MgAlxGeyO3:zPr3+ PHOSPHORS AS TRACERS IN OIL RECOVERY APPLICATIONS
20250264413 ยท 2025-08-21
Assignee
Inventors
Cpc classification
International classification
C09K8/58
CHEMISTRY; METALLURGY
Abstract
A method including exciting a nanophosphor tracer of a compound of formula MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles, where x+y=1, and z is 0.1-0.5% with light, and further injecting the nanophosphor tracer at a first location in a subterranean geological reservoir where the nanophosphor tracer mixes with a subsurface fluid in the subterranean geological reservoir. The method further includes collecting a fluid sample from a second location in the subterranean geological reservoir and analyzing the fluid sample to detect the presence of the nanophosphor tracer in the fluid sample.
Claims
1: A method, comprising: exciting a nanophosphor tracer with light; injecting the nanophosphor tracer at a first location in a subterranean geological reservoir, wherein the nanophosphor tracer mixes with a subsurface fluid in the subterranean geological reservoir; collecting a fluid sample from a second location in the subterranean geological reservoir; and analyzing the fluid sample to detect a presence of the nanophosphor tracer in the fluid sample, wherein the nanophosphor tracer, comprises: MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles, wherein x and y are each greater than 0 and x+y=1, wherein z is 0.1-0.5 at. %, relative to total number of atoms in the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles, and wherein following the exciting the nanophosphor tracer emits light for at least 3 hours.
2: The method of claim 1, further comprising: determining a subsurface fluid-flow pattern in the subterranean geological reservoir based on the presence of the nanophosphor tracer in the fluid sample.
3: The method of claim 1, wherein the analyzing comprises: acquiring a persistent luminescence spectrum of the fluid sample, wherein the acquiring does not include further exciting of the fluid sample.
4: The method of claim 1, wherein the analyzing comprises: acquiring a time-dependent persistent luminescence spectrum of the fluid sample, wherein the acquiring does not include further exciting of the fluid sample.
5: The method of claim 1, wherein the analyzing occurs up to 15 hours after the exciting.
6: The method of claim 1, wherein following the exciting the nanophosphor tracer emits light having a wavelength of 600-650 nm, 900-910 nm, and 1050-1100 nm.
7: The method of claim 1, wherein the nanophosphor tracer emits light having a wavelength of 600-650 nm for up to 15 hours following exciting with 200-300 nm light.
8: The method of claim 1, wherein the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have a formula of MgAl.sub.0.05Ge.sub.0.95O.sub.3:0.3% Pr.sup.3+.
9: The method of claim 1, wherein the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have an orthorhombic crystal structure.
10: The method of claim 1, wherein the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have an average size of 10-500 nm.
11: The method of claim 1, wherein the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have a concentration of 1-1,000 ppb, based on a total volume of the subsurface fluid.
12: The method of claim 1, wherein the exciting comprises irradiating the nanophosphor tracer with UV light having a wavelength of 200-300 nm for at least 1 minute.
13: The method of claim 1, wherein the analyzing is in real time at the second location.
14: The method of claim 1, further comprising repeating the collecting and the analyzing at 3-50 additional locations.
15: The method of claim 1, further comprising: repeatedly exciting the nanophosphor tracer following the injecting inside of the subterranean geological reservoir.
16: The method of claim 1, wherein the subsurface fluid comprises at least one of natural gas, crude oil, connate water, or seawater.
17: The method of claim 1, wherein the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles are made by a method comprising: mixing an Al salt, Mg salt, GeO.sub.2, and a Pr salt in solvent with a complexing agent to form a first mixture; dehydrating the first mixture to a temperature of 50-100 C. to form a polymeric complex; heating the polymeric complex for at least 10 hours at a temperature of 80-110 C. to form a foam; combusting the foam at a temperature of 400-600 C. to form a powder; and calcining the powder at a temperature of 500-1,500 C. to form the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles.
18: The method of claim 17, wherein a molar ratio of the Al salt, Mg salt, GeO.sub.2, and a Pr salt to the complexing agent is 1 to 1-5.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
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DETAILED DESCRIPTION
[0048] When describing the present disclosure, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.
