Introduction

Well cementing plays a crucial role in the petroleum industry by establishing a durable and secure connection between the well casing and the surrounding formations. This connection is vital for preventing the flow of unwanted fluids within the wellbore or behind the casing, thereby ensuring the safety and integrity of the entire oil well operation1,2,3,4,5,6. An important consideration is made for cement design, as it is crucial to establishing a robust linkage between the cement and the surrounding geological formation7. Inadequate cement sealing can lead to a range of complications and obstacles, including fluid invasion into the formation, fluids crossflow between adjacent layers (resulting in subsurface blowouts), contamination of freshwater reservoirs, and potential loss in hydrocarbon production8. As reported by the findings of Nelson and Guillot9, an unsuccessful cementing process can restrict the well from reaching its full production potential. Consequently, the formulation of resilient, enduring cement is pivotal in optimizing well productivity.

The cementing process involves injecting a mixture of cement and various additives into the well annulus, where it solidifies and forms a permanent seal2,5,10,11. In recent years, various supplementary additives have been utilized to enhance the cement slurry and matrix properties to adapt to specific subsurface conditions4,12,13,14,15,16,17,18. Retarders like natural lignosulfonates and cellulose are commonly used to extend the thickening time of cement12. Calcium chloride, on the other hand, is widely recognized as an efficient and cost-effective accelerator19. For reducing cement slurry density, additives such as bentonite and sodium silicate are frequently employed19,20. Conversely, to increase cement density, various additives like ilmenite and hematite have been developed21.

In the present time, the recycling and repurposing of industrial and agricultural materials have gained significant importance to align with environmental regulations. One such industrial byproduct is olive waste, generated during the extraction of olive oil. Numerous countries, including Jordan, Italy, Spain, Turkey, and France, are major producers of olive oil, leading to substantial olive waste production22. Numerous research investigations have explored the viability of utilizing olive waste ash as a supplementary component in concrete. In the concrete industry, several studies have explored the impact of olive waste ash on concrete properties23,24,25. Olive waste typically refers to the by-products generated during olive oil production, whereas olive waste ash is derived by burning these olive residues. Consequently, rather than disposing of olive waste in designated landfills, its utilization could prove benefits within the oil cementing industry. Al-Akhras26 conducted an analysis on how olive waste ash content influences the resistance of concrete subjecting to Alkali silica environment. The findings indicated that adding olive waste to concrete improves its resistance to deterioration from alkali-silica reactions, with greater resistance observed at higher olive waste content levels. Al-Akhras et al.27 also separately investigated the impact of temperature on the compressive strength of concrete, they carried out laboratory experiments using concrete mixes containing varying proportions of olive waste ash. The outcomes revealed that the inclusion of olive waste led to enhancements in the properties of concrete, particularly when subjected to higher temperatures.

Another study was conducted by Dahim et al.28 investigating the feasibility of incorporating olive waste ash into concrete by replacing varying amounts of cement with this ash. The results indicated that olive waste ash holds promise as a viable solution to enhance concrete strength and increase its elasticity. This is achieved by decreasing the water-to-cement ratio in the concrete mixture while simultaneously filling the pores within the concrete’s structural material. Kalkan et al.29 studied the impact of olive waste powder as a bio-polymeric admixture on cement mortars. They found that low usage rates hindered cement hydration, while higher rates enhanced it. Increased admixture levels improved flow diameter but reduced 28-day compressive and flexural strength. However, a 1.5 wt% admixture slightly improved the 150-day compressive strength.

In recent studies, Ali et al.30 highlighted the prospective utilization of olive waste as a retarder, showcasing its ability to significantly prolong thickening time. Additionally, Mahmoud & Elkatatny31 demonstrated how the incorporation of olive waste can enhance the cement’s resistance to carbonation when subjected to CO2-rich brine over a 20-days period. Muhammad et al.32 studied the impact of incorporating olive waste and granite on the properties of Class G cement. Their findings revealed that the addition of granite and olive waste enhanced the compressive strength by 106% and 110%, respectively, compared to the base cement.

