Abstract
In this paper we suggest a method for a quick indication of the absolute permeability for carbonate rock using the effective medium approximation (EMA) and pore size distribution obtained from 2-D images. A pore network is built from modified cubic lattices. Instead of using the well-known coordination number for cubic lattices, z = 6, a new correlation between z and the normalized pore radius is suggested for both sandstone and carbonate formations. The imaging of the rock sample is obtained by using a new tool called Micro Grain Imager (MGI) which works with visible light emitted through a scanning probe inserted in a drilled hole in the rock sample. An area of 12.5 x 37 mm2 of sidewall of the hole is obtained with a resolution of 25 mm. Processing the acquired images allows for obtaining the pore diameter and pore shape factor distributions. The hydraulic radius approximation is used to determine the pore conductance needed to predict the absolute permeability. When compared to the measurements done with conventional core measurements, our model provides better estimation for intermediate and high permeability than the predictions by the existing EMA models and the values obtained from the usual empirical formulas. This makes the effective medium approximation, our coordination number model, and the micro grain imager a powerful combination that can be used in the laboratory or surface measurement in the field. The combination provides the field engineer with a straight forward method for characterizing the rock.
