Patent Grant
11542812
This application relates to methods of measuring zeta potential in porous media.
Streaming potential is the voltage difference (ΔV) that arises when a liquid is forced to flow through a porous media by a pressure gradient. When a solid surface is contacted with a liquid medium, a charge forms on the surface, inducing a surface potential, which is balanced by an equal and opposite charge in the liquid medium. An electrical double layer is formed in which two parallel layers of charge surround a surface—a stationary layer formed on the surface and a diffuse layer of ions attracted to the charged stationary layer. The electrical double layer exists within a slipping plane, where liquid between a surface and slipping plane moves tangentially along the surface, and liquid beyond the slipping plane moves within the surrounding liquid. The electric potential at the slipping plane region is referred to as the zeta (←-) potential.
The ζ-potential is calculated from the slope of the streaming potential (E) versus pressure (P) using the classical Helmholtz-Smoluchowski formula:
where ε is the permittivity, λ is the electrical conductivity, and η is the viscosity of the solution. Thus, for a given material, the permittivity ε, electrical conductivity λ, and viscosity η are all known constants resulting in the zeta potential ζ being proportional to the ratio of the streaming potential (E) and the differential pressure (P) across the porous media.
Streaming potential measurements are applied in fields ranging from geology to medicine. For example, in the medical field, streaming potential measurements may be used to study bone growth, repair, and remodeling. Streaming potential measurements may also be applied in the oil and gas industry to evaluate subterranean formations and aid in development of improved methods of enhanced oil recovery.
Current methods of measuring ζ-potential of calcium carbonate solutions are obtained using a system in which the solid and the liquid are in equilibrium. While ζ-potential measurements are performed in closed systems, effluent samples are commonly collected in an environment open to atmosphere. Such practice underestimates the impact of CO2 dissolution on correctly evaluating processes that take place at a gas-liquid interface, as CO2 dissolution directly affects pH and ion concentration (Ca2+ and CO32−) of a liquid solution, which are metrics used to derive the ζ-potential.
The present disclosed embodiments include systems and methods for improved streaming potential measurements, which may be used to compute zeta potential, which in turn may be used to enhance oil recovery techniques due to the usefulness of zeta potential in determining the stability of oil and gas formations from a physical chemistry standpoint.
In one aspect, the present invention is directed to a system for determining a zeta potential of a porous medium, flat substrates, coarse particles, and/or granular samples including: fluid in fluid communication with both a first end and a second end of the porous medium; a first pressure sensor disposed upstream of the first end of the porous medium; a second pressure sensor disposed downstream of a second end of the porous medium, the first pressure sensor and the second pressure sensor collectively measuring a first pressure differential between an upstream and a downstream pressure of the fluid; a first probe disposed at the first end of the porous medium, the first probe measuring an upstream electrical characteristic of the fluid; and a second probe disposed at the second end of the porous medium, the second probe measuring a downstream electrical characteristic of the fluid, the first probe and the second probe collectively measuring a difference between the upstream and downstream electrical characteristic of the fluid. The zeta potential is determined based at least partially on a ratio of the first pressure differential between the upstream and downstream pressure of the fluid to the difference between the upstream and downstream electrical characteristic of the fluid.
In some embodiments, the electrical characteristic includes an electrical conductivity and/or a voltage.
In some embodiments, the fluid includes an aqueous solution.
In some embodiments, the system includes an inlet line fluidly coupled to the first end of the porous medium; and an outlet line fluidly coupled to the second end of the porous medium. The first pressure sensor is disposed in the inlet line, and the second pressure sensor is disposed in the outlet line.
In some embodiments, the system includes a first reservoir fluidly coupled upstream of the inlet line; and a second reservoir fluidly coupled downstream of the outlet line. A first pressure gradient between the first reservoir and the second reservoir drives the fluid through the porous medium.
In some embodiments, the system includes a first valve disposed in the inlet line; and a second valve disposed in the outlet line.
In some embodiments, the system includes a core holder for holding the porous medium.
