AADE-17-NTCE-129 Impact of Anionic Nanoparticles on the Rheological , Filtration and Hydraulic Properties of the Flocculated Water-Based Drilling Fluids

As “multi-function” additives, anionic nanoparticles can be used to enhance the properties of the water-based drilling muds (WBM) and simultaneously fulfill different drilling requirements. However, they may diminish the properties if they are poorly designed. Hence, the objective of this study is to experimentally investigate the potentiality of nanoparticles in the WBM. This is achieved by investigating and comparing the impact of very low concentrations of commercially affordable two types of nanoparticles on the rheological, hydraulic and filtration properties of flocculated water-based muds (WBMs). The optimum type and concentration that enhance these properties and optimize the hydraulics of the mud are targeted. In this research, the samples were prepared as high pH (11.5-12) WBMs and with two different types and various concentrations of anionic nanosilica and nanotitanium particles. Series of laboratory tests were carried out for all samples using standard API Low Pressure Low Temperature (LPLT) filtration and rheological devices. For the hydraulic evaluation, a commercially available software was used to estimate the impact of the nanoparticles on the equivalent circulation density (ECD) and the drillpipe pressure (DPP) in a typical directional well. Results show significant enhancements in the rheological and hydraulics properties of the flocculated WBMs treated by 0.1% wt. or less of nanosilica and 0.3% wt. or less of nanotitanium. The results show the ability of these concentrations to reduce the filtration, make the filter cake consistent, compacted, fragile, smooth, and thin and prevent the spurt water loss. However, the results reflect the poor impact of the concentrations above 0.3% by weight on the mud’s properties. As rheological modifiers and filtration inhibitors, nanoparticles used in this research play vital roles in reducing drilling problems and later costs if they are properly formulated. Hence, stuck pipe, formation damage, and shale swelling can be overcome. Thus, slim holes and horizontal wells can be drilled using water-based nanomuds instead of oil-based muds that are expensive and environmentally unacceptable. Introduction The failure to optimize or balance drilling fluid properties due to poor designs leads to many drilling problems and longer drilling times. This makes the drilling mud one of the major aspects that either increases or decreases the well cost and later the production capacity. Therefore, it has to be efficient enough to overcome the problems, thereby reducing the drilling costs. For instance, it has to overcome shale swelling, prevent stuck pipe, reduce bit balling, minimize generated torque and drag, prevent formation caving/sloughing, minimize surge and swab pressures, reduce reservoir damage, prevent mud circulation loss, and enhance insufficient hydraulics (Salih et al. 2016). All these problems are directly related to the rheological, filtration and hydraulics properties of the drilling muds. In turn, these properties are directly related to the flocculation level of the mud. Flocculation is one of the detrimental phenomena in the WBMs. It results in poor mud properties (Salih et al. 2016). The flocculated WBM is one of the causes of the abovementioned problems. It results in high filtration, yield point, viscosity, gel strength, mudcake thickness, and low mud pumpability, and its rheological behavior and filtration property are not stable under complicated drilling conditions. Therefore, oil-based mud is a more suitable solution to minimize drilling problems. However, unlike the water-based muds, it is environmentally and economically unfavorable. Exposing poorly designed WBMs to cationic bearingenvironments, containments, lead to the flocculation. Hence, various soluble contaminants such as salts, cement, anhydrite or gypsum that are present in drilling operations result in flocculation (Salih et al. 2016). In addition, high temperature and high mud pH cause flocculation. Therefore, the WBM’s properties must be enhanced to increase the resistance to contamination by various chemicals. This increases the stability under different conditions. Conventional chemicals are used to treat the mud with poor performance under harsh conditions. For example, conventional filtration inhibitors do not function under high temperatures since they reduce the filtration by increasing the viscosity of the water-based mud’s continuous phase. Therefore, researchers have recently incorporated the nanoparticles as new and smart additives to the water-based mud and have made it as a water-based nano mud. The water-based nano mud contains one or more chemical additive particles sized in nanoscale, 1m=10μ=10nm. Unlike AADE-17-NTCE-129 Impact of Anionic Nanoparticles on the Rheological, Filtration and Hydraulic Properties of the Flocculated Water-Based Drilling Fluids Salih, A. H. and Bilgesu, H. I. , West