SYNTHETIC NANOCOMPOUNDS IN THE FORM OF MICROPARTICLES, PROCESS FOR PRODUCING SAME, PROPPING AGENTS AND FRACTURING FLUIDS FOR GAS AND OIL EXTRACTION PROCESSES

Abstract

The invention relates to synthetic nanocompounds in the form of microparticles that allow major deformations before breaking and are especially useful for preparing low-density synthetic propping agents to be used in non-conventional oil and gas extraction processes (fracking). The invention also describes the process for obtaining said nanocompounds, propping agents and fracturing fluids for oil and gas extraction processes.

Claims

1. Synthetic nanocomposites in microparticle form formulated from polybutadienes, and other polydienes, capable of withstanding great deformation before breaking, with applications in diverse fields of industry, especially in the preparation of low density synthetic proppants to be used in unconventional oil and gas extraction processes (fracking), in bearings for the slide of very heavy parts in the construction and mechanical industries, in torque reducers for the drilling of oil wells and other types of wells, characterized by the fact that said microparticle nanocomposites exhibit a continuous glass phase with separation of other phases, which entail high Young's modulus values and an increase in their acceptable deformation of up to 40%.

2. The process for production of the nanocomposite particles of claim 1, comprising: suspension copolymerization in an aqueous medium of styrene drops containing crosslinking agents dissolved in said drops and having at least two bifunctional reactive sites; generating free radicals by means of peroxide thermal decomposition, with control of the stoichiometry of styrene and crosslinking agent and of the progression of reaction temperatures; the stoichiometric ratios of styrene double bonds to crosslinking agent double bonds ranging from 3 to 60 styrene double bonds per each crosslinker double bond in the original reaction mixture; and the reaction temperatures being in ascending slopes between 65° C. and 250° C.

3. The process of claim 2, characterized by the fact that the crosslinking agents are homopolymers and copolymers of isoprene, butadiene and other dienes.

4. The process according to any of claim 2 or 3, characterized by the fact that the homopolymers and copolymers of isoprene, butadiene and other dienes include molecular structures in block, statistical (random) and intermediate forms, in a wide range of molecular weights, with linear and branched structures, and mixtures thereof.

5. The process according to any of claim 2, 3 or 4, characterized by the fact that the comonomers of isoprene, butadiene and other dienes are selected from styrene, alpha-methyl-styrene, acrylic and methacrylic comonomers, ethylene, polypropylene and acrylonitrile, including their various partially hydrogenated versions.

6. Low density synthetic proppants comprising the microparticle nanocomposites from claim 1, wherein said proppants: a) have high Young's modulus values; and b) also have high acceptable deformation values of more than 40%.

7. Fracture fluid for unconventional oil and gas extraction processes, characterized by the fact that it comprises the proppant from claim 1, and further comprises a polymeric viscosity modifier selected from guar gum, tara gum or polyacrylonitriles; it may also comprise other proppants, crosslinkers, friction reducers, antifoaming agents, emulsifiers, corrosion inhibitors, scale inhibitors, paraffin inhibitors, clay stabilizers, biocides and chain breakers.

8. Synthetic nanocomposites in microparticle form formulated from polybutadienes, and other polydienes, capable of withstanding great deformation before breaking, with applications in diverse fields of industry, especially in the preparation of low density synthetic proppants to be used in unconventional oil and gas extraction processes (fracking), in bearings for the slide of very heavy parts in the construction and mechanical industries, in torque reducers for the drilling of oil wells and other types of wells, characterized by the fact that said nanocomposites are obtained by means of suspension copolymerization in an aqueous medium of styrene drops containing crosslinking agents dissolved in said drops and having at least two bifunctional reactive sites, generating free radicals by means of peroxide thermal decomposition, with control of the stoichiometry of styrene and the crosslinking agent and of the progression of reaction temperatures, the stoichiometric ratios of styrene double bonds to crosslinking agent double bonds ranging from 3 to 60 styrene double bonds per each crosslinker double bond in the original reaction mixture, and the reaction temperatures being in ascending slopes between 65° C. and 250° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0060] FIG. 1 shows a photograph of the particles from the prior art, after being subjected to pressure deformation tests;