In our recent study Ali et al.30, we found that olive waste can substitute a commercial retarder without impacting cement viscosity. Additionally, the addition of olive waste increases the slurry gel strength while decreasing permeability of the solidified cement matrix within specified content.

In cement design, it is crucial to consider all cement properties. One pivotal aspect during the design of cement slurry is ensuring favourable rheological properties for efficient placement16. Filtration characteristics also hold significant importance, as achieving minimal fluid loss to the formation helps in preventing the cement flash setting, formation of microchannels in the cement matrix, and deterioration of the cement strength17.

Moreover, it is essential for cement sheaths to ensure well stability, which typically involves meeting long-term criteria and is influenced by the elastic properties of the cement, including Young’s modulus and Poisson’s ratio, as well as cement strength4,18.

The primary objective of this study is to assess the influence of varying concentrations of olive waste on several properties of Saudi Class G oil well cement slurry and formed matrix. This comprehensive evaluation encompasses key characteristics which were not studied before, including filtration and elastic properties, compressive and tensile strength, and cement porosity.

Materials and methodology

Materials

According to the guidelines set forth by the American Petroleum Institute (API)33,34, a total of five cement samples were prepared to assess the impact of introducing olive waste as additive on cement properties. A detailed composition breakdown of these samples is presented in Table 1, encompassing Saudi Class G cement, water, dispersants, fluid loss additive and defoamer (quantities in gram). The base sample is devoid of olive waste. Conversely, the remaining samples incorporated varying proportions of olive waste content, spanning from 0.125 to 0.5% by weight of cement (BWOC). The utilized olive waste primarily consisted of sylvite, tridymite and 12.3% quartz. It was provided in a powder from as displayed in Fig. 1. Figure 2 graphically illustrates the particle size distribution of both Saudi Class G cement and olive waste30. This visualization underscores that the D50 (median particle size) of Saudi Class G cement measures 21.3 μm, while the D50 of the olive waste is significantly larger at 57.0 μm.

Table 1 The composition of cement slurries prepared in this study.
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Fig. 1
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Olive waste powder.

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Fig. 2
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Particle size distribution of Saudi Class G cement and olive waste30.

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Methodology

Following the formulation presented in Table 1, the cement slurries were prepared, and these mixtures were then used to be tested for their properties of the filtration, compressive and tensile strength, elastic characteristics and porosity. The following sections explained the testing procedure of the different properties of the cement sample used in this study.

Filtration properties

A High-pressure high-temperature (HPHT) filter press device was utilized to measure the volume of filtered water from the cement slurry. This measurement was conducted at a temperature of 200 °F, with an injection pressure of 1000 psi and a back pressure of 500 psi. The separated water was collected for 30 min which represents the cement fluid loss. This testing procedure was according to the recommendation of the API standards33,34.

Strength measurements

To evaluate the compressive strength of the samples, solidified cylindrical specimens measuring 1.5 inches in diameter and 3.0 inches in length were prepared as shown in Fig. 3, the compressive strength of these samples was measured through scratch testing. In this test, a scratch with a 0.25 mm depth and 1.0 cm width was created along the length of each sample to assess its resistance to scratch formation. After a 24-hour curing period at 95 °C, eight scratches were applied to each sample, and the compressive strength for each specimen was calculated as the average of these eight measurements, for more details about scratch testing refer to Ali et al.30. For examining the tensile strength, the samples were tested following the indirect Brazilian testing procedure outlined by Mahmoud et al.14 and Mahmoud and Elkatatny35.

Fig. 3
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Solidified cement samples with varying olive waste concentration.

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Elastic properties measurement

The cement samples’ Poisson’s ratio and Young’s modulus were assessed using cylindrical specimens measuring 1.5 inches in diameter and 3.0 inches in length, with their elastic properties determined through ultrasonic velocity measurements.

