Introduction

Drilling fluid is a vital component in any drilling process (Aftab et al. 2017). In this regard, the right choice of drilling fluid with proper additives is a crucial factor for successful drilling activity (Ali Esfandyari Bayat et al. 2018). Drilling muds are used for numerous functions which include reducing the friction by increasing lubrication, lifting and carrying the cutting up to the surface, maintaining hydrostatic head in the wellbore, providing seal against a permeable formation, and minimising the hole roughness and eliminating corrosive environment (Aftab et al. 2017; Ali Esfandyari Bayat et al. 2018; Elkatatny 2019; Lalji et al. 2021a, b; Kamath et al. 2022; Mohan et al. 2022). In general, drilling fluids are classified into three distinct categories, namely oil-based mud system (OBM), water-based mud system (WBM) and synthetic mud systems (Sharma et al. 2012). The synthetic mud systems and oil-based mud systems have some high operational, cost and environmental problems as compared to water-based mud systems (Al-Arfaj et al. 2014; Ali Esfandyari Bayat et al. 2018). Therefore, WBM is counted as the preferred option in spite of its limitations. Hence, it is imperative to study the properties of WBM for the purpose of improving its properties.

There are various drawbacks associated with water-based drilling fluids (WBDF) that include wellbore stability as a result of shale swelling, poor rheological properties, and high loss of filtrate volume that eventually gives rise to some severe differential pipe sticking problems (Al-Ansari et al. 2017; Adnan Aftab et al. 2020). These problems can be minimised using the OBM systems. However, environmental issues prohibited its use (Adnan Aftab et al. 2020). Therefore, WBM systems were counted as the main solution to the above-mentioned problems. These were the reasons that provoked researchers to concentrate on the modifications of properties of WBM systems, especially its rheological behaviour. The characteristics of WBM can be controlled and improved through the use of different additives that are mainly classified as salt, polymers and nanoparticles.

The distinctive properties of nanomaterials assist them to become part of a variety of disciplines (Chen and Huang 2021; Cheng et al. 2022; Duan et al. 2022; He et al. 2022; Shao et al. 2022; Si et al. 2022; Soares et al. 2022; Xie 2022a, 2022b; Zhang et al. 2022; Zhu et al. 2022; Qin et al. 2023). However, the addition of nanoparticles in the drilling industry has now opened new doors for the petroleum sector, and it is thought to be the most recent development in the oil and gas field. These materials are responsible for improving mechanical, rheological and thermal properties of mud systems (Abdo and Haneef 2013). Performances of different nanomaterials in drilling muds are studied by numerous researchers (Jung et al. 2011; Al-saba et al. 2018; Mohideen 2019; Lalji 2022a, 2022b). Modifications in the properties of drilling mud by the use of nanoparticle ultimately help the industry to minimise the non-productive time events.

Iron oxides, as a result of their technological significance, are considered to be the most significant transition metals (Asab et al. 2020). Magnetite (Fe3O4) is the most common iron oxide that is found in nature, and it also possesses some interesting characteristics (Babay et al. 2015; Asab et al. 2020). This oxide of iron consists of two valence states Fe2+ and Fe3+. However, its nanoparticle undergoes two major problems like oxidation in the presence of air, and second, rapid cluster formation (Babay et al. 2015). Therefore, coating the surface of iron oxide particle is the most common solution that can easily confront these above-mentioned problems (Babay et al. 2015). The coating can be through organic materials like alginate and dextran (Turrina et al. 2022), or it can be done with the help of inorganic material such as silica (Turrina et al. 2022). The inorganic coating with silica has now become a promising approach in order to improve the characteristics of iron oxide nanoparticles (Yong-Hui Deng et al. 2005). Silica coating layer is utterly responsible for developing a chemically inactive surface in the presence of any biological systems (Yong-Hui Deng et al. 2005); however, the problem of agglomeration is still associated with this material. Consequently, the rheological properties and the stability of drilling fluid need more suitable materials.