[0061] FIG. 2 shows an enlarged view of the particles from the prior art after being subjected to pressure deformation tests;

[0062] FIG. 3 shows a 60× magnification of the particles of the present invention;

[0063] FIG. 4 shows a photograph of the particles of the present invention after being subjected to pressure deformation tests;

[0064] FIG. 5 shows another photograph of the particles of the present invention after being subjected to pressure deformation tests;

[0065] FIG. 6 shows the measurements of the shear modulus values as a function of the temperature; and finally,

[0066] FIG. 7 shows the change in enthalpy values as a function of the temperature.

EMBODIMENTS OF THE INVENTION

[0067] In a more detailed description of the figures, it can be observed that FIG. 1 shows a photograph of particles from the prior art, after being subjected to pressure deformation, in which said particles, having a diameter of 0.45 mm, were subjected to “Crush Tests” (API 19C RP Standard, at pressures of 8,000 psi=551.7 Bar). The presence of non-recovered net spherical collapses produced by the force exerted by neighboring particles can be clearly observed.

[0068] FIG. 2 shows an enlarged view of particles from the prior art with a diameter of about 0.45 mm, after being subjected to pressure deformation. Tests were of the “Crush Test” type (API 19C RP Standard, at a pressure of 10,000 psi=689.6 Bar). Said particles clearly show the presence of more non-recovered net spherical collapses than those shown in FIG. 1, due to the force exerted by neighboring particles.

[0069] FIG. 3 shows a 60× magnified microscope photograph containing the particles of the present invention.

[0070] FIG. 4 shows a photograph of the particles of the present invention, after being subjected to pressure deformation in a “Crush Test” (API 19C RP Standard, at a pressure of 10,000 psi=689.6 Bar), where the deformation produced by the force exerted by nearby particles can be clearly seen. In this case, said deformation does not consist of net spherical collapses, but instead is partially recovered.

[0071] FIG. 5 shows a photograph of the particles of the present invention, after being subjected to pressure deformation in a “Crush Test” (API 19C RP Standard, at a pressure of 12,000 psi=827.6 Bar), where the deformation produced by the force exerted by nearby particles can also be clearly seen. In this case, said deformation does not consist of net spherical collapses either, but instead is partially recovered.

[0072] FIG. 6 shows the measurements of the shear modulus values as a function of the temperature. The glass transition temperature is calculated as the temperature where the abrupt drop in modulus values begins.

[0073] FIG. 7 shows the change in enthalpy values as a function of the temperature. The glass transition temperature is calculated as the half-way point between the abrupt spike in enthalpy change values. The values calculated from modulus measurements and calorimetry coincide closely.

[0074] FIGS. 1 and 2 show photographs of particles from the prior art, of a diameter of around 0.45 mm, after being subjected to a “Crush Test” (API 19C RP Standard, at pressures of 8,000 and 10,000 psi=551.8 and 689.6 Bar) where the non-recovered net spherical collapses produced by the force exerted by nearby particles can be clearly seen.

[0075] In the case of the present invention, a process of polymer-polymer phase separation, controlled in order to obtain a continuous vitreous phase and an elastomeric phase in domains of nanometric size with an elastomer volume percentage of up to 15%, preferably between 0.5 and 8%, allowing for a considerable increase in the capacity to withstand acceptable deformation without breaking, but since the separate elastomeric phase remains covalently bonded to the continuous matrix, the potential decrease in Young's modulus values is significantly lower, and a high percentage of the deformations produced in the “Crush Test” (API 19C RP Standard) are recoverable. FIGS. 4 and 5 show photographs of particles of the present invention, of a diameter of around 0.45 mm, after being subjected to a “Crush Test” (API 19C RP Standard, at pressures of 10,000 and 12,000 psi=689.6 and 827.6 Bar) where the deformation produced by the force exerted by nearby particles can be clearly seen, which does not consist of net spherical collapses, but instead is partially recovered.

