Oil & Gas Research
Open Access

Acid Stimulation; Carbonate Reservoirs; Chelating Agents; Seawater; Synergy; Formation Damage; Hydrocarbon Production

Introduction

Carbonate reservoirs play a significant role in global hydrocarbon production, characterized by their complex geological formations and diverse mineral compositions. However, the extraction of hydrocarbons from these reservoirs presents unique challenges, primarily due to their low matrix permeability and susceptibility to formation damage. Acid stimulation has long been recognized as a valuable technique for enhancing production rates by creating or enlarging flow channels within the reservoir matrix. Traditionally, hydrochloric acid (HCl) or hydrofluoric acid (HF) has been employed in acid stimulation treatments to dissolve carbonate minerals and improve reservoir permeability. However, the effectiveness of conventional acid treatments in carbonate reservoirs is often limited by factors such as mineralogical heterogeneity, formation damage, and the risk of secondary precipitate formation. In recent years, a novel approach has emerged to address these challenges by leveraging the synergistic effects of chelating agents and seawater in acid stimulation treatments [1].

Understanding Carbonate Reservoirs

Carbonate reservoirs, composed primarily of calcium carbonate (CaCO3) or dolomite (CaMg(CO3)2), possess intricate pore networks formed through the deposition of marine organisms over geological time. These reservoirs often exhibit low matrix permeability, necessitating stimulation to create pathways for hydrocarbon flow. However, conventional acid treatments, typically employing hydrochloric acid (HCl) or hydrofluoric acid (HF), face challenges in carbonate formations due to mineral dissolution kinetics and the potential for secondary precipitation reactions [2].

Challenges of Acid Stimulation in Carbonate Reservoirs

Carbonate reservoirs contain a diverse range of minerals, including calcite, dolomite, and various silicates, each with distinct reactivity to acids. Differential dissolution rates can lead to non-uniform etching and channeling, limiting the effectiveness of stimulation treatments. Acidizing can inadvertently cause formation damage through the precipitation of insoluble reaction products, such as calcium sulfate (CaSO4) or silica (SiO2), which can plug pore throats and reduce permeability. Achieving uniform acid distribution across the reservoir is challenging, particularly in heterogeneous formations. Without effective diversion techniques, acid may preferentially flow through high-permeability zones, leading to uneven stimulation [3].

The Role of Chelating Agents

Chelating agents, compounds capable of forming stable complexes with metal ions, offer a solution to the challenges of conventional acid stimulation. In carbonate reservoirs, chelating agents such as ethylenediaminetetraacetic acid (EDTA) or hydroxyethylenediaminetriacetic acid (HEDTA) can enhance acid penetration and dissolution by:

Metal Ion Chelation: Chelating agents bind with divalent metal ions, such as calcium (Ca2+) and magnesium (Mg2+), present in carbonate minerals [4]. By sequestering these ions, chelating agents prevent their precipitation as insoluble salts, reducing the risk of formation damage. Chelating agents can buffer the pH of the acid solution, maintaining it within the optimal range for dissolution reactions while minimizing the formation of secondary precipitates. The formation of soluble metalchelate complexes accelerates mineral dissolution kinetics, promoting uniform etching and enhancing the effectiveness of acid stimulation treatments [5].

Seawater as a Catalyst

In recent years, researchers have explored the use of seawater as a cost-effective and environmentally friendly alternative to conventional brine solutions in acid stimulation. Seawater, abundant in carbonate reservoir environments, contains a complex mixture of ions, including sodium (Na+), chloride (Cl−), sulfate (SO42−), and bicarbonate (HCO3−), which can influence acid-rock interactions [6]. When combined with chelating agents, seawater the presence of sulfate ions in seawater can facilitate the formation of soluble sulfate-chelate complexes, further enhancing metal ion chelation and preventing precipitation. Seawater provides a natural buffer against pH fluctuations, helping to maintain the stability of chelate complexes and prolonging their effectiveness during acid stimulation. Utilizing seawater as a base fluid reduces the environmental footprint of acid stimulation operations, minimizing the need for freshwater resources and mitigating the disposal of chemical waste [7].

Case Studies and Field Applications

Several case studies demonstrate the efficacy of combining chelating agents with seawater for acid stimulation in carbonate reservoirs. In one field trial, conducted in a carbonate formation with high magnesium content, the injection of an EDTA-seawater solution resulted in a significant improvement in well productivity compared to conventional acid treatments. Similarly, laboratory experiments have shown that the addition of chelating agents to seawater-based acid formulations can mitigate formation damage and prolong the longevity of stimulation effects [8].