The carbonaceous materials are other segments of compounds that are widely used in different commercial sectors. In the form of nanoparticles, these carbonaceous materials are generally classified into two separate categories—carbon nanoparticles and graphene nanoparticles. Their distinctive mechanical, physical and chemical behaviours enable the researchers to not only use them in pristine form but also encourage their use in different composite forms as well (Ibrahim Khan and Khan 2019). Their commercial applications include: fillers, sensing technologies and electronic devices (Chen et al. 2022; He et al. 2022; Tiwari Nidhi 2022; Wang et al. 2022a, 2022b; Xie et al. 2022a, b; Yan et al. 2022; Zhang et al. 2022; Kuang et al. 2023). However, poor dispersion of these particles in the water-base mud system is one of the serious problems associated with them (Cheraghian 2021). Therefore, the focus in this study is on activated carbon, another carbonaceous material with high adsorption capacity and fast reaction kinetics.

Activated carbon is defined as a porous carbonaceous material with some unique properties (Heidarinejad et al. 2020). This material has some vast applications in the field of wastewater treatment, desalination and air purification (Kosheleva et al. 2019; Heidarinejad et al. 2020; Ahmadi et al. 2021; Deng et al. 2021a, 2021b, 2022; Sun et al. 2021; Lu et al. 2022; Choi et al. 2023). 90% of this material is made from carbon (Samsuri et al. 2014; Heidarinejad et al. 2020). In addition, this compound contains high surface area with different associated functional groups that are mainly responsible for adsorption of any contaminants (Heidarinejad et al. 2020; Begum et al. 2022). Azeem et al. bind the activated carbon with polyamine dendrimers and use the compound for shale swelling inhibition (Azeem Rana 2022). The larger surface area, the nontoxic nature and the nano-carbon content related to activated carbon help it to bind effectively, which in turn enhances the drilling mud properties (Azeem Rana 2022). Limited applications of activated carbon in drilling are available in literatures; therefore, it is important to focus on this material in order to investigate its performance.

In the current study, for the first time, the rheological comparison is done between silica-coated iron oxide nanoparticles and activated carbon. To the best of our knowledge, this is the first rheological and mud stability comparison study for these two particles. Two different concentrations of each particle were investigated, and based on that all, the rheological parameters were obtained. In addition, for the first time, stability of the mud system was observed with the help of intensity profile plots and interactive 3D surface plots. The mud samples were kept stationary for the duration of five days, and based on that, different intensity plots were obtained. These plots show the settling and the dephasing of each sample after five days. It is a novel method for spotting the changes in mud stability when there is some circulation for any unknown event.

Materials and methods

Materials

The study aims to investigate rheological behaviour and stability of the mud system after the addition of activated carbon and silica-coated iron oxide nanoparticles. Activated carbon is attained from the chemical treatment of different carbonaceous resources. During this study, this compound was purchased from Sigma Aldrich. On the other hand, silica-coated iron oxide nanoparticles are the nanoparticles of iron oxide coated with silica. The purpose of this coating is to increase the force of repulsion between the iron oxide particles.

Scanning electron microscope (SEM) imaging of particles

Figure 1a, b shows the scanning electron microscope imaging (SEM) for both the particles in the study. The SEM instrument is manufactured in Japan by Joel, and the model used during the analysis is JSM 6380A. Figure 1a is the SEM imaging of activated carbon. It can be observed that the external surface of activated carbon consists of holes, cracks and fissures. Additionally, there are also some small fine particles over its surfaces, which are likely to be the ash particles (Fronczak et al. 2019). Figure 1b shows the SEM imaging of silica-coated iron oxide nanoparticles. It can be observed from the figure that the particles are spherical in shape just like magnetic beads.

Fig. 1
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a, b SEM imaging of particles a activated carbon b silica-coated iron oxide nanoparticles

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Preparation of water-based drilling fluid

During this study, 350 cc of salt polymer amine water-based drilling mud was prepared and tested. Table 1 shows the additives, quantity and its supplier used to prepare the base mud system.

Table 1 Additives used to prepare the water-based drilling mud
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The purpose of this study is to investigate the rheological variation in salt polymer amine water-based drilling mud after the addition of nanoparticle and a carbon-supported particle. The particles are added into two different concentrations (0.25 wt. % and 0.5 wt. %) respectively. In addition to rheological behaviour, the stability of the mud systems was also investigated using the image processing software. 10 mL of each mud sample was placed in the test tube after the addition of particles. These samples were monitored three times during the course of five days. The intensity profiles of the test tubes were recorded for each day, and the settling of the particles was observed based on the profile. Figure 2 shows the flowchart of the study conducted in this article. Table 2 shows four samples with their concentrations that are used in this work.