[0076] Styrene solutions of copolymers of isoprene and styrene, of butadiene and styrene, and of isoprene, butadiene and styrene were used. In these copolymers, both butadiene and isoprene contributed residual double bonds, which reacted in the crosslinking process at different rates according to their electronic structure and steric hindrance. Copolymerized styrene reduced the magnitude of the positive values of the χ parameter of the Flory-Huggins equation, and, since it does not have any available double bond to react as crosslinker, reduced the global reaction rate of the crosslinker, thus delaying to some extent the starting moment of the phase separation, with the aforementioned purpose. χ values for each crosslinking styrene-copolymer pair were not measured experimentally, as the effect of the change in N.sub.1 during the reaction rapidly cancels out any difference between the copolymers used. A qualitative evaluation of the clarity of the solution of copolymer in styrene was used instead; those types of copolymers whose 10% solutions in styrene at ambient temperature showed turbidity were ruled out. The proportion ranges of styrene in the copolymer used varied between 15% and 48%, and the proportion ranges of isoprene and butadiene varied between 12% and 85%. Random and block copolymers, with linear and branched structures, were used. The solvent in every case was styrene with a proportion of divinylbenzene between 2% and 15%. The crosslinking copolymer concentration varied between 2 and 15%. The peroxides used were chosen according to their temperature ranges corresponding to half-life values of 6 minutes and 60 minutes, in order to be able to estimate reaction rates and the possibility of autoacceleration of the reaction system. Temperature ranges corresponding to those 60 minute half-life values varied between 85° C. and 152° C.

[0077] A) The formulations for the production of proppant particles were designed following the basic qualitative rules detailed above. A multivariate statistical optimization system was used. In these optimization systems, the effects that different variables have on the final properties of interest are experimentally explored by means of small changes in the concentrations and types of reactants used in the formulation, and in the values of the parameters that define the process, such as temperatures and reaction times, the volumetric ratio between water and the organic phase of the suspension, height to diameter ratio of the suspension polymerization reactor, size, number and placement of baffles, size, number and placement of stirring blades, and speed and intensity of the stirring. The ranges of values over which these parameters are varied are chosen based on the experimental results published in the public literature by other authors and on the previous experience of the directors of the project. The optimum combination from among that group of values was chosen for the different variables. The process can be repeated more than once if a satisfactory combination is not achieved, thus further limiting the field of exploration in each case. This optimization method is a standard procedure for experts in the art versed in statistical methods, and was described in detail and with examples in the book Statistics for Experimenters—Design, Innovation and Discovery” (Box, Hunter & Hunter), Wiley, Interscience (Second Edition) (2005) under the title “Fractional Factorial Design”.

[0078] B) To test the different formulations developed to date, over fifty combinations of peroxides, crosslinking agents and temperature programs were used, as shown in the following table:

