Hydrophilic and hydrophobic superparamagnetic Fe.SUB.3.O.SUB.4 .nanoparticles as T.SUB.2.-contrast agents for oil reservoir applications
11479702 · 2022-10-25
Assignee
Inventors
Cpc classification
C09K8/03
CHEMISTRY; METALLURGY
E21B47/13
FIXED CONSTRUCTIONS
E21B49/00
FIXED CONSTRUCTIONS
H01F1/0054
ELECTRICITY
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
C09K2208/10
CHEMISTRY; METALLURGY
B82Y15/00
PERFORMING OPERATIONS; TRANSPORTING
B82Y25/00
PERFORMING OPERATIONS; TRANSPORTING
International classification
H01F1/00
ELECTRICITY
C09K8/03
CHEMISTRY; METALLURGY
E21B47/13
FIXED CONSTRUCTIONS
E21B49/00
FIXED CONSTRUCTIONS
Abstract
The invention is directed to hydrophilic and hydrophobic superparamagnetic nanoparticles and their use as contrast agents for NMR including agents that distinguish oil and water in NMR logging of geological formations containing oil or water. Methods of making these SPIONs are also described.
Claims
1. A method for making hydrophilic-Fe.sub.3O.sub.4 superparamagnetic iron oxide nanoparticles (SPIONs), comprising: mixing an iron-containing precursor with a hydrophilic ligand or capping agent to form a homogeneous suspension; heating the homogenous suspension to a temperature sufficient to bind the hydrophilic ligand to the iron-containing precursor, cooling the resulting homogenous suspension, adding a solvent to the cooled homogeneous suspension to precipitate hydrophilic-Fe.sub.3O.sub.4 SPIONs into a slurry, separating the precipitated hydrophilic-Fe.sub.3O.sub.4 SPIONs from the slurry, and washing the hydrophilic-Fe.sub.3O.sub.4 SPIONs to remove unbound hydrophilic ligands or capping agent, thereby making the hydrophilic-Fe.sub.3O.sub.4 SPIONs wherein the iron-containing precursor is iron(III) acetylacetonate, the hydrophilic ligand or capping agent is polyethylene glycol 400 (PEG-400), the heating is at a pressure of about 15 to about 45 psi and at a temperature ranging from 175 to 185° C. for at least 12 hours, the solvent is a mixture of absolute ethanol and diethylether, and the hydrophilic-Fe.sub.3O.sub.4 SPIONs are washed in ethanol.
2. The method of claim 1 that is a solvothermal method wherein the hydrophilic ligands or capping agents participate in reducing, stabilizing and capping of the hydrophilic-Fe.sub.3O.sub.4 SPIONs produced.
3. The method of claim 1, wherein the heating is performed in an autoclave or other closed controlled environment at a pressure ranging from about 15 to about 80 psi.
4. A method for making hydrophobic-Fe.sub.3O.sub.4 superparamagnetic iron oxide nanoparticles (SPIONs), comprising: mixing an iron-containing precursor with a hydrophobic ligand or capping agent to form a homogeneous suspension; heating the homogenous suspension to a temperature sufficient to bind the hydrophobic ligand or capping agent with the iron-containing precursor, cooling the homogenous suspension, adding a solvent to precipitate hydrophobic-Fe.sub.3O.sub.4 SPIONs into a slurry, separating hydrophobic-Fe.sub.3O.sub.4 SPIONs from the slurry, and washing the hydrophobic-Fe.sub.3O.sub.4 SPIONs to remove unbound hydrophobic ligand or capping agent, thereby making the hydrophobic-Fe.sub.3O.sub.4 SPIONs, wherein the iron-containing precursor is iron(III) acetylacetonate, the hydrophobic ligand or capping agent is oleylamine (OLA), the heating is at a pressure of 40 to 80 psi and at temperature ranging from 275 to 285° C. for at least 12 hours, the solvent is a mixture of absolute ethanol and diethylether, and the hydrophobic-Fe.sub.3O.sub.4 SPIONs are washed in ethanol.
5. The method of claim 4 that is a solvothermal method wherein the hydrophobic ligands or capping agents participate in reducing, stabilizing and capping of the hydrophobic-Fe.sub.3O.sub.4 SPIONs produced.
6. The method of claim 4, wherein the heating is performed in an autoclave or other closed controlled environment at a pressure ranging from about 15 to about 80 psi.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION OF THE INVENTION
(24) The inventors disclose herein a safe and simple single-step solvothermal method for the synthesis of highly-stable hydrophilic and hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) as T.sub.2-contrast agents. These SPIONs have contrast properties and stabilities that permit their employment in petroleum exploration and monitoring, such as in interrogation of oil reservoirs.
(25) The invention provides T.sub.2 contrast agents with several superior properties including (i) quenching of T.sub.2-relaxation signals with select SPIONs concentrations, (ii) excellent relaxivity properties due to ultra-small SPION size, and (iii) long-term stability including thermal stability in different media. These properties permit use of the SPIONs of the invention in harsh conditions often found in petroleum reservoirs.
(26) A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations and may be broadly classified as a conventional or unconventional reservoir. In a conventional reservoir, the naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability. While in an unconventional reservoir the rocks have high porosity and low permeability which keeps the hydrocarbons trapped in place.
(27) The SPIONs made by a method according to the invention may be used as contrast agents for magnetic (e.g., NMR) characterization or interrogation of a conventional or unconventional petroleum, gas or other liquid reservoir (or as contrast agents in magnetic imaging such as MRI).
