Clay Science in Drilling and Drilling Fluids

Clay Science in Drilling and Drilling Fluids starts from the fundamentals of clay science and drilling, then comprehensively presents the advances of clay science related to drilling and drilling fluids and ends with discussion of industrial clay products. The topics combine to present the whole picture of fundamental research and industrial applications of clays and clay minerals in drilling operations, which is of general interest to researchers and engineers working in the related fields.Oil and gas are the primary sources of energy in human society and the foundation of the petrochemical industry. However, extracting these resources present a number of drilling challenges, including high temperature and high pressure (HTHP), offshore drilling, high angle drilling, and even horizontal drilling, among others. As a result, it is crucial to develop advanced drilling and drilling fluid technologies. Clay science in drilling and drilling fluids should be clarified for this purpose because clays and clay minerals are one of the most important components of drilling fluids and have a significant impact on wellbore stability. Clay Science in Drilling and Drilling Fluids covers the different levels of clay science in drilling and drilling fluids, i.e., form fundamentals, the latest research results, applications, and commercial products.

• Covers the fundamentals of clay minerals, drilling, and drilling operations
• Discusses applications of the research and science to real world problems
• Introduces available commercial clay products and recommends their use for specific situations

• Language: English
• Publisher: Elsevier Science
• Release date: Jun 5, 2024
• ISBN: 9780443155994

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Chapter 1

The significance of clay minerals in drilling and drilling fluids

Guanzheng Zhuang¹, Qiang Li², Faïza Bergaya³ and Peng Yuan¹,    ¹School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou, P.R. China,    ²Sorbonne Université, Laboratoire d’Archéologie Moléculaire et Structurale (LAMS), CNRS UMR 8220, Paris, France,    ³CNRS-Université d’Orléans, ICMN (Interface, Confinement, Matériaux et Nanostructures), Orléans, France

Abstract

Oil and gas have been the most important energy sources for the modern world, since the 1960s and will continue to be crucial for economic growth and environmental management, despite being condemned for their CO2 emissions which are thought to be the cause of global warming. Until new low-carbon energy sources will completely replace fossil fuels in the ensuing decades, the world will need more oil and gas which are essential to its development. However, oil and gas extraction is becoming more difficult due to the more complex geological conditions. Wellbore instability caused by shales, where clay minerals are the main constituents, is the most frequent problem during drilling. In addition, high-temperature, high-pressure, and saline formation requires high-performance drilling fluids, in which clay minerals are critical additives. Clay minerals not only provide excellent rheological properties but also reduce fluid loss by forming low-permeability mud cake on the borehole wall. A good knowledge of clay science is fundamental to improving drilling efficiency, reducing drilling accidents, minimizing environmental pollution, and decreasing costs. Therefore drilling engineers, materials scientists, and other related personnel will benefit from a better knowledge of clay science. This chapter highlights the critical functions of clay minerals in drilling and drilling fluids (or muds), including rheology control, fluids loss control, and wellbore stability.

Keywords

Clay minerals; drilling; drilling fluids; drilling muds; oil and gas

1.1 Introduction

For more than two centuries, an abundance of fossil energy combined with modern agriculture, cities, governance, and knowledge has fueled a virtuous cycle of socioeconomic development, enabling people in many parts of the world to live longer, healthier, and to have more prosperous lives. The discovery and conversion of modern fuels arguably enabled sustained economic growth for the first time in human history. These energy sources, mainly coal, oil, and natural gas, have allowed rising living standards since the onset of the industrial revolution. Among fossil energy sources, oil and gas have been the world’s strategic resources for decades. Oil and gas are used as fuel not only for cars, ships, airplanes, and industrial machinery, but also for heating and cooking in daily life. Furthermore, oil is a crucial raw material for clothing, plastics, pharmaceuticals, and other chemical products. To some extent, people can no longer live and work without oil and gas. However, even though oil and gas have significantly improved the quality of our life over the past century, the oil and gas industry is increasingly criticized because oil and gas are the two major sources of CO2 emissions. As a greenhouse gas, CO2 has a significant impact on global warming. To reduce greenhouse gas emissions and achieve the goals of the Paris Agreement, many countries have made long-term plans that aim to gradually adopt alternative energies to replace oil and gas over decades. For instance, the Chinese government has proposed that China’s CO2 emissions will reach their peak by 2030 and become carbon neutral by 2060. Reducing oil and gas use is considered one of the immediate measures to decrease CO2 emissions. However, the World Energy Outlook 2022 published by the International Energy Agency (IEA) argues that the oil and gas industry still plays an essential role in reducing CO2 emissions (IEA, 2022). In fact, the demand for energy will continue to rise due to the growing global population and rapid economic expansion. The current fragile energy supply chain is already unstable, which is a result of, among other things, the energy crisis caused by wars and geopolitics. Hence, immediately or rapidly reducing the use of oil and gas is unrealistic. Moreover, global economic development is highly uneven, with a wide gap between the rich and the poor. As a result, some people will not soon be able to access new clean energy. Last but not least, achieving the international climate goals and transforming into a new landscape require a long-term process. As affordable and reliable energy sources, oil and gas will be a necessary part of achieving the future vision in this process.

