Feasibility Study of Biodegradable Vegetable Peels as Sustainable Fluid Loss Additives in Water-Based Drilling Fluids

Abstract

Drilling fluids are vital in oil and gas well operations, ensuring borehole stability, cutting removal, and pressure control. However, fluid loss into formations during drilling can compromise formation integrity, alter permeability, and risk groundwater contamination. Water-based drilling fluids (WBDFs) are favored for their environmental and cost-effective benefits but often require additives to address filtration and rheological limitations. This study explored the feasibility of using vegetable waste, including pumpkin peel (PP), courgette peel (CP), and butternut squash peel (BSP) in fine (75 μm) and very fine (10 μm) particle sizes as biodegradable WBDF additives. Waste vegetable peels were processed using ball milling and characterized via FTIR, TGA, and EDX. WBDFs, prepared per API SPEC 13A with 3 wt% of added additives, were tested for rheological and filtration properties. Results highlighted that very fine pumpkin peel powder (PP_10) was the most effective additive, reducing fluid loss and filter cake thickness by 43.5% and 50%, respectively. PP_10 WBDF maintained mud density, achieved a pH of 10.52 (preventing corrosion), and enhanced rheological properties, including a 50% rise in plastic viscosity and a 44.2% increase in gel strength. These findings demonstrate the remarkable potential of biodegradable vegetable peels as sustainable WBDF additives.

1. Introduction

The demand for hydrocarbon products, including natural gas and crude oil, is increasing globally. Yet, it is imperative to reduce the environmental impact of petroleum industry activities, including drilling operations. The fluid, also known as drilling mud, acts as a carrier for cutting from the formation to the rotary part and to the surface and cooling the drill string by providing sufficient lubrication and reducing friction. In addition, the mud provides stability to the uncased section of the borehole, seals permeable formations, controls pressure, and suspends cuttings when the pumps are off. There are generally three types of drilling mud used in the industry: oil-based, gas-based, and water-based mud. Oil-based mud primarily consists of oil, which offers excellent performance in maintaining fluid characteristics. In contrast, water-based mud primarily consists of water and can achieve the desired drilling performance when combined with appropriate additives and regulators. On the other hand, gas-based mud (GBM) is a drilling fluid primarily composed of gas (nitrogen, methane, or air) mixed with foaming agents and a small amount of water. It is ideal for high-pressure gas wells and unconventional reservoirs but is more expensive than water-based drilling mud (WBDM) due to specialized equipment. GBM also carries a high risk of explosion due to pressure from the gas phase and cannot be used in water-bearing formations, as the cuttings aggregate, preventing transport by air or gas [1,2]. The efficiency of the water-based drilling fluid (WBDF), along with the lower preparation cost, makes it the most popular drilling fluid, with over 80% usage in the drilling industry [3]. Nevertheless, fluid loss to the reservoir formation is one of the significant issues of WBDF during the drilling operation that needs to be addressed. Fluid loss occurs due to the differential pressure between borehole fluid and formation pressure, where the water phase separates from the drilling mud and invades the formation [4]. Drilling fluid loss leads to formation damage, permeability alteration, and production decline [5]. The volume of the fluid loss can be controlled by thin and low permeable mud cake on the borehole wall. A thick and highly permeable mud cake will increase the drag and torque of the drilling string. This would lead to pressure differential sticking, primary cementation issues, and a considerable increase in equivalent circulating density (ECD) [6]. Hence, designing a WBDF with the aim of reducing fluid loss is very important for reduc the cost of drilling and improving the performance of the fluid [7]. In addition to filtration properties and control fluid loss of drilling fluid, rheological properties such as plastic viscosity (PV), yield point (YP), and gel strength are also important to be investigated in developing high-performance WBDF. Various chemicals, synthesis polymers, and natural additives are added to the WBDF to regulate and control fluid loss and achieve the desired rheological properties [8]. Some examples are potassium chloride, sodium hydroxide, polyamine, potassium sulfate, chromium-containing thinners, and fluid loss additives [9]. However, many of those additives have long and short-term environmental impacts and are associated with high costs [10]. For instance, using chemical additives such as ferro-chrome lignosulfonate and sodium asphalt sulfonate, which contain excessive amounts of heavy metals like cadmium, mercury, and arsenic, has adverse effects on the environment and its inhabitants. In addition, the chemical-based drilling fluid can affect the neighboring aquifers, which imposes huge costs for groundwater and soil remediation [11]. To mitigate these risks, comply with stringent environmental regulations, and protect ecosystems, many types of WBDF that utilize environmentally friendly additives have been introduced [12,13,14,15,16,17,18,19]. Biodegradable semisynthetic materials such as carboxy-methyl-cellulose and poly-anionic-cellulose are mainly used in the petroleum industry to regulate drilling fluid loss but impose significant costs on overall drilling operations [20,21]. In recent years, waste materials, including but not limited to food waste, have been studied as potential options to optimize the rheological and filtration properties of drilling fluids.

Table 1. Overview of recent studies published on the development of biodegradable additives as water-based drilling fluids (WBDFs) loss agents utilizing waste materials.

