The total compressibility of porous rock and pore-saturating fluid is going to be:
c_t = c_r + c_f |
where
Some applications (like multi-phase pressure diffusion) account for the impact of cross-phase fluid exchange on the total compressibility which require some corrections to equation
:(3) | c_t(s,P) = c_r + c_w s_w + c_o s_o + c_g s_g + s_o [ R_{sp} + (c_r + c_o) R_{sn} ] + s_g [ R_{vp} + R_{vn}(c_r + c_g) ] |
where
R_{sn}, \; R_{vn} | normalized cross-phase exchange ratios as functions of reservoir pressure p and temperature T |
R_{sp}, \; R_{vp} | normalized cross-phase exchange derivatives as functions of reservoir pressure p and temperature T |
See Non-linear multi-phase pressure diffusion @model for derivation of (3).