[0049] Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings wherever applicable, in that some, but not all embodiments of the disclosure are shown.
[0050] In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words a, an and the like generally carry a meaning of one or more, unless stated otherwise.
[0051] Furthermore, the terms approximately, approximate, about, and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.
[0052] Where a numerical limit or range is stated herein, the endpoints are included. Also, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.
[0053] The use of the terms include, includes, including, have, has, or having should be generally understood as open-ended and non-limiting unless specifically stated otherwise.
[0054] As used herein, nanoparticles are particles having a particle size of 1 nm to 500 nm within the scope of the present invention.
[0055] As used herein, luminescence or photoluminescence is the spontaneous emission of radiation from an electronically excited species (or from a vibrationally excited species) not in thermal equilibrium with its environment. Generally, the emission of light is due to the movement of electrons between different energy levels within an atom after excitation by external factors.
[0056] As used herein, persistent luminescence or phosphorescence is a type of photoluminescence related to fluorescence. When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluorescence, a phosphorescent material does not immediately reemit the radiation it absorbs. Instead, a phosphorescent material absorbs some of the radiation energy and reemits it for a much longer time after the radiation source is removed.
[0057] As used herein, a nanophosphor is a nanoparticle which displays persistent luminescence.
[0058] As used herein a tracer refers a material used in the oil industry in order to qualitatively or quantitatively gauge how fluid flows through the reservoir. Tracers can be used in either interwell tests or single well tests. In interwell tests, the tracer is injected at one well along with the carrier fluid (e.g., water in a waterflood or gas in a gasflood) and detected at a producing well after some period of time, which can be anything from days to years. In single well tests, the tracer is injected into the formation from a well and then produced out the same well. Tracers can be radioactive or chemical, solid, gas or liquid.
[0059] As used herein, a geological reservoir or reservoir is a body of rock or geological formation having a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations.
[0060] As used herein, a borehole refers to a shaft that is drilled into the geological formation, for purposes such as extracting water, petroleum or natural gas, or mineral exploration and other environmental investigations. An average depth of the borehole is from 100 to 5,000 m, preferably 500 to 4,500 m, 1,000 to 4,000 m, 1,500 to 3,500 m, or 2,000 to 3,000 m. The borehole is drilled in any suitable location wherein the geological formation has a suitable thickness. The borehole may be empty, e.g., contain only ambient atmospheric air, or may contain other fluids such as gaseous and/or liquid hydrocarbons and/or aqueous compositions such as freshwater, salt water, seawater or formation water.
[0061] As used herein, an injection well or well is a device that places fluid deep underground into a rock formation. The injection well can be installed into the borehole to inject the liquid. For example, the liquid of the present disclosure includes the nanophosphor tracer. The injection well may be present mainly on the surface outside the borehole or may be fully or partially disposed inside the borehole. For example, pressurization equipment used to pressurize one or more fluids for injection into the borehole may be located outside the well preferably connected to a wellhead that is mainly outside the borehole. Other elements of an injection well such as a bore tube are preferably disposed mainly in the borehole, e.g., extending downwards into the borehole for a distance and may include devices such as packers to form a seal inside the borehole.
[0062] A nanophosphor tracer, also referred to as the nanoparticles, is described. The nanophosphor tracer includes MgGeO.sub.3 as a host material. In some embodiments, the MgGeO.sub.3 is doped with at least one first element selected from the group consisting of aluminum (Al), silicon (Si), gallium (Ga), zinc (Zn), copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), chromium (Cr), cadmium (Cd), tin (Sn), and antimony (Sb). In a preferred embodiment, the first element is Al, where the Al is Al(I), Al(II), or Al(III). In some embodiments, the Al replaces a portion of the Ge atoms in the MgGeO.sub.3, therefore the nanophosphor tracer has a formula of MgAl.sub.xGe.sub.yO.sub.3 where x+y=1. In some embodiments, the first element is included in an amount of 0.01-99 mol %, preferably 0.1-90 mol %, 1-80 mol %, 10-70 mol %, or 40-60 mol % relative to a total amount of the first element and the germanium (Ge) in the MgGeO.sub.3.
