Frontal Stability Analysis of Surfactant Floods

Abstract

Recent surfactant flooding experiments have shown very efficient oil recovery can be obtained without mobility control when the surfactant solution is injected below the critical velocity required for a gravity-stable displacement. The purpose of this study was to develop a method to predict the stability of surfactant floods at the reservoir scale based on gravity-stable surfactant flooding experiments at the laboratory scale. The scale up process involves calculation of the appropriate average frontal velocity for the reservoir flood. The frontal velocity depends on the well configuration. We have performed systematic numerical simulations to study the effect of key scaling groups on the performance of gravity-stable surfactant floods. We simulated three-dimensional heterogeneous reservoirs using a fine grid and a third-order finite-difference method to ensure numerical accuracy. These simulations have provided new insight into the behavior of gravity-stable surfactant floods and in particular the importance of the microemulsion properties. The capability to predict when and under what reservoir conditions a gravity-stable surfactant flood can be performed at a reasonable velocity is highly significant. When a surfactant flood can be done without polymer (or foam) for mobility control, cost and complexity are significantly reduced. Advantages are especially significant when the reservoir temperature is high and the use of polymer becomes increasingly difficult. Our simulations show that gravity-stable surfactant floods can be very efficient using horizontal wells in reservoirs with high vertical permeability.

Proper Use of Capillary Number in Chemical Flooding

“…In their test, the breakthrough recovery decreased as the capillary number increased with the exception of lowest injection rate (1 mL/min), and the major difference between conventional oil and heavy oil waterfloods accounted for that at water breakthrough, and residual heavy oil was bypassed due to adverse mobility ratio, not from capillary trapping. The importance of frontal stability of surfactant flooding without mobility control at velocity less than critical one required for a gravity stable displacement was well studied [15,16]. Their studies indicated that higher velocity may cause unstable displacement front, which may not make the lowest residual oil saturation.…”

“…CDC has various applications in not only water flooding but also chemical flooding [12,13,15,16,40]. According to capillary number theory and critical capillary number requirement, to get best/highest oil recovery, the capillary number must be increased to two or three orders of magnitude [4], as can be seen from Figure 1.…”

“…Traditionally, CDC was used to describe the relationship between capillary pressure and wetting/nonwetting phase saturation [1] while it was more and more frequently used in describing relationship between residual oil saturation ( or ) and capillary number (Nc) [3,4,6,[9][10][11]. In enhanced oil recovery like chemical flooding CDC has various applications in not only water flooding but also chemical flooding [12][13][14][15][16]; capillary number was frequently cited in explaining the mechanisms [10,12,17,18]. Typical classical CDC showed that larger capillary number leads to lower residual oil saturation and when capillary number increased to some certain critical value, the residual oil saturation could drop to a minimum value even zero.…”

Optimization of Gravity-Stable Surfactant Flooding

“…The experimental results and the proposed stability theory were found to be in good agreement. Tavassoli et al (2014aTavassoli et al ( , 2014b simulated these experiments and showed that fine-grid simlations could be used to predict the stable velocity. More recently, Tavassoli et al (2015) has extended the results to the reservoir scale and investigated optimization strategies using horizontal wells.…”