Fig. 2
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Flowchart of the work conducted in this study

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Table 2 Different samples under observation and their weight percentages
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Rheological properties

All the rheological parameters were measured using FANN 286 rheometer manufactured by Fann Instrument Company, Houston, Texas, USA. The rheological analyses are performed at ambient condition of 27 °C. Furthermore, each rheological parameter is recorded thrice using FANN 286 rheometer, and the average measurement is reported in the study. The accuracy of the six-speed rheometer used in this study is \(\pm 0.5\) of dial measurement. Eqs. (1, 2 and 3) are used to measure the rheological properties of the drilling fluid in this study (Ali Rafieefar et al. 2021).

$${\text{Plastic viscosity}}\,{\text{cP}}\,\theta_{600} - \theta_{300}$$
(1)
$${\text{Yield Point}}\,{\text{lb}}/{1}00{\text{ft}}^{{2}} \,\theta_{300} - PV$$
(2)
$${\text{Apparent Viscosity}}\,{\text{cP}}\,\frac{{\theta_{600} }}{2}$$
(3)

\(\theta_{600} and \theta_{300}\) are the dial measurements obtained from FANN 286 rheometer. The gel strength is recorded at 10 s interval for each fluid system under observation.

Results and discussion

Mud weight

Mud weight (MW) or usually denoted as mud density is a vital feature during any drilling activity. This parameter acts as a primary barrier; hence, the majority of the drilling problems are related to this factor (Fattah and Lashin 2016; Ismail et al. 2020). To effectively determine the effect of activated carbon and nanoparticles on the salt polymer amine water-based drilling mud, mud weight is the first parameter that was investigated. The expected mud weight for this mud system was 8.6 ppg, which was provided by the service operator. It was observed that no substantial changes in mud weights were observed with the addition of particles as shown in Fig. 3. A narrow range of variation was witnessed with the addition of these particles. Sample 1 and Sample 2 that are prepared from the activated carbon demonstrate an increase of 0.2 ppg MW from the operator provided MW. Sample 3 and Sample 4, which are prepared using the nanoparticles, show an increase of 0.1 ppg from the expected MW. These MW are not high enough to induce fractures or damage the formation. Hence, these particles are effective in maintaining the desired mud density.

Fig. 3
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Mud weight of all the sample in this study

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Rheogram of all the samples

Figure 4a shows the rheogram of all the samples in this study. Rheogram describes the flow comportment of any fluid (Jain et al. 2016). This curve consists of a relationship between the shear stress and shear rate, and classifies the fluid either as Newtonian or non-Newtonian in nature (Jain et al. 2016). A linear relationship shows the Newtonian characteristics in the fluid system, whilst a non-linear curve demonstrates non-Newtonian behaviour with either shear thinning or shear thickening properties. All the samples in the study reveal pseudo-plastic or shear thinning behaviour. Moreover, an increase in shear stress was observed with an increase in particle concentration. The maximum shear stress was witnessed in Sample 2. This sample comprises maximum concentration of activated carbon. On the other hand, the minimum shear stress was noted in Sample 3, which consists of the least weight percentage of silica-coated iron oxide nanoparticles.

Fig. 4
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a Rheogram b dynamic viscosity of all the samples in the study

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The rheogram results were also validated with dynamic viscosity results that are represented in Fig. 4b. An increase in shear rate corresponds to the decrease in dynamic viscosity in all the samples. At low shear rates, the flocculation of the particles and the aggregation of the polymer result in higher shear viscosity. However, as the shear rate increases, the particles and the polymers align in the direction of flow, which eventually reduces the drag force. During pumping and mixing, it is desirable to have fluid that demonstrates low viscosity (Jain et al. 2016). A complete opposite characteristics should be there when the same fluid returns to the surface.

