Exploring the Impact of Chelating Agents on Viscoelastic Surfactant Flooding on Sandstone Cores Using Magnetic Resonance Imaging

In this research, we advocate the utilization of chelating agents as a strategic approach to optimize the quantity of viscoelastic surfactant (VES) necessary for successful enhanced oil recovery (EOR), while concurrently ensuring that the essential viscosity is maintained. Our study employs magnetic resonance imaging (MRI) for real-time monitoring of oil saturation during core flooding experiments. Chelating agents, specifically diethylene triamine penta acetic acid (DTPA) and glutamic acid diacetic acid (GLDA), were employed at concentrations ranging from 2 to 8 wt %. The optimal VES concentrations were meticulously determined through comprehensive experiments, evaluating rheological properties and interfacial tension. Subsequently, the most effective GLDA/VES and DTPA/VES combinations were selected by using the same screening criteria. To render the aqueous phase undetectable to the MRI apparatus while exclusively capturing the oil signal, we incorporated deuterium oxide was incorporated. The NMR T2 distribution quantified the total oil volume in the rock, while a fast spin echo (FSE) imaging pulse sequence provided a 2D visualization of the spatial fluid distribution. Additionally, a 2D spatial T2 pulse sequence was employed to visualize microscopic displacement efficiency at pore sizes. Three fluid formulations, 1.25% VES, 1.25VES/8% DTPA, and 1.25% VES/4% GLDA, were scrutinized for EOR based on rheology and interfacial tension (IFT). The 2D FSE images unveiled a piston-like oil displacement mechanism. The optimal sweep efficiency for chemical flooding was achieved with 4% GLDA/1.25% VES, resulting in an ultimate recovery of 53% of the original oil in place. In contrast, the lowest recovery (39%) was observed with 8% DTPA and 1.25% VES, while pure VES at 1.25% yielded 50% ultimate recovery. Analysis of 1D and 2D spatial T2 data indicated that medium and large pores significantly contributed to oil recovery, while micropores played a minor role in the process.