Developing soil qualities has become unavoidable when it comes to identifying appropriate sites with substantial soil strength. Instead of observing regions with good geotechnical features, it is appropriate to apply soil stabilization techniques for site stability (Almajed et al., 2021). Soil stabilization increases the carrying capacity of the soil and reduces settlement and deformation. Soil stabilization is the most effective way to enhance ground strength (Wang et al., 2022). Several strategies have been explored by researchers (Afrin, 2017; Xue et al., 2021). The soil stabilization is performed through mechanical and chemical means (Firoozi et al., 2017; Ghadir & Ranjbar, 2018). The application of chemical soil stabilizers is on the rise and hundreds of chemicals are used for stabilization (Firoozi et al., 2017; Puppala and Pedarla, 2017; Mekonnen et al., 2020). Traditional ground or soil stabilization methods are costly, power intensive, and detrimental to the environment (Wang et al., 2023).

Biotechnology has acquired monumental attention and significance in the last few years. It is expanding its spans across many fields in boundless ways, and it is serving humanity through its applications in nutrition, food, medicines, and animal life sciences. It brings the advantage of living organisms and their goods to the enhancement of a sustainable environment and quality of human life (Verma et al., 2011). Biostabilization has lately emerged as a sustainable option capable of overcoming some of the limits of traditional soil improvement techniques (Umar et al., 2016; Rahman et al., 2020; Xue et al., 2023). Efforts are being made in soil stabilization by adapting bacteria to enhance soil performance (Banik et al., 2023; Sharma and Satyam, 2023). Enzyme-induced calcite precipitation (EICP) is a promising approach due to its simplicity of application in the field and compatibility across various types of soil (Saif et al., 2022). EICP in biofertilizers enhances soil geotechnical qualities by precipitating calcium carbonate (CaCO₃), which adheres soil particles together (Kavazanjian and Hamdan, 2015). In addition to that, soil stabilization by microorganisms that precipitate CaCO₃ is used in many soil types such as liquefiable soils, sand, sandy soil, and tropical residual soils; it is utilized for porous media remediation and the restoration of calcareous stone components (Xu et al., 2017; Zamani et al., 2021; Sharma et al., 2022). Winoto and Keawsawasvong used Sporosarcina pasteurii as a catalyst source for the reaction in the microbiologically induced calcite precipitation (MICP) and observed that the enzyme alone is sufficient for the required process to occur (Winoto and Keawsawasvong, 2022). EICP can also be used to seal rock fissures, clean wastewater, and minimize beach sand erosion (Xu et al., 2017). Furthermore, this bio-cementation technique is relatively recent and is used to improve soil quality. In EICP, calcium carbonate (CaCO₃) precipitates out of the solution as a result of the hydrolysis of urea catalyzed by numerous enzymes (Hu et al., 2021). Soil reinforcement, pollutant remediation, and enhanced oil recovery by bio-plugging are just a few examples of the unique and sustainable engineering applications that stand to benefit greatly from EICP (Finnerty and Singer, 1983; Gowthaman et al., 2021; Omoregie et al., 2021; Sharma et al., 2021). It is vital to have a solid theoretical knowledge of the pace and amount of CaCO₃ precipitation through the ureolytic chemical process for method improvement considering the vast number of alternative configurations for EICP (Ahenkorah et al., 2021b; Sharma et al., 2021). In a conventional EICP process, for example, the rate and amount of CaCO₃ precipitation can be heavily influenced by the enzyme activity, concentration, and kinetic parameters of the enzymatic utilized, as well as the interaction conditions, such as pH and temperature (Kim et al., 2018).

It becomes indisputable that petroleum and other fossil fuels will continue to make up a sizable part of the global energy portfolio for the foreseeable future (Ismail et al., 2017). Oil production and processing facilities are permanently growing to keep up with the rising demand for energy throughout the world. Though the increase in production rates of oil and gas can be economical for the producer it brings a lot of challenges such as sand production. The sand production increases the drag force and in situ stress. It causes sand particles to move from reservoirs to the wellbore and come into the production stream. Most of the oil and gas reservoirs have poor sand consolidation and the companies are spending millions of dollars on sand production controlling technologies.

