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Furthermore, lanthanoid-based taggants may be selected from the group consisting of: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium , ytterbium (Yb), lutetium (Lu), and mixtures thereof. In some non-limiting embodiments, taggant may be added during manufacture of nano-sized particles. Although taggant may occur in elemental form, it is more likely that the taggants occur as compounds. Non-limiting examples of potential types of compounds include fluorides, chlorides, bromides, nitrates, nitrides, iodates, oxides, hydroxides, carbonates, sulfates, sulfides, phosphates, silicates, alkoxides, organic acids such as manganese gluconate, and combinations thereof. It should be noted that the taggant may not remain in its original form; it may be modified such as during processing. In a non limiting example, Zn, or a zinc compound, may be added to a solution from which MgO nano-sized particles are produced so that the end product consists of Zn doped MgO. For instance, the taggant may be continuously distributed along the entire nano-sized particle. For example, during coating processes the taggant may be modified by a reducing agent, changed during vapor phase for deposition, or altered by interacting with a liquid phase if slurried or dissolved. One or more taggants may be included with, added to, or coated on the primary component of the nanoparticles.

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Nano-sized particles of similar composition may also be produced by using vapor phase processes. In order to assist the activation of the precursors during chemical vapor deposition, the process deposition process may make use of a plasma. In this configuration the taggant material does not enter in contact with the formation or liquid phase. Any suitable coating technique may be used to coat the nanoparticles such as without limitation, molten salt, plasma coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), chemical and electrochemical techniques such as without limitation electroless plating, and the like. The magnetic core may be used to separate the particles from the suspension for analysis or for direct identification, for instance if particles with the magnetic core are placed in one zone and particles without the magnetic core are placed in another zone. In this alternative, non-restrictive embodiment, the core-coating nanoparticles will behave as regular MgO nanoparticles in terms of fine adhesion. The magnetic core also eases separation of nanoparticles from the suspension by an applied magnetic field. Such deposition may take place by chemical vapor deposition processes (CVD) or physical vapor deposition (PVD) in which the precursors for the taggant are supplied from the vapor phase, and the nanoparticles are in a fluidized state. A non-limiting example of a core-shell nano-sized particle is the one where a magnetic core is surrounded by MgO. For instance, the taggant material may form the core of the nanoparticles, which has a structure consisting of a core and an outer layer of a different material such as the primary component. In one non-limiting example coating may take place by electroless plating using one or more easily reducible metals. Core-shell nanoparticles can be fabricated either by solution chemistry route or by vapor deposition route. In other non-limiting embodiments, the nanoparticles manufacturing process may consist of two of more sequential steps resulting in core-shell structure. In another example, a very thin film of the taggant material may be deposited on the nano-sized particles. In other non-limiting embodiments, the nanoparticles may be tagged post-manufacture such as by coating them with a coating material that includes the taggant.

The base fluid or aqueous-based fluid may be a brine.

Regardless of how the taggant is coated or deposited on the dual-function nanoparticles, the coating may be a low density or partial coating, a complete coating encapsulating individual nanoparticles, or a combination of partial and completely coated nanoparticles. In other embodiments, however, dual-function nano-particles may be pumped downhole in a base fluid or a carrier fluid as a particulate additive, where the base fluid or carrier fluid also contains proppant or gravel particles. In non-limiting embodiments, the brine may be prepared using salts including, but not necessarily limited to, NaCl, KCl, CaCl2, MgCl2, NH4Cl, CaBr2, NaBr, sodium formate, potassium formate, and other commonly used stimulation and completion brine salts. In another non-restrictive version, the base fluid may be foamed. In a specific, non-limiting example, from about 0.5% to about 10% by weight of the total nanoparticles added to proppant or within a fluid such as a treatment fluid are coated with a taggant. Alternatively, the lower threshold of the proportion range may be about 50 pptg (about 6 kg/1000 liters), while the upper threshold of proportion of the particles may independently be about 300 pptg (about 36 kg/1000 liters). Non-limiting examples of suitable water-based fluids include, but are not restricted to, EMERALD FRAQ aqueous fluid containing a crosslinked polymer and DIAMOND FRAQ aqueous (https://backtoglamour.com/blog/2020/07/14/you-can-thank-us-later-seven-reasons-to-stop-thinking-about-jewelry-sterling-italian-childrens-silver-charm-bracelets/) fluid containing a viscoelastic surfactant (VES), both available from Baker Hughes Incorporated. The amount of dual-function nano-sized particles in the base or carrier fluid may range from about 20 to about 500 pounds per thousand gallons (pptg) (about 2.4 to about 60 kg/1000 liters). In yet other embodiments coated dual-function nanoparticles, whether partially and/or completely coated, are mixed with nanoparticles that are not coated. In another non-limiting embodiment, the particle size may range from about 10 nanometers independently up to about 500 nanometers. As has been previously mentioned, dual-function nano-sized particles may be disposed on carrier particles such as proppant, gravel, or the like. The base fluid may be water-based, alcohol-based or oil-based, but in many embodiments the base fluid is expected to be water-based. The base fluid or aqueous-based fluid may be a brine. In another non-limiting embodiment, the dual-function nanoparticles may have a particle size of from about 1 nanometer independently up to about 1000 nanometers regardless of the presence or absence of taggant. In another non-restrictive version, the dual-function particles may have a mean particle size of about 400 nm or less, alternatively about 300 nm or less, and in another possible version about 200 nm or less, alternatively 100 nm or less.