In some embodiments, the system includes at least one temperature probe disposed the inlet line and/or the outlet line.
In some embodiments, the system includes at least one pH sensor disposed in the inlet line and/or the outlet line.
In some embodiments, the system includes at least one ionic sensor disposed in the inlet line and/or the outlet line.
In some embodiments, the ionic sensor includes at least one ionophore.
In some embodiments, the system includes a pressure source fluidly coupled to the first reservoir and/or the second reservoir; and a pressure regulator operatively coupled to the pressure source.
In some embodiments, the system includes a data acquisition system communicatively coupled to the first pressure sensor and the second pressure sensor; and a computer system communicatively coupled to the data acquisition system.
In some embodiments, the porous medium includes a core sample from a geologic formation.
In some embodiments, the porous medium includes a fluid-filled bone.
In some embodiments, the system includes a vent disposed in the first reservoir and/or the second reservoir. The fluid includes saline water, the porous medium includes carbonate, and each of the first pressure sensor and the second pressure sensor are calibrated to operate within a pressure range from about 0 bar to about 10 bar.
In another aspect, the present invention is directed to a method of measuring the zeta potential of a porous sample including: subjecting the porous sample to an injection of a first aqueous solution at an initial pressure with an initial ion concentration; measuring a first electrical conductivity and a first temperature of the first aqueous solution; measuring a first pH and a second pH of the first aqueous solution immediately before and after passing the first aqueous solution through the porous sample; measuring a first ion concentration and a second ion concentration of the first aqueous solution immediately before and after passing the first aqueous solution through the porous sample; and using the first pH, second pH, first ion concentration, and second ion concentration to derive a first zeta potential for the porous sample from the first electrical conductivity and the first temperature.
In some embodiments, subjecting the porous sample to an injection of the first aqueous solution includes subjecting the porous sample to an injection of the first aqueous solution without having exposed the aqueous solution to external environmental conditions.
In another aspect, the present invention is directed to a method of determining the zeta potential of a porous medium including: passing a fluid through the porous medium in a forward direction from a first end of the porous medium to a second end; measuring at least one electrical characteristic within the fluid at the first end of the porous medium; measuring at least one electrical characteristic within the fluid at the second end of the porous medium; measuring a pressure gradient of the fluid between the first end of the porous medium and the second end of the porous medium; and determining a first zeta potential based at least partially on a ratio of the pressure gradient to the difference between the electrical characteristic at the first end of the porous medium and the second end of the porous medium.
In some embodiments, the electrical characteristic includes an electrical conductivity and/or a voltage.
In some embodiments, the method includes passing the fluid through the porous medium in a reverse direction from the second end of the porous medium to the first end.
In some embodiments, the method includes determining a second zeta potential based at least partially on measurement of a pressure gradient of the fluid between the second end of the porous medium and the first end of the porous medium and measurement of a difference between at least one electrical characteristic at the second end of the porous medium and the first end of the porous medium when passing the fluid through the porous medium in the reverse direction.
In some embodiments, the method includes establishing a first pressure gradient across the porous medium prior to passing the fluid through the porous medium in the forward direction.
In some embodiments, the method includes establishing a second pressure gradient across the porous medium; and passing the fluid through the porous medium in a reverse direction.
In some embodiments, the second pressure gradient is opposite but otherwise approximately identical in magnitude to the first pressure gradient.
In some embodiments, the method includes establishing a third pressure gradient across the porous medium, the third pressure gradient being of a different magnitude than the first pressure gradient; and passing the fluid through the porous medium a second time in the forward direction.
In some embodiments, the method includes establishing a fourth pressure gradient across the porous medium; and passing the fluid through the porous medium a second time in the reverse direction.
In some embodiments, the fourth pressure gradient is opposite but otherwise approximately identical in magnitude to the third pressure gradient.
In some embodiments, the porous medium includes a rock matrix of a subterranean formation including a hydrocarbon reservoir.