(28) In some embodiments, the SPION-based methods for characterization or interrogation of a petroleum reservoir may be used in conjunction with a seismic survey, appraisal well, and computer modelling of a reservoir. These combined techniques may be used to assess the size, volume or uniformity of a reservoir, compartmentalization of a reservoir, the location of oil-water contact in a reservoir, height of oil-bearing sands, rock porosity, percentage of rock containing fluids or percentage of solid rock, estimate the amount of petroleum or gas or other fluid in a reservoir and recovery factor (proportion of recoverable oil or gas). Data obtained by use of the SPIONs of the invention and conventional techniques may be used to help build a computer model of a reservoir.
(29) A SPION is a superparamagnetic iron oxide nanoparticle. As demonstrated herein the surface of a SPION may be functionalized to make it more hydrophilic or hydrophobic, enhance its stability under particular conditions, such as in the presence of water, sea water, mixtures of water or sea water and oil, or in oil or other petroleum materials, or affect its ability to be magnetically detected or imaged (e.g., by NMR or MRI). It may be functionalized to reduce its ability to non-specifically bind to a substrate and to improve its ability to associate with a particular target substrate.
(30) A SPION may be made of magnetite Fe.sub.3O.sub.4 and/or its oxidized form maghemite or γ-Fe.sub.2O.sub.3. In some embodiments, a SPION of the invention will contain Fe.sub.2O.sub.3 or a mixture such as NiFe.sub.2O.sub.4, CuFe.sub.2O.sub.4, MnFe.sub.2O.sub.4 or CoFe.sub.2O.sub.4. In some embodiments a SPION, exclusive of functionalization, will consist of Fe.sub.2O.sub.3 and exclude other metallic components such as those described above or metals such as gadolinium. In many embodiments, the SPIONs of the invention will exhibit substantial thermal stability with no phase transformation between 200, 250, 300, 350, 400, 450 and 500° C.
(31) In NMR, T1 relaxation is the process by which the net magnetization (M) grows/returns to its initial maximum value (Mo) parallel to B.sub.o. Synonyms for T1relaxation include longitudinal relaxation, thermal relaxation and spin-lattice relaxation.
(32) T2 relaxation is the process by which the transverse components of magnetization (Mxy) decay or dephase. In medical MRI (NMR-based imaging), T1 images are used to highlight fat tissue, while T.sub.2 images highlight fat and water.
(33) The relaxation rates (r.sub.2 or 1/T2) for PEG-SPIONs of the invention may range between 60, 61, 62, 63, 64, 65, 66, 66.7, 67, 68, 69, 70, 71, 72-73 mM.sup.−1 s.sup.−1, preferably about 66.7; and for OLA-SPIONS from about 44, 45, 46, 47, 48, 49.0, 50, 51, 52, 53-54 mM.sup.−1s.sup.−1, preferably about 49.0.
(34) SPIONs are usually T.sub.2-based contrast agents and T.sub.2 contrast is one aspect of the invention. Hydrophilic-SPIONs help to alter T.sub.2 signal produced from water, while hydrophobic SPIONs change T.sub.2 signal produce from oil. T.sub.2 signals coming from brine saturated with hydrophilic SPIONs are different than T.sub.2 signals of brine alone. Similarly, T.sub.2 signals received from oil having with hydrophobic SPIONs is different than T.sub.2 signals of oil alone. T.sub.1-based contrast agents provide positive contrast enhancement (i.e., brighter image) which also help to distinguish the water and oil phases in the porous rock. T.sub.1-based contrast agents provide positive contrast enhancement (i.e., brighter image) which also help to distinguish the water and oil phases in the porous rock.
(35) Moreover, there is no significant advantage to use the combination of hydrophilic and hydrophobic SPIONs. T.sub.2 signals coming from brine saturated with hydrophilic SPIONs is different than T.sub.2 signal of brine alone. Similarly, T.sub.2 signal receive from oil having with hydrophobic SPIONs is different than T.sub.2 signal of oil alone.
(36) Advantageously, PEG-SPIONs (hydrophilic) can exhibit colloidal stability in water as well as in seawater. However, OLA-SPIONs (hydrophobic) can provide the colloidal stability in model oil.
(37) The average diameter of a SPIONs as disclosed herein may range from nm, 2 to 30 nm such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25, 26, 27, 28, 29 to 30 nm, and advantageously from 9, 10, 11, 12, 13, 14, or 15 nm. When the size of a SPION is greater than 30 nm, coercive forces may dominate and can cause aggregation in the presence of strong external magnetic field.
(38) The preferred average diameter of particles is ≤20 nm in order to achieve better relaxometry properties.
(39) Polyethylene glycols useful in a method according to the invention may be selected from liquid PEGs, such as those having number average molecular weights (Mn g/mol) of 200, 300, 400, 500, or 600 g/mole as well as all intermediate values within this range. PEGs may act as reducing and/or stabilizing agents that confer hydrophilic properties on a SPION. Advantageously, PEG having an average molecular weight of about 400 is used in a method according to the invention.
(40) The preferred average molecular range for PEG can be 300-500 g/mol because PEG moieties having MW<300 lack sufficient hydrophilicity while PEG moieties having MW>500 g/mol. impair permeability or stability.
(41) An unsaturated fatty amine may be used in a method according to the invention as a mild reducing and stabilizing agent or to produce a more hydrophobic SPION. Advantageously, oleylamine is used. An unsaturated fatty amine such as oleylamine can function as a solvent for a reaction mixture, as coordinating agent to stabilize the surface of nanoparticles, or as a coordinator with metal ions, and thus affect the kinetics of nanoparticle formation during their synthesis.
