Patent Publication Number: US-2023148198-A1

Title: Multifunctional polysaccharide-based mud logging barcode tracers

Description:
TECHNICAL FIELD 
     This document relates to methods and compositions used in tagging and tracing subterranean rock cuttings produced during drilling. 
     BACKGROUND 
     Subterranean rock cuttings that are produced during drilling operations can provide critical information, for example, the lithology and mineral composition of the subterranean formation. However, cuttings produced at the drill head travel to the surface via the annulus, and it is difficult to accurately determine or even estimate lag time during this upward trip. This makes analyzing the depth at which these cuttings originated difficult. 
     Mud tracers can be used to determine mud cycle time, for example, the circulation time, however, the estimating the origin depth of rock cuttings based on circulation time is inaccurate, especially if the wellbore includes long horizontal sections or the return trip time is lengthy. For example, when the return trip is longer than half an hour, it is common to have depth uncertainties of more than 6 meters (20 feet). This, in turn, compounds errors in characterizing the formation according to the depth of the cuttings. More efficient mud tracer materials and rapid detection techniques for these tracers are highly desirable. 
     SUMMARY 
     This disclosure describes compositions and methods that can be used to determine the origin depth of a wellbore rock cutting. 
     In some implementations, a nanoparticle tag includes a natural polysaccharide, a fluorescent dye, and superparamagnetic nanoparticles. 
     In some implementations, a method of making a nanoparticle tag includes functionalizing a natural polysaccharide with a fluorescent dye, and incorporating superparamagnetic nanoparticles into the nanoparticle tag. 
     In some implementations, a method of determining the origin location of a subterranean rock sample includes mixing a nanoparticle tag into a fluid. The nanoparticle tag includes a natural polysaccharide core that includes a fluorescent dye and superparamagnetic nanoparticles. The method includes flowing the fluid through a work string into a subterranean formation, recovering subterranean rock samples from the subterranean formation, separating tagged rock samples from untagged rock samples using a magnet, and determining the origin location of the subterranean rock sample by analyzing the fluorescent signal of the nanoparticle tag. 
     In some implementations, a method of tagging and tracing cut subterranean rock includes using a barcode mud tracer in a drilling fluid to tag a cut subterranean rock produced during drilling. The barcode mud tracer includes a nanoparticle tag. The nanoparticle tag includes a natural polysaccharide, a fluorescent dye, superparamagnetic nanoparticles, and a polymer coating. The method includes identifying the barcode mud tracer using two or more orthogonal analytical techniques. 
     The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description that follows. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1    shows a schematic of an example of a drilling operation. 
         FIG.  2 A  shows an example of a first implementation of a fluorescent natural polysaccharide with iron oxide nanoparticles. 
         FIG.  2 B  shows an example of a second implementation of a fluorescent natural polysaccharide with iron oxide nanoparticles. 
         FIG.  2 C  shows an example of a first implementation of a fluorescent natural polysaccharide with iron oxide nanoparticles coated with a polymer shell. 
         FIG.  2 D  shows an example of a first implementation of a fluorescent natural polysaccharide with iron oxide nanoparticles dotted with a polymer shell. 
         FIG.  3 A  shows an example schematic of a reaction scheme for functionalizing the natural polysaccharide and creating a composite nanoparticle tag. 
         FIG.  3 B  shows a visual representation of the reaction scheme shown in  FIG.  3 A . 
         FIG.  4 A  shows a representative structure of chitosan. 
         FIG.  4 B  shows a representative structure of cellulose. 
         FIG.  4 C  shows a representative structure of starch. 
         FIG.  4 D  shows a representative structure of alginic acid. 
         FIG.  5    shows an example reaction between an amine and an isothiocyanate to yield a thiourea. 
         FIG.  6    shows an example reaction of chitosan with FITC to yield a fluorescent chitosan polymer. 
         FIG.  7    shows an example reaction of cellulose with an isothiocyanate dye, FITC, under basic conditions to yield a fluorescent cellulose polymer. 
         FIG.  8    shows an example reaction of starch with silane-PEI followed by a reaction with FITC to yield a fluorescent starch polymer. 
         FIG.  9    shows an example reaction of alginic acid with EDC to form an o-acylisourea followed by reaction with FITC. 
         FIG.  10    shows a flowchart of an example method of determining the origin location of a subterranean rock cutting produced during drilling. 
         FIG.  11    shows an example photograph of chitosan labeled with FITC and RBITC. 
         FIG.  12    shows an example SEM image of chitosan functionalized with FITC. 
         FIG.  13    shows an example photograph of the chitosan functionalized with FITC and RBITC with attached superparamagnetic Fe 3 O 4  nanoparticles in suspension. 
         FIG.  14    shows an example photograph of the chitosan-dye-Fe 3 O 4  complexes magnetically separated by an external magnet. 