In some embodiments, the electrical characteristic includes an electrical conductivity and/or a voltage.
It should be understood that the order of steps or order for performing certain actions is immaterial as long as a described method remains operable. Moreover, two or more steps or actions may be conducted simultaneously.
The following description is for illustration and exemplification of the disclosure only, and is not intended to limit the disclosure to the specific embodiments described.
The mention herein of any publication, for example, in the Background section, is not an admission that the publication serves as prior art with respect to any of the present claims. The Background section is presented for purposes of clarity and is not meant as a description of prior art with respect to any claim.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention and are not intended as a definition of the limits of the invention. For purposes of clarity, not every component may be labeled in every drawing. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
It is contemplated that systems, devices, methods, and processes of the present application encompass variations and adaptations developed using information from embodiments described in the following description. Adaptation and/or modification of the methods and processes described herein may be performed by those of ordinary skill in the relevant art.
Throughout the description, where devices and systems are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are devices and systems of the present application that consist essentially of, or consist of, recited components, and that there are processes and methods according to the present application that consist essentially of, or consist of, recited processing steps.
It should be understood that the order of steps or order for performing certain actions is immaterial so long as a described method remains operable. Moreover, in some embodiments, two or more steps or actions are conducted simultaneously.
Headers are provided for convenience of the reader and are not intended to be limiting with respect to claimed subject matter.
The present disclosed embodiments include devices, systems, methods, and processes for accurately determining zeta potential, which may be used for enhanced hydrocarbon recovery. One manner of enhanced hydrocarbon recovery is water flooding, where an aqueous solution is injected into a reservoir formation to displace residual oil (and/or other hydrocarbons). For example, in certain instances, a water flooding method includes injection of a brine solution, injection of a carbonated water solution, and/or injection of a carbonated saline solution. In certain instances, an aqueous injection solution may include calcium carbonate.
An equilibrium state of a calcium carbonate suspension depends on the partial pressure of CO2 in surrounding air. As dissolution of CO2 in an aqueous solution (such as a brine) increases, pH decreases due to formation of carbonic acid species. When brine is in contact with calcite, such as in subterranean carbonate (or other geologic) formations, in the presence of atmospheric CO2, most carbonate ions in a suspension are present as bicarbonate at equilibrium. Consequently, at equilibrium, aqueous concentration of carbonate and carbonic acid is minimized and concentration of bicarbonate is maximized. The pH of brine will initially increase rapidly as OH− and CO32− concentrations increase, then decrease as equilibrium is reached, at which point most of the OH− has reacted with CO2 to form bicarbonate. A resultant increase in mineral dissolution rate will yield an increase in calcium concentration of the solution, affecting the sign and magnitude of the zeta potential.
Additionally, dissolution of atmospheric CO2 leads to variation in activity of H2CO3*(H2CO3*═H2CO3°—F—CO2(aq)), HCO3−, and CO32− in calcite-brine solutions near equilibrium, leading to a slow exchange of CO2 between dissolved and gaseous states at basic pH, due to the formation of inactive H2CO3* species. Consequently, buffering of carbonate species formed during calcite dissolution is especially challenged in multi-phase measurements at high pH.
Encompassed in the present embodiments is the recognition that in-line monitoring of pH and concentration of key ions of a brine solution before and after applying hydraulic pressure enforcement in streaming potential measurements increases the accuracy of zeta potential determination. A pH at which the charge of a solid surface reverses, also known as an isoelectric point (IEP), is a fundamental parameter in determination of zeta potential. Variation in concentration of Ca2+ and CO32− due to surface dissolution/adsorption/complexation that accompanies CO2 dissolution can modify the structure of an electrical double layer, and consequently alter measured potential. The ability to monitor pH and ion concentrations in-line yields reliable streaming potential measurements. Improving accuracy of streaming potential measurements in subterranean formations, for example, will consequently improve optimization of enhanced oil recovery techniques.