(42) As alternatives to oleylamine, oleic acid and other unsaturated amines such as oleylamine acetate, oleylamine hydrofluoride may be utilized to synthesized SPIONs having hydrophobic characteristics. NMR is often applied to the human body in clinical applications. The same physical principles involved in clinical imaging also apply to imaging any fluid-saturated porous media, including reservoir rocks. Nuclear magnetic resonance (NMR) may be used as a tool to interrogate a geological formation that may contain a liquid reservoir, such as a gas, oil or water reservoir. Typically an external magnetic field is imposed in the formation to make a measurement that is proportional to the porosity, regardless of lithology. This allows identification of the free- and bound-fluid volumes and the free-fluid type (gas, oil or water) and indication of permeability. In some embodiments of the invention the SPIONs disclosed herein are used as contrast agents for NMR or MRI; see http://_www.halliburton.com/public/lp/contents/Books_and_Catalogs/web/NMR-Logging-Principles-and-Applications.pdf (last accessed Aug. 20, 2018, incorporated by reference).
(43) In some embodiments of the invention, hydrophilic and/or hydrophobic SPIONS are injected during drilling of a borehole and permit NMR interrogation along the length of the borehole. In contrast to MRI where a subject is placed at the center of an MRI instrument, geological logging places the instrument itself in a wellbore at a location within the geological formation to be analyzed by magnetic resonance imaging logging or MRIL. In some embodiments, hydrophilic SPIONs are incorporated into a water-based mud and hydrophobic SPIONs into an oil-based mud during logging.
(44) Generally, SPIONs are injected into the borehole as oil-based or water-based colloidal dispersion itself. However, these SPIONs can be a part of drilling fluid and enhanced oil recovery (EOR) package. Commercially available NMR probes may be used to measure T.sub.1 and T.sub.2 relaxation signals.
(45) In other embodiments, the hydrophilic and/or hydrophobic SPIONs of the invention may be contacted or incorporated into a rock sample obtained from a geological formation which is then interrogated by NMR in a laboratory to assess porosity, permeability, water saturation, fluid displacement, hydrocarbon typing, etc.
(46) Generally, cylindrical rock cores are selected for NMR measurements. Briefly, the cores are saturated with a brine solution followed by saturation with crude oil or vice versa. The brine-oil saturated cores are completely scanned with NMR spectrometer. Then cores are cleaned by adopting a standard cleaning procedure using toluene. Similarly, the cores are saturated with a brine solution having hydrophilic SPIONs followed by saturation with crude oil. The saturated cores having contrast agents are scanned again with NMR spectrometer. Nuclear magnetic resonance (NMR) logging is a type of well logging that uses the NMR response of a formation to directly determine its porosity and permeability. It provides a continuous record along the length of a borehole. NMR logging measures the induced magnet moment of hydrogen nuclei (protons) contained within the fluid-filled pore space of porous media (reservoir rocks). Unlike conventional logging measurements (e.g., acoustic, density, neutron, and resistivity), which respond to both the rock matrix and fluid properties and are strongly dependent on mineralogy, NMR-logging measurements respond to the presence of protons (e.g., in hydrogen). Because these protons primarily occur in pore fluids, NMR effectively responds to the volume, composition, viscosity, and distribution of these fluids, for example, oil, gas or water.
(47) An important mechanism affecting NMR relaxation is grain-surface relaxation. Molecules in fluids are in constant Brownian motion, diffusing about the pore space and bouncing off the grain surfaces. Upon interaction with the grain surface, hydrogen protons can transfer some nuclear spin energy to the grain contributing to T1 relaxation or irreversibly dephase contributing to T2 relaxation. Therefore, the speed of relaxation most significantly depends on how often the hydrogen nuclei collide with the grain surface and this is controlled by the surface-to-volume ratio of the pore in which the nuclei are located. Collisions are less frequent in larger pores, resulting in a slower decay of the NMR signal amplitude and allowing a petrophysicist to understand the distribution of pore sizes.
(48) NMR logs provide information about the quantities of fluids present, the properties of these fluids, and the sizes of the pores containing these fluids. From this information, it is possible to infer or estimate the volume (porosity) and distribution (permeability) of the rock pore space, rock composition, type and quantity of fluid hydrocarbons, and hydrocarbon producibility. NMR logging provides measurements of a variety of critical rock and fluid properties in varying reservoir conditions (e.g., salinity, lithology, and texture), some of which are unavailable using conventional logging methods and without requiring radioactive sources. Whether run independently as a standalone service or integrated with conventional log and core data for advanced formation and fluid analyses, NMR logging has significantly contributed to the accuracy of hydrocarbon-reservoir evaluation. Wireline-logging devices are commercially available as are logging-while-drilling (LWD) devices and downhole NMR spectrometers; see https://_petrowiki.org/Nuclear_magnetic_resonance_(NMR)_logging (last accessed Aug. 13, 2018, incorporated by reference).
(49) NMR logging is typically performed using wireline tool or logging-while-drilling (LWD) tools. In the conventional wireline-logging technology, NMR logging is performed as the logging tool is being lowered into a drilled borehole. In the emerging LWD technology, the logging tools are generally rigged up as a part of the drilling string and follow a drill bit during actual well drilling. Each tool type has its own advantages. The wireline-tools enable high logging speeds and high-quality measurements. The LWD tools, on the other hand, provide real-time data during drilling operations that may be used to prevent loss of circulation, blowouts, stuck pipes, hole instability and other disastrous consequences of borehole drilling.
(50) The SPIONs disclosed herein may be suspended in water or sea water or other aqueous, non-aqueous, or emulsion compositions, such as drilling muds and used as contrast agents.
