Evaluation of the capillary pressure curve techniques for determining pore size distribution — a network approach

Abstract

Porous media are inter-connected networks of void spaces having different shapes and sizes. Attempts at developing analytical expressions describing fluid flow through them them have not been satisfactory to date for the lack of a satisfactory characterization of the structure of void spaces. The classical model, of bundle of tubes, is too simplified a model to be realistic and useful in most real situations. In the present work the flow behaviour in porous media was modelled by a network of inter-connected tubes of different sizes. An attempt was made to evaluate and synthesize various techniques of relating pore-size distribution to the capillary pressure behaviour of a medium. The validity of the “ink-bottle” effect and the techniques of Fatt and Meyer were tested by comparing the pore-size distributions obtained from capillary pressure data with the actual tube-size distribution of the network. It was seen that the existing techniques of obtaining pore-size distribution yield poor results even in the case of highly idealized network representations of porous media. Some modifications for making these techniques more realistic are discussed. The extent of inter-connections between the pores in a network was found to be a very important factor in influencing the shape of the capillary pressure ( P c) curves. This effect has been tested by allowing 2, 6, 10 and 14 inter-connections (on the average) between pores in the network, thus simulating parallel and intersecting tube models. In order to improve the reliability of results, it must be ascertained that there is, indeed, a one-to-one correspondence between pore-size distributions and capillary pressure curves.