         FIG.  15    shows an example SEM image of chitosan labeled with FITC and Fe 3 O 4  nanoparticles. 
         FIG.  16    shows an example of chitosan-FITC-Fe 3 O 4  coated with polystyrene. 
         FIG.  17    shows an example fluorescence spectrum of FITC, as well as modified chitosan polymers chitosan-FITC, chitosan-FITC-Fe 3 O 4 , and polystyrene-coated chitosan-FITC-Fe 3 O 4 -PS. 
         FIG.  18    shows an example photograph of starch functionalized with FITC and RBITC. 
         FIG.  19    shows an example SEM image of starch functionalized with RBITC. 
         FIG.  20    shows an example photograph of the starch functionalized with FITC and RBITC with attached superparamagnetic Fe 3 O 4  nanoparticles in suspension. 
         FIG.  21    shows an example photograph of the starch-dye-Fe 3 O 4  complexes magnetically separated by an external magnet. 
         FIG.  22    shows an example SEM image of functionalized starch-RBITC with Fe 3 O 4 . 
         FIG.  23    shows an example SEM image of Starch-RBITC-Fe 3 O 4  coated with polystyrene. 
         FIG.  24    shows an example fluorescence spectrum of RBITC, as well as modified starch polymers starch-RBITC, starch-RBITC-Fe 3 O 4 , and polystyrene-coated starch-RIBTC-Fe 3 O 4 -PS. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter. 
     Provided in this disclosure, in part, are tags, methods, and systems for tagging rock cuttings produced during a drilling operation. These tags, methods, and systems can be used to determine the origin location of a rock cutting or subterranean rock sample. The tags can absorb to, permanently, or semi-permanently decorate rock cuttings or subterranean rock samples. The tags can be identified by multiple orthogonal techniques, and therefore the various combinations of orthogonally detectable features create a library of uniquely identifiable tags. 
       FIG.  1    illustrates an example of a drilling operation  10  for a well  12 . The well  12  can be in a wellbore  20  formed in a subterranean zone  14  of a geological formation in the Earth&#39;s crust. The subterranean zone  14  can include, for example, a formation, a portion of a formation, or multiple formations in a hydrocarbon-bearing reservoir from which recovery operations can be practiced to recover trapped hydrocarbons. Examples of unconventional reservoirs include tight-gas sands, gas and oil shales, coalbed methane, heavy oil and tar sands, gas-hydrate deposits, to name a few. In some implementations, the subterranean zone  14  includes an underground formation including natural fractures  60  in rock formations containing hydrocarbons (for example, oil, gas, or both). For example, the subterranean zone  14  can include a fractured shale. In some implementations, the well  12  can intersect other suitable types of formations, including reservoirs that are not naturally fractured in any significant amount. 
     The well  12  can include a casing  22  and well head  24 . The wellbore  20  can be a vertical, horizontal, deviated, or multilateral bore. The casing  22  can be cemented or otherwise suitably secured in the wellbore  20 . Perforations  26  can be formed in the casing  22  at the level of the subterranean zone  14  to allow oil, gas, and by-products to flow into the well  12  and be produced to the surface  25 . Perforations  26  can be formed using shape charges, a perforating gun, or otherwise. 
     For a drilling treatment  10 , a work string  30  can be disposed in the wellbore  20 . The work string  30  can be coiled tubing, sectioned pipe, or other suitable tubing. A drilling tool or drill bit  32  can be coupled to an end of the work string  30 . Packers  36  can seal an annulus  38  of the wellbore  20  uphole of and downhole of the subterranean zone  14 . Packers  36  can be mechanical, fluid inflatable, or other suitable packers. 
     One or more pump trucks  40  can be coupled to the work string  30  at the surface  25 . The pump trucks  40  pump drilling mud  58  down the work string  30  to lubricate and cool the drilling tool or drill bit  32 , maintain hydrostatic pressure in the wellbore, and carry subterranean rock cuttings to the surface. The drilling mud  58  can include a fluid pad, proppants, flush fluid, or a combination of these components. The pump trucks  40  can include mobile vehicles, equipment such as skids, or other suitable structures. 
     One or more instrument trucks  44  can also be provided at the surface  25 . The instrument truck  44  can include a drilling control system  46  and a drilling simulator  47 . The drilling control system  46  monitors and controls the drilling treatment  10 . The drilling control system  46  can control the pump trucks  40  and fluid valves to stop and start the drilling treatment  10 . The drilling control system  46  communicates with surface and subsurface instruments to monitor and control the drilling treatment  10 . In some implementations, the surface and subsurface instruments may comprise surface sensors  48 , down-hole sensors  50 , and pump controls  52 . 
     Additives  81  can be mixed with drilling mud  58  and flowed through the reservoir. In some implementations, the additives are tags that can embed into, permanently, or semi-permanently decorate the surface of rock cuttings produced by the drill bit. When drilling mud is introduced into the subterranean formation via the drill bit, tags that are included in the mud will contact the subterranean formation for the first time at the drill head. If the depth or relative position of the drill head and the lag time of the mud in the drill string are known, rock cuttings that are tagged with a specific tag can be accurately assigned an origin depth or position. Accordingly, the origin location of the rock cutting can be accurately determined. 