Rheological properties

Figure 5 shows the rheological parameters of all the samples in this article. Figure 5a shows the plastic viscosity (PV) of activated carbon and silica-coated iron oxide nanoparticles. This feature of drilling fluid usually increases with an increase in solid content in the fluid system (Aftab et al. 2016). It is the friction that arises between the different fluid layers or between the solid particle and the fluid layer (Elkatatny 2019). Higher values of PV will develop several problems like high swab and surge pressure, high equivalent circulation density and high probability of pipe sticking (Aftab et al. 2016). The plastic viscosity of the base mud was 13 cP. After the addition of the particles in the base mud system, an improvement in PV was recorded. The Sample 2 maintained the PV in the desired operating range of (20–29 cP). This sample comprises the highest weight percentage of activated carbon. In the remaining samples, PV was on the lower side. Sample 4, which comprises a higher weight percentage of nanoparticles (NP) shows higher PV value as compared with its lower weight percentage Sample 3. Similar trend was witnessed in Sample 1 and Sample 2. Overall, it was observed that as the concentration of the studied particles increases in the fluid, PV of the system increases. The improvement in PV will eventually assist in cutting transportation mechanisms and will eradicate problems associated with sticking of drill pipe and re-drilling of the formation (Elkatatny 2019).

Fig. 5
figure 5

Rheological properties of all the samples a plastic viscosity b yield point c apparent viscosity d ratio of yield point to plastic viscosity

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Figure 5b shows the yield point (YP) of all the samples. YP is denoted as the capability of drilling fluids to carry the drilled cutting up to the surface (Ismail et al. 2020). The presence of electrical charges on the exterior side of the particle gives rise to electrochemical forces that ultimately give rise to flow resistance in fluids (Ali Esfandyari Bayat et al. 2018). The YP for the base mud system was 10 lb/100ft2. An improvement in the YP was observed in samples 1, 2 and 4. The maximum YP was observed in sample 1 that consists of activated carbon. Fluids that yield higher YP are more effective in terms of lifting and carrying the drilled cutting up to the surface.

Figure 5c represents the apparent viscosity (AV) of all the samples in the study. The feature of drilling fluid is extremely crucial as it ensures the thixotropic characteristics of drilling muds (Aftab et al. 2016). An increase in AV was observed in Samples 2 and 4 as the concentration of the particles increased. The maximum AV was observed in Sample 2, which consisted of activated carbon. The improvement was because of the hydrophobic nature of activated carbon. Furthermore, as the solid content increased in Samples 2 and 4, the increase in viscosity in these fluid systems was recorded. Figure 5d represents the ratio between the yield point and plastic viscosity (YP/PV) of all the systems in this study. Field experience shows that if the ratio yield point-to-plastic viscosity is equal to 0.75–1 \(\frac{{{\raise0.7ex\hbox{${lb}$} \!\mathord{\left/ {\vphantom {{lb} {100ft^{2} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${100ft^{2} }$}}}}{cP}\), then that fluid demonstrates efficient cutting carrying capacity and is effective in hole-cleaning process (Zhihua Luo et al. 2017). During this study, fluid samples 1 and 4 were efficient in terms of maintaining this ratio. This clearly indicates that using either activated carbon or silica-coated iron oxide nanoparticles will effectively clean the hole and minimise the possibility of pipe sticking problems. However, concentration of these particles in the drilling fluid is the key parameter in achieving the desired hole-cleaning properties.

Gel strength of the samples

Gel strength (GS) is another important feature of drilling fluid, which represents the capability of the fluid to ensure the suspension of drill cutting under static conditions (Ali Esfandyari Bayat et al. 2018). It is present in the drilling fluid because of the electrochemical attraction within any fluid system (Ali Esfandyari Bayat et al. 2018). Figure 6 shows the 10 s GS for all the samples. The GS that was recorded for the base mud system was 9 lb/100ft2. It was observed that Samples 1 and 3 that comprise lower concentrations of activated carbon and NPs show similar magnitude and classified as flat rheology. However, when the weight percentage of the particles in the system increased, a corresponding increase in GS was also recorded. The highest GS measured was in Sample 2, which consisted of maximum concentration of activated carbon. An abnormal increase in GS is usually undesirable as it requires higher pumping pressure to break the GS and to initiate the circulation (Elkatatny 2019). In this case, no such irregularity was witnessed in any of the samples.