For the abovementioned reasons, oil and gas will continue to be the world’s primary energy sources for a long period before they are displaced by new energies. It is predicted by IEA that the world’s demand for oil and gas may continue to increase until 2050 in the stated policies scenario (Fig. 1.1) (IEA, 2022). Although the share of oil and gas in world energy may gradually decline after 2030 in the announced pledge scenario, their total amount will remain very large. Consequently, more oil and gas should be produced in the future to satisfy the large energy demand. The ever-increasing global demand for energy, coupled with declining production from some key areas of the world, is expected to uphold the growing interest in discovering unconventional plays that have the potential to drive oil and gas field operations into new technology frontiers. These could arise from changes in the operational depth, length of horizontal departure in extended-reach wells, the complexity of drilling operations, and the strict environmental regulations enacted by different governing bodies. To meet the challenges of the future, the oil and gas industry is going to need more than just discovering untapped reserves in every corner of the Earth. It is going to need a means to develop these unconventional plays and other hydrocarbon resources, which are not recoverable with current technologies. Understanding the geological characteristics and drilling fluid properties, so as to select and design fluids that could address the wide range of difficulties encountered in drilling operations, is one key portfolio that has garnered considerable attention, and the inherent concern on how they could be substantially modified for success becomes very critical to justifying project economics.

Figure 1.1 (A) Oil and (B) natural gas demands in the past years and prediction. Data from IEA World Energy Outlook 2022 edition. Notes: STEPS=Stated Policies Scenario, APS=Announced Pledge Scenario.

There are two severe challenges in drilling engineering, that is, (1) rheology and filtration control under complex conditions, such as high temperature, high pressure, and salt contamination (Mao et al., 2020; Agwu et al., 2021a; Sulaimon et al., 2021; Gautam et al., 2022) and (2) wellbore instability caused by shales (Anderson et al., 2010; Gholami et al., 2018; Muhammed et al., 2021a; Fang et al., 2022). After decades of extraction, oil and gas in shallow reservoirs are depleting. As a result, drilling engineering is shifting to deep, offshore, and other complex reservoirs. In this case, the rheological and filtration properties of drilling fluids become difficult to control as the colloidal behaviors of drilling fluids are very sensitive to temperature, pressure, and electrolytes. Furthermore, wellbore instability caused by shale hydration is one of the most common problems in drilling engineering. In recent years, the global exploitation of shale gas has increased the risk of wellbore instability (Sun et al., 2021; Zhang et al., 2022).

The causes of the aforementioned issues are complex, but they are all closely linked to clay minerals. For example, the stability of shale formations is governed by the hydration behavior of clay minerals, mainly montmorillonite (Mt), mixed-layer minerals, and illite, etc. The content, type, and physical–chemical properties of clay minerals deeply influence the hydration, colloidal behavior, and mechanical properties of shales (Lal, 1999; Aadnoy and Ong, 2003; Anderson et al., 2010; Carman and Lant, 2010; Wilson and Wilson, 2014; Karpiński and Szkodo, 2015; Gholami et al., 2018; Muhammed et al., 2021a). To ensure drilling efficiency and safety, the hydration of clay minerals in shale formation should be strictly inhibited (Sehly et al., 2015; Luo et al., 2017; Shi et al., 2019; Muhammed et al., 2021b; Ren et al., 2021b; Bai et al., 2023).