In subterranean formations treated by water flooding, an electrical double layer occurs at the interface between the formation rock matrix and water within formation pores, with a negative charge coating surface of a rock matrix balanced by a positive charge of water filling matrix pore. As pressure is applied and water moves through a formation under a pressure gradient, an electrical current is generated, inducing a streaming potential.
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In operation, a porous medium 14 such as a core sample (for example, a carbonate core) may be placed in the core holder 12. In one embodiment, the core sample 14 may include one or more porous core plugs with dimensions ranging from about 1 inch to about 3 inches in diameter and from about 2 inches to about 12 inches in length. In other embodiments, the core sample 14 may be from about 1.5 inches to about 2.5 inches in diameter, or from about 0.5 inches to about 4 inches in diameter. In some embodiments, the core sample 14 may include a length from about 1 inch to about 18 inches, or from about 3 inches to about 15 inches, or from about 4 inches to about 10 inches, or from about 6 inches to about 8 inches. The first reservoir 16 may be filled with an aqueous solution (for example, an aqueous electrolyte such as saline water with a predetermined and/or selected ionic strength). The aqueous solution may then flow through the first valve 24 (in an open position) and the inlet to the core holder 12 and porous medium 14. A positive pressure in the first reservoir 16 drives the aqueous solution through the porous medium 14 (for example, a carbonate core) due to the second valve 26 also being open as well as the second reservoir 18 being exposed to atmosphere (for example, due do the second vent 62 being open). Stated otherwise, a higher pressure in the first reservoir 16 than the second reservoir 18 drives the aqueous solution through the porous medium 14. As the aqueous fluid flows in a forward direction 51 and passes the sensors 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 disposed in the inlet and outlet lines characteristics of the aqueous fluid are measured both upstream of (that is, in the inlet line 20) and downstream of (that is, in the outlet line 22) the porous medium 14. For example, as the aqueous fluid passes through the inlet line 20, the temperature and pressure may be measured via the temperature probe 28 and pressure sensor 44. In addition, the electrical conductivity of the aqueous solution may be recorded by the electrical conductivity probe 32. The streaming potential 72 may be measured via a first electrode 73 disposed at an upstream end of the porous medium 14 (for example, at a first end 13 of the porous medium 14 adjacent the inlet line 20) and a second electrode 71 disposed at a downstream end of the porous medium 14 (for example, at a second end 15 of the porous medium 14 adjacent the outlet line 22), the upstream and downstream ends 13, 15 of the porous medium 14 being defined relative to a forward flow direction 51. Each of the first and second electrodes 71, 73 may be communicatively coupled to the data acquisition system 64. The streaming potential 72 and the pressure gradient 74 (and/or differential pressure 74 using the first and second pressure sensors 44, 46, upstream and downstream of the porous medium 14) may be used to determine the zeta potential (for example, using the Helmholtz-Smoluchowski formula above).
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The present disclosure describes in-line monitoring of pH of an electrolyte using a modular process sensor, thereby preventing misleading interpretations due to CO2 dissolution in brine, which shifts pH from the IEP and produces an unreliable measurement. In addition, in-line monitoring of Ca+2 and CO3−2 concentrations before and after injection using an ion selective sensor, eliminates uncertainty in the measurement of rock dissolution rates under high temperature and streaming potential conditions. Real-time monitoring of CaCO3 dissolution rate and calculation of total calcium and carbonate concentrations in a closed system eliminates complications caused by CO2 exposure. By taking the pH, ionic concentrations, and other factors such as temperature (which can cause variation in both the permittivity and viscosity due to the inverse relationships of temperature with both permittivity and viscosity) and electrical conductivity into account, an accurate zeta potential can be determined, which is useful in assessing the stability of porous media such as a core sample 14. In addition, using the present disclosed methods and system, the streaming potential 72 (and thus the zeta potential) may be assessed in multiple flow directions to account for differences in pressure gradients and voltage differentials attributed to the direction of fluid flow through the porous medium 14.
