Dynamic Wettability Alteration at Pore-Scale Using Viscoelastic Surfactant/Chelating Agents Systems

The role of wettability is crucial in the extraction of hydrocarbons as it determines how well the oil adheres to the rock surface, directly impacting the efficiency of the extraction process. Numerous studies have been conducted to modify the wettability of rocks to a favorable state. In this study, we delve into the microscopic level to observe the actual process of altering the contact angle during flooding using microfluidic technology within a glass micromodel. Initially, the micromodel is saturated with formation water and subsequently displaced by oil to establish the initial oil saturation. The microfluidic setup consists of a precise pump for flood control and a high-speed microscope to capture images for later analysis using image processing software to obtain the actual contact angle. The contact angle is measured at five arbitrary locations, and the average is calculated at specific time intervals based on image analysis. Three different fluid systems were utilized: pure Viscoelastic Surfactant (VES), VES with DTPA, and VES with GLDA. The concentration of these systems was selected based on optimal rheology and interfacial tension performance. The contact angle was measured at various injection stages to observe its dynamic change from the initial state to the final state and assess the resulting recovery from each fluid system. The pure VES system modified the wettability from slightly oil-wet to slightly water-wet and achieved a 48% recovery of the original oil in place (OOIP). On the other hand, the addition of DTPA altered the wettability from slightly oil-wet to extremely water-wet; however, this did not lead to higher recovery, and water breakthrough occurred, reducing the sweep efficiency with a 45% recovery. The GLDA VES system altered the wettability to moderately water-wet, which proved to be the most favorable wettability condition, resulting in a 56% ultimate recovery. This investigation successfully demonstrated the effectiveness of using VES-assisted chelating agents in altering rock wettability and increasing oil recovery at the pore scale.