Moreover, clay minerals and their derivatives are the most commonly used additives in drilling fluids. Generally, drilling fluids that are water or oil based are called muds and can be classified into water-based muds (WBMs), oil-based muds (OBMs), and synthetic-based muds (SBMs) for fluids prepared with synthetic oils (organic solvents). In some literature, the terms of WBDF (water-based drilling fluids), OBDF (oil-based drilling fluids) and SBDF (synthetic-based drilling fluids) are also used, referring sometimes to the same meaning as WBM, OBM, and SBM, respectively. Strictly speaking a drilling fluid, using an array of gases, is a fluid but fluids that are water or oil based are called muds. In this book, WBM, OBM, and SBM abbreviations will be used when describing specific drilling fluids (muds) for consistency.

In WBM, Mt, palygorskite (Pal), and sepiolite (Sep) are among the most important additives as they provide the fundamental colloidal and rheological properties (Luckham and Rossi, 1999; Abdo, 2014; Altun and Osgouei, 2014; Al-Malki et al., 2016; Afolabi et al., 2017; Abdo and Haneef, 2022). Accordingly, organically modified clay minerals are also critical additives of OBMs (Zhuang et al., 2017a,b, 2018a,b, 2019a,b,c; Weng et al., 2018; Martin-Alfonso et al., 2021; Buriti et al., 2022). In a word, clay minerals control the efficiency, cost, and safety of drilling operations by regulating the colloidal and rheological behaviors of drilling fluids and the hydration of shales.

1.2 Clay minerals influence the wellbore stability

Oil and gas formation typically involves source, reservoir, and caprocks. A favorable source-reservoir-cap association is essential for forming abundant oil and gas accumulations, particularly for large oil and gas reservoirs. This association ensures that hydrocarbons produced in source rocks can migrate to the reservoir in time, while the caprock ensures that the hydrocarbons transported to the reservoir do not escape. Clay minerals are the most important components of source rocks because they are involved in the formation of kerogen and facilitate the catalytic cracking of kerogen to form source rocks (Fan et al., 2004). In sandstone reservoirs, clay minerals not only occupy pore spaces and form coatings on sand grains (Wu et al., 2012) but also serve as the major minerals of the most common caprocks, namely shales. Shale is a type of fine-grained, laminated sedimentary rocks rich in clay minerals like Mt, illite, and mixed-layer minerals. Shale serves as a hydrocarbon source rock as well as a storage space in shale gas reservoirs. As a result, clay minerals are intimately linked to the formation and storage of oil and gas, particularly in shale formations.

Shale is the most abundant sedimentary rock, accounting for roughly 70% of this rock type in the crust of the Earth. Shale formation is very likely to occur during drilling (Fig. 1.2). Shale, on the other hand, is the leading cause of wellbore instability, which is one of the most serious technical issues in petroleum exploration and a major source of lost time and revenue. Shales are responsible for more than 90% of wellbore instability problems, which are estimated to cost the industry at least 1 billion US dollars per year. Shale instability manifests itself in a variety of ways. As a result, the wellbore may collapse through caving, sloughing, or heavy, inevitably leading to enlarged holes. Cuttings from the drilled shale may disintegrate and disperse through the drilling fluid, or the shale may agglomerate around the drill bit (called bit-balling) and drill pipe, accreting onto the walls of the wellbore and significantly reducing its diameter. These problems result in tight holes and stuck drill pipes, which may lead to hole abandonment. Indirect problems include clogging of surface flow lines and shakers following shale dispersion and disintegration, lost circulation, as well as difficulties in logging and running casing.

Figure 1.2 Schematic geology of oil and natural gas resources.

Clay minerals are usually considered the primary cause of shale instability, although various interacting mechanical factors may exacerbate the situation. These may be associated with the drilling operation itself, such as contact between the drill string and the shale formation, fluid erosive action, and pressure surges. Furthermore, the distribution of the overall in situ vertical and horizontal stresses, and particularly the existence of overpressure, may be major or contributory factors in causing such instability. Nevertheless, the nature of the clay minerals that make up shales, together with the overall shale texture, structure, and fabric, remain as the most often cited primary causes of wellbore instability. The fundamental cause of this instability is the hydrophilic and charged nature of clay minerals, enabling them to swell and participate in cation exchange reactions. In attempting to elucidate the role of clay mineralogy in relation to shale instability, emphasis is almost always placed on the expandability of smectite (mostly Mt), particularly when saturated with Na+. There is currently a wealth of evidence derived from both experimental and modeling techniques that have characterized the nature of swelling in smectite. Generally, the swelling pressure following the interlamellar expansion and hydration of smectites, when combined with pore pressure, overcomes in situ vertical and horizontal stresses and any cementation bonds bolding the clay minerals particles together. The same mechanism is considered to result in wellbore instability by the dispersion of cuttings. This interpretation attributes a vital role to the physicochemical activity in the interlayer space of the expandable clay minerals derived primarily from the hydration and solvation of the clay mineral surfaces and exchangeable cations. There are two types of swelling that can occur in smectites, including crystalline swelling and osmotic swelling. Crystalline swelling refers to the expansion of the interlayer spacing in discrete steps related to the number of water layers. For example, a one-layer-water structure has a basal spacing of ~12.5 Å; a two-layer structure has a basal spacing of ~15 Å; and a three-water layer structure has a basal spacing of ~20 Å. Osmotic swelling results from the large difference in the ion concentration close to the clay mineral surfaces and the pore water.

