range of diameters of SLS glass particles which will be transportable in a given stimulation fluid.

[0104] The SLS glass has density pp=2500 kg m.sup.−3. Liquid propane which has a density @ 25° C. pf=493 kg m.sup.−3 can be shown to be a suitable stimulation liquid. V.sub.s is calculated for a series of diameters of glass particles d ranging from 20 μm-600 μm (0.00002-0.0006 m), as shown in Table 1.

TABLE-US-00001 TABLE 1 Calculated suspension velocity V.sub.s as a function of proppant diameter d for SLS glass in liquid propane stimulation fluid. Mesh Diameter Diameter Suspension velocity, size d/μm d/m V.sub.s/m s.sup.−1 693 20 0.00002 0.0492 365 40 0.00004 0.0695 250 60 0.00006 0.0852 192 80 0.00008 0.0984 156 100 0.0001 0.110 132 120 0.00012 0.120 114 140 0.00014 0.130 101 160 0.00016 0.139 90 180 0.00018 0.148 82 200 0.0002 0.156 75 220 0.00022 0.163 69 240 0.00024 0.170 64 260 0.00026 0.177 60 280 0.00028 0.184 56 300 0.0003 0.190 53 320 0.00032 0.197 50 340 0.00034 0.203 48 360 0.00036 0.209 45 380 0.00038 0.214 43 400 0.0004 0.220 41 420 0.00042 0.225 39 440 0.00044 0.231 38 460 0.00046 0.236 36 480 0.00048 0.241 35 500 0.0005 0.246 34 520 0.00052 0.251 33 540 0.00054 0.256 32 560 0.00056 0.260 31 580 0.00058 0.265 30 600 0.0006 0.269

[0105] The suspension velocities from Table 1 are shown plotted in FIG. 2. For comparison, the suspension velocities of 40/70 sand in slick water are also shown for corresponding particle sizes.

[0106] Taking the maximum suspension velocity to be 0.143 m s.sup.−1 as determined from the 40/70 sand, we can calculate, using equation 1, that the corresponding maximum particle diameter for the SLS glass that will be transported in propane stimulation fluid is 160 μm (95 mesh). The minimum suspension velocity can be taken to be 0.108 m s.sup.−1 as determined from the 40/70 sand, so we can calculate, using equation 1, that the corresponding minimum particle diameters for the SLS glass that will be transported in propane stimulation fluid is 88 μm (170 mesh). Hence, a range of SLS glass particle diameters in the range of 95/170 mesh (around 88 μm-160 μm) can be selected for use in a propane stimulation fluid.

[0107] As shown in FIG. 3, Equation 1 can be used to calculate the maximum and minimum proppant particle diameter as a function of proppant densities that will be successfully transported in the propane stimulation fluid (given the criteria that the maximum and minimum suspension velocities may be based on the 40/70 mesh sand data, that is, the maximum suspension velocity is 0.143 m s.sup.−1 and the minimum suspension velocity 0.108 m s.sup.−1). This shows that for SLS glass, with a density of p.sub.p=2500 kg m.sup.−3>, that the minimum SLS glass particle diameter is 88 μm and the maximum SLS glass particle diameter is 160 μm. FIG. 3 illustrates that it is possible to manipulate the proppant particle diameter to meet other needs (such as crush resistance, conductivity, or cost) by selecting a proppant with a different density.

[0108] It is desirable to be able to exploit the higher hydrocarbon fluids that are naturally present in natural gas as a stimulation fluid, to avoid the need to transport large quantities of stimulation fluid to the site. The hydrocarbon fluids will have a composition which is similar to the commercial LPG test fluid illustrated in Table 2 which shows the composition of the fluid and the density of the components.