Study	Material	Combination	Purpose
[22]	Tree bark (douglas fir)	Unknown	Control Fluid Lost
[23]	Ground peach seeds	Unknown	Control Fluid Lost
[24]	Rice fraction (rice hulls, rice tips, rice straw and rice bran)	N/A	Control Fluid Lost
[25]	Corn cub outers	N/A	Control Fluid Lost
[26]	Sugar cane ash (300 microns)	0.1, 0.4, and 0.5 wt% of sugar cane ash was mixed with WBDF	Control Fluid Lost
[20]	Grass (300 µm, 90 µm and 35 µm particle sizes)	0.25, 0.50, 0.75 and 1.0 g of grass with different particle sizes added to WBDF	Control Fluid Lost and water control agent
[27]	21 types of food and green waste	Between 0 to 10 ppb concentrations of different green and food waste materials added to the WBDF	Control Fluid Lost
[28]	Eggshell waste	15 g added to the total WBDF mud	Control Fluid Lost
[7]	Grass powder (GP)	1% and 2% GP added to the WBDF	Control Fluid Lost
[29]	Black sunflower seeds’ shell powder	0.5, 1.5, 2.5, and 3.5 wt% added to WBDF	Fluid Lost Control
[30]	Wheat Husk Powder (WHP)	Concentrations of 1, 2, 3, and 4 wt% WHP were added to the WBDF	Control Fluid Lost
[31]	Waste banana peels	Various percentages were added to the WBDF	Control Fluid Lost
[15]	Wild Jujube Pit Powder (WJPP)	0.5, 1, 2, 3 and 5 wt% WJPP were added to WBDF	Control Fluid Lost
[18]	Cassava starch	0 to 10 g was added to the WBDF	Control Fluid Lost
[9]	Waste Mandarin Peel	concentrations of 0.5, 1, 1.5, and 2wt%	Shale swelling inhibitor
[16]	Wheat nano-biopolymers	2 wt% concentrations added to WBDF	Fluid loss control

summarizes the recent studies in a race to find environmentally friendly and biodegradable WBDF additives using green and food waste.

To this end, three materials from food waste, including pumpkin, courgette, and butternut squash peels, have been chosen, and these will be discussed briefly hereafter. With a global production of 27 million metric tons, pumpkin (Cucurbita moschata) is one of the major food wastes, and many millions are wasted every year [32]. In fact, about 18,000 tons of pumpkins (approximately 12.8 million) are wasted during Halloween in the UK, and 453,000 tons are wasted in the USA [33,34]. Many added-value products from the pumpkin’s constituents in various sectors, including baking [35], beverage products [14,36], meat production, and dairy products [37], have been produced in recent years. Specifically due to its physiochemical properties, the pumpkin seeds were subjects of many studies for the preparation of high internal phase emulsions [38], enhanced egg-white protein [39], and functional food ingredients [32]. The second material that was used was courgette peel waste. Courgette is regarded as a health-promoting, low-calorie vegetable and, according to the Waste and Resources Action Programme (WRAP), shares 0.5% weight of all vegetable waste (7800 tons per year), which costs the UK economy GBP 20 million per year [40]. The composition of courgette comprises water containing 93.5–95%, 2.3–4.2 g/100 g of carbohydrates, 1.3–3.2 g/100 g of sugars, and 1–2.5 g/100 g of proteins [41]. The predominant minerals found in courgettes include calcium, phosphorus, magnesium, and potassium, with higher concentrations typically observed in the skin compared with the flesh of the fruit. The third material that we selected for this study was butternut squash. It is a fruit consisting of 82.98% pulp and 12.36% of skin with an average weight of 884.1 g. The skin largely ends up in landfills as waste products. Its significance in the food sector is considerable, spanning from its seeds to its pulp, which is utilized in the production of pastries, beverages, pickles, confections, and preserves [42]. Utilizing pumpkins, courgettes, and butternut squash peels waste in the drilling industry is scarce, and to our knowledge, there is not any study that offers the production of WBDF additive based on them. The amount of waste, associated costs, and production of greenhouse gases encourage the repurposing of the selected food waste materials in the hydrocarbon drilling industry. The aim of this study was to develop environmentally friendly additives based on food waste to enhance the filtration and rheological properties of WBDF. Hence, in this study, pumpkin, courgette, and butternut squash peel waste powders with two particle sizes of 10 and 75 µm and 3% concentration were utilized in formulating WBDFs. The scope of the research was determined to reduce drilling fluid loss and investigate the effect of the additives produced on rheological properties. The API filtration test guidelines were followed to perform the filtration and rheological tests [43].

2. Materials and Methodology

The outlines of the process for evaluating the effectiveness of biodegradable drilling fluids derived from courgette, pumpkin, and butternut squash peels are shown in Figure 1. Initially, conventional water-based reference drilling fluid as per [43] was prepared, and then different formulated additives using pumpkin, courgette, and butternut squash peel powders with different particle sizes were added to make biodegradable drilling fluids. Then, a series of tests, including mud balance, API filtration, rheological properties assessment, and pH analysis, was carried out. The final stage is the result analysis, which leads to the conclusion of this study.