The petroleum industry has access to a wide range of methods for managing and controlling sand production. Among these methods are production rate control, mechanical ones like gravel packing or standalone screens, as well as chemical ones like resins (Weirich et al., 2013; Saghandali et al., 2022). Running the well at the maximum sand-free rate (MSFR) and performing effective sand management are another technique for limiting sand production (Stein et al., 1974; Rahim et al., 2010). In comparison to chemical methods, mechanical techniques are typically more expensive and time-consuming (ben Mahmud et al., 2020). They also face other issues like a decline in productivity index, complicated installation equipment, installation-related damage, workover difficulties, zonal isolation issues, collapsed screens, and equipment erosion and plugging (Arukhe et al., 2005; Abduljabbar et al., 2022). Additionally, they are useless at containing tiny sand particles. On the other hand, chemical methods are commonly used with a different strategy for managing the unconsolidated formation that generates a wide variety of sand. Since the beginning of 1940, sand production has been managed using chemical sand consolidation techniques, specifically plastics and resins (Parker et al., 1967). To create a bonding force between the loose sand grains, chemical sand consolidation methods involve injecting reactive chemicals into a target loose sand formation. With growing environmental concerns, there is a vital need for solutions that are economical, cost-effective, and environmentally friendly. Bio cementation techniques such as EICP is an effective tool to counter such environmental concerns. The EICP process can be an economical and viable means for sand consolidation to solve sand production issues in oil and gas wells (Alarifi et al., 2022). Calcium carbonate precipitated in the spaces as a result of chemical action, making the surface more compact and so enhancing the structural integrity. More than that, it is noteworthy that EICP has the potential to restrict CO₂ leakage from a storage reservoir under a specific scope of temperature and pH (Phillips et al., 2013; Zamani et al., 2019).

Several enzymes have been used in Enzyme Induced Calcite Precipitation (EICP) for inducing the precipitation of calcium carbonate (CaCO₃) from a supersaturated solution. These enzymes are typically calcium carbonate precipitation-inducing proteins, which are naturally occurring proteins found in various organisms that can induce the precipitation of calcite crystals (Polowczyk et al., 2016). Carbonic anhydrase is an enzyme that catalyzes the reversible hydration of carbon dioxide to form bicarbonate ions and protons (Noshi and Schubert, 2018; Molina-Fernández and Luis, 2021). Carbonic anhydrase can increase the concentration of bicarbonate ions in the solution, which promotes the formation of calcium carbonate crystals (Rodriguez-Navarro et al., 2019).

One of the most used enzymes in EICP is the urease enzyme (Hamdan and Kavazanjian, 2016; Yuan et al., 2016; Alarifi et al., 2022). This enzyme is abundant in microorganisms, plants, and some animals, particularly in legume seeds like jack beans. Urease facilitates the hydrolysis of urea into ammonia and carbon dioxide, which is crucial in the nitrogen cycle and has various industrial applications. The precipitation of calcite through enzymatic activity depends on factors such as enzyme type, reactivity, and purity. Therefore, the extraction and purification of enzymes should be cost-effective to make the EICP approach practical. The main source of urease used in commercial products is jack bean, which needs to be refined to achieve high-purity enzyme. However, performing EICP using urease enzymes on a large scale may be too expensive, making it necessary to find alternative sources of the enzymes. One possible alternative to jack bean urease is the amylase family enzymes which are plentifully available and cost effective alternate.

The amylase enzymes are one of the main enzymes that are widely employed in the industry which is a great incentive to utilize it for the petroleum industry. There are several different types of amylase enzymes, including alpha-amylase, beta-amylase, and glucoamylase, which differ in their specificities and mechanisms of action. Alpha-amylases account for 33% of the global enzyme output (Hu and Liu, 2021). The variety and magnitude of its applications make it a highly indispensable enzyme (Farooq et al., 2021). One exciting potential use of alpha-amylase is for sand stabilization in the oil and gas industry. However, before it can become a reality, extensive laboratory testing is required to confirm its suitability. This testing should investigate factors such as precipitation product, pH effect, temperature effect, and salinity effect to ensure the enzyme can be effectively applied in oil and gas operations. By harnessing the power of alpha-amylase, the petroleum industry could benefit from improved sand stabilization and other applications.

These enzymes’ main role is to hydrolyze starch molecules into polymers made up of glucose units. Amylases have the potential to be used in a broad range of commercial processes, including those in the food, fermentation, and pharmaceutical sectors. Animals, plants, and microbes may all produce amylases. Nevertheless, enzymes derived from fungi and bacteria have predominated in industrial applications (de Souza and e Magalhães, 2010). Bacillus subtilis is a well-known alpha-amylase producer (Raul et al., 2014; Lahiri et al., 2021). The activity of alpha-amylase refers to the ability of the enzyme to break down long-chain carbohydrates, such as starch, into smaller molecules like maltose, glucose and dextrin. This activity is measured in a laboratory setting using a variety of methods, including colorimetric assays, iodine-starch test and gel electrophoresis.

In this study, we investigated the process of EICP (Enzyme-Induced Calcium Carbonate Precipitation) using a new enzyme called alpha-amylase. The objective of the study is to optimize the parameters involved in EICP to achieve maximum calcite precipitation. The study examines several parameters that affect the process of EICP, including enzyme concentration, enzyme volume, the concentration of calcium chloride (CaCl₂), temperature, the synergistic impact of magnesium chloride (MgCl₂) and CaCl₂, the concentration of xanthan gum, and solution pH. By studying these parameters, optimal conditions for EICP involving alpha-amylase as enzyme, can be identified. The output of this study could be valuable in a variety of applications, such as biomineralization, soil stabilization, and remediation of contaminated soils in the geotechnical as well as in the oil and gas industry.