Fig. 6
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Effect of activated carbon and silica-coated iron oxide nanoparticles on the gel strength (recorded at ambient condition)

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Stability of the mud systems

Figure 7a–d shows the stability of the mud systems observed on two consecutive days. The stability of each mud system was transformed to intensity profile, and the settling of the particles was studied. For the first time, the stabilities of mud systems were observed using these profile plots. Figure 7a shows the intensity profile of Sample 2. This sample comprises 0.5 wt. % of activated carbon in the mud system. According to the Day 1 intensity profile plot, it was observed that settling of solid particles in this system started rapidly. At the top of the test tube, we observed higher intensity regions. This clearly indicates towards the liquid region from which light can easily pass or be transmitted. Towards the lower end of the test tube, and as the distance increased from the top, it was witnessed that intensity decreased, which specified the presence of solid particles. Moreover, an inversely proportional trend between distance and intensity was recorded in this sample. On Day 2 of the observation, it was detected that the area for the high intensity region prolonged further into the test tube and the lower intensity region got smaller in area. This clearly indicates that solid particles move deeper into the test tube.

Fig. 7
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a–d Intensity profiles measuring the stability of mud at day 1 and day 2 a sample 2 b sample 1 c sample 4 d sample 3

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Figure 7b represents the Sample 1 that comprises lower concentration of activated carbon. The solid additives are distributed equally throughout the test tube. The intensity profile plot clearly demonstrates a horizontal trend in the test tube. There are some regions where light intensity drops significantly. These are the areas that represent the higher concentrations of the solid additives that are either flocculates or are not properly dispersed. Same sample when analysed on Day 2 showed no substantial changes in the intensity of the test tube. There were some regions where intensity dropped rapidly. In these areas, solid particles are higher in concentration and they will eventually settle down if no movement is provided to the sample.

Figure 7c shows the stability of Sample 4, which consists of 0.5 wt. % of silica-coated iron oxide nanoparticles. The intensity of the test tube throughout its length is on the higher side. This analysis indicates that the particles in this mud system are well dispersed and no coagulation is observed. It starts to get reduced towards the bottom side of the test tube. However, the intensity was still on the higher side. On Day 2 of the observation, a sudden increase in the intensity profile was recorded. This increase was mainly because of the separation of the water phase from the mud system. However, still the overall intensity profile was on the higher side and it started to drop at the bottom side of the test tube. This drop is mainly as a result of solid particles that separate out and are falling under the action of gravity. The nano-sized particles of the additive are not substantial in size to create an impact on the intensity. Hence, it was on the higher side.

Figure 7d shows the intensity profile for Sample 3 that comprises 0.25 weight percentage of nanoparticles. The particles are well dispersed with no signs of coalescences. The intensity peaks throughout the course of the test tube are on the higher side. This clearly demonstrates that the particles are not able to form any flocculation and they are dispersed all the way through the test tube. The negative outer charge of a nanoparticle is forming a shield that prevents the merging of the particles. On Day 2 of the stability test, a strong peak was observed at the distance of 0.1 in. This is mainly due to the separation of water from the mud system. The lower density of water takes it to the top of the test tube where it is able to increase the intensity profile. At a distance of 0.58, the intensity rapidly decreases. This might be due to the accumulation of some particles at this point in the test tube. Nevertheless, apart from that point, the intensity profile was similar in nature throughout the entire length of the test tube. This demonstrates an even distribution of particle with no effect of coagulation.

Stability test on day 5

The intensity profiles for all the mud samples were also recorded on Day 5. Figure 8a–d shows these profiles for each sample. According to Fig. 8a, it was observed that the higher concentration of activated carbon was not feasible in terms of stability. Substantial reduction in intensity peak was recorded, which clearly indicates towards the settling of solid particles. The activated carbon interaction with the mud system was in the opposite manner, and flocculation throughout the test tube was noted through the intensity profile plot. The concentration of activated carbon became half in Sample 1, and it was observed that the intensity profile also changed significantly as shown in Fig. 8b. The top region profile was on the higher side, which showed the dispersion of the particles. However, towards the later end of the test tube, the profile drops, which corresponds to the settling of the solid particle under the action of gravity. Figure 8c demonstrates the profile for higher concentration of nanoparticles. The liquid phase that was separated out on Day 2 gets higher in volume, which can be observed by an initial larger peak. Moving down the test tube, no substantial changes in peak were recorded, and the behaviour was similar to Day 2. It can be concluded that this sample was quite stable throughout the experimentation. This similar behaviour was also witnessed in a sample that is having lower concentration of silica-coated iron oxide nanoparticles as demonstrated in Fig. 8d.