2.1. Preparation of Biodegradable Materials and Drilling Fluids

Figure 2 illustrates the preparation and characterization of biodegradable materials used as WBDF fluid additives. Pumpkins, courgettes, and butternut squashes were peeled, cut, dehydrated, and ground into powder. A ball milling machine was used to further refine the particles to sizes below 75 µm and 10 µm. The fine materials were analyzed for elemental composition and morphology using the Hitachi S-3400N microscope (Hitachi High-Tech Corporation, Tokyo, Japan) with energy-dispersive X-ray (EDX) (Oxford Instruments, Abingdon, UK) and Field Emission Scanning Electron Microscopy (FESEM). Then, functional groups were identified using Fourier Transform Infrared (FTIR) spectroscopy (Thermo Fisher Scientific, Waltham, MA, USA) with the Perkin Elmer Spectrum 100 series, scanning from 650 to 4000 cm⁻¹ with 64 scans per sample. Furthermore, thermal stability was evaluated with thermogravimetric analysis (TGA) using the PerkinElmer STA 6000 (PerkinElmer Inc., Waltham, MA, USA), heating samples from 0 to 995 °C at 10 °C/min in an argon atmosphere with a flow rate of 100 mL/min [1,8,18].

Then, after preparing the materials, water-based drilling mud (BM) was prepared following American Petroleum Institute guidelines [40], mixing 700 mL of deionized water, 1 g of caustic soda (NaOH), and 40 g of bentonite. Afterward, the mixture was homogenized for 10 min using a Hamilton Beach GM20 mixer and left to settle for 24 h to ensure proper hydration and viscosity stabilization. Six biodegradable drilling muds were then prepared by adding 21 g (3%) of fine and very fine particles of the additives (

Table 2. Composition and properties of reference and biodegradable drilling fluids with different particle sizes of vegetable peel additives.

Drilling Fluid	Additives	Acronym	Particle Size (µm)	Concentration (%)	Caustic Soda (gm)	Bentonite (gm)	Distilled Water (mL)
Reference		BM	-		1	40	700
Biodegradable drilling fluids	Pumpkin Peel	PP_10	10	3	1	40	700
		PP_75	75	3	1	40	700
	Courgette peel	CP_10	10	3	1	40	700
		CP_75	75	3	1	40	700
	Butternut Squash peel	BSP_10	10	3	1	40	700
		BSP_75	75	3	1	40	700

), based on the findings by [44,45,46,47], which showed that 3% concentration of various biodegradable materials enhanced filtration and rheological properties of WBDF. Altogether, six different WBDFs mixed with biodegradable additives were prepared. The mixtures were blended for 30 min and prepared for the rheological and filtration tests.

2.2. Fluid Circulation Loss and Filter Cake Thickness Measurements

This study evaluated filtration characteristics, including fluid loss and filter cake formation, utilizing a Series 300 LPLT Filter Press at a pressure setting of 100 psi and constant room temperature. The procedure began with the careful placement of filter paper within the cell of the filter press, followed by the loading of the sample material. A graduated cylinder was positioned below the filtrate tube to collect the filtered material. Once the setup was complete, the testing phase commenced with the activation of a timer for a duration of 30 min. Throughout this period, the amount of filtrated mud collected was periodically recorded at several intervals. Upon the conclusion of the test, the thickness of the resulting filter cake was measured and recorded. This methodology enabled the observation of filter cake thickness after a 30 min period and the tracking of fluid loss at specified time intervals within the same timeframe.

2.3. Measurement of the Rheological Properties of Drilling Fluid

A digital viscometer was employed at ambient temperature to assess the rheological characteristics of the drilling fluid samples, including parameters like apparent viscosity, yield point, gel strength, and plastic viscosity. The procedure began by filling the viscometer’s cup with the BM and preparing the device for operation. Upon activating the gear switch, the rotor was set to rotate at different speeds, with readings recorded at 600 rpm, 300 rpm, 200 rpm, and 100 rpm. Then, readings at 6 rpm and 3 rpm were recorded. These readings play an important role in determining the yield point, plastic viscosity, and apparent viscosity of the fluid. To measure the gel strength of the biodegradable drilling mud, the mud was stirred at 600 rpm for 15 s to break any gels. After switching to a low speed, the viscometer was turned off for 10 s to allow it to settle. The viscometer was then switched on at 300 rpm, and the initial gel strength was recorded. The mud was stirred again at 600 rpm for 15 s, then left to settle for 10 min. After this period, the viscometer was turned on at 300 rpm, and the final gel strength was recorded. The plastic and apparent viscosities were then calculated using the conventional drilling mud viscosity equations [22,41]. This process was consistently applied to each sample and involved calculating shear rates and shear stresses from the viscometer’s deflections at varying speeds. The plastic viscosity and apparent viscosity were computed using the following equations.

$${\mu }_{\mathrm{P}}={\varnothing }_{600}\mathrm{r}\mathrm{p}\mathrm{m} \mathrm{r}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g}-{\varnothing }_{300}\mathrm{r}\mathrm{p}\mathrm{m} \mathrm{r}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g},$$

(1)

$${\mu }_{\mathrm{a}}={\displaystyle \frac{{\varnothing }_{600}\mathrm{r}\mathrm{p}\mathrm{m} \mathrm{r}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g}}{2}},$$

(2)

where ${\mu }_{\mathrm{P}}$ denotes plastic viscosity, ${\mu }_{\mathrm{a}}$ stands for apparent viscosity, measured in centipoise (cP), and ∅ indicates the deviation of the viscometer reading at 300 and 600 rpm.