TABLE-US-00002 TABLE 2 Composition of LPG test fluid. Compounds Density Density fraction C.sub.nH.sub.2B+2 (n) Wt % (kg/m.sup.3) (kg/m.sup.3) C.sub.10H.sub.22 0.101 730 0.737 C.sub.11H.sub.24 2.024 740 15.0 C.sub.12H.sub.26 5.732 750 43.0 C.sub.13H.sub.28 9.995 756 75.6 C.sub.14H.sub.30 12.757 764 97.5 C.sub.15H.sub.32 15.606 769 120 C.sub.16H.sub.34 17.813 793 141 C.sub.17H.sub.36 18.632 777 145 C.sub.18H.sub.38 11.932 777 92.7 C.sub.19H.sub.40 4.452 783 34.9 C.sub.20H.sub.42 0.849 791 6.72 C.sub.21H.sub.44 0.103 792 0.816 C.sub.22H.sub.46 0.004 770 0.0308

[0109] Based upon the data in Table 2, the density of the fluid ppis 772 kg m.sup.−3. As the LPG has a higher density (p.sub.p=772 kg/m.sup.−3 than liquid propane (p.sub.p=493 kg/m.sup.−3), for a given density of proppant particle, the LPG allows for larger proppant particle to be successfully transported than propane.

[0110] FIG. 4 shows a plot of maximum and minimum proppant particle diameter for a given proppant particle density calculated according to Equation 1 for the LPG stimulation fluid, again using the criteria that maximum suspension velocity is 0.143 m s.sup.−1 and the minimum suspension velocity 0.108 m s.sup.−1. For the SLS glass particles with density p.sub.p=2500 kg m.sup.−3, the minimum SLS particle diameter is 150 μm and the maximum SLS particle diameter is 300 μm. Hence, the LPG stimulation fluid can support SLS particles of larger diameter than propane.

[0111] The calculations described above may be repeated for any combinations of proppant materials and stimulation fluid to work out the range of proppant particle dimeters of a particular proppant material which would be suitable for transport in a particular stimulation fluid. In this way, it is straightforward to design and manufacture a proppant which is suitable for any kind of fracture stimulation situation, regardless of rock type, fracture size and depth, and operational requirements such as cost and productivity.

[0112] Although the suspension velocity relationship has been described as being derived from Newton's equation, the suspension velocity relationship could instead be derived from other physical relationships, such as Stoke's law. Examples of Proppants

Example 1—Proppant Formulations

[0113] A range of proppants were prepared from soda-lime silicate glass of the composition comprising: Si02 74 wt %, Na20 13 wt %, CaO 10.5 wt %, Al2O31.3 wt %, MgO 0.2 wt %

[0114] The proppants were prepared according to the fifth aspect of the invention and are described below in Table 3. Further features are provided in Table 5 below.

TABLE-US-00003 TABLE 3 Proppant Name Physical Features GTS big Average particle diameter - 563.3 μm, average sphericity - 0.87. GTS big sieved at 30M Average particle diameter - 462.2 μm, average sphericity - 0.87. GTS small Average particle diameter - 68.2 μm, average sphericity - 0.89. GTS big annealed Average particle diameter - 650 μm (32.5 mesh). GTS 0-63 micro Average particle diameter - 7.68 μm, average sphericity - 0.89. GTS 45-90 micro Average particle diameter - 48.7 μm, average sphericity - 0.89. GTS 75-150 micro Average particle diameter - 52.7 μm, average sphericity - 0.88. GTS 106-212 micro Average particle diameter - 114.1 μm, average sphericity - 0.87.

[0115] Proppants used for comparative purposes are described below in Table 4. Further features are provided in Table 6 below.

TABLE-US-00004 TABLE 4 Proppant Name Composition and Physical Features Sand > 212 micro Conventional sand composition, average particle diameter - 220 μm. Sand 106-212 micro Conventional sand composition, average particle diameter - 100.8 μm, average sphericity - 0.49. CARBOLITE Aluminosilicate proppant, average particle diameter - 864.6 μm, average sphericity - 0.78. Kuhmichel Pure alumina proppant, average particle diameter - 290.8 μm, average sphericity - 0.81.

Example 2—Proppant Properties

[0116] The proppants described in Tables 3 and 4 were analysed according to the following methods.

[0117] Sieving Test

[0118] Reference: ISO 13503-2 § 6

[0119] Method description: J. Getty, Petroleum Engineering, Montana Tech. Overview of Proppants and Existing Standards and Practices. [0120] http://www.astm.org/COMMIT/images/6D_Getty_ProppantTestingStandards_AS T M_Mtg18.26_Jan2013V2.pdf

[0121] Modifications:

[0122] It was necessary to introduce a modification of the method for the small proppants, due to the size of these materials is consider as fines by the ISO method.

