Calculating total compressibility for a liquid + porous solid system
 

Hello all:

Apologies if this is a silly question... I'm a chemist and I'm making a simple code that deals with combined fluid flow and chemistry. I'd like to check that I have the right idea about total compressibility.

For a system made up of a porous solid (like rock), where the pores are totally saturated with liquid (let's say water--no gas, just liquid), would the total compressibility (Ct) be:

Ct = porosity * Cliquid + (1-porosity)*Crock

where Cliquid is liquid compressibility and Crock is rock compressibility.

The reason I ask is that I came across a paper in which someone multiplied the left hand side by liquid density. I can't imagine why this would be correct. Am I missing something here, or might this be a typo?

Thanks a lot for any advice.