[0063] In some embodiments, the MgGeO.sub.3 is doped with the first element and at least second one element selected from the group consisting of lanthanum (Ln), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and praseodymium (Pr). In a preferred embodiment, the second element is Pr, where the Pr is Pr.sup.3+. In some embodiments, the second element is included in an amount of 0.1-10 at %, preferably 0.5-9 at %, 1-8 at %, 2-7 at %, 3-6 at %, or 4-5 at % relative to a total amount of atoms in the nanoparticles.
[0064] In a most preferred embodiment, the nanophosphor tracer includes MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles, where x+y=1, and z is in a range of 0.1-0.5%. In an embodiment, x is in the range of 0.01 to 0.99, preferably 0.02 to 0.9, preferably 0.03 to 0.8, preferably 0.035 to 0.6, preferably 0.04 to 0.4, preferably 0.05 to 0.1, more preferably about 0.05. In an embodiment, y is in the range of 0.01 to 0.99, preferably 0.1 to 0.98, preferably 0.2 to 0.97, preferably 0.3 to 0.96, preferably 0.5 to 0.95, preferably 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, and more preferably about 0.95. In an embodiment, z is 0.1, 0.2, 0.3, 0.4, or 0.5, preferably 0.3, and refers to an atomic percent based on a total number of atoms in the nanoparticles. In a preferred embodiment, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have a formula of MgAl.sub.0.05Ge.sub.0.95O.sub.3:0.3Pr.sup.3+.
[0065] In some embodiments, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, or cubic crystal structure. In some embodiments, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have an orthorhombic crystal structure. In some embodiments, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have various morphological shapes, such as nanowires, nanocrystals, nanorectangles, nanosheets, nanotriangles, nanopentagons, nanohexagons, nanoprisms, nanodisks, nanocubes, nanoribbons, nanoblocks, nanobeads, nanotoroids, nanodiscs, nanobarrels, nanogranules, nanowhiskers, nanoflakes, nanofoils, nanopowders, nanoboxes, nanostars, tetrapods, nanobelts, nano-urchins, nanoflowers, etc. and mixtures thereof. In some embodiments, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have varied particle sizes of 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500 nm, with the average size of the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles in the range of 10-500 nm.
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[0067] At step 52, the method 50 includes exciting a nanophosphor tracer with light. In some embodiments, the nanophosphor tracer may be dissolved in a suitable solvent prior to excitation. It is generally preferred to choose a solvent that offers a high degree of solubility in fluids that naturally occur and circulate in reservoirs (for example, water or hydrocarbon compounds) and a relatively weak affinity for the various bedrock and earth formations that the tracers are exposed to while moving through the reservoir. In an embodiment, the solvent is water. In some embodiments, the solvent is an oil, preferably a crude oil, or a mixture of oil and water. Optionally, other oils known in the art may be used as well.
[0068] After dissolving the nanophosphor tracer in a suitable solvent, the nanophosphor tracer is excited by irradiating the nanophosphor tracer with light having a wavelength of 200-300 nm, preferably 205-300 nm, preferably 210-300 nm, preferably 220-300 nm, preferably 230-300 nm, preferably 240-300 nm, preferably 240 nm, preferably 250 nm, preferably 260 nm, preferably 270 nm preferably 280 nm, preferably 290 nm, and more preferably 240-260 nm, and yet more preferably 250-254 nm for at least 1 minute, preferably 2 minutes, preferably 3 minutes, preferably 4 minutes, and more preferably for 5 minutes. However, in some embodiments, the nanophosphor tracer may be excited at higher wavelengths in a range of 300-700 nm, preferably 400-650 nm, preferably 400-600 nm, preferably 430-500 nm for at least 1 minute, preferably 2 minutes, preferably 3 minutes, preferably 4 minutes, and more preferably for 5 minutes. In some embodiments, the excitation by irradiation at the suggested wavelengths may be carried out in periodic regular/irregular intervalsfor example, the irradiation may be carried out after every 10 seconds, 15 seconds, 30 seconds, 45 seconds, 1 minute, 2 minutes, 3 minutes, etc. In an embodiment, the nanophosphor tracer is irradiated by ultraviolet (UV) light.