Virginia University 2 Salih, A. H. and Bilgesu, H. I. AADE-17-NTCE-129 their parents, these nanoparticles are characterized by high surface area to volume ratio, by providing surplus charges to the mud, by having tiny sizes, by having super sensitivity, and by having perfect particles distribution (Amanulah et al. 2011). Figure 1 illustrates the new particles after crashing a parent particle. As chemicals, they are strongly charged particles and they are classified into cationic and anionic nanoparticles according to the ion (atom) types on their surface. Therefore, few amounts of them can play significant roles and perform multi-functions in the drilling mud. The result is the waterbased nano mud with the advantages of the oil-based mud, but it is cheaper and environmentally acceptable (Salih et al. 2016). Figure 1: Surface Area to Volume Ratio of Nanoparticles (Salih et al. 2016) Due to their features, they can change the internal link process and distribution of the clay particles, Bentonite platelets. The result is a wide range of drilling fluid behaviors and filtration properties that is also based on their types, concentrations, sizes, structure, pH, and charging types. Recently, various nanoparticles were investigated and their performances were reported by many researchers such as Sharma et al. (2012), Sensoy et al. (2009), Cai et al. (2011), Li et al. (2012), Riley et al. (2012), etc. based on different methodologies. Hence, different performance of nanoparticles was described. For instance, some nanoparticles work as a perfect bridging agent due their tiny sizes. Therefore, they physically plug the nanometer-sized pores and shut off water loss in shale formations, thereby preventing shale swelling and its related problems. Properly formulated nanoparticles with water-based mud can replace the oil-based mud used as a shale swelling inhibitor. For the same reason, the nanoparticles can reduce the filtration and enhance the associated mudcake properties—they result in thin, compacted, smooth, and plaster like mudcake ((Srivatsa & Ziaja 2011), (Javeri et al. 2011), (Salih et al. 2016), (Zakaria et al. 2012), and (Ismail et al. 2014)). However, selecting the optimum size and structure of nanoparticles that show superior plugging is challenging. The water-based nano mud with hydrophilic film forming capability on the surface of drillbit can mitigate the bit balling problem— this is due to the high surface area to volume ratio and very low concentration requirements of the nanoparticles (El-Diasty and Ragab 2013). This occurs especially in sticky formations such as marl and shale rocks. As a result of minimizing the bit balling, the rate of penetration will increase. The nanoparticles play significant roles in reducing the torque and drag forces throughout drilling operations. They work as lubricants, reducing the friction between the drill string and the well wall interface. Similarly, this feature helps in reducing the plastic viscosity—they work as ball bearings to facilitate the solids movement in the mud. Hence, the stuck pipe, equivalent circulation density (ECD), and circulation pressure loss can be reduced. By reducing the ECD, the mud circulation loss problem can be minimized. Proper shape and size of the nanoparticles should be selected for high performance. Interestingly, only few amounts of the nanoparticles can enhance the rheological properties of the WBM due to high sensitivity and superior interaction with the Bentonite particles. However, based on their properties, they may increase or decrease the rheological properties such as the yield point and gel strength. Therefore, critical concentrations must not be exceeded in order to avoid damage to rheological properties ((Amanullah et al. 2011), (Contreras et al. 2014 a&b), (Jung et al. 2011), (Fakoya and Shah 2013), and (Nasser et al. 2013)). It has been reported by Amanulah et al. (2011) that the nanoparticles have less kinetic energy impact, thereby increasing the life of the downhole tools. It is well known that wear and tear decrease the life of the tools. They are caused by the forces created due to the extreme kinematic energy associated with the large particles continuously added to the mud either naturally such as drilled cuttings or by rig crew for specific purposes during drilling operations (Salih et al. 2016). These forces can be minimized by replacing the large quantities of micro particle additives with a small amount of nanoparticles for the same purposes. By replacing the big particles with tiny particles, the plastic viscosity will decrease which is desirable. According to the above-cited researches, it is obvious that the nano-based drilling fluids are regarded as a new generation of drilling fluids—they have been recently discovered. This implies the possibility of a wide range of further studies and improvements using nanoparticles with drilling fluids. In addition, it is seen that not all the used nanoparticles enhanced all the mud properties simultaneously. Therefore, the researchers need