Development of a Citric Acid-Promoted Betaine Surfactant for an Integrated Fracturing-Oil Displacement Fluid System: Experimental and Nuclear Magnetic Resonance Studies

To address the growing demand for clean and efficient fracturing fluids suitable for low-permeability reservoirs, this study explored the impact of organic acids with varied molecular structures on the rheological behavior of erucic amide propyl betaine (EAPB) and developed an EAPB/citric acid (CA) clean fracturing fluid system. After 2 h of continuous shearing at 170 s –1 and 90 °C, the fluid viscosity retained 38 mPa·s. The system also showed excellent shear recovery ability even under a shear rate as high as 300 s –1 . Although the EAPB/CA system initially showed limited salt resistance, the addition of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and diethylenetriaminepenta (methylenephosphonic) acid (DTPMP) significantly enhanced its salt resistance. The fracturing fluid also demonstrated favorable sand-carrying performance (0.0003 mm·s –1 ) and anti-swelling efficiency (92%). With 30% kerosene, the viscosity dropped below 5 mPa·s within 30 min at 90 °C, and the surface tension decreased to 23.21 mN/m. At a gel-breaking fluid concentration of 0.3%, the interfacial tension reached 10 –2 mN/m, and the contact angle shifted from 91° to 42°, indicating strong interfacial activity and wettability alteration that promoted crude oil stripping. To verify the dual fracturing-oil displacement function, static imbibition tests were performed using the gel-breaking fluid, achieving a spontaneous imbibition recovery of 45% at 60 °C. Nuclear magnetic resonance (NMR) results further confirmed that the gel-breaking fluid exhibited exceptional crude oil mobilization capability in small pores. These findings highlight the potential of the EAPB/CA system as an integrated fracturing and enhanced oil recovery fluid for low-permeability reservoirs.