I am performing core flooding experiments as a research work. I started by initially saturating the core sample by the crude oil (Stock tank oil). However, I did not do enough vacuuming of the core sample before saturating it. I tried to measure the base permeability of the core with the crude oil but I did not get any stabilization on the pressure drop across the sample. Could the problem be attributed to the insufficient vacuuming?
How can the problem by solved?
I completely agree with the answer given by Dr. Foroozesh. I must also add that the standard process for any type of core flooding follows an initial vacuum and dryness process. Vacuuming process assures that the core gets fully saturated with desired fluid, making an accurate measurement of effective porosity to that fluid, and also a fast stabilized flow regime for permeability measurements. Darcy's law stands only for a core being fully saturated with the fluid. In case vacuuming is not sufficient, you would not be sure whether the core gets fully saturated or not, air/water might be trapped.
Before resaturating the sample with brine, it is common practice to clean the sample with solvents to remove all volatiles (hydrocarbons...). This can be done with a cyclic cleaning by flushing first with an azeotrope of chloroform and methanol, then with tetrahydrofuran, until the effluent flows clean. then dry in an oven, and finally pull a vacuum on the sample in a Hassler sleeve to be sure no volatiles remain. Other solvents are CO2-Toluene, but these do not clean well enough....volatiles will remain after many pore volumes.
The importance of vacuuming your core samples before saturation are: 1)To open-up the pore, 2) To remove air bubbles, 3) To extract dry clay/silt or very fine grains that may lodge or bridge the pores. You did not say how log you aged the cores or at what pressure. Are the cores cleaned or native sate? What is your routine Ka value of the cores like? For stabilization check:- 1) Air bubble 2) Flow rate. 3) Your guage
Thank you all for you collaboration and responses.
I am actually saturating the core initially with stock tank crude oil. I put it for almost 6 hours to vacuum then added the oil to the cell to get it saturated. I pressurized the cell to almost 3500 psi and left it for three days to ensure that the oil is entering the pores. I put the sample in the core holder and started injecting the oil to measure the absolute permeability to oil. However, the pressure drop was not stabilized. Then, I decided to increase the rate and flood the core with oil for almost 2 hours to remove any air trapped in the core yet the problem has not been solved.
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