Although the swelling mechanism is certainly essential, it cannot be the sole cause of shale instability because many problematic shales are not swellable. For example, caving and hole enlargement are common in older and consolidated shales that lack Mt. Such shales are so-called brittle shales, where illite is the primary clay mineral. Previously, brittle shales were proved to develop extremely high swelling pressure when confined and being in contact with water. However, illite is a nonswelling clay mineral because the attraction between layers is very strong, making it difficult for water molecules to enter its interlayer space. Typically, brittle shales do not exhibit obvious swelling behavior. Wilson and Wilson (2014) proposed a new possible mechanism involving the diffuse double layer (DDL) to explain the instability of illite-rich shales. As illite usually has higher surface charge density than smectite, the DDL associated with illite basal surfaces exposed in the pores of illite-rich shales tends to be thicker than that of smectite basal surfaces. Therefore the clay mineral basal surfaces on both sides of the pores are subject to electrostatic repulsion when the thickness of DDL is larger than the pore diameters. Unfortunately, there is currently no direct experimental evidence to support this hypothesis.

In addition to smectite and illite, many other clay minerals, such as mixed-layer clay minerals, chlorite, and kaolinite, frequently occur in shale formation. Nevertheless, the influences of these clay minerals on wellbore instability are often neglected. For example, the illite-smectite mixed-layer contains both illite and smectite layers and exhibits swelling behavior like smectite. The previous investigation only considered its swelling mechanism, ignoring the role of illite layers. Besides, kaolinite and chlorite were thought to be inactive minerals before (O'Brien and Chenevert, 1973), but recent research indicated that these clay minerals might also affect the wellbore stability (Siyao et al., 2022). Understanding the mechanisms of clay mineral hydration is fundamental to solving the shale instability problem. Therefore further studies on the hydration behaviors and mechanisms of clay minerals are required. This is critical for developing high-performance shale inhibitors to control the wellbore stability while improving the drilling efficiency and reducing costs.

1.3 Clay minerals regulate the rheology of drilling fluids

Drilling fluids are critical for drilling operations as they have the following fundamental functions (Caenn et al., 2017a): (1) cleaning the hole by transporting cuttings to the surface, where they can be mechanically removed from the fluid before it is recirculated downhole; (2) overcoming formation pressures in the wellbore to reduce the risk of well-control issues; (3) supporting and stabilizing the walls of the wellbore until casing can be set and cemented or open hole-completion equipment can be installed; (4) preventing damage to the producing formation; (5) cooling and lubricating the drill string and bit; and (6) transmitting hydraulic horsepower to the bit, etc. These functions are profoundly related to the rheology of drilling fluids. For example, the viscosity and yield stress govern the penetration rate and the ability to carry cuttings. The high viscosity of drilling fluids will decrease the rotating rate of the drill bit, while small viscosity will result in drilling fluids not effectively suspending and transporting cuttings (Agwu et al., 2021b). In addition, excellent shear thinning behavior and thixotropy are also necessary for drilling fluids, as they ensure a small viscosity around the drill bit (high penetration rate) but high viscosity of fluids in the annular to suspend and transport cuttings (Skadsem et al., 2019). Therefore the successful completion of an oil/gas well depends to a considerable extent on the rheological properties of drilling fluids. As the major component and the most common rheological controller in drilling fluids, clays and clay minerals are the key materials in controlling the rheological properties of drilling fluids (Fig. 1.3) (Luckham and Rossi, 1999). Therefore drilling and production personnel should be familiar with clay mineralogy, chemistry, and material science.

