Single and two phase flow equations in low-permeability porous media.

Mass and momentum balances were derived to study the single and two phase flow behaviour of gas and liquid through low permeability porous media such as 'tight sand' formations. The characteristic curves for the two phase system are real with negative slope of the capillary pressure versus saturation curve. The absolute value of the slope increases as saturation approaches unity or small values, which is in agreement with experimental data. The single phase flow equations were linearized and the resulting equation was solved analytically for flow of gas through a tight sand core sample. The results were compared with those obtained from the 'conventional' diffusivity equation for flow through porous media. (A)