Abstract
Capillary number theory is very important for chemical flooding enhanced oil recovery. The difference between microscopic capillary number and the microscopic one is easy to confuse. After decades of development, great progress has been made in capillary number theory and it has important but sometimes incorrect application in EOR. The capillary number theory was based on capillary tube bundles and Darcy’s law hypothesis, and this should always be kept in mind when used in chemical flooding EOR. The flow in low permeability porous media often shows obvious non-Darcy effects, which is beyond Darcy’s law. Experiments data from ASP flooding and SP flooding showed that remaining oil saturation was not always decreasing as capillary number kept on increasing. Relative permeability was proved function of capillary number; its rate dependence was affected by capillary end effects. The mobility control should be given priority rather than lowering IFT. The displacement efficiency was not increased as displacement velocity increased as expected in heavy oil chemical flooding. Largest capillary number does not always make highest recovery in chemical flooding in heterogeneous reservoir. Misuse of CDC in EOR included the ignorance of mobility ratio, Darcy linear flow hypothesis, difference between microscopic capillary number and the microscopic one, and heterogeneity caused flow regime alteration. Displacement of continuous oil or remobilization of discontinuous oil was quite different.
Highlights
Capillary number theory is regarded as the basic theory in polymer flooding, surfactant flooding, polymer-surfactant flooding (SP), and alkali-surfactant-polymer flooding (ASP), which are more appealing enhanced oil recovery (EOR) techniques in low oil price era
Typical classical capillary desaturation curve (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
Low permeability chalks based CDC indicated that the minimum residual oil saturation was about 0.2 when capillary number increased to 10−2, and some of the curves have a trend of dropping to zero while other curves did not according to the wettability difference [20]
Summary
Capillary number theory is regarded as the basic theory in polymer flooding, surfactant flooding, polymer-surfactant flooding (SP), and alkali-surfactant-polymer flooding (ASP), which are more appealing enhanced oil recovery (EOR) techniques in low oil price era. The basic mechanism of chemical flooding in EOR can be summarized into mobility control based enlarging sweep efficiency and capillary number theory based improving displacement efficiency. 1.0E + 00 recent literatures showed that CDC was often misunderstood by ignoring the difference between remaining oil saturation and residual oil saturation and the fundamental hypothesis in conducting capillary number definition. Flow behaves as some kind of non-Darcy feature, while in heavy oil chemical flooding the viscosity ratio is big enough to consider the mobility ratio and frontal stability. Systematical review of capillary number in chemical flooding is helpful to understand the importance of mobility control and enlarging sweep volume in chemical enhanced oil recovery (EOR)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