Figure 1.3 The relationship between clay mineralogy and the properties of drilling fluids.

Clay minerals used in drilling fluids include Mt, Pal, Sep, hectorite (Ht), and Laponite (Lap) (Table 1.1). Mt, the main component of bentonite, is the most used clay mineral in WBM. Usually, an average of 6–8 t of bentonite is consumed to complete an oil well. For deep or difficult wells, more bentonite is necessary. The microstructure, flow behavior, rheological mechanism, and applied properties of Mt in WBM have been studied in detail. Mt improves the rheological properties of WBM by forming a house of cards network after being dispersed, hydrated, swelled, and even exfoliated in water (Luckham and Rossi, 1999; Ganley and van Duijneveldt, 2015; Leong et al., 2018, 2021a,b; Du et al., 2019, 2020a,b). This network structure will be destroyed after shearing, resulting in a decrease in viscosity (shear-thinning). However, when shearing is stopped, the network can gradually recover, a phenomenon known as thixotropy (Katsuya, 1997; Dolz et al., 2007; Lee et al., 2012). The excellent colloidal behavior of Mt contributes to forming different high-performance WBM. Unfortunately, there are two drawbacks of Mt: (1) Mt-based drilling fluids are very sensitive to salts due to the large surface charge density of Mt (Sehly et al., 2015; Huang et al., 2016; Wu and Adachi, 2016; Ahmad et al., 2018; Montoro and Francisca, 2019; Raheem and Vipulanandan, 2020; Lin et al., 2021; Ren et al., 2021a); and (2) WBM based on Mt cannot suffer from high temperatures of more than 180°C (Kelessidis et al., 2007; Wang et al., 2012; Vryzas et al., 2017; Ahmad et al., 2018; Liu et al., 2022a,b). To overcome these two issues, Mt needs to be modified. For example, water-soluble polymers were considered to be useful for enhancing the rheological properties of WBM at high temperatures (Liu et al., 2020, 2022c; da Câmara et al., 2021; Du et al., 2021; Xie et al., 2021; Zhong et al., 2021). In this case, the polymer–clay interactions and the environmental impact of polymers should be specified.

Table 1.1

In addition to the layered Mt, fibrous clay minerals, that is, Pal and Sep, are also used in WBM (Galan, 1996; Neaman and Singer, 2000; Suliman and Al-Zubaidi, 2020; Ferraz et al., 2021). Their fibers are hundreds of nanometers to several micrometers in length, 10–30 nm in width, and 5–10 nm in thickness (Galan, 1996; Álvarez et al., 2011). Pal and Sep are excellent rheological materials because their fibers can easily disperse in water and form a stable network structure (Neaman and Singer, 2000; Cinar et al., 2009; Ruiz-Hitzky et al., 2021). Furthermore, the dispersions of Pal or Sep are not sensitive to electrolytes (e.g., NaCl, CaCl2, and CaSO4) as the surface charge density of Pal and Sep is much less than that of Mt (Xu et al., 2012., 2013; Altun and Osgouei, 2014; Liu et al., 2014; Zhou et al., 2015; Santanna et al., 2020). Therefore Pal and Sep are added to WBM when drilling saline, gypsum formations, and offshore wells. Sep is reported to be one of the most stable clay minerals at high temperatures (Carney and Guven, 1980). For this reason, Sep is used in WBM for geothermal wells. Recent studies confirmed that Pal and Sep are high-performance nanomaterials for nano-enhanced drilling fluids (Abdo and Haneef, 2010, 2012, 2013, 2022; Abdo, 2014; Al-Malki et al., 2016). The size and concentration of fibrous clay minerals control the rheological properties of WBM. Nano processing (e.g., defibering or disaggregation) helps to improve the rheological properties of WBM. For example, the addition of Sep and Pal to WBM results in a stable yield point, plastic viscosity, and gel strength at temperatures and pressures up to 180°C and 100 MPa (Abdo and Haneef, 2022).