Following this, the yield point (YP), expressed in (lb/100 ft²), was calculated using the subsequent equation:

$$YP={\varnothing }_{300}-{\mu }_{\mathrm{P}}$$

(3)

2.4. Relationship Between Shear Rate, Viscosity, and Shear Stress

The impact of shear rate and shear stress on drilling fluid performance is crucial. As drilling fluids undergo shear stress, their viscosity may notably decrease, impacting their capacity to transport drill cuttings and furnish essential lubrication to drill bits [48]. A reduction in fluid viscosity may hinder the fluid’s capacity to move drill cuttings to the wellbore’s surface, potentially leading to blockages due to the accumulation of cuttings. Furthermore, reduced lubrication from low-viscosity fluids can increase wear and damage on the drill bit, adversely impacting drilling operations [49]. To analyze experimental data related to shear stress, viscosity, and shear rate, the methods specified in API SPEC 13A (1993) [43] are adhered to, utilizing the Fann 35 viscometer. According to API guidelines, the apparent viscosity, shear rate, and shear stress are determined using the equations below:

$$\mathrm{a}\mathrm{p}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{n}\mathrm{t} \mathrm{v}\mathrm{i}\mathrm{s}\mathrm{c}\mathrm{o}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}={\displaystyle \frac{\mathrm{s}\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{r} \mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s}}{\mathrm{s}\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{r} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}}}\times 100={\displaystyle \frac{\tau }{\gamma }}\times 100,$$

(4)

$$\mathrm{S}\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{r} \mathrm{r}\mathrm{a}\mathrm{t}\mathrm{e}={\mathrm{K}}_1\mathrm{N},$$

(5)

where K₁ is the shear rate constant of 1.7023 S⁻¹, and N is the viscometer speed in rpm. The shear stress can be determined using the following:

$$\mathrm{S}\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{r} \mathrm{s}\mathrm{t}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{s}={\mathrm{K}}_2{\mathrm{K}}_3ϴ,$$

(6)

where K₂ represents the torsion constant, measured at 386 dyne-cm/degree deflection, K₃ denotes the shear stress constant, which equals 0.01323 cm⁻², and ϴ signifies the viscometer reading.

3. Results and Discussion

This study evaluated the potential of biodegradable butternut squash peel (BSP), courgette peel (CP), and pumpkin peel (PP) as additives in water-based drilling fluids (WBDFs). The results demonstrate that all utilized materials with various particle sizes have significant potential to improve the rheological and filtration properties of WBDFs. Filtration testing showed that 10 µm pumpkin peel (PP_10) was the most effective at reducing fluid loss, with a 43.5% reduction, followed by butternut squash peel (BSP_10) at 40% and courgette peel (CP_10) at 30%. This suggests that PP_10 creates a more efficient seal, reducing fluid loss into the formation. Meanwhile, adding 3 wt% (PP_10) significantly improved rheological properties, including plastic viscosity by 50% from 4 cP to 8 cP, apparent viscosity by 41% from 10 cP to 17 cP, and yield point by 33% from 12 lb/100 ft² to 18 lb/100 ft². The gel strength also increased from 7 lb/100 ft² to 11.5 lb/100 ft² after 10 s and to 20.6 lb/100 ft² after 10 min, indicating a stronger gel structure that enhances cuttings suspension and wellbore stability.

3.1. Characterization of Wasted Vegetable Peels

EDX and FTIR analysis was used to determine the chemical composition of all three wasted materials: butternut squash peel (BSP), courgette peel (CP), and pumpkin peel (PP). EDX and FTIR are important for identifying unknown compounds of the selected materials and their effect on fluid loss and rheological properties [50]. In addition, FESEM was used to characterize the samples. The EDX analysis of butternut squash peel (BSP), courgette peel (CP), and pumpkin peel (PP) are shown in Figure 3a–c. The results are also tabulated in

Table 3. Elemental composition of butternut squash peel, courgette peel, and pumpkin peel.

Biodegradable Material	Element (wt%)
	O	Na	Mg	Si	P	S	Cl	K	Ca
Butternut Squash peel	78.2	0.3	1.7	1.4	2.3	0.9	1.3	12.1	1.9
Courgette peel	74.4	0.6	1.6	0.7	1.7	1.2	5.0	13.0	1.8
Pumpkin peel	76.0	0.4	1.8	1.9	2.0	1.3	2.3	12.0	2.4

. The EDX results revealed significant amounts of oxygen (O) and potassium (K), followed by phosphorus (P), chlorine (Cl), magnesium (Mg), calcium (Ca), and silicon (Si) in all three tested materials. The particle size of each sample was determined using the FESEM imaging, as shown in Figure 3d–f. Two sizes of fine (75 µm) and very fine (10 µm) were measured using high-resolution imaging in FESEM. The overall surface morphology of the samples indicates that the pumpkin peel powder has higher porosity compared with courgette and butternut squash. This is highlighted by the large smooth surface areas in the image (Figure 3f). Nevertheless, the other two materials have a more compact crystalline structure.

FTIR results for butternut squash peel, courgette peel, and pumpkin peel are shown in Figure 4a, Figure 4b, and Figure 4c, respectively. The FTIR test exposed the functional chemical groups and the bonding present among the constituents of each sample within the range of 650–4000 cm⁻¹ [51,52]. The occurrence of the surface hydroxyl (O–H) functional group within the spectral range of 3000 to 3600 cm⁻¹ suggests the presence of compounds featuring intra-molecular hydrogen bonding, such as phenols, carboxylic acids, and alcohols [53]. This suggests that hydroxyl groups and carboxylic acids exist within this broad vibrational range. Moreover, another obvious pick on the graph is between 2915–2925 cm⁻¹ for all three studied materials. This pick corresponds to the existence of organic compounds such as hydrocarbons (CH3 and CH2), alkanes, and fatty acids. Moreover, the wide peak spanning from 1200 to 1800 cm⁻¹ indicates the presence of the C=O functional group, which is most probably associated with carboxylic acid. Furthermore, the wide band from 1000 to 1200 cm⁻¹ signifies the presence of the single-bond carbon and oxygen (C–O) functional group, implying the existence of lignin and cellulose in the samples [54].