[0069] At step 54, the method 50 includes injecting the nanophosphor tracer at a first location in a subterranean geological reservoir (also referred to as the reservoir). The nanophosphor tracer is injected into the first location (or an injection well) in the reservoir. Inside the reservoir is a subsurface fluid. The subsurface fluid includes at least one of natural gas, crude oil, connate water, and seawater. The nanophosphor tracer can mix with the subsurface fluid under the first location. For example, the nanophosphor tracer can diffuse into the fluid or mix with the fluid due to advection. In some embodiments, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles have a concentration of 1-1,000 parts per billion (ppb), preferably 100-900 ppb, 200-800 ppb, 300-700 ppb, or 400-600 ppb, based on a total volume of the subsurface fluid. In some embodiments, the amount of MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles injected is based on such concentrations.
[0070] The subsurface fluid including the nanophosphor tracer, may take various pathways/patters inside the reservoir. Inside the reservoir, the nanophosphor tracer emits light with wavelengths of 600-650 nm, 900-910 nm, and 1050-1100 nm, preferably 610-640 nm, 902-908 nm, 1060-1090 nm, and more specifically, 625 nm, 905 nm, and 1089 nm. The nanophosphor tracer imparts persistent luminescence properties where it emits light for at least 3 hours, preferably 3-15 hours after excitation, 4-14 hours, 5-13 hours, 6-12 hours, 7-11 hours, or 8-10 hours. In a specific embodiment, the nanophosphor tracer emits light having a wavelength of 600-650 nm, preferably 610-640 nm, preferably 620-630 nm, preferably 625 nm, for up to 15 hours following excitation with 200-300 nm light.
[0071] At step 56, the method 50 includes collecting a fluid sample from a second location in the subterranean geological reservoir. The second location is the location from which the fluid sample is extracted or collected from the reservoir (also referred to as a point of extraction). In an embodiment, the fluid sample collected from the second location may include, in addition to the nanophosphor tracer, materials and compounds typically found in the earth's crust, for example, water, heavy metals (for example, iron, manganese, chromium, vanadium, or zirconium), salts (for example, potassium salts, calcium salts, magnesium salts, or sodium salts (for example, sodium chloride)), naturally occurring radioactive material (for example, uranium, thorium, radium, or radon), zinc, lead, sulfur, barium, or any combination thereof. In some embodiments, the fluid sample includes hydrocarbons (for example, hydrocarbons derived from various forms of petroleum including, but not limited to, paraffinic petroleum, paraffinic-naphthenic petroleum, naphthenic petroleum, paraffinic-naphthenic-aromatic petroleum, and aromatic petroleum) and polyaromatic hydrocarbons. In some embodiments, the fluid sample collected from the second location may be purified before analysis to eliminate spectral contributions from the other components (that is, background noise) during measurement. In some embodiments, the fluid sample may be collected from multiple locations, for example, at least 3-50 locations, preferably 5-45, 10-40, 15-35, or 20-30 locations. Collecting the fluid sample at multiple locations helps to determine the fluid flow pattern and specifically the well contributing towards hydrocarbon production.
[0072] At step 58, the method 50 includes analyzing the fluid sample to detect a presence of the nanophosphor tracer in the fluid sample. The fluid sample from the second location is analyzed to detect the presence of the nanophosphor tracer. The presence of the nanophosphor tracer at the point of extraction/second location is indicative of a connection existing between the point of injection (the first location) and the point of extraction (the second location) and, if connected, can also indicate how fluid flows through the reservoir. For example, if the nanophosphor tracer is introduced into the first location and subsequent sample extraction from the second location shows the presence of the nanophosphor tracer, a connection exists between the point of injection and the point of extraction. The luminescence imparted by the nanophosphor tracer is captured by well-known imaging techniques known in the art such as but not limited to a spectrofluorometer or a cooled charge-coupled device (CCD) camera.
[0073] The method may further include determining a subsurface fluid-flow pattern in the subterranean geological reservoir based on the presence of the nanophosphor tracer in the fluid sample. The fluid flow pattern within the reservoir is determined based on the detected luminescence emitted by the nanophosphor.
