**David Asks PERM:**

Dear Perm,

My name is David. I am studying petroleum engineering, and I read the article from your web page about the Jamin effect. At the bottom of the page, it said that we can ask question to you about the subject. I therefore have a question about the article on you web page about the Jamin effect:

The above equations was taken from the article from your web page. This is the static pressure difference between each side of the droplet due to the capillary forces. Is it correct that in order to get the droplet to move, we must have a pressure difference greater than the pressure difference only caused by the capillary forces?

And if we increase the pressure in point A by a certain amount, why will not also the pressure in point B increase by the same amount, and therefore still be trapped? (from equation 2-112).

My last question is the following: Why is high capillary pressure very bad for the flow? Is it not only that the pressure decreases over the droplet, so the pressure in point B decreases? Or must the pressure in B be the same pressure as before, meaning that we have to increase the pressure in A equal to the amount of the capillary pressure?

Best regards

David

**Dr. Jonathan Bryan from PERM Answers:**

Hello,

Thank you for your question. Basically as I understand it, it has three parts:

1) Is it correct that in order to get the droplet to move, we must have a pressure difference greater than the pressure difference only caused by the capillary forces?

Yes, this is correct. The capillary pressure is higher in the narrower region (B) so you could re-write the equation a little differently:

This is the pressure drop holding the oil droplet in this pore. If we want to move the oil droplet, P_{A} needs to exceed this pressure drop or no flow will happen.

2) And if we increase the pressure in point A by a certain amount, why will not also the pressure in point B increase by the same amount, and therefore still be trapped? (from equation 2-112).

The capillary pressure terms are governed by the pore radii and the interfacial tension (assuming constant wettability). So the pressure holding the oil in place is the difference of the capillary pressure terms. So let’s say that we have a reservoir that has been waterflooded to a pressure of P_{B}. At this point we have droplets of oil trapped because of capillary forces. In order to move those trapped droplets, our injection pressure (P_{A}) would need to increase to some value higher than the differential pressure equation given above.

3) Why is high capillary pressure very bad for the flow? Is it not only that the pressure decreases over the droplet, so the pressure in point B decreases? Or must the pressure in B be the same pressure as before, meaning that we have to increase the pressure in A equal to the amount of the capillary pressure?

Hopefully this part is now clear based on the questions above. But if not, we will be happy to respond further.

Regards,

Dr. Jonathan Bryan

**IF YOU HAVE A QUESTION, PLEASE FEEL FREE TO ASK PERM AT [email protected] OR ON THE CONTACT US PAGE!**