More recently, Ht and its synthetic counterpart, that is, Lap, have recently been reported to be used in WBM (Huang et al., 2019, 2021; Xiong et al., 2019a,b). Ht is a layered trioctahedral clay mineral from the smectite family (Christidis et al., 2018; Zhang et al., 2019). Although Ht, as well as lap, shares a similar structure to Mt, its dispersity and gelling ability in water are better than Mt (Au et al., 2015; Leong et al., 2021b; Liu et al., 2021a,b, 2022d). For example, 1.5 wt.% of Lap can form gels, while at least 3 wt.% of Mt forms gels. Therefore Ht and Lap are very suitable for colloidal systems. However, natural Ht is rare. Lap is the most common commercial product. Therefore Lap is used extensively as a high-performance rheological modifying or thixotropic agent in many liquid or dispersion products in agriculture, building, household and personal care, surface coating, paper, and polymers film industry (Zhang et al., 2019). Due to its high cost, Lap had never been considered to be used in drilling fluids before. In recent years, the situation has changed. The increasing difficulties require high-performance rheological materials for drilling fluids. Compared with the cost, drilling engineers and companies are more concerned about the performance of the materials. Xiong et al. (2019a) first reported the potential use of Lap in WBM and found that Lap dispersion (2 wt.%) exhibited stable apparent viscosity at 180°C–240°C. This finding encouraged that Lap is a promising rheological additive. Later investigations confirmed that Lap could significantly improve the rheological properties under high temperatures due to its unique structure, morphology, colloidal behavior, and the interaction between Lap and polymers (Huang et al., 2019, 2021; Xiong et al., 2019b; Mohamed et al., 2021).

In summary, clay minerals are the most important rheological additives in drilling fluids. These materials are inexpensive and environment-friendly, in addition to having excellent rheological properties. Although traditional clay mineral–based colloidal materials struggle to meet the requirements of complex drilling, new clay-based materials and nanotechnology enable the development of high-performance drilling fluids.

1.4 Clay minerals control fluid loss

To maintain pressure equilibrium and prevent the flow of formation fluids (e.g., water, oil, and gas) into the drilling fluid during the drilling process, the pressure of the drilling fluid must be greater than the formation pressure. However, liquids (mostly water and oil with chemicals) can easily infiltrate the formation and filter solids onto the borehole wall, forming filter cakes (Caenn et al., 2017b). This process is referred to as filtration or fluid loss (Fig. 1.4). The fluid loss of drilling fluids results in the following problems: (1) The fluid loss requires more drilling fluids, which increases the costs; (2) The intrusion of drilling fluids into the formation probably damages the reservoir and causes wellbore instability; and (3) the large loss of drilling fluids contributes to a thick filter cake, which reduces the effective diameter of the hole and causes various problems, such as excessive torque when rotating the pipe, an excessive drag when pulling it, and arid high swab and surge pressures. Thus it is essential to control the filtration properties of drilling properties.

Figure 1.4 The roles of conventional clay minerals and nanoclays in controlling fluid loss.

Previous investigations demonstrated that the quality of drilling fluids depended on the volume of filtrate lost to the formation, filter thickness, and the strength of the filter cake (Elkatatny et al., 2012, 2013; Ba geri et al., 2013; Yao et al., 2014). The volume of filtrate depends on the magnitude of differential pressure between the drilling fluid and the formation, and the nature of fluid solids making up the filter cake. Bentonite and the corresponding organoclay are the key materials to create a low-permeability filter cake on the formation and to reduce the volume of liquids, because the platy particles and even exfoliated layers can block the pores and form a low-permeability cake (Fig. 1.4). Thus clay minerals and organoclays provide a fundamental filtration property for drilling fluids. Although some other additives, such as starch, lignite, and polymers, are often added to control fluid loss (Balaga and Kulkarni, 2022), they have to work with clay minerals and organoclays. Particularly, drilling fluids prepared with Pal or Sep usually show large fluids loss because their nanofibers form a porous filter cake. In this case, suitable fluid loss reducers must be developed. Therefore the interaction between clay minerals and fluids loss reducers is essential to high-performance drilling fluids.