(51) Drilling muds are classified based on their fluid phase, alkalinity, dispersion and chemical components. They may be dispersed systems such as freshwater muds that have a low pH (7.0-9.5) and may include spud, bentonite, natural or artificial polymers, phosphate treated muds, organic mud and organic colloid treated mud. Other freshwater muds include high pH muds such as alkaline tannate-treated muds having a pH of 9.5 or more. Water based drilling muds can repress hydration and dispersion of clay and include high pH lime muds, low pH gypsum, seawater and saturated salt water muds. Water-based drilling mud most commonly contains or consists of bentonite clay (gel) with additives such as barium sulfate (barite), calcium carbonate (chalk) or hematite. Various thickeners are used to influence the viscosity of the fluid, e.g. xanthan gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. Defloculants can be used to reduce viscosity of clay-based muds; anionic polyelectrolytes (e.g. acrylates, polyphosphates, lignosulfonates (Lig) or tannic acid derivates such as Quebracho) are frequently used.
(52) Non-dispersed system muds include low solids mud and emulsions. Low solids muds contain less than 3-6% solids by volume and weight less than 9.5 lbs/gal. Most muds of this type are water-based with varying quantities of bentonite and a polymer. Two types of emulsion muds are oil in water (oil emulsion muds) and water in oil (invert oil emulsion muds). Oil based muds contain oil as the continuous phase and water as a contaminant, and not an element in the design of the mud. They typically contain less than 5% (by volume) water. Oil-based muds are usually a mixture of diesel fuel and asphalt, however can be based on produced crude oil and mud.
EXAMPLES
(53) The following examples illustrate various aspects of the present invention. They are not to be construed to limit the claims in any manner whatsoever.
(54) As described in more detail below, the surfaces of SPIONs were functionalized by bonding polyethylene glycol (PEG-400) or oleylamine (OLA) on their surfaces to respectively provide hydrophilic and hydrophobic properties to incorporate into aqueous (e.g., water, seawater, brine) or oil (e.g., crude oil) materials in a geological reservoir. Uncoated SPIONs were also prepared by coprecipitation method using NH.sub.4OH as a reducing agent for comparison. Stability of hydrophilic SPIONs was monitored in deionized (DI) water and/or artificial seawater (ASW), while stability of hydrophobic SPIONs was investigated in model oil (cyclohexane-hexadecane 1:1).
(55) X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) profiles confirmed the magnetite (Fe.sub.3O.sub.4) phase of synthesized nanoparticles (NPs). The presence of C—O (532.4 eV) and —NH.sub.2 (399.7 eV) in XPS spectra of N1s and O1s substantiated the surface functionalization of Fe.sub.3O.sub.4 NPs with PEG and OLA, respectively. Transmission electron microscopy (TEM) images demonstrated the spherical shape NPs having particle diameters 11.6±1.4, 12.7±2.2 and 9.1±3.0 for PEG-Fe.sub.3O.sub.4, OLA-Fe.sub.3O.sub.4, and Fe.sub.3O.sub.4, respectively. NMR T.sub.2-relaxation measurements were performed by an acorn area analyzer and demonstrated meaningful results for NP (SPION) use in targeted reservoir applications, for example, the transversal relaxivity (r.sub.2) values for PEG-Fe.sub.3O.sub.4 (66.7 mM.sup.−1 s.sup.−1) and OLA-Fe.sub.3O.sub.4 (49.0 mM.sup.−1 s.sup.−1) were surprisingly found to be 2.07 and 1.53 times higher than those for Fe.sub.3O.sub.4 (32.2 mM.sup.−1 s.sup.−1) NPs, respectively.
(56) Synthesis of Hydrophilic SPIONs.
(57) The hydrophilic magnetite (Fe.sub.3O.sub.4) NPs (SPIONs) were prepared by a solvothermal method using PEG-400 (Aldrich). Briefly, 6 mmol (2.185 g) of iron(III) acetylacetonate Fe(acac).sub.3 (97%, Fluka) and 75 g of PEG-400 were mixed with the help of a Silverson mixer (L5M-A, USA) in an 125 mL polytetrafluoroethylene (PTFE) vessel for 1 hr to obtain a homogenous red suspension at room temperature. The PTFE vessel was placed in a stainless steel autoclave reactor (Parr, USA) and kept in a synthetic oven (280A, Fisher Scientific) at 180° C. for 24 h. Then, the mixture was cooled down to room temperature and the black slurry of Fe.sub.3O.sub.4 was precipitated by the addition of absolute ethanol (>99%, Fisher Scientific) with an excess amount of diethyl ether (>99%, Sigma-Aldrich). The NPs were centrifuged at 10,000 rpm for 10 min using 3-30KS centrifuge (Sigma, Germany). To remove unbound PEG-400, the NPs were redispersed in absolute ethanol and centrifuged again at 20,000 rpm for 30 min. The purification procedure was repeated three-times. The final black product was labeled as PEG-Fe.sub.3O.sub.4 and divided into two equal parts. Then, half of the product was dispersed in Milli-Q water while remaining half was dried in vacuum oven at 50° C. for 24 h.
(58) Synthesis of Hydrophobic SPIONs.
(59) The hydrophobic Fe.sub.3O.sub.4 NPs were synthesized by a solvothermal method using OLA (70%, Aldrich). Briefly, 5 mmol (1.820 g) of Fe(acac).sub.3 precursor and 25 mL of OLA were mixed with the help of a Silverson mixer in 125 mL PTFE vessel for 1 h to obtain a homogenous red suspension. The PTFE vessel was placed in a stainless steel autoclave reactor and kept at 280° C. for 24 h. Then, the mixture was cooled down to room temperature. The precipitation and purification procedure of the synthesized NPs remained same as described above for the synthesis of hydrophilic Fe.sub.3O.sub.4. The final black product was labeled as OLA-Fe.sub.3O.sub.4 and divided into two equal parts. Then, half of the product was dispersed in cyclohexane-hexadecane (1:1) mixture, while the remaining half was dried in vacuum oven at 50° C. for 24 h.
(60) Synthesis of Uncoated SPIONs.