[0074] In some embodiments, the method of analyzing the fluid sample includes acquiring a persistent luminescence spectrum of the fluid sample, wherein the step of acquiring does not include further exciting of the fluid sample. The persistent luminescence spectrum shows the presence of the nanophosphor tracer in the fluid sample and if the sample is analyzed within the timeframe of the persistent luminescence of the nanophosphor tracer (i.e., within 15 hours at 600-650 nm) the sample does not need to be re-excited. Without the need for re-excitation, there is less background noise imparted by the photoluminescence of the components of the oil (such as aromatic compounds) and provides a more accurate and higher sensitivity analysis.
[0075] In some embodiments, the method of analyzing the fluid sample includes acquiring a time-dependent persistent luminescence spectrum of the fluid sample, wherein the step of acquiring does not include further exciting of the fluid sample. The time-dependent persistent luminescence spectrum shows the presence of the nanophosphor tracer in the fluid sample and if the sample is analyzed within the timeframe of the persistent luminescence of the nanophosphor tracer (i.e., within 15 hours at 600-650 nm) the sample does not need to be re-excited. Without the need for re-excitation, there is less background noise imparted by the photoluminescence of the components of the oil (such as aromatic compounds) and provides a more accurate and higher sensitivity analysis. However, unlike the persistent luminescence spectrum the time-dependent persistent luminescence spectrum can provide insight into the length of time required for the nanophosphor tracer to reach the extraction location. For example, when the nanophosphor tracer is injected at the first location and then extracted at the second location, the amount of time left in the photoluminescence of the nanophosphor determined from the time-dependent persistent luminescence spectrum, gives insight in how long it took to arrive at the second location. As an example, the elapsed time between injection and the appearance of the tracer in the extracted fluid can provide information about the fluid flow capacity of the reservoir, the interconnected-ness of flow pathways, and residual oil saturation, which is difficult to acquire directly by other means.
[0076] The method of the present disclosure allows for real-time or near real-time characterization of the reservoirs. This process is repeated for all the samples collected from each second location. In some embodiments, the analysis process can occur up to 15 hours after the excitation process, as the nanophosphor tracer has persistent luminescence up to 15 hours between 600-650 nm. In some embodiments, to extend the time period for the analysis, the nanophosphor tracer may be repeatedly excited by irradiation at the wavelength ranges as described earlier, following the injection of the nanophosphor inside the subterranean geological reservoir.
[0077] Referring to
[0078] At step 102, the method 100 includes mixing an Al salt, Mg salt, GeO.sub.2, and a Pr salt in a solvent with a complexing agent to form a first mixture. Suitable examples of Al salt include, but are not limited to, aluminum chloride, aluminum bromide, aluminum iodide, aluminum fluoride, aluminum nitrate, aluminum acetate, aluminum formate, aluminum sulphate, and/or combinations thereof. In a preferred embodiment, the Al salt is Al nitrate. Suitable examples of magnesium salt include, but are not limited to, magnesium hydroxide, magnesium sulphate, magnesium carbonate, magnesium citrate, magnesium trisilicate, magnesium nitrate, magnesium nitrite, magnesium acetate, magnesium formate, and/or combinations thereof. In a preferred embodiment, the magnesium salt is magnesium nitrate. Suitable examples of the Pr salt include, but are not limited to, PrF.sub.3, PrCl.sub.3, Pr(NO.sub.3).sub.3, and Pr(CH.sub.3COO).sub.3. In a preferred embodiment, the Pr salt is Pr(NO.sub.3).sub.3. In some embodiments, the salts of other rare-earth lanthanides, such as lanthanum, ytterbium, europium, lanthanum, cerium, rubidium, caesium, niobium, tantalum, tellurium, terbium, lanthanum, gold, iridium, osmium, silver, platinum, palladium, rhenium, ruthenium, rhodium, hafnium, and/or indium, may be used in combination with the Pr salt to form the first mixture. The Al salt, Mg salt, GeO.sub.2, and Pr salt are mixed in a solvent. The solvent may be an organic or an aqueous solvent. In an embodiment, the solvent is water. Suitable examples of the complexing agents include, but are not limited to, citric acid, lactic acid, nitriloacetic acid, ethylene diamine acetic acid (EDTA), etc. In a preferred embodiment, the complexing agent is citric acid. The molar ratio of the Al salt, Mg salt, GeO.sub.2, and a Pr salt to the complexing agent is 1 to 1-5, preferably 1 to 1:4, preferably 1 to 1:3, preferably 1 to 1:2, preferably 1:2.
