Chelating agents for oilfield stimulation: Lessons learned and future outlook

Abstract

Chelating agents were introduced because of the several issues associated with inorganic acids during oilfield stimulation. Carbonate and sandstone rocks have been stimulated using different kinds of acid systems and there is an engaging debate on chelating agents as an effective acid system. Several shortcomings of inorganic acid systems need to be addressed by chelating agents in order to be its constructive replacement. The complex nature of these chelating agents led to accelerated research and developmental efforts in understanding its applicability at different environmental conditions. The past two decades of research in chelating agents for oilfield stimulation has resulted in researchers branching out in several directions to realize the potential of this acid system. There is a requirement to link these branches and provide a holistic view of the lessons learned during this time. Various researchers have also provided guidance for future work that is commonly disregarded. This paper provides a nexus of the research conducted in this field and could direct plans for future research. Hydrochloric acid for carbonate acidizing and mud acid for sandstone damage removal have been found to cause issues such as face dissolution, reaction product precipitation, chemical incompatibility, high corrosion rates, toxic gas generation, emulsion issues, amongst many others. The recent interest in chelating agents led to researchers conducting tests to understand its interactions with the formation rock and other oilfield fluids. Experiments such as coreflooding, corrosion tests, compatibility, Inductively Coupled Plasma (ICP), Environmental Scanning Electron Microscope (ESEM), and X-Ray Diffraction (XRD) helped in highlighting the advantages of chelating agents. From these studies, researchers were able to find synergistic blends that could help improve traditional treatment practices. Mechanisms of chelating agent reactions with sandstone and carbonate rock were elucidated in this work. The future outlook of chelating agents' application lies in making the treatment more cost-effective, environmentally friendly, and target focused. Chemical formulations must be designed to take advantage of high-temperature stability, low reprecipitation potential, low sludging tendency, high dissolving capacity, high iron controlling potential, and low corrosion rates offered by chelating agents. Some field experiences were noted, which could encourage operators to perform more such treatments in the future. The reader of this review article would gain knowledge of the complex chemistry of chelating agents and describes the research done for acid stimulation and iron control. Through the process of review, the paper also connects the wealth of research in this field and provides a measured guidance for technology development to promote the use of chelating agents in the industry. It can help future researchers in academics or the industry to enhance the quality of research.