A Comprehensive Review on Screening, Application, and Perspectives of Surfactant-Based Chemical-Enhanced Oil Recovery Methods in Unconventional Oil Reservoirs

Surfactant-based chemical-enhanced oil recovery (EOR) methods have been recognized to be effective in both conventional and unconventional oil reservoirs. However, the nanopore size and low permeability characteristics of unconventional reservoirs hinder the wide application of the chemical EOR methods and have greater requirements for chemical agents. Thorough understanding of the rock-fluid-chemical interactions is the key to production improvement and economy development of unconventional formations. This paper is a systematic review of the literature focused on the performance evaluation and application potential of chemical EOR methods. To address the technical requirement, crucial features of the tight and shale formations and properties of the typically used chemicals are introduced. Many studies in recent decades have revealed that surfactant-based formulations have the capability to increase oil recovery through reducing interfacial tension, altering surface wettability, enhancing aqueous penetration, improving oil mobility, and then promoting spontaneous imbibition. The probable mechanisms of chemical EOR are summarized to demonstrate their potential and to guide the formulation development for reservoirs. Laboratory experiments of chemical screenings are presented to discuss the selection criteria of the appropriate formulation for respective EOR projects. Traditional measurements and novel experimental methods provide a comprehensive understanding of the chemicals corresponding to their application conditions. The outcome of recent pilot field tests in major formations is summarized to show the application feasibility and improvement schemes of chemical EOR. Problems currently existing and possible solutions are discussed to point out future research directions of the related field. Summarizing and analyzing of the problems, challenges, and future respects could help guide the design of chemical EOR projects. This review provides a more comprehensive understanding of the chemical performance in unconventional reservoirs and addresses the significance of appropriate screening methods and sufficient field knowledge for the success of chemical EOR operations.