[0079] At step 104, the method 100 includes dehydrating the first mixture to a temperature of 50-100 C., preferably 50-90 C., preferably 50-80 C., preferably 50-70 C., preferably 50-60 C., preferably 60 C., to form a polymeric complex.
[0080] At step 106, the method 100 includes heating the polymeric complex for at least 10 hours, preferably between 10-14 hours, at a temperature of 80-110 C., preferably 90-100 C. to form a foam.
[0081] At step 108, the method 100 includes combusting the foam at a temperature of 400-600 C., preferably at about 500 C. to form a powder.
[0082] At step 110, the method 100 includes calcining the powder at a temperature of 500-1,500 C., preferably at about 1000 C., 1100 C., or 1200 C. for 30-120 minutes, preferably 60 mins to form the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles. In a preferred embodiment, the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ nanoparticles are calcined at 1200 C. for 60 min.
[0083] While not wishing to be bound to a single theory, it is thought that the co-doping of both Al and Pr along with the unique synthetic method, results in a nanophosphor with large amounts of defects and extended persistent luminescence. The high temperature calcining causes the formation of intrinsic defects but results in large sizes of the materials. The ionic radius of Al.sup.3+ as a co-doping ion is 0.675 , which substitutes the Ge.sup.4+ ion (0.67 ) sites in hexacoordination in the MgGeO.sub.3 lattice, which increases the number of lattice defects because the trivalent Al.sup.3+ ions occupy the tetravalent Ge.sup.4+ sites. The charge mismatch between these ions leads to spontaneous defect creation for charge compensation. Thus, the defects created by Al.sup.3+ doping could be the potential electron trapping center during persistent luminescence.
EXAMPLES
[0084] The following examples demonstrate methods for reservoir characterization using a nanophosphor tracer, as described herein. The examples are provided solely for illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.
Example 1: Chemicals
[0085] GeO.sub.2 (99.999%) was purchased from GFI, Advanced Technologies, Inc. USA. Al(NO.sub.3).sub.3.Math.9H.sub.2O (98.0-102%), NH.sub.4OH (28% NH.sub.3), MgO (99.99%), and Pr(NO.sub.3).sub.3.Math.6H.sub.2O (99.99%) were purchased from Alfa Aesar, ThermoFisher (Kandel) GmbH, Germany. HNO.sub.3 (69%) was purchased from Loba Chemie Pvt. Ltd., Mumbai, India. The citric acid (>99.5%) was obtained from Honeywell International India Pvt. Ltd. India. All the solutions were prepared in deionized (DI) water.
Example 2: Synthesis of MgAl.SUB.0.05.Ge.SUB.0.95.O.SUB.3.:0.3% Pr.SUP.3+ Nanophosphor
[0086] The MgAl.sub.0.05Ge.sub.0.95O.sub.3.Math.0.3% Pr.sup.3+ phosphor was synthesized by a citrate sol-gel method with subsequent calcination. The amount of Pr is expressed in atomic percent (at. %) relative to the total atoms in the MgAl.sub.xGe.sub.yO.sub.3:zPr.sup.3+ phosphor. The corresponding nitrates of the metals were dissolved in DI water, and citric acid was used as a complexing agent. Briefly, the stoichiometric amount of GeO.sub.2 was added to 20 mL of deionized (DI) water. NH.sub.4OH was added to it, followed by the addition of MgO. The MgO was converted to its nitrate form by the addition of HNO.sub.3. Pr(NO.sub.3).sub.3 was added to the above mixture, followed by the addition of Al(NO.sub.3).sub.3. Lastly, citric acid was added to the reaction mixture. The molar ratio of metal cations to citric acid was 1:2. The solution mixture was stirred and heated at 60 C. The solution was then dehydrated at 95 C. to form a polymeric complex. The sample was then kept in the oven overnight at 95 C. to form foam with enormous swelling. The sample was then combusted on a hot plate at 500 C. to form a fine black powder. The powder was then ground in a mortar, transferred to ceramic crucibles, and calcined at various temperatures at different times, including 1200 C. for 60 min, 1100 C. for 90 min, 1000 C. for 120 min, and 1000 C. for 30 min.