Discussion

This paper explores the mechanisms underlying the synergy between chelating agents and seawater in enhancing acid stimulation treatments in carbonate reservoirs. Through a comprehensive review of theoretical principles, laboratory experiments, and field applications, we elucidate the potential of this synergistic approach to unlock untapped hydrocarbon reserves while advancing environmental sustainability in oil and gas operations. In the realm of oil and gas extraction, carbonate reservoirs present both promise and challenge. These formations, characterized by their complex pore structures and susceptibility to formation damage, often necessitate stimulation techniques to maximize production. Among these techniques, acid stimulation stands out as a versatile and effective method to enhance permeability and facilitate hydrocarbon flow. However, in the case of carbonate reservoirs, conventional acid treatments may encounter limitations due to mineralogical composition and the risk of precipitate formation. In recent years, a novel approach has emerged, leveraging the synergistic effects of chelating agents and seawater to optimize acid stimulation in carbonate reservoirs. Through a comprehensive review of theoretical principles, laboratory experiments, and field applications, this paper elucidates the mechanisms underlying the synergy between chelating agents and seawater in acid stimulation. Case studies highlight the efficacy of this approach in improving well productivity and minimizing environmental impact [9].

Future directions and challenges are discussed, emphasizing the potential of this synergistic strategy to unlock the full production potential of carbonate reservoirs while advancing environmental sustainability in oil and gas operations. Chelating agents, such as ethylenediaminetetraacetic acid (EDTA) or hydroxyethylenediaminetriacetic acid (HEDTA), have the ability to form stable complexes with metal ions present in carbonate minerals. These chelate complexes enhance acid penetration and dissolution kinetics while mitigating the risk of formation damage by preventing the precipitation of insoluble salts. Concurrently, seawater, abundant in carbonate reservoir environments, serves as an environmentally friendly and cost-effective base fluid for acid stimulation treatments. Seawater offers inherent buffering capacity and compatibility with chelate complexes, thereby further optimizing the efficacy of acid stimulation in carbonate reservoirs [10].

Conclusion

The synergistic combination of chelating agents and seawater represents a promising advancement in the field of acid stimulation for carbonate reservoirs. Through their complementary mechanisms of action, chelating agents enhance acid penetration and dissolution while mitigating formation damage, while seawater serves as an environmentally friendly and cost-effective base fluid. This synergistic approach addresses key challenges associated with conventional acid treatments in carbonate formations, including mineralogical heterogeneity, formation damage, and environmental impact. The efficacy of chelating agents and seawater in acid stimulation has been demonstrated through laboratory experiments, field trials, and case studies, highlighting improvements in well productivity and environmental sustainability. By unlocking the full production potential of carbonate reservoirs while minimizing environmental impact, this synergistic strategy offers significant benefits to the oil and gas industry.

1. Chen C, Su M, Yang Z, Liu G (2014)Evaluation of the environmental impact of the urban energy lifecycle based on lifecycle assessment. Front Earth Sci 8:123-130.

Indexed at,Google Scholar,Crossref

2. Chen L, Yang Z, Chen B (2013)Scenario analysis and path selection of low-carbon transformation in China based on a modified IPAT model.PLOS ONE 8: 1-9.

Indexed at,Google Scholar,Crossref

3. Dhina N, Permana T (2021)Natural gas transportation business contribution to Indonesia’s national energy policy and carbon emission offset by on-grid solar PV utilization: Surabaya, East Java, Indonesia.IOP Conf Ser Earth Environ Sci 753: 23.

Indexed at,Google Scholar,Crossref

4. Feng Y,Zhang LX (2012)Procedia Environmental Sciences Scenario analysis of urban energy saving and carbon abatement policies: a case study of Beijing city. China 13: 632-644.

Indexed at,Google Scholar,Crossref

5. Gan Y, El-Houjeiri HM, Badahdah A, Lu Z, Cai H, et al. (2020)Carbon footprint of global natural gas supplies to China.Nat Commun 11

Indexed at,Google Scholar,Crossref

6. Hayes RE (2004)Catalytic solutions for fugitive methane emissions in the oil and gas sector.Chem Eng Sci 59: 4073-4080.

Indexed at,Google Scholar,Crossref

7. Hilpert M, Rule AM, Adria-Mora B, Tiberi T (2019)Vent pipe emissions from storage tanks at gas stations: implications for setback distances.Sci Total Environ 650: 2239-2250.

Indexed at,Google Scholar,Crossref

8. Huang L, Liao Q, Yan J, Liang Y, Zhang H (2021)Carbon footprint of oil products pipeline transportation.Sci Total Environ 783.

Indexed at,Google Scholar,Crossref

9. Drünert S, Neuling U, Zitscher T, Kaltschmitt M (2020)Power-to-Liquid fuels for aviation – processes, resources and supply potential under German conditions. Appl Energy 277: 115578.

Indexed at,Google Scholar,Crossref

10. Lobo P, Hagen DE, Whitefield PD (2011)Comparison of PM emissions from a commercial jet engine burning conventional, biomass, and Fsischer-Tropsch fuels.Environ Sci Technol 45: 10744-10749.

Indexed at,Google Scholar,Crossref