It is generally observed that metallic oxides form nanoparticles which tend to increase the yield point of the drilling mud. Metallic oxides exhibiting the ability to form ionic bonds results in the increment of the Plastic viscosity and simultaneously enhances the Gel Strength of the drilling fluid. Dealing with metallic oxides nanoparticles is rather easy because they are easily available and economical but oxides of some transition metals like TiO2, CuO, and other transition metal oxides may be toxic and can be harmful to the environment.
Initial researches have been carried out using Polypropylene resin using CaCO3 (98.5% pure) as a filler to increase the Yield Point of the drilling fluid . But somehow, the effect on other rheological properties wasn’t explained. Due to advancement in technology much more research work in the coming decade various other works were proposed which successfully explained the effect of nanoparticles on the rheology of drilling fluids.
Research carried out by taking 5% Bentonite as a base fluid and adding Fe2O3 nanoparticles (3-30 nm) with composition (0.5 and 5 wt.%) showed an increased amount of yield stress at a temperature (20-200° C) and a pressure ranging between 1-100 atm . This was the first convincing research work and then further research works were performed to enhance the plastic viscosity, gel strength and filtration properties of the drilling mud.
Various tests and researches have also been carried out to use nanomaterials as CLM (Circulation Lost Material). The use of these nanoparticles will help in drilling the shale formations and other porous formations. The tests carried out reported that there was a slight decrement in the viscosity and also a reduction in fluid loss was found out to be 70% by the API Filtration Tests. Also, a thin filter cake was formed which resulted in reducing the formation damages .
Further researches gained popularity by using ZnO nanoparticles as additives in the drilling fluid. ZnO nanoparticles were formed by using Zn(CH3COO)2.2H2O, Methanol, and NaOH. The results showed that there was an increase in the Yield stress of the drilling mud and the viscosity of the mud was also increased .
Since the wellbores are drilled deep up to 10,000 feet so, there was a need to develop such nanofluids which can be operated at high pressure and temperature conditions. So, further researches were carried out to operate such fluids at HTHP conditions.
Modifying CaCO3 nanoparticles with stearic acid resulted in increased Yield Point of the bentonite water-based mud . Also, Polystyrene Butadiene Rubber Copolymer (PSBR) and ZnO nanocomposite have shown better results by increasing the Yield Point and a Plastic viscosity at High Temperatures for the oil-based mud . PBSR/CaCO3 nanoparticles were used with oil-based mud to increase the Yield point of the mud at High Temperature .
According to an investigation on iron-based and calcium-based nanoparticles with glime graphite as a CLM (Circulation Lost Material) with an oil-based mud tends to provide stability by minimizing the formation damage at 120° C and at atmospheric pressure. Also, it is noticed that samples of Calcium nanoparticles tend to increase the plastic viscosity of the drilling fluid whereas samples containing Iron nanoparticles led to a reduction in the yield point of the drilling fluid. It was further investigated by using a ceramic disc of 775 mm which concluded that Iron nanoparticles at HTHP conditions had higher fluid reduction than those operated at LTLP conditions at lower concentrations whereas Calcium nanoparticles exhibited higher fluid losses at higher concentrations .
It has also been seen that mixing Fe2O3 nanoparticles of different concentrations with the base drilling fluid containing 7% aqueous Na-bentonite helped in enhancing the rheological properties of the drilling fluid. The research reported a reduction in filtrate loss up to 42.5% upon mixing Iron nanoparticles 0.5% by weight. At Higher temperatures it was also found that the yield stress of the drilling fluid increased as there was an increase in the plastic viscosity of the drilling fluid at 250° F and 300 psi differential pressure and keeping it for 10 minutes and the concentration of the Iron Nanoparticles was found to be 0.5% by weight [24,25,32,35].
A novel approach for introducing Calcium nanoparticles (51±11 nm) of 0.5% by weight helped in reducing the fluid loss by 20-30% during normal drilling operations at High Temperature and High-Pressure Conditions .
Developments in drilling fluid were very successful but still, there was a need of such nanofluids which could significantly reduce the filter losses.
Studies have also shown that taking 5% Bentonite as a base fluid and adding Fe2O3 nanoparticles along with two other Clay-based hybrids ICH (Iron Oxide Clay Hybrid) and ASCH (Alum inosilicate Clay Hybrid) tends to affect the rheological properties of the drilling fluid. At high-pressure ICH showed improved yield stress whereas, on the other hand, ASCH showed lower yield stress for lower shear rates. The filtration tests showed that at Low Temperature and Pressure conditions, ICH and ASCH were able to reduce fluid loss by 37% and 47% respectively. However, at High Temperature and Pressure conditions, 0.5% by weight of Iron Oxide Nanoparticles of 3 nm and 30 nm were able to reduce the fluid loss up to 27.6% and 23.4 %. The further results stated that due to the replacement of Na+ ions with Fe2O3 nanoparticles was responsible for lower permeable filter cake, thus adding of ICH and ASCH provided good dispersion and thus avoided flocculation and coagulation .