[0087] MgGeO.sub.3: 0.3% Pr.sup.3+ was also produced by the same method but without doping with Al as a comparative example. The MgGeO.sub.3: 0.3% Pr.sup.3+ was calcined at various temperatures at different times, including 1200 C. for 60 min, 1000 C. for 60 min, and 1000 C. for 30 min.
[0088] The size of the particle was refined through grinding in a MICROCER grinder from NETZSCH Micro & Mini-Serie (2801047-10), Feinmahltecnik GmbH. The MgAl.sub.0.05Ge.sub.0.95O.sub.3.Math.0.3% Pr.sup.3+ particles were ground for 3 h in different solvents. The bigger particles can be removed by centrifuging at lower rotations. The particles were freeze-dried by Millrock Bench-Top Freeze-Dryer. The size and distribution of the as-synthesized MgAl.sub.0.05Ge.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs were checked by the Zetasizer Nano-ZS, Malvern, UK.
Example 3: Spectral Characterization Techniques
[0089] The spectral characterizations were done on a Horiba NanoLog spectrofluorometer set up with a 75 W xenon arc lamp and an R928 photomultiplier tube (PMT) and LN2-cooled InGaAs (DSS-IGA020L) detector. The photoluminescence excitation and emission spectra, persistent luminescence emission spectra, and persistent luminescence decay curves were acquired. The spectra analysis from 300 to 850 nm was done by using a photomultiplier tube (PMT) detector, while the liquid nitrogen cooled InGaAs detector was used for measurement from 850 to 1550 nm. For persistent luminescence spectra and decay curves, the samples were excited by using a 254 nm ultraviolet (UV) lamp. To avoid stray light in the spectral measurements, appropriate optical filters were used.
Example 4: Detection of MgAl.SUB.0.05.Ge.SUB.0.95.O.SUB.3.:0.3% Pr.SUP.3+ NPs in Oil/Water Emulsion Techniques
[0090] The unrefined crude oil from Saudi Arabia was used without any pre-treatment. Different amounts of MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ dispersed in the water were mixed with the crude oil in a 50/50 volume ratio or otherwise specified to form the emulsions. 3.5 mL, 10 mm path-length quartz cuvettes were used for measurements. The spectral acquisition of the samples was done using the Horiba NanoLog spectrofluorometer.
[0091] The imaging of the samples was performed on an IVIS Lumina III imaging system (PerkinElmer) equipped with a cooled charge-coupled device (CCD) camera in the bioluminescence mode. The samples containing MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs/water/crude oil in the quartz cuvettes were irradiated by a 254 nm UV light for 5 min. The images were taken after 15 seconds, 30 seconds, and 1 minute of the stoppage of excitation. Different exposure times for the images, i.e., 30 seconds and 1 minute, were taken. The images were processed by living image software (Version 4.7.2, PerkinElmer, Inc.). The images were taken under similar conditions for comparison. The average intensity was found by processing the obtained images by Living Image software at a binning of 8 and smoothing of 33 by the region of interest (ROI) tool.