(61) The uncoated-Fe.sub.3O.sub.4 NPs were prepared by coprecipitation of Fe(III) and Fe(II) in the molar ratio (2:1) using NH.sub.4OH solution as a reducing agent. The complete reaction was carried out under an Ar atmosphere and the stirring was carried out by using overhead Teflon stirrer (IKA Eurostar, Germany). In a typical procedure, 100 mL of Milli-Q water was acidified with 1.0 mL of concentrated HCl (37%, Sigma-Aldrich) and purged with Ar gas for 15 min. Then, 1.2 M FeCl.sub.3.6H.sub.2O (>99%, Sigma-Aldrich) and 0.6 M FeCl.sub.2.4H.sub.2O (>99%, Sigma-Aldrich) aqueous solutions were prepared in acidified water. The solutions were filtered-off with 0.2-micron hydrophobic PTFE membrane filter (Millex-FG, Millipore). Then, Fe(II) solution was mixed dropwise with Fe(III) solution in a three-neck round bottom flask. The reaction mixture was heated up to 80° C. and 20 mL of NH.sub.4OH (28-30%, Sigma-Aldrich) solution was poured into the iron precursors at 500 rpm. The color of dispersion changed from golden brown to black indicating the formation of Fe.sub.3O.sub.4 NPs. The dispersion was continuously stirred, refluxed and heated for 1 hr followed by the addition of 5 mL tetramethylammonium hydroxide (25%, Sigma-Aldrich) solution to stabilize the NPs. Then, the reaction mixture was allowed to cool down to room temperature. The magnetic NPs were washed several times with absolute ethanol as described above. The final product was labeled as Fe.sub.3O.sub.4 and divided into two equal parts. Half of the product was dispersed in milli-Q water while remaining half was vacuum dried in the oven at 50° C. for 24 h.
(62) Functionality and Colloidal Stability Test.
(63) The hydrophilic functionality and colloidal stability of as-synthesized SPIONs (i.e., PEG-Fe.sub.3O.sub.4 and Fe.sub.3O.sub.4) were tested in deionized (DI, pH 7.0) water as well as artificial seawater (ASW, pH ˜8.0). ASW was prepared which meets American standard for testing and materials (ASTM). Briefly, ASW according to the ASTM D1141-98 standard was prepared by dissolving 36.03 g.Math.L.sup.−1 of a salt mixture in DI water. The composition of salt mixture was as follows; NaCl (99.5%, 24.53 g), MgCl.sub.2 (98%, 5.20 g), Na.sub.2SO.sub.4 (99%, 4.09 g), CaCl.sub.2 (99.9%, 1.16 g), KCl (99%, 0.695 g), NaHCO.sub.3 (99.7%, 0.201 g), KBr (99%, 0.101 g), H.sub.3BO.sub.3 (99.5%, 0.027 g), SrCl.sub.2 (99.9%, 0.025 g) and NaF (99%, 0.003 g). The estimated density and salinity of ASW were 1.020 g.Math.mL.sup.−1 and 36.0 gL.sup.−1 respectively. However, the hydrophobic functionality and colloidal stability of as-synthesized OLA-Fe.sub.3O.sub.4 NPs was monitored in standard model oil composed of the mixture of cyclohexane and hexadecane (1:1). For each test, as-synthesized SPIONs were dispersed in a bottle containing both, the model oil and ASW (1:1). Then, the functionality of NPs was investigated in terms of their hydrophilic or hydrophobic characteristics, while the stability of NPs was monitored in their respective media.
(64) Material Characterization.
(65) The diffraction patterns of various SPIONs were recorded using a Smart Lab X-ray diffractometer (Rigaku, Japan) with a diffraction angle (2θ) range of 15-80° at a scan rate of 2°/min. Surface analysis of the synthesized magnetic materials was performed using an X-ray photoelectron spectrometer (ESCALAB 250Xi, Thermo Scientific, UK). The thermal behavior of functionalized NPs was studied using differential scanning calorimeter (DSC 204 F1 Phoenix, NETZSCH, Germany). DSC measurements were performed in the temperature range 20-500° C. with a scan rate of 10° C./min under N.sub.2 environment to avoid material oxidation. The surface morphology, size, and shape of the synthesized SPIONs were evaluated by using a field emission scanning electron microscope (FESEM-Tescan Lyra-3) as well as a transmission electron microscope (JEM-2100, JEOL, USA). TEM grids were coated by putting slurry of the analyte onto 200 mesh copper grids. The grids were examined after 1 hr of initial degassing under vacuum. An inductively coupled plasma atomic emission spectrometer (ICP-AES, Varian) was used to estimate the Fe content in as-synthesized SPIONs.
(66) To determine the feasibility of contrast agents, T.sub.2-relaxation curves for various concentrations of SPIONs were attained using an acorn area analyzer (Xigo Nanotools, UK), which is normally used for surface area measurements; R. Tantra, Nanomaterial Characterization: An Introduction, John Wiley & Sons, 2016. The suitability of this miniaturized technique to obtain meaningful results is demonstrated here first time by showing its potential for targeted reservoir applications. For all the measurements, values of tau (τ) and the total number of scans were kept constant, i.e., τ=0.5 ms, scans=4.
(67) Functionality and Colloidal Stability of Synthesized SPIONs.
(68) The functionality and colloidal stability of SPIONs are important factors related to their ultimate use in oil exploration industries for reservoir applications.
(69) The colloidal stability of as-synthesized SPIONs was monitored in mixed oil-DI water and oil-seawater phases.
(70) Similarly,
(71) Crystal Structure, Phase, and Chemical Composition Analysis.
(72) The phase, purity and crystal structures of as-synthesized SPIONs were examined via XRD analysis.