It is seen that with increase in concentration of nanoparticles up to 0.25% by volume, nanoparticles like TiO2 (21 nm), Al2O3 (50 nm) and SiO2 (10-20 nm) show an enormous increase in the surface tension of the drilling fluids as compared to the addition of 0.20% by volume of the mentioned nanoparticles .
Further investigations have found out that using custom-based Fe3O4 nanoparticle (8 nm) along with the Na-Bentonite based drilling fluid helped in enhancing the rheological and filtration properties. At 250° F and a concentration of 0.5% by weight of the nanoparticles, there was a significant increase in the yield stress and at the same time, it was reported to reduce up to 40% of the filtrate losses. Upon aging, the mixture to 350° F and 16 hours the properties of the base fluid were affected and hence it was found that upon adding the nanoparticles there was an increase in the thickness of the filtrate and hence there was an increase in the reduction in the filtrate losses up to 43%. The filter cake obtained by the Fe3O4 nanoparticles exhibited chain-like structure which was rather more efficient to stick to the surface [33,35-38].
Performance of drilling fluids has also been evaluated of 7% Bentonite by mixing commercial Fe2O3 and SiO2 nanoparticles of different concentrations up to 2.5% by weight. The results obtained were of great significance as adding of Iron Oxide nanoparticles exhibited higher Yield Point and Plastic Viscosity at Higher Temperature (more than 200° F) but adding Silica nanoparticles gave lower yield point at high temperatures. Certain aging tests were also carried out at 350° F and for about 16 hours, the results showed that Silica-based Bentonite drilling fluid had better rheological properties than that of the Iron Oxide Nanoparticles. Properties like Gelation and Stability of the drilling fluid were enhanced. Also, results showed that at a concentration of 0.5% by weight of Iron Nanoparticles helped in reducing the filtrate loss by volume up to 42.7% and thus by increasing the thickness of the filter cake by 17.32% [30,31].
Researches have also been carried out involving Nanofluid Enhanced Water-Based Drilling Mud (NWBM) which are being invented by using the nanofluids such as CuO and ZnO (<50 nm) taking Xanthan Gum as a base fluid (0.4 % by weight). Additives like prehydrated bentonite slurry (5cP), Polyanionic Cellulose (PAC-L, to prevent fluid loss), KCl and KOH (pH between 9.0-9.5) were added and mixed in an ultra-sonication tank. The results obtained are quite convincing as there is an increment in the NWBM electrical and thermal properties by around 35% as compared to the Water-Based Drilling Mud (WBM). The research shows that addition of CuO and ZnO helps in increasing the thermal and electrical properties which means that NWBM can be operated at HTHP conditions. However, the effect of Pressure on the rheology of the NWBM at High Temperature was more significant and it was also reported that such nano mods exhibit a higher viscosity at High Temperatures [34,39].
In a recent research, it was seen that upon increasing the concentration of Hematite nanoparticles to the concentration of Barite which was preset to 5%, which led an increase in the rheological properties of the drilling mud like yield point, plastic viscosity and gel strength. It was also noticed that ratio of the yield point to the plastic viscosity was more in case of laminar flow. Higher yield point means that cuttings can be easily transported to the surface .
There seems a greater need of controlling the yield stress and plastic viscosity of the nanofluids. Various tests and researches have been carried out to deal with such situations. Using TiO2 and Polyacrylamide (PAM) nanocomposite along with the water-based drilling fluid helps in gaining the yield strength and plastic viscosity of the drilling mud. However, there is negligible change in the filtration properties .
Despite so many works on the metal oxide nanoparticle-based drilling fluid, there still seems to be ample of work yet to be carried out. Effect of magnetic field on the iron nanoparticles and how it influences the properties of the drilling fluid is one of the major challenges. Also, studying the effects of these nanoparticles on the formation is also one of major concern.
Designing a drilling fluid is a daunting challenge as various rheological properties have to be controlled. Also keeping the environmental aspects in mind, it is a bit tough to design such nanofluids which could drastically change the drilling industry. It seems a great challenge to deal with such magnetic nanoparticles whose rheological properties change under the effect of a magnetic field. Few types of research have been carried out on the effect of magnetic field on the properties like yield point and viscosity of such magnetic nanofluids.
It is reported that upon increasing the magnetic field intensity by 0.7T, the Fe2O3 water-based drilling fluids constituting of bentonite (5%) exhibited greater viscosity . However, this research was unable to explain the effect of the magnetic field intensity on the yield strength of the drilling fluid.
Further researches based on the hematite nanoparticles (0.5% and 1% by weight) shows that with an increase in the magnetic field intensity from 0 to 0.7T there was an increase in the shear stress and viscosity of the nanofluids. The results show that a chain-like structure exhibiting high yield points up to 386% for 0.5% and 609% for 1% by weight were observed. Finally, it was observed that particles recovered back to their original position after the removal of the magnetic field .
Thus, it is seen that with a change in the magnetic field intensity, the plastic viscosity and Yield points change extensively.
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