TABLE-US-00001 % % % % % Polybutadiene of Perox. Perox. Perox. Perox. Tg type % # DVB #1 #2 #3 #4 (° C.) G* (MPa) N/A 0 1 0 0.20% — 0.30% — — N/A 0 2 5 132 723.5 ± 16.5 N/A 0 3 10 126 ± 6 839.5 ± 28.5 N/A 0 4 0 0.20% 0.60% — 100 332 ± 23 N/A 0 5 5 118 ± 4 605.55 ± 72.5  N/A 0 6 10 130 623.5 ± 47.5 N/A 0 7 0 0.20% — 0.30% — — N/A 0 8 5 120 770 ± 10 N/A 0 9 10 127  760 ± 100 N/A 0 10 0 0.20% 0.60% — — — N/A 0 11 5 115 780 N/A 0 12 10 130 ± 3 900 ± 50 1 5 13 0 0.20% 0.30% — 97.5 835.2 1 5 14 0 98.6 368.5 1 5 15 3 111.82 847.2 1 5 16 3 111.82 720.7 2 5 17 0 0.20% 0.30% — 101.19 835.2 2 5 18 0 106.15 652.2 2 5 19 3 112.22 674.3 2 5 20 3 115.03 940.7 3 5 21 0 0.20% 0.30% — 100.79 884.3 3 5 22 0 101.22 413.1 3 5 23 3 114.58 815.6 3 5 24 3 114.58 839.2 1 5 26 0 0.20% 0.30% — 102.64 823.4 1 5 27 3 105.72 954.2 2 5 28 0 0.20% 0.30% — 103.47 918.6 2 5 29 3 112.46 1154.23 3 5 30 0 0.20% 0.30% — 113.05 823.4 3 5 31 3 112.75 954.2 1 5 32 0 0.20% 0.30% 0.30% 101.6 976.8 1 5 33 3 113.23 964.7 2 5 34 0 0.20% 0.30% 0.30% 102.2 976.8 2 5 35 3 113.02 909.5 3 5 36 0 0.20% 0.30% 0.30% 100 796.3 3 5 37 3 111.6 785.1 3 3 38 0 0.30% 0.30% 0.30% 98.2 823 3 6 39 0 0.30% 0.30% 0.30% 97.6 872 3 9 40 0 0.30% 0.30% 0.30% 97.2 1026 5 3 41 0 0.30% 0.30% 0.30% 98.3 941 5 6 42 0 0.30% 0.30% 0.30% 97.4 — 5 9 43 0 0.30% 0.30% 0.30% 99.1 — 3 5 44 0  0.3%  0.3%  0.3%  0.3% 94.3 — 3 5 45  0.3% 0.50% 96.7 — 3 5 46  0.3% 0.30% 97 — 3 5 47 0 0.20%  0.3% 0.30% 98.9 — 3 5 48  0.3% 0.30% 99.1 — 3 5 49 0 0.20%  0.3% 0.30% 101.3 — 3 5 50 0.3% B 0.30% 99.7 3 5 57 3% 0.20% 0.3% B — 110.5 1030 3 5 58 0.20% — 0.30% 110.4 1150 3 5 59 0.20%  0.3% 0.30% 0.30% 106.4 1090 3 5 60 0.20%  0.3% 0.30% 108.6 1040 3 5 61 —  0.3% 0.30% 111.7 925

[0079] C) For each formulation, several cylindrical samples (6 mm in diameter and 80 mm in length) were produced in glass tubes with 0.5 mm wall thickness. This method allowed for the labor-intensive system of setting up a complete suspension polymerization for each of the formulations and conditions of the process to be tested to be discarded, along with the associated cost and work it entails, and allows for use of only one reactor to simultaneously test polymerizations with different formulations (up to 1 per tube; up to a high number of tubes depending on the diameter of the reactor used), with a group of shared process parameter values for all of the formulations tested in this set. Since polymerization in these tubes must be equivalent to the industrial suspension process, and since the suspension process can be modeled as a group of small mass polymerization reactors (suspended in a medium providing very efficient heat transfer for an adequate temperature control), the requirements to be met by this tube polymerization system are that the ratio of the external area of the tube to the reacting mass volume is sufficiently high, and that the temperature difference between the center of the reacting cylindrical mass and the internal surface of the glass tube is no more than 3° C. The temperature difference between the center of the reacting cylindrical mass and the internal surface of the glass tube was calculated based on the reaction heat that has to be evacuated, with satisfactory results for these dimensions. Various diameters and numbers of glass tubes were tested in a water bath within a reactor with temperature and atmosphere control, until an operational zone with an adequate combination of sample size and efficient temperature control was determined, the parameter of interest in this case being the heating and cooling capacity of the reactor. Some of the formulations polymerized in glass tubes were also polymerized in suspension, in identical process conditions, yielding physical property results (Young's modulus and glass transition temperature) very similar to those measured in the samples polymerized in glass tubes.

[0080] Table 1 shows the modulus value results obtained through measurements performed on samples polymerized in glass tubes and in suspension. PB IV is a copolymer of butadiene and DVB is divinylbenzene.