(73) TABLE-US-00001 TABLE 1 Comparison of various parameters of as-synthesized SPIONs. Crystallite Unit cell Unit cell TEM Synthesis Reducing size parameter volume Phase diameter SPIONs method agent (nm) (Å) (Å.sup.3) composition (nm) PEG-Fe.sub.3O.sub.4 Solvothermal Polyethylene 13.3 8.377 587.9 Magnetite 11.6 ± 1.4 180° C. 24 h glycol-400 OLA-Fe.sub.3O.sub.4 Solvothermal Oleylamine 14.1 8.385 589.4 Magnetite 12.7 ± 2.2 280° C. 24 h Fe.sub.3O.sub.4 Coprecipitation Ammonium 9.6 8.299 571.7 Magnetite 9.1 ± 3.0 80° C. 1 h hydroxide
(74) The comparison indicates that PEG-Fe.sub.3O.sub.4 and OLA-Fe.sub.3O.sub.4 have almost similar values of unit cell parameters, perhaps owing to the same synthetic protocol (solvothermal method). However, the uncapped-Fe.sub.3O.sub.4 NPs synthesized via the co-precipitation method possess lower unit cell parameters. This difference of values suggests that synthetic protocols play a pivotal role in controlling the crystal structure of NPs; Y. V. Kolen'ko, M. Bañobre-López, C. Rodríguez-Abreu, E. Carbó-Argibay, A. Sailsman, Y. Piñeiro-Redondo, M. F. Cerqueira, D. Y. Petrovykh, K. Kovnir and O. I. Lebedev, J. Phys. Chem. C, 2014, 118, 8691-8701. It is well-documented that magnetite (Fe.sub.3O.sub.4) and maghemite (γ-Fe.sub.2O.sub.3) exhibit almost similar XRD patterns; X. Zhang, Y. Niu, X. Meng, Y. Li and J. Zhao, CrystEngComm, 2013, 15, 8166-8172. Therefore, the phase analysis of as-synthesized SPIONs was further explored via XPS technique, which exclusively determines various phases of iron oxides, i.e., magnetite, maghemite, and hematite.
(75) A survey of PEG-Fe.sub.3O.sub.4, OLA-Fe.sub.3O.sub.4, and Fe.sub.3O.sub.4 spectra (
(76) Surface Functionalization.
(77) The presence of hydrophilic and hydrophobic coating on the surface of SPIONs was investigated using two complementary techniques: XPS and DSC.
(78) The XPS profiles also give evidence for the presence of an amorphous coating on the surface of the NPs. The presence of amine (—NH.sub.2) groups in XPS spectrum of OLA-Fe.sub.3O.sub.4 indicates surface functionalization of the NPs. It is reported that the binding-energy values corresponding to bonded amines are observed in the range 398-400 eV; M. Aslam, E. A. Schultz, T. Sun, T. Meade and V. P. Dravid, Cryst. Growth Des., 2007, 7, 471-475. A symmetric peak with low intensity detected at 399.7 eV in the N1s spectrum (
(79) DSC was further employed to investigate the organic surface coating, thermal stability and phase transformations of the magnetite NPs at elevated temperature.
(80) Surface Morphology and Particle Size Analysis.
(81) Surface morphology and particle size of as-synthesized SPIONs were investigated via FESEM and TEM techniques. High and low-resolution FESEM images of (a) PEG-Fe.sub.3O.sub.4, (b) OLA-Fe.sub.3O.sub.4, and (c) Fe.sub.3O.sub.4 are shown in
(82) The comparison indicates that the solvothermal protocol allows control of shape and size of NPs as compared to the coprecipitation method. Spherical shaped NPs are predominantly formed in the synthesis of Fe.sub.3O.sub.4 owing to the low surface area per unit volume, and hence minimum surface free-energy; D. K. Kim, M. Mikhaylova, Y. Zhang and M. Muhammed, Chem. Mater., 2003, 15, 1617-1627. This is attributed the nucleation rate per unit area which is isotropic at the NP interfaces, which results in minimization of surface free-energy; D K. Kim, et al., 2003, id. Therefore, the equivalent growth rate in all directions of nucleation leads to the formation of high and low resolution TEM images of (a) PEG-Fe.sub.3O.sub.4, (b) OLA-Fe.sub.3O.sub.4, and (c) Fe.sub.3O.sub.4 are shown in
(83) Growth Mechanism of SPIONs.
(84) The possible growth mechanism of these as-synthesized SPIONs is proposed below. The PEG-400 and OLA can be considered high-boiling solvents playing three roles (reducing, stabilizing, and capping agents) in the solvothermal synthesis of SPIONs. The mechanism of Fe.sub.3O.sub.4 NPs formation may become more complicated when metal-organic salts Fe(acac).sub.3 are used as precursors. At an elevated temperature, Fe(acac).sub.3 precursor decomposes and liberate Fe.sup.3+ ions. PEG-400 and OLA are oxidized at high temperature and generate electrons reducing Fe.sup.3+ to Fe.sup.2+. PEG-400 is a stronger reducing agent and generates Fe.sub.3O.sub.4 NPs at a relatively low temperature (e.g., 180° C.), whereas OLA, being a mild reducing agent generates the NPs at a relatively higher temperature (e.g., 280° C.). These organic solvent/additives effectively controlled the particle growth and prevented aggregation. Spherical-shaped NPs were predominantly formed due to the minimum surface free-energy. However, the synthesis of SPIONs by the coprecipitation method using Fe.sup.3+ and Fe.sup.2+ ions was pH-dependent based on the following chemical reaction (F. Sayar, G. Güven and E. Pişkin, Colloid Polym. Sci., 2006, 284, 965):
2 Fe.sup.3++Fe.sup.2++8 OH.sup.−.fwdarw.Fe.sub.3O.sub.4+4H.sub.2O (1)
(85) According to above equation (1), a complete co-precipitation of Fe.sub.3O.sub.4 NPs was observed for pH above 7, while also keeping the molar ratio (2:1) between Fe.sup.3+ and Fe.sup.2+ under a non-oxidizing environment. In this case, pH was adjusted to ˜9.0 using NH.sub.4OH as a precipitating agent and the NPs were stabilized with tetramethylammonium hydroxide solution.