Thermogravimetric analysis (TGA) was conducted to evaluate the heat resistance of proposed biodegradable additives used in drilling mud. TGA is an analytical method that quantitatively measures alterations in a sample’s mass in relation to temperature or time [55]. It is important to understand the degradability of the samples at high temperatures. In this process, a sample is placed in a container within the furnace, which can heat the sample to a constant temperature of up to 1000 °C. The container is linked to a precise microbalance within the apparatus, enabling accurate weighing of the samples within the sealed furnace [56]. The microbalance records the initial weights of the samples, which are then compared to their weights at different temperatures. Figure 5a–c illustrates the TGA analysis results for the courgette peel, butternut squash peel, and pumpkin peel, respectively. The results indicate that there is a direct positive correlation between the heat flow rate and the percentage weight loss of the materials. For all three tested materials, increasing the heat flow would increase the percentage of weight loss. Upon heating up the samples, three distinctive phases of weight loss were identified for each material, as shown in the graphs. The first phase is the drying phase, which involves the evaporation of free moisture from the samples and effectively removing any absorbed moisture content. The second phase is the decomposition phase, where the volatile compounds are formed due to the breakdown of the organic matter. The remaining organic matter in the samples at the end of the second phase will be further degraded in the third phase [55]. The percentage weight loss of each phase was also calculated using the following relation [57].

$$Percentage weight loss at each phase=W_i-W_e,$$

(7)

where w_i is the weight of the sample at the beginning of the phase, and w_e is the weight of the sample at the end of the respective phase. In the first phase, which is between 0 and 245 °C, the courgette, butternut squash, and pumpkin peel powders lost their weight by 10.95%, 12.38%, and 11.27%, respectively. In the second phase, which is between 210 and 420 °C, the rate of degradation rose, and courgette, butternut squash, and pumpkin peel powders lost weight by 49.1%, 40.86%, and 42.55%, respectively. Further degradation of the organic compounds within the courgette, butternut squash, and pumpkin peel powders lead to 20.81%, 35.53%, and 34.51% weight loss in the third phase. The results revealed that all three tested samples are within a similar range in terms of heat sensitivity and operation in high temperatures. The results suggest that courgette, butternut squash, and pumpkin peel powders offer promising and practical solutions for high-temperature drilling applications in the industry.

3.2. Rheological Property

The impact of adding the biodegradable courgette, butternut squash, and pumpkin peel powders on rheological properties and gel strength of the water-based drilling mud was experimentally investigated and is shown in Figure 6 and Figure 7. The viscosity of the drilling mud, which represents the ability of the mud to flow, is a critical parameter that needs to be tested. Two types of apparent and plastic viscosity are measured and presented in this section. The apparent viscosity represents the viscosity of the mud at the specified shear rate. On the other hand, the amount of solid contents in the mud is determined by the plastic viscosity [58]. The WDBM or base mud (BD) sets a baseline with a plastic viscosity of 4 cP, an apparent viscosity of 10 cP, and a yield point of 12 lb/100 ft². The gel strength rises from 7 lb/100 ft² at 10 s to 15 lb/100 ft² after 10 min. The addition of 3 wt% very fine particle size (10 µm) pumpkin powder (PP_10) enhances the plastic viscosity to 8 cP, apparent viscosity to 17 cP and yield point to 18 lb/100 ft², alongside a gel strength increase to 11.5 lb/100 ft² at 10 s and 20.6 lb/100 ft² at 10 min, suggesting a more robust gel structure. Conversely, the addition of 3 wt% fine particle size pumpkin powder (PP_75) to WBDF was associated with a slight reduction of plastic viscosity and yield point values yet maintained a higher gel strength than the BM after 10 min. Adding very fine particle size courgette peel (CP_10) records higher plastic viscosity, apparent viscosity, and yield point compared with the fine sized (CP_75), yet both display a reduction in gel strength after 10 min relative to their 10 s readings, indicating less gel stability over time. Butternut squash peel presents an intriguing profile. The addition of very fine particle size butternut squash peel (BSP_10) delivers a lower plastic viscosity but a significantly higher yield point than its fine particles (BSP_75). However, BSP_75 exhibits the highest plastic viscosity of all samples at 9 cp but lower yield point and gel strength values at 10 min than BSP_10, suggesting a more viscous but less yielding and gel-strengthening effect. When comparing these results, PP_10 emerges as the most effective in enhancing the rheological properties and gel strength, possibly due to a balanced interaction between the particle size and the drilling mud components.

The results of this study are in line with the recent literature on biodegradable materials as drilling mud additives. Ref. [6] has shown that wheat straw improves rheological properties and gel strength, a trend similar to the pumpkin peel effects observed [16]. Similarly, ref. [46] report that Cupressus cones powder enhances the plastic viscosity, yield point, and gel strength, which supports the beneficial impact of vegetable-based additives. These improvements, along with the broader research trend, support the use of biodegradable additives for their environmental benefits and ability to enhance drilling fluid performance. Such materials can provide an environmentally friendly alternative to conventional additives, often associated with higher toxicity and disposal issues. The use of biodegradable additives not only aligns with the increasing environmental regulations but also offers potential cost savings and improved biocompatibility in drilling operations.