     In some implementations, more than one tag can be used. The tags can be uniquely identifiable. Accordingly, rock cuttings that include or are decorated with a first tag can be assigned to a first depth or position, and rock cuttings that include or are decorated with a second tag can be assigned to a second depth or position. 
     The tags described herein are multi-modal tags, meaning that each tag includes a unique combination of features that can be orthogonally detected. Accordingly, the variations in the features of the tags can act as a uniquely identifiable “barcode.” In addition, the combination of orthogonally detectable features expands the number of uniquely identifiable tags that can be produced and uniquely identified. 
     Further, the tags described herein can be rapidly detected with high sensitivity. In some implementations, the tags can be detected at the drilling site, making detection more rapid and allowing the drill operators to make drilling decisions based on real-time data. 
     Another advantage of the tags described herein is that they can be identified in two stages. In a first stage, tagged rock samples can be separated quickly from untagged rock samples in a first procedure. After the separation, the tagged materials can be subjected to additional analysis, either off-site or on-site. Accordingly, the multi-stage approach includes a first separation that acts as a screening process. The screening process concentrates the tagged rock samples. In addition, if the rock samples require subsequent off-site analysis, the screening process reduces the number of rock samples that need to be transported and subsequently analyzed. This approach saves time, labor, and laboratory costs. In addition, this multi-modal identification allows for rapid identification and real-time analysis that can aid in drilling operations. 
     Provided herein are tags for identifying the origin depth of a rock cutting produced during drilling. The tags are composite nanoparticles, with multi-functional aspects that can be detected through multiple types of analysis, including through orthogonal analytical techniques. 
       FIG.  2 A  shows an example tag  200 . The tags can include natural polysaccharides  202 . The natural polysaccharide forms a stable core from material that is abundantly available and inexpensive. In some implementations, the natural polysaccharide core is loaded with fluorescent dyes  204  and superparamagnetic iron oxide nanoparticles  206 . Superparamagnetic iron oxide nanoparticles (SPION) are small synthetic γ-Fe 2 O 3  or Fe 3 O 4  particles with a core size of &lt;15 nm. In sufficiently small nanoparticles, magnetization can randomly flip direction under the influence of temperature. This behavior allows the particles colloidal stable in suspension, while they can respond to external magnetic field. Superparamagnetic iron oxide particles (SPIONs) can be magnetized by an external magnetic field, however, SPIONs do not show magnetic interactions after the external magnetic field is removed. In some implementations, the iron oxide nanoparticles can be clustered in the center of the tag, as shown in  FIG.  2 A . In some implementations, the superparamagnetic iron oxide nanoparticles  206  can be randomly distributed in the tag, as shown in  FIG.  2 B . The fluorescent and magnetic properties allow the tag to be separated and uniquely identified. 
     In some implementations, the tag includes a polymer shell  208 , for example a thermally depolymerizable or degradable polymer. In some implementations, the polymer shell  208  encapsulates the natural polysaccharides, fluorescent dyes, and iron oxide nanoparticles, as shown in  FIG.  2 C . In other implementations, the polymer shell  208  is dotted on the tag, as shown in  FIG.  2 D . The depolymerizable or degradable polymer  208  can be used to further identify the tag or differentiate one tag from another. Advantageously, all of the components of these tags are inexpensive and environmentally friendly. 
       FIG.  3 A  shows an example schematic of a reaction scheme  300  for functionalizing a natural polysaccharide and creating a composite nanoparticle tag. At  302 , a natural polysaccharide is provided. At  304 , the natural polysaccharide is functionalized with dye molecules to yield a fluorescent natural polysaccharide (FNP). At  306 , superparamagnetic iron oxide nanoparticles are incorporated into the FNP by co-precipitation to yield a magnetic FNP. Optionally, at  308 , the magnetic FNP can be decorated or coated with a polymer by radical induced polymerization.  FIG.  3 B  shows a visual representation of the reaction scheme shown in  FIG.  3 A . 
     Tags that include a natural polysaccharide core have several advantages. Natural polysaccharides are ubiquitous, abundant, and inexpensive. Further, natural polysaccharides are inherently multivalent, which enables targeted functionalization. Suitable natural polysaccharides can include chitosan, cellulose, starch, alginate, or a combination thereof. 