In this study, precipitation tests were conducted to investigate the activity of enzyme and precipitation using a novel enzyme, Alpha-amylase. The chemicals utilized in the study are urea, calcium chloride, magnesium chloride, potassium hydroxide, and xanthan gum which were acquired from Sigma Aldrich. The Alpha-amylase was supplied by MN-CHEM Saudi Arabia.

In this test, the reactant and enzyme were prepared in different test tubes and mixed later. The tests were conducted in closed tubes without exposure to the air. The tests were conducted at different concentrations of reagents and enzymes and the best optimum concentrations were selected for detailed investigations. The enzymatic reaction and precipitation were observed for 48 h. At the end of the reaction time, precipitations were measured by weight%.

Upon finding the optimum recipe, the further impact of different parameters was investigated on precipitation. The studied parameters are enzyme concentration, enzyme volume, the effect of MgCl₂, xanthan gum concentration, pH, and temperature.

In the study, two distinct mechanisms were proposed: 1. Calcite precipitation 2. Dolomite precipitation. To produce calcite or CaCO₃, a solution of calcium chloride and urea was created by mixing the two substances, and then a catalytic agent, in the form of an enzyme, was added. During the process, the carbonate ions released from urea hydrolysis combined with the calcium ions that were released when CaCl₂ dissociated in water, ultimately resulting in the formation of CaCO₃. The enzymes served as a catalyst to facilitate the urea hydrolysis reaction. The basic chemical reactions that lead to the production of CaCO₃ may be represented by the following (Eqs 4–6) (Putra et al., 2017b). The reactions responsible to produce calcite and dolomite are detailed in Figures 9, 10 (Tariq et al., 2022). There are some other reaction products formed during enzyme activity which were identified in XRD analysis. The products included aragonite and sylvite. Here only reactions were reported on the formation of calcite and dolomite. C O N H 2 2 + 2 H 2 O →   c a t a l y s t   2 N H 4 + + C O 3 2 − (4) C a C l 2 → C a 2 + + 2 C l − (5) C a 2 + + C O 3 2 − → C a C O 3 ↓ p r e c i p i t a t e d (6)

The mechanism of calcite precipitation in Enzyme-Induced Calcite Precipitation (EICP) involves several steps (van Paassen et al., 2010; Putra et al., 2017b; Kong et al., 2019; Nayanthara et al., 2019; Ahenkorah et al., 2021b; Weinhardt et al., 2021):

1 Mixing of Urea and Salt: Mixing of CaCl₂ saturated sand or rock with Urea.

Overall, the EICP process involves the hydrolysis of urea by microorganisms to produce carbonate ions, which react with calcium ions to form calcite. The process can be used for soil or sand stabilization, slope stabilization, and other applications, providing a sustainable and cost-effective alternative to traditional sand improvement techniques.

The predictable reactions to acquire precipitation of dolomite are given in (Eqs 7, 8). M g C l 2 → M g 2 + + C l 2 − (7) M g 2 + + C a C O 3 s → C a M g C O 3 2 s (8)

In this study, the precipitation of calcium carbonate using alpha-amylase as an enzyme was investigated. Several experimental sensitivities were assessed, including enzyme concentration, enzyme volume, MgCl₂ and xanthan gum effects, pH, and temperature. The results showed that a 15% enzyme concentration yielded the highest precipitate. The best molar ratio combination for CaCl₂ and MgCl₂ was (0.6:0.4) for the highest CaCO₃ precipitation (32.2%). Enzyme volume in the solution did not significantly affect precipitation at a specific molar ratio. pH significantly affected precipitation; the precipitation yield increased with an increase in pH. The highest precipitate (87%) was obtained at 75°C with 2.5 g/L xanthan gum as a stabilizer. The temperature affects the enzyme activity and 75°C was found to be an effective temperature limit for the tested enzyme. TGA analysis revealed that the precipitated samples remained stable at temperatures and showed the reaction product was composed of CaCO₃ and other complexes as decomposition occurred at 600°C. XRD analysis showed that the sample consisting of 1 M urea, 0.6 M CaCl₂, 0.4 M MgCl₂, 15 wt% enzyme, and 0.5 M KOH had the largest proportion of dolomite (53%). In contrast, the sample consisting of 1 M urea, 0.6 M CaCl₂, 0.4 M MgCl₂, 15 wt% enzyme, and 1 M KOH showed 29% calcite and 4.8% dolomite. The application of EICP in sand consolidation is increasing at a high pace. The limitation of this study is associated with the enzyme activity measurement, long-term and thermal stability, and utilization in producing sand pack samples.