Porosity measurement

Porosity measurements were conducted using cylindrical samples with dimensions of 1.5 inches in diameter and 0.5 inches in length. After curing the samples at 95 °C, the measurements were carried out under atmospheric conditions using a porosimeter.

Results and discussion

Filtration properties

Filtration properties of five cement slurry samples were investigated using an HPHT filter press. Figure 4 illustrates a significant impact on fluid loss in the cement samples with the addition of olive waste. The base cement sample had the highest fluid filtration loss at 67 ml in 30 min, while cement sample of 0.125% olive waste reduced it to 50.96 ml. The lowest fluid filtration loss was 27.54 ml in 30 min, occurred with 0.5% olive waste. In summary, it can be concluded that the introduction of olive waste can lead to a significant reduction in filtration loss up to 58% of the fluid filtration of the base cement sample.

These results highlight the practical importance of using olive waste in well cementing applications. The significant reduction in filtration loss will enhances zonal isolation, reduces formation damage, and improves cement integrity under challenging downhole conditions. The use of olive waste this way will offer a sustainable, cost-effective solution for improving cement slurry performance in real-world applications.

Fig. 4
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The changes in fluid filtration with olive waste concentration.

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Compressive strength

By the scratch test, Fig. 5 summarizes changes in compressive strength due to olive waste incorporation according to the former described scratch test in the methodology section. The compressive strength of the base sample was 34.4 MPa. With the introduction of olive waste, there was an observed increase in compressive strength, reaching a peak of 40.5 MPa with 0.375% BWOC olive waste and reflecting a notable enhancement of 17.7% compared to the cement without olive waste. Even with 0.5% BWOC olive waste, there was a notable increase in compressive strength (38.6 MPa), which is 12.2% higher than the base cement (i.e. the sample prepared with no olive waste).

The observed increase in compressive strength due to olive waste incorporation is crucial for well cementing applications. Enhanced compressive strength improves the cement’s ability to withstand downhole stresses, ensuring better zonal isolation and long-term well integrity. This sustainable approach offers a practical solution to improve cement performance in challenging wellbore environments.

Fig. 5
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The compressive strength for the five cement samples with varying olive waste content.

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Tensile strength

Figure 6 depicts the variation in tensile strength as a function of olive waste concentration. There is a consistent downward trend in tensile strength with the incorporation of olive waste. The base sample, without any olive waste, exhibits a tensile strength of 5.48 MPa. When 0.125% BWOC olive waste was added, this value decreased to 5.2 MPa. The lowest tensile strength reported was 4.55 MPa, and it was found in the sample containing 0.5% BWOC olive waste. Comparing cement samples containing 0.25%, 0.375%, and 0.5% BWOC olive waste with the base cement, a noticeable decrease in tensile strength by 9.12%, 13.13%, and 16.97%, respectively, was observed. In summary, this minor reduction can slightly affect cement ability to withstand tension forces.

This minor reduction in tensile strength with olive waste incorporation is noteworthy for well cementing, as tensile strength influences the cement’s ability to resist cracking under stress. While the decrease is modest, careful optimization of olive waste concentration is necessary to balance environmental benefits with maintaining adequate mechanical properties for effective well integrity.

Fig. 6
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The tensile strength for the five cement samples with varying olive waste content.

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Young’s modulus

The impact of incorporation of olive waste on Young’s Modulus was illustrated in Fig. 7 through investigating five cement samples after curing for 24 h. The cement matrix becomes more stable (elastic) under shear deformation when Young’s modulus decreases substantially35. The results displayed in Fig. 7 illustrates that adding olive waste leads to a decreasing trend on Young’s modulus. Young’s modulus of the base cement sample was 17.3 GPa, and then decreased to 15.9 GPa when adding 0.125% BWOC olive waste. The lowest Young’s modulus obtained was 13.5 GPa by adding 0.375% BWOC olive waste. Meanwhile, Young’s Modulus for cement sample of 0.25% and 0.5% BWOC olive waste was very close to the lowest measurement (14.3 and 14.5 GPa, respectively). Therefore, the incorporation of live waste into the cement slurry had a positive impact on the cement elasticity.