     For example, chitosan can be used as the natural polysaccharide core. Chitosan is a close derivative of poly(acetylglucosamine). Poly(acetylglucosamine) is also known as chitin. Chitin can be found in the shells of shrimp or other crustaceans, and is the second most abundant biopolymer in the world. The derivative chitosan can be made by treating chitin with an alkaline substance, for example with sodium hydroxide. Chitosan is a linear polysaccharide composed of randomly distributed β-(1→4)-linked D-glucosamine (deacylated unit) and N-acetyl-D-glucosamine (acetylated unit).  FIG.  4 A  shows a representative structure of chitosan, with n number of repeating units. 
     A second suitable natural polysaccharide is cellulose, the most abundant organic polymer on earth. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae, and oomycetes. Cellulose is a polysaccharide consisting of a linear chain of several hundred to many thousands of β-(1→4) linked D-glucose units.  FIG.  4 B  shows a representative structure of cellulose, with n number of repeating units. 
     Another suitable biopolymer is starch, also known as amylum. Starch is a polymeric carbohydrate that includes numerous glucose units joined by glycosidic bonds. 
     Starch is produced by most green plants as energy storage. It is the most common carbohydrate in human diets and is contained in large amounts in staple food such as potatoes, corn, rice, cassava, as well as in Emmer wheat ( Triticum amyleum ).  FIG.  4 C  shows a representative structure of starch, with n and m number of repeating glucose units joined by glycosidic bonds. 
     Alginic acid, also called algin, is a polysaccharide that is distributed widely in the cell walls of brown algae. Algin is hydrophilic and forms a viscous gum when hydrated. With metals such as sodium and calcium, algin can form salts known as alginates.  FIG.  4 D  shows a representative structure of alginic acid. Alginic acid is a linear copolymer with homopolymeric blocks of (1→4)-linked β-D-mannuronate with n repeating units and its C-5 epimer α-L-guluronate residues with m repeating units, covalently linked together. 
     In some implementations, the natural polysaccharides can be functionalized with fluorescent dyes. The fluorescent dye molecules can be grafted onto these natural polysaccharides via covalent bonds to form a fluorescent natural polysaccharide (FNP). In some implementations, the natural polysaccharide contains primary amines that can react with isothiocyanates to yield substituted thioureas. This reaction can occur at room temperature.  FIG.  5    shows an example reaction between an amine and an isothiocyanate to yield a thiourea. The functional groups R I  and R II  can be H, alkyl, or aryl groups. In chitosan, there are many primary amine functional groups. Therefore, fluorescent dye molecules that contain isothiocyanate can be covalently grafted into the polymer network of chitosan, functionalizing the chitosan and yielding a fluorescent natural polysaccharide (FNP). Suitable isothiocyanate-containing fluorescent dyes include fluorescein isothiocyanate (FITC), rhodamine B isothiocyanate (RBITC), and tetramethylrhodamine isothiocyanate (TRITC). These dyes have demonstrated stability at subterranean and reservoir conditions, such as high temperatures and pressures. Accordingly, these dyes are suitable for use in drilling and wellbore operations.  FIG.  6    shows an example reaction of chitosan with FITC to yield a fluorescent chitosan polymer.  FIG.  7    shows an example reaction of cellulose with an isothiocyanate dye, FITC, under basic conditions to yield a fluorescent cellulose polymer. 
     Alternatively or in addition, the natural polysaccharides can be modified via hydroxyl groups, for example by reacting the naturally occurring hydroxyl groups with an amine. For example, the hydroxyl groups in starch can be modified via a reaction with silane-polyethylenimine (silane-PEI). Next, dye molecules can be linked to the imine functional groups of the silane-polyethylenimine to yield a fluorescent starch.  FIG.  8    shows an example reaction of starch with silane-PEI followed by a reaction with FITC to yield a fluorescent starch polymer. 
     Isothiocyanate dyes can also be grafted onto the natural polysaccharides at basic conditions or via a reaction with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC reaction). The EDC reacts with carboxylic acid groups to form an active O-acylisourea intermediate and then reacts with primary amines to form an amide bond with the original carboxyl group.  FIG.  9    shows an example reaction of alginic acid with EDC to form an o-acylisourea followed by reaction with FITC. 
       FIGS.  7 - 9    show a reaction with the isothiocyanate dye FITC, however, it is understood that any isothiocyanate-containing dye can be used in these reactions, for example RBITC and TRITC. 
     In some implementations, the natural polysaccharide core and/or fluorescent natural polysaccharide (FNP) is loaded with superparamagnetic nanoparticles, for example superparamagnetic iron oxide nanoparticles. These superparamagnetic iron oxide nanoparticles can be formed in situ and attached to a natural polysaccharide or a dye functionalized FNP. When the primary size of magnetic iron oxide nanoparticles is less than 15 nm, the nanoparticles exhibit superparamagnetism. Superparamagnetic iron oxide particles (SPIONs) can be magnetized by an external magnetic field, however, SPIONs do not show magnetic interactions after the external magnetic field is removed. SPIONs can be formed by co-precipitation of ferric and ferrous ions in solution by reaction with a base. Equation 1 shows an example co-precipitation reaction: 
       2Fe 3+ +Fe 2+ +8OH − →Fe 3 O 4 ↓+4H 2 O  Eq. 1
 