3.3. Rheological Modelling

To evaluate the rheological properties of the bentonite-based and proposed biodegradable drilling muds, viscosity measurements were taken at various speeds using the FANN rotational viscometer. These experimental viscosity readings were then used in the shear rate and shear stress equations (Equations (5) and (6)) to calculate the corresponding shear stress and shear rate values. Then, the data were fitted to the well-known rheological models of Bingham, Herschel-Bulkley [59], Weibull [60], and Vipulanandan [61]. The details of these models can be found in their respective publications. Figure 8 represents the relationship between shear stress and shear rate of conventional base mud, as well as various other muds combined with biodegradable vegetable peel additives. Starting with base mud, it shows that higher shear stress is apparent as the shear rate increases, and there is a positive correlation. Adding a pumpkin peel with 3 wt% concentration at two different particle sizes of 75 µm and 10 µm increases the shear rate and shear stress in a positive direction, where raising the shear rate increases the shear stress. The shear stress rate for the PP_75 µm is within the range of 51 to 138 dynes/cm², while for the smaller particle size of 10 µm, the range is within 29 to 173 dynes/cm². On the other hand, adding butternut squash peel with particle sizes of 75 µm and 10 µm reveals the shear stress range between 34 to 143 dynes/cm² and 34 to 141 dynes/cm², respectively. This increase in shear stress was also observed while adding courgette peel at a similar 3 wt% concentration for both particle sizes of 10 µm and 75 µm. The results reveal that at a lower shear rate, the shear stress remained low, adding biodegradable vegetable peel waste compared with the base mud. Utilizing the existing literature rheological models for the experimental results shows a similar trend, which verifies the validity of this study.

3.4. Relationship Between Shear Rate, Viscosity, and Shear Stress

The performance of drilling fluid can be greatly influenced by the shear stress and shear rate. When drilling fluid is subjected to shear stress, its viscosity may decrease, altering its overall effectiveness [48]. The viscosities of drilling fluids modified with vegetable peels at various shear rates are shown in Figure 9a. For base mud, viscosity increases with decreasing shear rate, from 9.99 cP at a shear rate of 1021.38 s⁻¹ to 27.59 cP at 170.23 s⁻¹. This behavior is typical for non-Newtonian fluids used in drilling operations, where viscosity increases as the shear rate decreases [62]. The pumpkin peel-enhanced mud shows a notable increase in viscosity, with a decrease in shear rate for both particle sizes. Adding fine particle size of pumpkin peel (PP_75) resulted in a viscosity increase from 13.49 cP to 59.99 cP, while very fine particles PP_10 changed the viscosity significantly from 16.99 cP to 33.59 cP. The highest viscosity observed is with PP_75 at the lowest shear rate, indicating that larger particle sizes may enhance the viscosity-retaining capacity of the fluid under lower shear conditions. Courgette peel shows similar viscosity trends. Adding CP_75 altered the viscosity from 13.49 cP to 38.99 cP, whereas the CP_10 starts at 15.34 cP and ends at 33.59 cP. Again, the 75 µm particles demonstrate a higher viscosity at lower shear rates compared with the 10 µm particles. In addition, butternut squash peel (BSP) muds demonstrate an increase in viscosity as the shear rate decreases. Specifically, adding BSP_75 to the water-based drilling fluid (WBDF) increases viscosity from 13.99 cP to 36.59 cP, while adding BSP_10 results in an even greater increase, from 13.84 cP to 46.49 cP. Notably, BSP_10 exhibits the most significant viscosity enhancement at lower shear rates, indicating its superior thickening effect under such conditions, which is critical for carrying cuttings and maintaining good stability.

Figure 9b presents shear stress responses of drilling muds enhanced with vegetable peels at different particle sizes and various shear rates. At the highest shear rate (1021.38 s⁻¹), PP_75 shows a lower shear stress (102.13 dynes/cm²) compared with its PP_10, with a shear stress of 137.88 dynes/cm², indicating that PP_10 can withstand higher stress before yielding. Courgette peel at the same particle sizes shows a higher shear stress for CP_75 at 173.63052 dynes/cm² compared with CP_10, suggesting better shear resistance for larger particles in courgette peel. Butternut squash peel exhibits similar shear stress for both particle sizes at this rate, with BSP_75 at 156.77 dynes/cm² and BSP_10 at 141.45 dynes/cm². As the shear rate decreases, a constant trend is observed: the shear stress decreases across all samples. Notably, for the BM, there is a steep decline in shear stress as the rate drops, maintaining lower values compared with enhanced mud. This behavior reveals the thickening power of biodegradable additives, as they show higher resistance to flow (higher shear stress) at varying shear rates. At the lowest shear rates (5.10 s⁻¹ and 10.21 s⁻¹), PP_10, CP_10, and BSP_10 exhibited higher shear stresses than PP_75, CP_75, and BSP_75, suggesting that finer particles may contribute to a stronger network within the mud, offering better resistance at lower shear rates. However, BSP_10 demonstrates the best performance at the lowest shear rate, indicating that it might be the most effective additive for enhancing low shear rate viscosity, a desirable property for carrying cuttings to the surface and maintaining hole cleaning. This finding is in line with [16] showing that wheat particles can enhance the viscosity and yield stress of drilling fluids, improving their ability to suspend and transport cuttings [16].

