3) Dimensional analysis Trapping of crude oil in pores is a principal factor oil

Question

3) Dimensional analysis Trapping of crude oil in pores is a principal factor oil recovery. Hydraulic fracturing is often used to recover this oil, by injecting a fluid into the pores to extract the trapped oil as shown in the figure below. water flooded through pore channel residual oil film grain narrow pore throat with trapped oil oil-filled pore channel mage credis btp://www.mrnnitechzon.nol up-content uploadsl2015/04/ Naipe-juids pn a. b. c. Why is it preferable to design an oil recovery system with a high capillary number? Why would it be preferable to decrease surface tension rather than increase velocity? How could the surface tension be altered? (author:Daniel Viju [modified])

Explanation / Answer

capillary number lead to lower residual oil saturation and when capillary number increased to a certain critical value(first critical value), the residual oil saturation could drop to a minimum value even zero. CDC shapes were different in water-wet and oil-wet media. Recovery can be improved by increasing flooding rate, though invalid and impractical, displacement phase viscosity or/and reducing oil/water interfacial tension, which are actually adopted by chemical flooding.After capillary number increased to a certain value (second critical value), the residual oil saturation may increase or decrease as capillary number increase. Surface tension is the property of any liquid by virtue of which tries to minimize its free surface area. Surface tension of a liquid is measured as the force acting per length on an imaginary line drawn tangentially on the free surface liquid surface  tension computed from contact angle measurements carried out on oil-wet core demonstrated that the surface tension alteration during water flooding is a result of physicochemistry occurring. The concentration of reservoir water as well as the presence of divalent ions was found to react with polar group of the crude oil which subsequently alter the surface tension. Moreover, salinity and the ratio of divalent-to-monovalent ions by altering the polarity of crude oil, were found promoted pore blocking.

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