     When SPIONs are synthesized in the presence of fluorescent natural polysaccharides (FNPs), the resulting SPIONs are attached to the natural polysaccharides to yield magnetic FNPs. The iron oxide nanoparticles have strong sorption on natural polymers. The magnetic FNPs can be separated and collected from a suspension or mixture by a strong magnet, for example by a neodymium (NdFeB) magnet. 
     In some implementations, the FNPs and/or magnetic FNPs can be coated with a thermally depolymerizable or degradable polymer coating. For example, monomer molecules can be dissolved in water in presence of FNPs and/or magnetic FNPs, and then the polymerization reaction occurs by adding an initiator to the suspension, yielding nanoparticles that are coated by the polymer. In some implementations, the initiator is Na 2 S 2 O 8  or (NH 4 ) 2 S 2 O 8 . In some implementations, the magnetic FNPs can be coated with polystyrene or a polystyrene based polymer. Styrene based polymers cleanly decompose into their constituent monomers at elevated temperatures. Accordingly, the entire polymer mass contributes to the generation of detectable units, maximizing atom economy. The constituent monomers can be identified and therefore the polymer coating can be identified. Unique combinations of unique monomers can be used to create a plurality of polymer coatings that can be differentiated by mass spectrometry. In other words, using different monomers as starting materials for the polymer coatings, the resulting polymer shells carry different “barcode” information and enable unique identification of their original monomer structures. For example, the constituent monomers of the polymer can be determined by pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS) analysis or by gas chromatography-flame ionization detection/mass spectrometry (GC-FID/MS). The polymer can include monomers derived from styrene, p-methylstyrene, p-methoxystyrene, 2,4-dimethyl styrene, 2,4,6-trimethylstyrene, 4-chlorostyrene, or 4-bromostyrene, or any combination thereof. 
     In some implementations, the polymer can include monomers derived from phenyl methacrylate, hexyl methacrylate, or butyl methacrylate, or any combination thereof. 
     In some implementations, the polymer shell fully encapsulates the multifunctional core. Alternatively, in some implementations the polymer shell does not fully encapsulate the multifunctional core. Brush-like or dot-like decoration of styrene-based polymers on to the magnetic FNP can likewise result in a tag that can be identified by the unique monomers present in the styrene-based polymer. Brush-like or dot-like decoration can result in a polymer coating that is a continuous thin layer or a polymer coating that is in discrete patches. 
     Fluorescence spectroscopy has demonstrated that the FNPs exhibit strong fluorescence, and that the inclusion of SPIONs and polystyrene coatings does not significantly quench or suppress the fluorescence from the dye molecules. Accordingly, these tags are detectable by fluorescence analysis. 
     The natural polysaccharide based tags mix well with drilling mud, and there is no phase separation observed in a mud-tag mixture for up to months at a time. Accordingly, the tags can be used in combination with drilling mud to tag rock cuttings or subterranean rock samples. The tags are suitable for use in both oil-based and water-based mud. 
     For example, the tags can be mixed with the drilling mud and flowed or pumped down a work string into a subterranean formation. The mud and tag mixture exits the work string at the drill bit. Accordingly, the tags come into contact with the subterranean formation for the first time as they exit the drill bit. The tags can embed into or decorate the subterranean formation and the rock cuttings produced by the drill, for example, through physical sorption on a rock surface. The drilling mud carries the rock cuttings to the surface of the wellbore, where they can be recovered and analyzed. 
     In some implementations, the tagged rock cuttings or rock samples are separated from the untagged rock samples using a magnet. Advantageously, this also pre-concentrates the tagged rock samples, and reduces the number of samples that need to be subsequently analyzed. In some implementations, the magnetic properties of the tag can be used to separate unbound tags from drilling mud. Accordingly, these tags can be removed from the mud for re-use. Further, the mud can be used again, either without tags or with a new tag. This prevents residual tags from contributing to background signals or interfering with subsequent drilling operations. 