3.5. pH Analysis and Mud Balance Test of Drilling Fluids

To assess the relative acidity or alkalinity of the drilling mud, the pH level is measured. This is important to understand as the acidic drilling mud has potential negative impact on the environment and the drilling equipment [8]. A drilling mud with the pH below 7 considered to be acidic. Typically, water-based drilling fluids exhibit optimal performance within the pH range of 8.0 to 10.5 [63].

Another important rheological property that we included here is mud density. The optimal mud weight for water-based drilling fluid (WBDF) is slightly greater than the reservoir pore pressure but less than the fracture pressure of the well formation [64]. Figure 10a,b presents the pH level and mud density of formulated drilling mud incorporating vegetable peels of varying particle sizes compared with a BM. BM has a density of 8.6 ppg and a pH of 11.33. When comparing this to the formulated muds, there is no significant change in mud density, which remains consistent for most additives, either at 8.6 ppg or slightly increasing to 8.7 ppg. This indicates that the addition of vegetable peel particles does not substantially alter the density of the mud. However, there is a noticeable impact on pH levels. The pH levels decreased when vegetable peels were added to the base mud, suggesting that these biodegradable materials have a buffering effect. For instance, pumpkin peel (PP_10) lowers the pH to 10.52, and PP_75 turns it to a slightly higher pH of 11.02. Courgette peel shows a similar trend with pH levels of 10.7 for CP_10 and 10.56 for CP_75. Butternut squash peel results in pH levels of 10.74 for 10 BSP_10 and 10.95 for BSP_75. Although adding biodegradable materials lowers the pH in comparison to the BM; however, it still remains within an acceptable range of 8 to 10.5, which is important for protecting the drilling equipment from corrosion. The results also indicate a potential preference for smaller particle sizes for pH control. Biodegradable additives like the vegetable peels provided table offer a promising possibility for sustainable drilling practices. These materials can improve mud properties such as pH without significantly altering mud density, indicating that they can be effective in creating more environmentally friendly drilling fluids.

3.6. Filtration Properties

The filtration rates of drilling mud modified with vegetable peels over a period of 30 min are measured and shown in Figure 11. For base mud, the filtration rate starts at 7.8 cc after 5 min and progressively increases to 19.5 cc at 30 min. This increase suggests that the BM allows more fluid loss over time, which is less ideal in drilling operations where controlling fluid loss is critical. Adding fine pumpkin peel (PP_75) shows an initial filtration rate of 4.7 cc at 5 min, which stabilizes at 12 cc from 25 min onward. This behavior indicates better fluid loss control compared with the BM. Adding very fine pumpkin peel powder (PP_10) has an even lower filtration rate, starting at 3.5 cc at 5 min and capping at 11 cc by 30 min, making it the most effective among the three vegetable peel variants in controlling filtration. Butternut squash peel also exhibits improved filtration control over the BM. The proposed WBDF mud using (BSP_75) as an additive starts the filtration at 5.2 cc at 5 min and peaks at 14 cc by 30 min. However, using BSP_10 shows better performance, beginning at 4 cc at 5 min and reaching only 13 cc by 30 min, indicating a more stable and effective fluid loss control. Courgette peel demonstrates a similar trend, where adding fine particle (CP_75) has an initial filtration rate of 6.5 cc at 5 min, increasing to 16 cc at 30 min. Very fine courgette peel powder (CP_10) shows a filtration rate, starting at 5 cc at 5 min and ending at 14 cc at 30 min, which represents a moderate control of fluid loss. When comparing the effectiveness of these biodegradable additives, utilizing very fine pumpkin peel powder (PP_10) stands out as the best-performing additive with the lowest overall filtration rates, indicating its superiority in minimizing fluid loss in the drilling mud.

In addition to the fluid loss, the formed filter cake thickness of the formulated muds and base mud were measured and presented in Figure 12. The base mud demonstrates a mud cake thickness of 5 mm, which serves as a reference point for evaluating the effectiveness of the proposed additives. A thinner mud cake is generally preferred as it indicates better fluid loss control. Adding PP_75 reduces the mud cake thickness by 40% from 5 mm to 3 mm, showing an improvement over the BM. However, using PP_10 further reduces the mud cake thickness to 2.5 mm (50%), which is the thinnest mud cake achieved in this study, and it signifies the most effective reduction in mud cake thickness among all the samples tested. For butternut squash peel, adding fine particles (BSP_75) produces a mud cake of 4.5 mm thickness, while very fine particles (BSP_10) result in a thinner mud cake of 3 mm, aligning with the trend that smaller particles tend to enhance fluid loss control. Using fine particle courgette peel powder (CP_75) does not show any improvement in mud cake thickness compared to the BM, maintaining a thickness of 5 mm. However, very fine courgette (CP_10) reduces the thickness to 3 mm, demonstrating the potential of smaller particle sizes to improve the performance of the drilling mud. Among the samples, using very fine particles of pumpkin peel powder (PP_10) formed a mud cake thickness of 2.5 mm, indicating the best fluid loss control, which is crucial in maintaining wellbore stability and preventing excessive filtration [65]. The effectiveness of the best-performed proposed water-based drilling mud (PP_10) in this study, in terms of fluid loss and filter cake thickness, was compared to some of the existing literature in

Table 4. The percentage reduction in fluid loss and filter cake thickness of water-based drilling fluids (WBDFs) with the inclusion of proposed PP_10, biodegradable waste, nanoparticles, and biopolymer additives.