Furthermore, nanotechnology and nanomaterials have been emphasized recently in controlling the filtration properties of drilling fluids (Esmaeili, 2011; Abdo and Haneef, 2012; Hoelscher et al., 2012; Vryzas and Kelessidis, 2017; Ali et al., 2020). The application of nanomaterials not only improves the rheological properties of drilling fluids but also reduces the fluid loss volume. Such nanomaterials include nanoparticles and nanoclays (Cheraghian, 2021; Al-Shargabi et al., 2022). Nanoparticles, including nano Fe2O3, SiO2, TiO2, ZnO, and CuO, are often used to reduce fluid loss by bridging pores and to improve rheological properties. The filtration properties of drilling fluids depend on the interaction between nanoparticles and clay minerals (mostly Mt), except for the nature of nanoparticles (e.g., particle size and colloidal behavior). More recently, nanoclays, including natural and synthetic clay minerals, were proved to have remarkable performance in controlling fluid loss (Fig. 1.4). Shakib et al. (2016) compared the filtration properties of a nanoclay and several nanoparticles in WBM. These authors found that nanoclay showed the best performance in controlling filtration compared to nano TiO2, CuO, and Al2O3. The nanoclay reduced the filtration rate by about 5% more than conventional additives. In addition to natural nanoclays, some synthetic clay minerals and clay mineral-like materials are also reported to have excellent filtration properties. For example, the dispersion of 2 wt.% of magnesium aluminum silicate (MAS), a Mt-like material, dispersion maintained better rheological properties than the dispersion of 8 wt.% bentonite, and MAS reduced the fluid loss volume by forming a much smoother filtrate cake for plugging nanopores (Wang et al., 2018). In addition, Lap is also confirmed to be excellent in controlling the filtration of WBM due to its disk-like nanostructure and the negative-charged surface (Huang et al., 2018, 2021). When Lap was used, the thickness of filter cakes and the fluid loss volume were reduced by 15%–20% when compared to the fluids without Lap (Mohamed et al., 2021).

Previous studies have shown that clay minerals are the basis for controlling the filtration of drilling fluids. On the one hand, conventional bentonite is the basic material used to form cakes, and the interaction between clay minerals and fluid loss reducers governs the final filtration of drilling fluids. On the other hand, nanoclays are thought to be the next generation of filtration controllers. The synthesis, processing, and application of nanoclays should be given more attention.

1.5 Conclusions

The World Energy Agency and other energy agencies predict that the global demand for oil and natural gas will remain very high in the coming decades. Natural gas, the cleanest fossil fuel, will be particularly crucial in bridging the gap between old and new energy sources. As conventional and easily extractable oil and gas resources have declined significantly, the main growth of oil and gas in the future will primarily come from the deep earth, offshore, and unconventional oil and gas resources (mainly from shales). There are significant obstacles to extracting and utilizing these oil and gas resources, such as high temperatures, high pressures, high salinity, and unstable shale. These problems call for high-performance additives capable of providing excellent rheological and filtration properties for drilling fluids under challenging circumstances while maintaining wellbore stability. In addition, environmental pollution involved in the drilling process has attracted much attention from the public. Future additives should not only meet the requirements of high performance, but also be environment-friendly.

Clay minerals are a group of natural colloidal materials. Clay mineral–based materials are less expensive and less harmful to the environment than colloidal polymers, and they have better rheological and thermal stability in drilling fluids. As a result, clay mineral–based materials are ideal colloidal materials for drilling fluids. The clay products represented by bentonite have already played a great role in regulating drilling fluid performance. The clay minerals used in traditional drilling fluids are mainly Mt, with a few Pal and Sep. These clay minerals lack deep processing, and cannot meet the requirements of high temperature, high pressure, high salt concentration, and other difficulties. In addition, the hydration of illite-rich shales is an important bottleneck limiting the exploitation of shale oil and gas. Illite and its interaction with organic matter are the key factors controlling the hydration behavior of these shales. However, the microstructure of such shales and the surface interactions of clay minerals are still poorly understood. Therefore there is an urgent need to design and develop new high-performance clay mineral-based colloidal materials for different geological conditions (e.g., mineral composition, depth, temperature, and pressure) and to control the stability of shales from the perspective of mineralogy.

Drilling is a geological engineering technique that is closely linked to clay mineralogy. Clay science underpins all aspects of drilling engineering, including formation condition assessment, wellbore stability control, and drilling fluids chemistry. Future drilling engineering and drilling fluids cannot develop without clay minerals. Therefore clay minerals will continuously play an important role in the next generation of drilling technology.

This Volume aims to provide an introduction to clay science related to drilling and drilling fluids, including fundamentals, research advances, challenges, and future directions. It contains 12 chapters, including this chapter that provides a general introduction. The interactions and applications of clay minerals in WBM and of organoclays in OBM are described, respectively, in Chapters 2–4 and in Chapters 8–10. The wellbore stability related to clay minerals by inorganic and organic inhibitors is described in Chapters 5–7. In Chapter 11, the industrial clay products used in drilling fluids are presented and finally clay-related challenges in drilling are provided in the last Chapter 12.

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