     The identity of the tags can be determined by a number of techniques, including fluorescent analysis and mass spectrometry. Fluorescent analysis can be used to determine the identity of the fluorescent dye present in the FNP by fluorescence imaging or spectroscopy. The fluorescence images can be taken by camera system under UV or visible light excitation, while the fluorescence spectra can be recorded by a portable spectroscopic system on site. In some implementations, the fluorescent analysis can occur at the wellbore or drilling site. The fluorescent analysis can provide a first set of real-time data about the tags and rock cuttings. This data can be used to make subsequent decisions about drilling operations. Alternatively or in combination, the tags can be analyzed with mass spectrometry, for example pyrolysis-gas chromatography-mass spectrometry or gas chromatography—FID/MS, as described herein. In some implementations, the mass spectrometry analysis can be done at the wellbore or drilling site. In other implementations, the mass spectrometry analysis occurs off-site, for example in a laboratory. 
     The tags described herein can be engineered with unique fluorescence and mass spectrometry signals, as described in detail above. Accordingly, different combinations of different fluorescence and mass spectrometry signals can create a library of uniquely identifiable tags. In some implementations, a first tag can be introduced to a subterranean formation at a first time point, and a second tag can be introduced to a subterranean formation at a second time point. Therefore, when the position of the drill bit and the lag time of the tags as they travel down the work string is known, rock cuttings or subterranean rock samples tagged with a first tag can be assigned a first origin location, and subterranean rock samples tagged with a second tag can be assigned to a second origin location. The number of tags is not limited to two, and a plurality of tags can be used to assign a plurality of origin locations. 
       FIG.  10    shows a flowchart of an example method  1000  of determining the origin location of a subterranean rock cutting produced during drilling. At  1002 , a magnetic FNP tag is mixed into a fluid. At  1004 , the fluid is flowed through a work string into a subterranean formation. At  1006 , subterranean rock samples are recovered from the subterranean formation. At  1008 , a magnet is used to separate tagged rock samples from untagged rock samples. At  1010 , the origin location of the subterranean rock sample is determined by analyzing the magnetic FNP tag. 
     Example 1—Fluorescent Labeling of Chitosan 
     For the synthesis of fluorescently labeled chitosan, chitosan 1.0 g (medium molecular weight) was dispersed in 100 mL deionized (DI) water, and 10 mg of FITC dye or RBITC dye was dissolved into 50 mL water-ethanol (9:1) mixture, respectively, and then the chitosan and dye mixed and react for 6 hours under stirring. Upon completion of the reaction, the dye molecules are grafted onto chitosan (containing 1 wt % of dye). The chitosan particles labelled by dye were separated by centrifugation.  FIG.  11    shows an example photograph of chitosan labeled with FITC (i) and RBITC (ii).  FIG.  12    shows an example SEM image of chitosan functionalized with FITC. 
     Example 2—Inclusion of SPIONs in Fluorescent Chitosan 
     For the synthesis of SPIONs in fluorescent chitosan, in 150 mL chitosan-FITC or chitosan-RBITC from Example 1, 8.1 g FeCl 3 .6H 2 O and 4.2 g FeSO 4 .7H 2 O were dissolved under N 2  atmosphere, giving 2:1 molar ratio of Fe 3+ /Fe 2+ . Next, 7.5 mL of 29.5 wt % ammonia solution was added dropwise at a rate of 2.5 mL/min into the solution under vigorous stirring. With the addition of ammonia solution, magnetite (Fe 3 O 4 ) nanoparticles formed immediately, and the solution turns to black and viscous and then to deep brown and becomes more fluid. The reaction was allowed to continue at room temperature for 2 hours to ensure the formation of chitosan-dye-Fe 3 O 4  composites. The chitosan-dye-Fe 3 O 4  composite particles can be separated from solution by a magnet. The weight ratio of chitosan-dye to magnetic Fe 3 O 4  in the composite is about 1:2, although the ratio is adjustable. The samples, casted film on silicon wafer, were imaged by scanning electron microscopy (JEOL 7100 TFE SEM) operated at 15 kV voltage. 
       FIG.  13    shows an example photograph of chitosan functionalized with FITC (i) and RBITC (ii) with attached superparamagnetic Fe 3 O 4  nanoparticles in suspension.  FIG.  14    shows an example photograph of the chitosan-dye-Fe 3 O 4  complexes (i) and (ii) magnetically separated by an external magnet.  FIG.  15    shows an example SEM image of chitosan labeled with FITC and Fe 3 O 4  nanoparticles. 
     Example 3—Polystyrene Coating of SPION/Fluorescent Chitosan 