The present disclosed system 10 for measuring zeta potential in a porous medium 14 directly measures the streaming potential (voltage difference across the porous medium 14) and pressure gradient (pressure drop across the porous medium 14). The other measurements may be approximated for a given material. The zeta-potential calculation may be improved by also measuring temperature, since both permittivity and viscosity can vary (inversely) with temperature. Measuring the electrical conductivity directly may also improve the zeta-potential calculation (that is, compared to assuming an electrical conductivity of the aqueous solution). Measuring both the pH and the ion concentration (or alternatively, measuring either individually) help to account for CO2 adsorption/dissolution, thereby further improving the accuracy of the zeta-potential calculation.
In order that the application may be more fully understood, the following examples are set forth. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting in any manner.
The following example illustrates a method and system for measuring streaming potential in porous materials to determine zeta potential. In this illustrative embodiment, zeta potential may be determined for carbonate core samples. In a typical experiment, the following steps may be performed:
In another exemplary embodiment, the present disclosed methods 80 and systems 10 may be used to monitor calcium concentration before and after injection of electrolytes in a fluid filled bone. In the field of orthopedics, fluid filled bones possess piezoelectric properties which are responsible for the electrical signals generated when external forces are applied to bone. The bones may be extracted and placed within an analyzer (for example, system 10). Those stress-generated potentials may be studied using a streaming potential analyzer (for example, system 10) to address bone growth, repair, and remodeling. In this embodiment, the bone is the porous medium 14 and the fluid within the bone is the aqueous solution. The piezoelectric properties may be measured via the electrical conductivity probes 32, 34 and/or electrodes 71, 73 (for example, low voltage, low amperage (that is, 4-20 milliamp) micro-electrodes) which may be brought in contact with either end of the fluid-filled bone 14. The addition of Ca+2 ions to the solutions may be associated with a reduction in the magnitude of the streaming potential 72 consistent with the assumption that Ca+2 is specifically adsorbed. In-line monitoring of Ca+2 concentration (for example, via the ionic sensor 40, 42) before and after injection will keep track of Ca+2 level in the bone and allow for a high level of tissue engineering studies that target the stress-generated potential (SGP) in bones, which is dominated by streaming potential. Stated otherwise, using the present disclosed system 10 and methodologies 80, a more accurate determination of both the streaming potential 72 and the zeta potential may be made, thereby allowing for enhanced orthopedic patient treatments.
In another exemplary embodiment, a system 10 for determining zeta-potential in a hydrocarbon reservoir of a subterranean formation (for example, a geologic formation) may include pressure sensors 44, 46 positioned across a porous medium 14 (for example, a rock matrix of the hydrocarbon reservoir). The system 10 may include first and second electrodes 71, 73 positioned across the rock matrix 14, as well as a first pH sensor 36 and a first ionic sensor 40 positioned just prior to an entrance to the hydrocarbon reservoir through which a water flooding treatment flows. The water flooding treatment may include injecting an aqueous solution into the rock matrix 14. Voltage potential may be measured by the first and second electrode 71, 73. The system 10 may also include a second pH sensor 38 and a second ionic sensor 42 positioned within the subterranean formation at or near where the water flooding treatment exits the hydrocarbon reservoir.