TABLE-US-00002 TABLE 1 Modulus of Styrene PB IV DVB Perox. Modulus of in glass suspension % in % in % in % in polymerization polymerization Formulation weight weight weight weight (GPa) (GPa) A 100 0 0 0.2 3.1 3.1 B 91 6 3 0.2 3.0 2.95 C 85 12 3 0.2 2.55 2.7

[0081] D) Cylindrical samples are very useful in rapidly and precisely measuring values for Young's modulus and glass transition temperatures in a mechanical spectrometer with temperature control. The mechanical spectrometer, Anton-Paar model Physica II, consists of two coaxial axes ending in cylindrical clamps with adjustable conic nozzles that accept cylindrical samples from both ends. One of the axes is connected to the electric motor that applies and measures torque, and precisely measures the angular deformation as rotation of one of said coaxial axes. The system is contained within a chamber with temperature control by means of forced nitrogen convection. The shear modulus versus temperature graphs allow for calculation of the glass transition temperature as well. FIG. 6 shows the results of measurements performed with the mechanical spectrometer on cylindrical samples of some formulations differing in their glass transition temperatures. FIG. 7 shows enthalpy versus temperature characteristic curves, measured by a differential scanning calorimeter, for several formulations. Glass transition temperature values corresponding to formulations 52, 54 and 56, measured using both methods, showed a high coincidence.

[0082] E) For some formulations, Young's modulus values were also measured by means of a Hysitron brand nanoindenter (TI-950 Triboindenter), running at ambient temperature. These values coincided very well with the values measured by said mechanical spectrometer in point D). The nanoindenter does not have temperature control nor does it allow for the glass transition temperature to be estimated, but it is useful in measuring some mechanical properties, such as Young's modulus, directly on particles produced in suspension. There is no other available instrument capable of measuring mechanical properties in samples this small.

[0083] F) Enthalpy versus temperature characteristic curves for several samples were measured in a Perkin-Elmer Pyris II Differential Scanning calorimeter (DSC) in order to calculate the glass transition temperature in standard form, such as the average increase in specific heat capacity, and compare it with the results obtained by the mechanical spectrometer. The results showed high coincidence. This verification is necessary to verify whether the products obtained by glass tube polymerization are identical in behavior to those obtained via suspension polymerization. Some results are included in FIGS. 6 and 7 described above in point D) of this section.

[0084] G) Glass transition temperature values were also measured indirectly for particles obtained through suspension polymerization, by means of the mechanical spectrometer. For selected formulations, particles were included in a high glass transition temperature crosslinked homopolymer epoxy plate; the plate was subjected to a torsion test in the mechanical spectrometer, yielding modulus versus temperature curves. These curves show two drops in the modulus values: one corresponding to the epoxy resin and the other corresponding to particles polymerized in suspension. The glass transition temperature of the epoxy resin was measured in another similar plate without added particles.

[0085] H) Spherical particles of selected formulations produced in a pressurized stainless steel reactor equipped with stirring means and temperature control. The reactor has a 3 liter capacity, a hermetic lid with O-rings, pressurization and vent valves, thermocouple for measurement and temperature control which is submerged in the liquid, and a vertical shaft with blades specifically designed to lightly and evenly stir the whole liquid contained within it. It also has a system of vertical baffles. The group of baffles and stirring blades were experimentally tested in a glass container of similar dimensions to those of the reactor, to verify vertical recirculation of water and styrene solution with crosslinking polymer, in order to program the most convenient shaft rotation regimen to control the size of the particles to be produced. Reactor temperature is efficiently controlled by means of a system of band-type stainless steel heaters, powered by a PID control system based on the aforementioned thermocouple readings. Reactor refrigeration is solely carried out by free convection from its external surface.

[0086] I) Size distributions of the particles produced in the suspension reactor range from 0.1 mm to 3 mm. Particles in the range of proper size to be used as proppants were obtained by means of normalized sifting, using the fractions obtained between sieves 20/40 and 50/70 for the assays.

[0087] J) Particles selected by sifting were subjected to a compression test (Crush Test) (ISO 13503 Standard, API RP19C).

[0088] K) Particles were photographed after the compression test. FIGS. 4 and 5 show photographs of particles manufactured according to the procedure described in this invention after being subjected to a “Crush Test” (API 19C RP Standard) at pressures of 10,000 and 12,000 psi=689.6 and 827.6 Bar, respectively.