(86) T.sub.2-Relaxation and Relaxometric Studies.
(87) Spin-spin relaxation NMR (T.sub.2-relaxation) measurements were performed to investigate the possibility employing these SPIONs as T.sub.2-contrast agents for oil reservoir applications. The measurements were carried out for various concentrations of Fe in the as-synthesized SPIONs as shown in
(88) Before T.sub.2-measurements, the Fe contents present in the samples were estimated with the help of ICP-AES analysis and were determined to be 57.9, 61.5 and 68.8 wt % of Fe content for PEG-Fe.sub.3O.sub.4, OLA-Fe.sub.3O.sub.4, and Fe.sub.3O.sub.4, respectively. Six concentrations of Fe (mM), i.e., 0.012, 0.024, 0.060, 0.12, 0.24 and 0.48 were prepared to determine the relaxometric properties of hydrophilic and hydrophobic samples in ASW and model oil, respectively.
(89) T.sub.2-relaxation measurements of (a) PEG-Fe.sub.3O.sub.4, (b) OLA-Fe.sub.3O.sub.4, and (c) Fe.sub.3O.sub.4 SPIONs with respect to Fe concentration are shown in
(90) The relaxation process took place due to energy exchange between neighboring protons in solvent molecules. SPIONs induced inhomogeneity in the presence of an applied magnetic field, which resulted in the de-phasing of magnetic moments of protons and led to the quenching of the T.sub.2 signal. This decrease in T.sub.2-relaxation time with Fe concentration indicates that these NPs can act as T.sub.2-contrast agents for oil reservoir applications.
(91) The relaxivity properties were investigated by plotting various Fe concentration (mM) against relaxation time (1/T.sub.2, s.sup.−1), as shown in
1/T.sub.2=1/T.sub.2º+r.sub.2[Fe] (2)
(92) Where, T.sub.2, T.sub.2º, r.sub.2, and [Fe] are the relaxation time of NPs dispersion, pure solvent, transversal relaxivity and iron concentration (mM). The estimated r.sub.2 values were found to be 66.7, 49.0, and 32.2 mM.sup.−1 s.sup.−1 for PEG-Fe.sub.3O.sub.4, OLA-Fe.sub.3O.sub.4, and Fe.sub.3O.sub.4 SPIONs respectively.
(93) The higher r.sub.2 values for PEG-Fe.sub.3O.sub.4 and OLA-Fe.sub.3O.sub.4 indicated that the capped-Fe.sub.3O.sub.4 showed excellent relaxivity properties owing to their higher dispersion in the respective media as compared to uncapped Fe.sub.3O.sub.4.
(94) The estimated r.sub.2 value for PEG-Fe.sub.3O.sub.4 was competitive with the commercial contrasting agents such as SHU-555C (r.sub.2=69 mM.sup.−1 s.sup.−1) and 10 times higher than Gd-DTPA (r.sub.2=5.3 mM.sup.−1 s.sup.−1).sup.19. A comparison of various T.sub.2-contrast agents is provided in Table 2.
(95) TABLE-US-00002 TABLE 2 Comparison of various T.sub.2-contrast agents for MRI applications. Particle Field Sample Synthesis Colloidal size strength r.sub.2 composition method stability (nm) (T) (mMs.sup.−1) Refs. Fe.sub.3O.sub.4 Polyol H.sub.2O, PBS 8 1.5 82.7 A USMIO-Fe.sub.3O.sub.4 Coprecipitation H.sub.2O 6.6 0.47 33.9 B MION-Fe.sub.3O.sub.4 Coprecipitation — 4.6 — 34.8 C USPIO-Fe.sub.3O.sub.4 Coprecipitation 0.9% saline 4.9 0.47 53.1 D US-Fe.sub.3O.sub.4 Coprecipitation pH: 5.3-8.5 4.6 7 64.4 E US-Fe.sub.3O.sub.4 Coprecipitation pH: 5.3-8.5 2.2 7 28.6 E PEG-Fe.sub.3O.sub.4 Solvothermal H.sub.2O, seawater 11.6 1.5 66.7 Inv. OLA-Fe.sub.3O.sub.4 Solvothermal H.sub.2O, seawater 12.7 1.5 49.0 Inv. US: Ultra-small, MIO: Magnetic iron oxide, PIO: Paramagnetic iron oxide, PBS: Phosphate buffered saline. Inv = invention. A = J. Wan, W. Cai, X. Meng and E. Liu, Chem. Commun. (Cambridge, U.K.), 2007, 5004-5006. B = E. V. Groman, J. C. Bouchard, C. P. Reinhardt and D. E. Vaccaro, Bioconjugate Chem., 2007, 18, 1763-1771. C = T. Shen, R. Weissleder, M. Papisov, A. Bogdanov and T. J. Brady, Magn. Reson. Med., 1993, 29, 599-604. D = H. K. Pannu, K. P. Wang, T. L. Borman and D. A. Bluemke, J. Magn. Reson. Imaging, 2000, 12, 899-904. E = G. Wang, X. Zhang, A. Skallberg, Y. Liu, Z. Hu, X. Mei and K. Uvdal, Nanoscale, 2014, 6, 2953-2963,
(96) These outcomes suggest that theses functionalized SPIONs can be effectively used as T.sub.2-contrast agents for reservoir applications due to their excellent relaxivity properties.