Fig. 8
figure 8figure 8

Intensity profile for the for different mud system obtained at day 5 a sample 2 b sample 1 c sample 4 d sample 3

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Interactive 3d surface plot for day 5 sample

Figure 9a–d shows the interactive 3D surface plots for the Day 5 samples in the study. These plots show the intensity within the test tube. Figure 9a represents the interactive 3D plot for Sample 2. This sample consists of a higher weight percentage of activated carbon. On Day 5, it is evident that the intensity decreases towards the bottom of the test tube. The higher intensity region as indicated with blue colour is mainly because of the liquid phase, whilst the greenish colour indicates lower intensity due to the settling of particles at the bottom. Overall, the intensity of the test tube is on the lower side because of the higher concentration of activated carbon. Figure 9b depicts the interactive 3D surface plot for Sample 1 that comprises the least concentration of activated carbon. The overall intensity in the test tube is on the higher side as compared with Sample 2. However, a similar trend as observed in Sample 2 is also detected in this sample. Nevertheless, the intensity at the top of the test tube is higher. This clearly indicates that the separation of water from this sample is higher in volume as compared with Sample 2. Figure 9c represents the Sample 4 3D surface plot. This sample has the higher weight % of silica-coated iron oxide nanoparticles. The overall intensity is on the higher side as compared with Samples 1 and 2. However, some settling of the solid particles is observed with the decrease in intensity profile. On the contrary, when the concentration of the nanoparticles decreases as in the case of Sample 3, the surface plot as indicated in Fig. 9d demonstrates a linear trend with no high fluctuations. This clearly indicates that this sample does not suffer any major stability change after five days. However, some de-phase was witnessed at the top part of the test tube with a higher intensity peak. This shows that the liquid phase from the mud separates out and moves to the top.

Fig. 9
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a–d 3D interaction surface plot a sample 2 b sample 1 c sample 4 d sample 3

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Previous studies

The influence of activated carbon on the rheological behaviour of water-based drilling mud was also investigated by (Mahto 2013). Slight improvements in rheological properties were observed with the addition of 3% of this particle in the base mud system. Moreover, when compared to conventional additives like calcium carbonate (CaCO3), it was observed that this improvement was achieved at very less concentration (Mahto 2013). On the other hand, no application of silica-coated iron oxide nanoparticles in drilling mud exists in literature. However, the iron oxide particle as a separate entity is used by researchers in drilling muds (Alvi et al. 2020). The agglomeration of this particle is utterly responsible for increase in gelation and viscosity (Alvi et al. 2020). Moreover, literatures lack the comparison of these particles. Therefore, it was the main core objective of this study.

Conclusion

In the current study, for the first time, the rheological comparison is done between silica-coated iron oxide nanoparticles and activated carbon. Additionally, for the first time, stability of the mud system was observed with the help of intensity profile plots. The following results were gathered based on the experimental investigation:

  1. 1.

    No substantial changes in mud weight were recorded after the addition of both particles. The mud weight was close to the base mud weight provided by the operator.

  2. 2.

    All the samples demonstrate shear thinning characteristics, with dynamic viscosity reduces as shear rate increases.

  3. 3.

    Samples that consist of activated carbon exhibit rheological properties in the desired operating range. These samples showed good cutting carrying capacity.

  4. 4.

    No abnormal changes in gel strength were recorded. All samples showed GS closer to base mud system.

  5. 5.

    According to intensity profile plots, the sample with the least concentration of activated carbon was the most stable sample. No substantial change in stability was recorded after two days of experiment.

  6. 6.

    The silica-coated iron oxide nanoparticle starts to de-phase on Day 1, and separation was visible on Day 2.

  7. 7.

    On Day 5, each sample experiences either settling of solids or dephasing problems as indicated in surface plots.