Material	Reduction in Fluid Loss After 30 min (%)	Reduction in Filter Cake Thickness (%)	Reference
Best performed additive (very fine particle pumpkin peel powder PP_10)	43.5	50	Current study
Broad bean peel powder	31.86	28.57	[45]
Potato peel powder	30	40	[7]
Grass powder	42	33.33	[7]
Nanoparticle (CuO)	30.20	27.60	[66]
Pistachio Shell Powder	38.57	20.54	[3]
Palm Tree leaves powder	28	36.67	[67]
Rice husk ash	10	Increased	[17]
Wild Jujube Pit Powder (WJPP)	42.5	Not provided	[15]
Biopolymer (Rhizophora, Mucronata Tannin)	33.33	3.33	[65]

. In the comparison of the results with the documented literature, different biodegradables, nanoparticles, and biopolymers exhibited different outcomes. Broad bean powder reduced filter cake and mud loss to the formation by 28.57% and 31.86%, respectively, while grass powder achieved a considerable 42.5% reduction in fluid loss and a 33.33% reduction in filter cake. Furthermore, potato peel powder reduced fluid loss and filter cake of the water-based drilling mud by 30% and 40%, respectively, while rice husk ash effect was less, reduced fluid loss by 10%, and increased the filter cake thickness. Other specialized materials like nanoparticle (CuO) also reduced the fluid loss and filter cake by 30.20% and 27.60%, whereas biopolymer Rhizophora Mucronata Tannin reduced the same properties by 33.33% and 3.33%, respectively. In addition, pistachio shell powder demonstrated a 38.57% reduction in fluid loss and a 20.54% reduction in filter cake thickness, while the palm tree leaves powder had less effect on fluid reduction (28%) and more impact on filter cake thickness reduction (36.67%). This comparison highlights the various effectiveness of different materials in preventing fluid loss and reducing the thickness of the filter cake of water-based drilling muds. Essentially, it emphasizes the significant potential of using various biodegradable materials investigated in this study, which produce results that are either superior or the same as those reviewed in the existing literature.

Figure 13 illustrates the mechanism of filter cake formation on the borehole wall during drilling with base mud (BM) and biodegradable drilling fluids containing vegetable peel additives at particle sizes of 75 µm and 10 µm. The filter cake acts as a seal, minimizing fluid loss and stabilizing the wellbore. Base mud forms a thicker, potentially more permeable cake, leading to higher fluid loss. However, when enhanced with vegetable peel additives, the cake becomes thinner and denser, with smaller particles (75 µm and 10 µm) improving the seal quality. The 10 µm particles create the most compact and effective filter cake, significantly reducing fluid loss. This supports the idea that finer particles enhance filter cake performance, as shown by experimental data and recent research on biodegradable additives, which provide both environmental and technical benefits for improved fluid loss control and sealing capabilities [52,62].

4. Conclusions

In this study, several biodegradable water-based drilling fluid additives based on courgette, butternut squash, and pumpkin peel powders with two different particle sizes of 10 µm and 75 µm and a weight concentration of 3% were developed. The formulated drilling muds were analyzed using industry-standard filtration and rheological tests, and the results were compared to the reference WBDF. The outcome of the study is summarized as follows.

• Adding 3 wt% of very fine particle size pumpkin peel powder (PP_10) to the WBDF reduce the fluid loss and filter cake thickness by 43.5% and 50% in comparison to the reference mud;
• The minimum fluid loss of 3.5 cc at 5 min and capping at 11 cc by 30 min was obtained using very fine (10 µm) pumpkin peel powder (PP_10), outperforming other additives, including PP_75, CP_10, and BSP_10;
• The results showed the yield point of base mud was increased from 12 lb/100 ft² to 18 lb/100 ft² by adding 3% of finer particle size pumpkin peel powder, indicating the higher ability of the drilling fluid to transport cutting from the wellbore and maintain its stability;
• Adding biodegradable additives from courgette, butternut squash, and pumpkin peel powders keep the pH level of the drilling mud above 10, which is important for corrosion protection of the drilling equipment.
• Vegetable peel additives, particularly pumpkin peel at 10 µm (PP_10), enhance shear stress across all shear rates. PP_10 demonstrates higher shear stress compared with the 75 µm counterpart (PP_75), indicating that finer particles provide better shear resistance;
• Incorporation of 3 wt% fine particle size (10 µm) pumpkin powder (PP_10) enhances rheological properties, increasing plastic viscosity to 8 cP, apparent viscosity to 17 cP, yield point to 18 lb/100 ft², and gel strength to 11.5 lb/100 ft² at 10 s and 20.6 lb/100 ft² at 10 min;
• The TGA results showed that all utilized additives (pumpkin, courgette, and butternut squash) exhibited similar thermal stability, with three weight loss phases: 10–12% in the first (0–245 °C), 40–50% in the second (210–420 °C), and 20–35% in the third phase. These results indicate good thermal stability, making the powders suitable for high-temperature drilling applications;
• This research provides a fundamental understanding of using biodegradable vegetable peels as WBDF additives. Future studies could explore the application of these materials under high-pressure and high-temperature conditions.