(97) As shown herein, highly-stable hydrophilic and hydrophobic SPIONs contrast agents were successfully prepared using a single-step solvothermal method. Hydrophilic and hydrophobic characteristics were induced on the surfaces of the magnetite NPs by adsorbing either PEG-400 or OLA, respectively. The additives (PEG-400 and OLA) played three roles, i.e., as reducing, stabilizing, and capping agents during the synthesis processes.
(98) The hydrophilic and hydrophobic SPIONs were found to be stable in ASW (36.03 gL.sup.−1 salt in distilled water) and model oil (cyclohexane-hexadecane 1:1), respectively, which is a requirement for efficient use in a harsh oil reservoir environment.
(99) The magnetite phase having cubic inverse spinel structure with Fd-3m space group was confirmed by XRD.
(100) The surface functionalization of capped-NPs was established by the presence of C—O and —NH.sub.2 groups in XPS spectra. TEM images demonstrated the spherical shape of as-synthesized NPs having ultra-small diameters <15 nm, which is a suitable size for passing through reservoir rock cores.
(101) The suitability of NMR T.sub.2-relaxation as a measurement tool, i.e., miniaturized acorn area analyzer in this case was successfully demonstrated here for the first time for oil reservoir applications.
(102) The estimated r.sub.2 value for PEG-Fe.sub.3O.sub.4 (66.7 mM.sup.−1 s.sup.−1) is competitive with the commercial contrasting agents such as SHU-555C (r.sub.2=69 mM.sup.−1 s.sup.−1) and higher than Gd-DTPA (r.sub.2=5.3 mM.sup.−1 s.sup.−1) (Z. Li, et al., 2012, id.) as well as reported values in literature (Table 2).
(103) The observed excellent relaxivity properties due to their ultra-small sizes and long-term stability in the respective medium show these hydrophilic and hydrophobic SPIONs to be useful T.sub.2-contrast agents for oil reservoir applications. Moreover, these properties are consistent with their utility as contrast agents for MRI and nanosensors for remote interrogation in both biomedical and oil reservoir applications.
(104) Terminology.
(105) Terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
(106) The headings (such as “Background” and “Summary”) and sub-headings used herein are intended only for general organization of topics within the present invention, and are not intended to limit the disclosure of the present invention or any aspect thereof. In particular, subject matter disclosed in the “Background” may include novel technology and may not constitute a recitation of prior art. Subject matter disclosed in the “Summary” is not an exhaustive or complete disclosure of the entire scope of the technology or any embodiments thereof. Classification or discussion of a material within a section of this specification as having a particular utility is made for convenience, and no inference should be drawn that the material must necessarily or solely function in accordance with its classification herein when it is used in any given composition.
(107) As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
(108) It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.
(109) As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”.
(110) Links are disabled by deletion of http: or by insertion of a space or underlined space before www. In some instances, the text available via the link on the “last accessed” date may be incorporated by reference.
(111) As used herein in the specification and claims, including as used in the examples and unless otherwise expressly specified, all numbers may be read as if prefaced by the word “substantially”, “about” or “approximately,” even if the term does not expressly appear. The phrase “about” or “approximately” may be used when describing magnitude and/or position to indicate that the value and/or position described is within a reasonable expected range of values and/or positions. For example, a numeric value may have a value that is +/−0.1% of the stated value (or range of values), +/−1% of the stated value (or range of values), +/−2% of the stated value (or range of values), +/−5% of the stated value (or range of values), +/−10% of the stated value (or range of values), +/−15% of the stated value (or range of values), +/−20% of the stated value (or range of values), etc. Any numerical range recited herein is intended to include all subranges subsumed therein.
(112) Disclosure of values and ranges of values for specific parameters (such as temperatures, molecular weights, weight percentages, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if parameter X is exemplified herein to have values in the range of 1-10 it also describes subranges for Parameter X including 1-9, 1-8, 1-7, 2-9, 2-8, 2-7, 3-9, 3-8, 3-7, 2-8, 3-7, 4-6, or 7-10, 8-10 or 9-10 as mere examples. A range encompasses its endpoints as well as values inside of an endpoint, for example, the range 0-5 includes 0, >0, 1, 2, 3, 4, <5 and 5.
(113) As used herein, the words “preferred” and “preferably” refer to embodiments of the technology that afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the technology. As referred to herein, all compositional percentages are by weight of the total composition, unless otherwise specified. As used herein, the word “include,” and its variants, is intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that may also be useful in the materials, compositions, devices, and methods of this technology. Similarly, the terms “can” and “may” and their variants are intended to be non-limiting, such that recitation that an embodiment can or may comprise certain elements or features does not exclude other embodiments of the present invention that do not contain those elements or features.
(114) Although the terms “first” and “second” may be used herein to describe various features/elements (including steps), these features/elements should not be limited by these terms, unless the context indicates otherwise. These terms may be used to distinguish one feature/element from another feature/element. Thus, a first feature/element discussed below could be termed a second feature/element, and similarly, a second feature/element discussed below could be termed a first feature/element without departing from the teachings of the present invention.
(115) The description and specific examples, while indicating embodiments of the technology, are intended for purposes of illustration only and are not intended to limit the scope of the technology. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features, or other embodiments incorporating different combinations of the stated features. Specific examples are provided for illustrative purposes of how to make and use the compositions and methods of this technology and, unless explicitly stated otherwise, are not intended to be a representation that given embodiments of this technology have, or have not, been made or tested.
(116) All publications and patent applications mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference, especially referenced is disclosure appearing in the same sentence, paragraph, page or section of the specification in which the incorporation by reference appears.
(117) The citation of references herein does not constitute an admission that those references are prior art or have any relevance to the patentability of the technology disclosed herein. Any discussion of the content of references cited is intended merely to provide a general summary of assertions made by the authors of the references, and does not constitute an admission as to the accuracy of the content of such references.