**3. Nanoparticles: classification and attributes in formulations**

The science and technology of fine particles is known as micromeritics. Through understanding of their characteristics, thousands of nanoproducts exist, and they are mainly used in drug delivery [6, 7]. Introduction of nanoparticles in drilling fluid have been under investigation, and have been applied over a decade ago. They have the potential to create changes in size and composition that result into formulations that could be adopted for a wide range of operating conditions even in small concentrations. Nanoparticles can be organic or inorganic on the basis of molecular weight and durability. Similarly, organic nanoparticles can be natural or synthetic and involves organic or polymeric molecules. These biopolymer nanoparticles are biodegradable and highly stable in fluids and storage [8] and include cellulose nanoparticles (CNP) where cellulose nanofibers and cellulose nanocrystals are examples [9], chitosan nanoparticles, starch nanoparticles (SNP), lignin and pullulan nanoparticles, alginate and gliadin nanoparticles, polylactic acid (PLA) nanoparticles, and polycaprolactone (PCL) nanoparticles. Conventional carboxymethyl cellulose (CMC) and polyanionic cellulose (PAC) ground into smaller nanosize particles are also important substances. Cellulose is considered the most abundant biopolymer in the world.

The influence of size on the physic0-chemical properties of a substance cannot be overemphasized. Since the presentation made in 1959 by Richard P. Feynman, a Nobel laureate, on nanotechnology titled "*There's plenty of room at the bottom*", various strides in the field of nanotechnology have been recorded [10]. Nanotechnology enables evaluation of matter at nanoscale and enhances synthesis. Materials have been produced at nanoscale level. A particle size of matter in the range of 1 to 100 nanometers in diameter (d.nm) is referred to as nanoparticle, and could be 0D, 1D, 2D or 3D as reference dimension. Their surface to volume ratio is extremely high due to their submicroscopic size. It is an overlap of mesoscale, 1 to 1000 nm (polymeric nanoparticles), such as used in colloid science.

In drilling fluid formulations, with additives in the nanoparticle size range, significant improvement in drilling fluid properties have been documented [11]. Such fluids are referred to as nanofluids. This is further categorized as simple nanofluids with nanoparticles of single magnitude of particle distribution, and advanced nanofluids with diverse nanosize ranges of additives. They exhibit unique characteristics, hence, extraordinary potential for application in science and engineering [12], with particular interest in drilling fluid formulation. The base fluid could be water or oil. They have the potential to modify drilling fluid properties such as plastic viscosity, yield point, gel strength, barite sag, fluid loss volume, filter cake thickness as well as improve thermal and wellbore stability. They are also used as pollution filters for cadmium and hydrogen sulphide, for improved lubricity, heavy metal absorption [13] and reduction of torque and drag. They are applicable both in atmospheric and hightemperature high-pressure (HPHT) conditions.

They possess a variety of morphologies or shapes which help serve their objectives. **Figure 1** shows a comparison of nanoparticles with smaller and larger sized particles such as atoms and cancer cells respectively. Structures of nanoparticles contain hundreds of atoms. In other words, nanoparticles are larger in size than simple molecules and atoms by hundredfold. By size, bacteria are larger in size than nanoparticles

#### **Figure 1.**

*Comparison of nanoparticles with other cells and atomic particles.*

**Figure 2.** *Diverse shapes of nanoparticles [2, 14].*

which can be used as barrier to prevent their activity. Their application in medicine has shown remarkable progress.

Nanoparticles exist in several shapes (**Figure 2**), and can further be classified based on crystallinity (amorphous and crystalline), nature of material (bimetallic, metallic chalcogenides, metallic oxides, organic, pure metals), origin and source (anthropogenic and natural), phase composition (multiphase solids, single phase solids), and shape and dimension (0D, 1D, 2D, 3D). Prism and helical shaped nanoparticles also exist.

For polymeric nanoparticles of organic origin such as cellulose and starch that are polysaccharides, the nanofluids formed exhibit unique properties and are called nanogels. They have been used both in water-based and oil-based drilling fluid formulations, where they served as viscosifier and fluid loss control additives. They are biodegradable, can act as antibacterial agents and are economically efficient since a relatively small quantity is required to create the nanogel. Generally, ceramic nanoparticles can be used for purification and pollution control activities. For instance, zinc oxide has been used to remove hydrogen sulphide in drilling muds. This

## *Polymeric Nanoparticles in Drilling Fluid Technology DOI: http://dx.doi.org/10.5772/intechopen.106452*

is because hydrogen sulphide can dissolve in metal ions. At low concentrations, zinc oxide has been applied for antibacterial control due to high surface area to volume ratio in addition to distinctive physical and chemical characteristics. The metal nanoparticles have applications in catalysis, packaging, bio-engineering, cosmetics, water treatment, medicine and drug delivery, electronics, semiconductors, automobiles, paints, biosensors and soil pollutant removal. Carbon-based nanoparticles such as graphene can be combined with corrosion-protection chemicals to be an anti-corrosive material. In drilling fluid, it can act as a barrier to retard oxidation of hydrogen sulphide that can cause corrosion. In salty water based muds and situations where the mud becomes acidic due to intrusion of substances, graphene can serve as barrier against the chemical attack that causes corrosion. Categories of nanoparticles is shown in **Figure 3**, while their influences on drilling fluid properties and size ranges and concentrations applied are shown in **Tables 1** and **2**, respectively.

Three types of gels are recognized in drilling fluid engineering. They include (i) zero-zero gels with gel strength too low and initial or 10 s and 10 min gel strengths close to zero. It is easier for cuttings to settle or barites to sag in this system, (ii) flat gels with initial and 10 min gel strengths having similar values. Gel strength would be maintained and mud will remain pumpable after left quiescent and (iii) progressive gels where there would be appreciable difference between the initial and 10 min gel strengths, with higher 10 min gel strength value [15]. This signifies rapid gelling of drilling fluid and excessive pump pressure would be required to pump the fluid with time. Multi-walled carbon nanotubes and Yttrium oxide showed flat gels, whereas copper (II) oxide, aluminum oxide and bismuth ferrite showed progressive gels (**Table 1**). However, Silicon dioxide and Zinc oxide, both synthetic polymeric nanoparticles exhibited both flat and progressive gels. No clear trend was observed. The issue of progressive gel might be addressed by application of those materials in smaller concentration if other properties are satisfactory. Similarly, it could be

**Figure 3.** *Classification of nanoparticles.*


#### **Table 1.**

*Nanoparticles used in drilling fluids and properties recorded [11].*

observed that the carbon-based nanoparticles such as graphene, carbon and multiwalled carbon nanotubes were applied at lower concentrations (**Table 2**). Multiwalled carbon nanotube yielded a flat gel. Also, Silicon dioxide did not show any clear trend in optimal concentration when nanoparticle size was considered. In summary, carbon-based nanoparticles where the natural polymers in particular belong required addition in small concentrations to provide good gels and fluid loss properties. All the materials presented provided relatively good fluid loss properties irrespective of the types of gels observed.

Bismuth ferrite (BiFeO3) 13 20 7.8