     To coat the chitosan-FITC-Fe 3 O 4  or chitosan-RBITC-Fe 3 O 4  composite particles, the above collected composite particles were redispersed in 150 mL 0.25 wt % sodium dodecyl sulfate (SDS) solution. 2.5 mL styrene was added and the mixture was stirred for 2 hours to allow adsorption of the styrene on the particles. Then, 0.2 g ammonium persulfate was added and the reaction mixture was heated to 70° C. for 2 hours. The resulting chitosan-FITC-Fe 3 O 4 -PS or chitosan-RBITC-Fe 3 O 4 -PS composite particles were separated and collected form solution by a magnet.  FIG.  16    shows an example SEM image of chitosan-FITC-Fe 3 O 4  coated with polystyrene. 
     Example 4—Fluorescence of Modified Chitosan 
       FIG.  17    shows an example fluorescence spectrum of FITC, as well as modified chitosan polymers chitosan-FITC, chitosan-FITC-Fe 3 O 4 , and polystyrene-coated chitosan-FITC-Fe 3 O 4 -PS. The spectra were measured with a Horiba NanoLog-3 fluorescence spectrometer, and the concentration of samples was approximately 1 wt % in water suspension. As shown in  FIG.  17   , the inclusion of chitosan, Fe 3 O 4 , and polystyrene does not significantly alter the fluorescence signal of FITC. Accordingly, the modified chitosan polymers can exhibit fluorescent signals and can be used as fluorescent tags in wellbore and subterranean applications. 
     Example 5—Fluorescent Labeling of Starch 
     For the fluorescent labeling of starch, 1.0 g starch (from potato) was dispersed in 100 mL DI water and 2 mLNH 3 .H 2 O (29.5 wt %) was added. After stirring the starch dispersion for 2 hours, 50 mL ethanol with 1 mL dissolved polyamine, trimethoxysilylpropyl modified (polyethylenimine) (Gelest, 50% in isopropanol), was added under stirring. After 12 hours, 10 mg dye FITC or RBITC was added to the reaction mixture and the reaction continues for additional 6 hours. Upon completion of the reaction, the dye molecules are grafted onto starch, and the starch particles labelled by dye were separated by centrifugation.  FIG.  18    shows an example photograph of starch functionalized with FITC (i) and RBITC (ii).  FIG.  19    shows an example SEM image of starch functionalized with RBITC. 
     Example 6—Incorporation of SPIONs in Fluorescent Starch 
     To incorporate SPIONs in the fluorescent starch, the above FITC or RBITC labeled starch (Example 5) was separated from reaction mixture and redispersed into 150 mL DI water. Next, 8.1 g of FeCl 3 .6H 2 O and 4.2 g FeSO 4 .7H 2 O were dissolved in the dispersion under N 2  atmosphere, followed by adding 7.5 mL of 29.5 wt % ammonia solution drop by drop at a rate of 2.5 mL/min with vigorous stirring. With the addition of ammonia solution, magnetite (Fe 3 O 4 ) nanoparticles formed immediately, and the solution turns to black and viscous and then to deep brown and becomes more fluid. The reaction was allowed to continue at room temperature for 2 hours to ensure the formation of starch-dye-Fe 3 O 4  composites. The starch-dye-Fe 3 O 4  composite particles can be separated from solution by a magnet. The weight ratio of starch-dye to magnetic Fe 3 O 4  in the composite is tunable as needed by changing relative ratio of the chemicals.  FIG.  20    shows an example photograph of the starch functionalized with FITC (i) and RBITC (ii) with attached superparamagnetic Fe 3 O 4  nanoparticles in suspension.  FIG.  21    shows an example photograph of the starch-dye-Fe 3 O 4  complexes (i) and (ii) magnetically separated by an external magnet.  FIG.  22    shows an example SEM image of functionalized starch-RBITC with Fe 3 O 4 . 
     Example 7—Polystyrene Coating of SPION/Fluorescent Starch 
     To form the polymer coated composite particles, the above collected starch-RBITC-Fe 3 O 4  composite particles (from Example 6) were redispersed in 150 mL 0.25 wt % sodium dodecyl sulfate (SDS) solution and then 2.5 mL styrene was added. After stirring for 2 hours, 0.2 g ammonium persulfate was added to initiate the polymerization and the reaction was allowed to finish at 70° C. for 2 hours. The resulting starch-RBITC-Fe 3 O 4 -PS composite particles were separated and collected form solution by a magnet.  FIG.  23    shows an example SEM image of Starch-RBITC-Fe 3 O 4  coated with polystyrene. 
     Example 8—Fluorescence of Modified Starch 
       FIG.  24    shows an example fluorescence spectrum of RBITC, as well as modified starch polymers starch-RBITC, starch-RBITC-Fe 3 O 4 , and polystyrene-coated starch-RIBTC-Fe 3 O 4 -PS. As shown in  FIG.  24   , the inclusion of starch, Fe 3 O 4 , and polystyrene does not significantly alter the fluorescence signal of RBITC. Accordingly, the modified starch polymers can exhibit fluorescent signals and can be used as fluorescent tags in wellbore and subterranean applications. The spectra were measured with a Horiba NanoLog-3 fluorescence spectrometer, and the concentration of samples was approximately 1 wt % in water suspension. 
     The term “about” as used in this disclosure can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range. 
     The following units of measure have been mentioned in this disclosure: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Unit of Measure 
                 Full form 
               