For Well Cementing, a balanced Young’s modulus is often ideal. Too high, and the cement may become brittle and prone to cracking. Too low, and it may lack the necessary rigidity to support the well structure. The optimal modulus depends on specific well conditions such as pressure, temperature, and formation stress. The reduction in Young’s Modulus with olive waste incorporation enhances the cement’s elasticity, allowing it to better absorb stresses and resist cracking under downhole conditions. This improvement in flexibility is crucial for maintaining zonal isolation and well integrity, particularly in challenging environments where the cement must adapt to dynamic loads and thermal cycles.

Fig. 7
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The changes in Young’s Modulus with olive waste concentration.

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Poisson’s ratio

After 24-hour curing period, Fig. 8 presents the variations in Poisson’s ratio for five cement samples with varying concentrations of olive waste. The figure demonstrates that an increase in the olive waste content leads to a reduction in the cement’s Poisson’s Ratio. The base cement possessed a Poisson’s ratio of 0.30, which decreased by 3.33% and 6.66% when 0.125% and 0.25% BWOC olive waste was introduced, respectively. There was a substantial decrease of 16.67% in Poisson’s ratio by adding 0.5% BWOC olive waste, as compared to the base cement sample. This reduction makes the cement more compressible and easier to expand. In summary, the reduction in poison’s Ratio is not preferable for the cement matrix, as it will make the cement have less resistance to compressional forces.

The reduction in Poisson’s ratio with olive waste incorporation highlights a trade-off in cement performance. While increased compressibility as indicated by the decrease in Poisson’s ratio can enhance flexibility and adaptability under stress, the highly decreased resistance to compressional forces may compromise structural integrity. Optimizing olive waste content is essential to balance these effects, ensuring reliable performance in well cementing applications.

Fig. 8
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The changes in Poisson’ ratio with olive waste concentration.

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Porosity

Figure 9 reveals the impact of adding olive waste on cement porosity, demonstrating that an increase in the olive waste percentage leads to a reduction in the pore space within the cement sheath. The porosity of the base cement was 24.5% and decreased to 23.7% when 0.125% BWOC olive waste was introduced. As the percentage of olive waste content increases, there is a further reduction in porosity, with decreases of 6.9% and 9.38% observed when incorporating 0.25% and 0.375% BWOC olive waste, respectively. Additionally, the porosity of the 0.5% BWOC olive waste sample was 5.7% lower than that of the base cement sample. Overall, it appears that the incorporation of olive waste leads to a reduction in the volume of pore space within the cement sheath. In Addition to this impact on porosity, Ali et al. summarized that the addition of olive waste had a decreasing effect on the permeability of the cement matrix30.

The reduction in porosity with olive waste incorporation is critical for improving cement sheath performance in well cementing. Lower porosity combined with the decreased fluid permeability reported earlier by Ali et al.30, enhancing the cement’s ability to provide zonal isolation and prevent fluid migration. This improvement supports long-term well integrity, especially in high-pressure, high-temperature environments where sealing efficiency is crucial.

Fig. 9
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Cement porosity with varying olive waste content.

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Conclusions

The study evaluated the impact of incorporating olive waste into well cement slurry and solidified matrix properties, with a focus on fluid loss, compressive and tensile strength, elastic properties, and porosity. The key findings can be summarized as follows:

  • The addition of olive waste to cement slurry significantly reduces filtration loss by up to 58% compared to the base cement sample. This reduction helps prevent premature cement solidification.

  • The inclusion of olive waste enhances the compressive strength of cement, contributing to its overall robustness. However, it has a slight negative impact on tensile strength.

  • The increase in of olive waste resulted in a decrease in Young’s Modulus. Additionally, it reduces Poisson’s ratio, indicating decreased resistance to compressive forces.

  • The addition of olive waste improves cement sealing efficiency by reducing porosity.