Influence of Grain Size and Consolidation Pressure on Porosity of Rocks

Microfocus x-ray computed tomography is used to study the effect of grain size distribution and consolidation pressure on the spatial distribution of porosity of synthetic rock cores. CT scans were conducted on 12 synthetic rock cores having different grain size distributions and consolidation pressures. Density calibration as described by ASTM standards was performed to correlate the CT number to the bulk density, then to the porosity. A computer algorithm was developed to calculate the porosity for every five voxels of the rock cores, producing about 15 million porosity values within each core. The porosity distributions for all the cores were compared with each other to determine the effect of changing the grain size distribution and the consolidation pressure. CT data showed a good ability to capture the changes in the porosity distribution, for the different cores. Moreover, it was noted that the degree of homogeneity of the pore sizes within the cores could clearly be indicated by the standard deviation of the porosity distribution (i.e. the width of the porosity distribution histogram). However, some mixed trends were observed especially with the cores prepared at very high consolidation pressures. Crushing of the particles was considered as a possible reason for these trends.