[0123] New smaller sizes were chosen for the called “small proppants”, using the fines after the crush test at 4000 psi of GTS big proppant as reference. Around 1 g of the fines was manually sieved at different mesh sizes, finding three different kinds of particles: >200 μm, >125 μm and >50 μm.

[0124] The sieves used for “small proppants” are 200 μm (70 Mesh), 125 μm (120 Mesh) and 50 μm (270 Mesh).

[0125] Purchased Equipment: [0126] Sieves 20/40 (Endecotts: 008SAW1.18, 008SAW.850, 008SAW.710, 008SAW.600, 008SAW.500, 008SAW.425, 008SAW.300, 0085/STL&R). [0127] Sieves 70/270 (VWR: 510-0708, 510-0718 and 510-0724). [0128] Shaker (Endecotts: MIN200/23050).

[0129] Density Test

[0130] Reference: ISO 13503-2 § 10

[0131] Method description: J. Getty, Petroleum Engineering, Montana Tech. Overview of Proppants and Existing Standards and Practices. [0132] http://www.astm.org/COMMIT/images/6D_Getty_ProppantTestingStandards_AS T M_Mtg18.26_Jan2013V2.pdf

[0133] Necessary Materials: [0134] Low density liquid.

[0135] Sphericity and Roughness Tests

[0136] Reference: ISO 13503-2 § 7

[0137] Method description: J. Getty, Petroleum Engineering, Montana Tech. Overview of Proppants and Existing Standards and Practices. [0138] http://www.astm.org/COMMIT/images/6D_Getty_ProppantTestingStandards_AS T M_Mtg18.26_Jan2013V2.pdf

[0139] Necessary Equipment:

[0140] Scanning Electron Microscope

[0141] Crush Tests Reference: ISO 13503-2 § 11

[0142] Method description: T. T. Palisch, M. Chapman, R. Duenckel, and S. Woolfolk; CARBO Ceramics, Inc, SPE 119242. How to Use and Misuse Proppant Crush Tests—E i th T 10 M th Exposing the Top 10 Myths. [0143] http://images.sdsmt.edu/learn/John %20Kullman.pdf

[0144] Modifications:

[0145] The discrimination of the fines for “small proppants” is 270 Mesh, or 53 μm.

[0146] Purchased Equipment: [0147] Pneumatic press (Power Tool: CP86150 Compact bench press). [0148] Crushing test cell (Test Resources: GS-13503-2 Test Cell).

[0149] Conductivity Tests

[0150] Reference: ISO 13503-5

[0151] Method description: Petroleum and natural gas industries—Completion fluids and materials—Part 5: Procedures for measuring the long-term conductivity of proppants. [0152] http://www.iso.org/iso/catalogue_detail.htm?csnumber=40531

[0153] Alternative Method:

[0154] Volumetric flow rate measurement described by S. Alexander et al. (Journal of Colloid and Interface Science 466 (2016) 275-283).

[0155] Purchased Equipment: [0156] Pneumatic press (Power Tool: CP86150 Compact bench press). [0157] Conductivity test cell (Matest: A137, A136-01, A137-02, A137-03, A137-04, A141-02).

[0158] The results for the proppants identified in Tables 3 and 4 are shown below in Tables 5 and 6, respectively.

TABLE-US-00005 TABLE 6 NAME Sand > 212 micro Sand 106-212 micro CARBOLITE Kuhmichel Suspension velocity in  0.001809269  0.000380303  0.05686776  0.0066331 propane (cm/s g) Particle size — 0-212 710-1180 300-425 distribution (micron) Particle diameter 220 100.864 864.578 290.802 (micron) Density (g/ml)  1.602  1.602  2.75  2.82 Permeability (mD) —  4.36  29.71  6.22 Crush strength —  11.93  17.56  17.5 (% fines at 6000 psi) Sphericity —  0.49  0.78  0.81 Roughness —  0.12  0.87  0.465 Values underlined were measured as an average of 200 particles from SEM images.

[0159] It should be appreciated that the proppants and uses of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.