Certain embodiments of the present application were described supra. It is, however, expressly noted that the application is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described in the present disclosure are also included within the scope of the application. Moreover, it is to be understood that the features of the various embodiments described in the present disclosure were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express, without departing from the spirit and scope of the application. Therefore, the disclosure should not be limited to certain implementations, but rather should be limited only by the spirit and scope of the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6939719 | Chun | Sep 2005 | B2 |
| 7028711 | Scott | Apr 2006 | B1 |
| 8302687 | Chen et al. | Nov 2012 | B2 |
| 10000687 | Al-Yousef et al. | Jun 2018 | B2 |
| 10429372 | Al-Yousef et al. | Oct 2019 | B2 |
| 20110112815 | Stukan | May 2011 | A1 |
| 20140253116 | Freedman | Sep 2014 | A1 |
| 20180259499 | Al-Yousef | Sep 2018 | A1 |
| Number | Date | Country |
|---|---|---|
| 101 54 790 | May 2003 | DE |
| WO-2021245450 | Dec 2021 | WO |
| Entry |
|---|
| Alroudhan, A. et al., Zeta potential of intact natural limestone: impact of potential-determining ions Ca, Mg and SO4, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 493:83-98 (2016). |
| Ayirala, S.C. et al., Effect of salinity and water ions on electrokinetic interactions in carbonate reservoir cores at elevated temperatures, SPE Reservoir Eval. Engin., 21.03:733-746 (2018). |
| Choi, Y.S. et al., Determination of oceanic carbon dioxide using a carbonate-selective electrode, Anal. Chem., 74.1:2435-2440 (2002). |
| De Beer, D. et al., A microsensor for carbonate ions suitable for microprofiling in freshwater and saline environments, Limnology and Oceanography: Methods, 6.1:532-541 (2008). |
| Delgado, A.V. et al., Measurement and interpretation of electro-kinetic phenomena, Jrnl. Coll. Inter. Sci., 309(2):194-224 (2007). |
| Electro-Chemical Devices, Calcium Sensor: S80 Calcium Sensors—the ECD Advantage, <https://ecdi.com/portfolio-item/calcium-sensor/>. Retrieved Nov. 26, 2019. |
| Gross, D. and Wendell, W.S. et al., Streaming potential and the electromechanical response of physiologically-moist bone, Jrnl. Biomech., 15.4:277-295 (1982). |
| Heberling, F. et al., Structure and reactivity of the calcite-water interface, Jrnl. Coll. Inter. Sci., 354(2):843-857 (2011). |
| Jackson, M.D. et al., Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding, Sci. Repo., 1-12 (2016). |
| Lee, H.J. et al., Potentiometric evaluation of solvent polymeric carbonate-selective membranes based on molecular tweezer-type neutral carriers, Anal. Chem., 72.19:4694-4699 (2000). |
| Meyerhoff, M.E. et al., Role of trifluoroacetophenone solvents and quaternary ammonium salts in carbonate-selective liquid membrane electrodes, Anal. Chem., 59.1:144-150 (1987). |
| Otter, M. et al., Streaming potentials in chemically modified bone, Jrnl. Ortho. Res., 6.3:346-359 (1988). |
| Pokrovsky, O.S. et al., Dissolution kinetics of calcite, dolomite and magnesite at 25 C and Oto 50 atm pCO2, Chem. Geo., 217(3-4):239-255 (2005). |
| Alotaibi, M. B. et al., Dynamic interactions of inorganic species at carbonate/brine interfaces: An electrokinetic study, Coll. Surf. Phys. Engin. Aspec., 550:222-235 (2018). |
| Collini, H. et al., Zeta potential in intact carbonates at reservoir conditions and its impact on oil recovery during controlled salinity waterflooding, Fuel, 266, 16 pages (2020). |
| Esmaeili, S. et al., Investigation of streaming potential coupling coefficients and zeta potential at low and high salinity conditions: Experimental and modeling approaches, Jrnl. Petro. Sci. Engin., 145:137-147 (2016). |
| International Search Report for PCT/IB2020/056629, 5 pages (dated Feb. 15, 2021). |
| Jackson, M.D. et al., Supplementary Information for Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding, Sci. Repo., 10 pages (2016). |
| Jackson, M.D. et al., Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding, Sci. Repo., 13 pages (2016). |
| Vinogradov, J. et al., Measurement of streaming potential coupling coefficient in sandstones saturated with natural and artificial brines at high salinity, Jrnl. Geophys. Res., 115, 18 pages (2010). |
| Written Opinion for PCT/IB2020/056629, 9 pages (dated Feb. 15, 2021). |
| Number | Date | Country | |
|---|---|---|---|
| 20210372275 A1 | Dec 2021 | US |