Example 5: Characterization of the MgAl.SUB.0.05.Ge.SUB.0.95.O.SUB.3.:0.3% Pr.SUP.3+ Nanophosphor
[0092]
[0093] The persistent luminescence intensity and the persistent luminescence decay time of the synthesized phosphor were increased by co-doping with Al.sup.3+ with the Pr.sup.3+. The preferred amount of Al.sup.3+ was found to be 5 mol %. The persistent luminescence properties also increase with the increase in annealing temperature. The high temperature causes the formation of intrinsic defects but results in large sizes of the materials. The undoped MgGeO.sub.3:Pr.sup.3+ sample has very poor persistent luminescence possession, which was greatly increased by the doping of the Al.sup.3+ ion (
[0094] The photoluminescence excitation and emission spectra of the synthesized phosphor were carried out and the results are shown as normalized graphs in
4f.sup.2(.sup.3H.sub.4).fwdarw.4f.sup.15d.sup.1; .sup.3P.sub.J[=0,1,2]Eq. 1
4f.sup.15d.sup.1.fwdarw..sup.1D.sub.2Eq. 2
[0095] In the dispersion of MgAl.sub.0.05Ge.sub.0.95O.sub.3:0.3% Pr.sup.3+ in an aqueous medium, the 4f.sup.15d.sup.1 state of Pr.sup.3+ localized below the conduction band. The excited electron moves to lower energy level, and then there is a weak emission from 3P0 state. The 4f.sup.15d.sup.1 state now feeds the .sup.3P.sub.J state in the absence of an exciton-like state. So, the emission from the .sup.3P.sub.J state is also observed.
[0096] When the sample was excited at 254 nm under UV light for 5 minutes and then irradiation was ceased, the persistent luminescence in the visible, NIR, and SWIR regions was observed in the synthesized phosphor (
[0097] Spectral techniques were also used to detect the MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs in the crude oil/water emulsion. The MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs dispersed in water emit similar three bands in the photoluminescence spectra (
[0098] The low sensitivity of the spectral method, the inherently low afterglow signals of MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs in oil emulsion, and the dense oil phase cause excitation problems of the NPs and resulted in the lower detection of NPs in the oil/water emulsion. Therefore, the IVIS Lumina III imaging system was used for the detection of MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs in the crude oil/water emulsion. The emulsions were tested in quartz cuvettes and were irradiated at 254 nm UV light for 5 min. The images were taken after 1 min of the excitation in a bioluminescence mode with different exposure times of 15 s, 30 s, and 1 min.
[0099] The persistent luminescence images of the different concentrations (0, 1, 5, 10, 50, 100, and 1000 ppb) of the MgAl.sub.0.05G.sub.0.95O.sub.3:0.3% Pr.sup.3+ NPs in the 50/50 crude oil/water emulsions are shown in
TABLE-US-00001 TABLE 1 The images were processed by living image software (Version 4.7.2, PerkinElmer, Inc.). For the comparison of the images, the images were taken under similar conditions. The average intensity was found by processing the obtained images by Living Image software at a binning of 8 and smoothing of 3 3 by the region of interest (ROI) tool. Concentration of Image Total Flux Avg. Radiance St. dev. MAGO:Pr NPs ROI Layer [p/s] [p/s/cm.sup.2/sr] Radiance Min Radiance Max Radiance 1000 ppb ROI 1 Overlay 7.73E+05 1.53E+05 9.06E+03 1.35E+05 1.75E+05 100 ppb ROI 1 Overlay 6.53E+05 1.29E+05 7.05E+03 1.02E+05 1.44E+05 50 ppb ROI 1 Overlay 5.96E+05 1.19E+05 1.94E+04 5.04E+04 1.45E+05 10 ppb ROI 1 Overlay 5.13E+05 1.03E+05 1.16E+04 7.06E+04 1.26E+05 5 ppb ROI 1 Overlay 4.94E+05 9.79E+04 1.60E+04 6.77E+04 1.35E+05 1 ppb ROI 1 Overlay 4.48E+05 8.82E+04 1.12E+04 6.12E+04 1.12E+05 50/50 oil/water ROI 1 Overlay 3.04E+05 5.98E+04 7.39E+03 3.78E+04 8.55E+04 emulsion
[0100] MgAl.sub.0.05Ge.sub.0.95O.sub.3:0.3% Pr.sup.3+ nanophosphors were synthesized by the sol-gel method. The sol-gel method is an alternative to the solid-state synthesis of the said materials. The synthesized persistent phosphor emits in the visible region peaking at 625 nm, the NIR region peaking at 905 nm, and the SWIR region peaking at 1089 nm. The persistent luminescence data shows that when the NPs were excited at 254 nm for 5 minutes the spectra can be obtained after 5 h and the emission at 625 nm can be monitored after 15 h of the stoppage of the excitation. The spectral and imaging methods were used to detect the prepared NPs in the crude oil/water emulsion.
[0101] Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.