               
                   
                   
               
             
            
               
                   
                 g 
                 gram 
               
               
                   
                 mg 
                 milligram 
               
               
                   
                 nm 
                 nanometer 
               
               
                   
                 mL 
                 milliliter 
               
               
                   
                 min 
                 minute 
               
               
                   
                 kV 
                 kilovolts 
               
               
                   
                 wt % 
                 weight percent 
               
               
                   
                   
               
            
           
         
       
     
     In some implementations, a nanoparticle tag includes a natural polysaccharide, a fluorescent dye, and superparamagnetic nanoparticles. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The natural polysaccharide includes at least one of chitosan, cellulose, starch, or alginate. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The fluorescent dye includes an isothiocyanate functional group. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The fluorescent dye is at least once of fluorescein isothiocyanate, rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The superparamagnetic nanoparticles include iron oxide. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The nanoparticle tag includes a polymer shell. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer shell includes a polystyrene-based polymer. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polystyrene-based polymer includes a derivative of styrene, p-methyl styrene, p-methoxy styrene, 2,4-dimethyl styrene, 2,4,6-trimethyl styrene, 4-chlorostyrene, or 4-bromostyrene, or any combination thereof. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer shell includes a derivative of phenyl methacrylate, hexyl methacrylate, or butyl methacrylate, or any combination thereof. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer shell encapsulates the natural polysaccharide, fluorescent dye, and superparamagnetic nanoparticles. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer shell is dotted on the nanoparticle tag. 
     In some implementations, a method of making a nanoparticle tag includes functionalizing a natural polysaccharide with a fluorescent dye, and incorporating superparamagnetic nanoparticles into the nanoparticle tag. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The natural polysaccharide includes at least one of chitosan, cellulose, starch, or alginate. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The fluorescent dye includes an isothiocyanate functional group. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The fluorescent dye is at least once of fluorescein isothiocyanate, rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The superparamagnetic nanoparticles include iron oxide. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The method includes coating the nanoparticle tag with a polymer. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer is a polystyrene-based polymer. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polystyrene-based polymer includes a derivative of styrene, p-methyl styrene, p-methoxy styrene, 2,4-dimethyl styrene, 2,4,6-trimethyl styrene, 4-chlorostyrene, or 4-bromostyrene, or any combination thereof. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The polymer shell includes a derivative of phenyl methacrylate, hexyl methacrylate, or butyl methacrylate, or any combination thereof. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. Coating the nanoparticle tag with a polymer includes fully encapsulating the nanoparticle tag with the polymer. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. Coating the nanoparticle tag with a polymer includes dotting the nanoparticle tag with a polymer. 
     In some implementations, a method of determining the origin location of a subterranean rock sample includes mixing a nanoparticle tag into a fluid. The nanoparticle tag includes a natural polysaccharide core that includes a fluorescent dye and superparamagnetic nanoparticles. The method includes flowing the fluid through a work string into a subterranean formation, recovering subterranean rock samples from the subterranean formation, separating tagged rock samples from untagged rock samples using a magnet; and determining the origin location of the subterranean rock sample by analyzing the fluorescent signal of the nanoparticle tag. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The nanoparticle tag includes a polymer shell. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. The method includes analyzing the polymer shell of the nanoparticle tag with mass spectroscopy. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. Analyzing the polymer shell with mass spectroscopy includes analyzing the polymer shell with pyrolysis-gas chromatography-mass spectrometry. 
     This aspect, taken alone or combinable with any other aspect, can include the following features. Analyzing the polymer shell with mass spectroscopy includes analyzing the polymer shell with gas chromatography-flame ionization detection/mass spectrometry. 
     In some implementations, a method of tagging and tracing cut subterranean rock includes using a barcode mud tracer in a drilling fluid to tag a cut subterranean rock produced during drilling. The barcode mud tracer includes a nanoparticle tag. The nanoparticle tag includes a natural polysaccharide, a fluorescent dye, superparamagnetic nanoparticles, and a polymer coating. The method includes identifying the barcode mud tracer using two or more orthogonal analytical techniques. 
     The term “substantially” as used in this disclosure refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more. 
     The term “solvent” as used in this disclosure refers to a liquid that can dissolve a solid, another liquid, or a gas to form a solution. Non-limiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids. 
     The term “room temperature” as used in this disclosure refers to a temperature of about 15 degrees Celsius (° C.) to about 28° C. 
     The term “downhole” as used in this disclosure refers to under the surface of the earth, such as a location within or fluidly connected to a wellbore. 
     As used in this disclosure, the term “drilling fluid” refers to fluids, slurries, or muds used in drilling operations downhole, such as during the formation of the wellbore. 
     As used in this disclosure, the term “fracturing fluid” refers to fluids or slurries used downhole during fracturing operations. 
     As used in this disclosure, the term “fluid” refers to liquids and gels, unless otherwise indicated. 
     As used in this disclosure, the term “subterranean material” or “subterranean zone” refers to any material under the surface of the earth, including under the surface of the bottom of the ocean. For example, a subterranean zone or material can be any section of a wellbore and any section of a subterranean petroleum- or water-producing formation or region in fluid contact with the wellbore. Placing a material in a subterranean zone can include contacting the material with any section of a wellbore or with any subterranean region in fluid contact the material. Subterranean materials can include any materials placed into the wellbore such as cement, drill shafts, liners, tubing, casing, or screens; placing a material in a subterranean zone can include contacting with such subterranean materials. In some examples, a subterranean zone or material can be any downhole region that can produce liquid or gaseous petroleum materials, water, or any downhole section in fluid contact with liquid or gaseous petroleum materials, or water. For example, a subterranean zone or material can be at least one of an area desired to be fractured, a fracture or an area surrounding a fracture, and a flow pathway or an area surrounding a flow pathway, in which a fracture or a flow pathway can be optionally fluidly connected to a subterranean petroleum- or water-producing region, directly or through one or more fractures or flow pathways. 
     As used in this disclosure, “treatment of a subterranean zone” can include any activity directed to extraction of water or petroleum materials from a subterranean petroleum- or water-producing formation or region, for example, including drilling, stimulation, hydraulic fracturing, clean-up, acidizing, completion, cementing, remedial treatment, abandonment, aquifer remediation, identifying oil rich regions via imaging techniques, and the like. 
     As used in this disclosure, a “flow pathway” downhole can include any suitable subterranean flow pathway through which two subterranean locations are in fluid connection. The flow pathway can be sufficient for petroleum or water to flow from one subterranean location to the wellbore or vice-versa. A flow pathway can include at least one of a hydraulic fracture, and a fluid connection across a screen, across gravel pack, across proppant, including across resin-bonded proppant or proppant deposited in a fracture, and across sand. A flow pathway can include a natural subterranean passageway through which fluids can flow. In some implementations, a flow pathway can be a water source and can include water. In some implementations, a flow pathway can be a petroleum source and can include petroleum. In some implementations, a flow pathway can be sufficient to divert water, a downhole fluid, or a produced hydrocarbon from a wellbore, fracture, or flow pathway connected to the pathway. 
     As used in this disclosure, “weight percent” (wt %) can be considered a mass fraction or a mass ratio of a substance to the total mixture or composition. Weight percent can be a weight-to-weight ratio or mass-to-mass ratio, unless indicated otherwise. 
     A number of implementations of the disclosure have been described. 
     Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure.