Investigation of Salt-Bearing Sediments Through Digital Rock Technology Together With Experimental Core Analysis

摘要

In this study, digital rock analysis was combined with a variety of experimental core-analysis measurements to investigate the effect of salt saturation and distribution on the porosity and permeability of halite-cemented core samples. Medical and micro-X-ray CT scans of core sections and 2.54-cm (1-in.) diameter plugs indicated that the halite generally occurred in the form of distinct layers. High-resolution micro-X-ray computed tomography (MXCT) images acquired of 0.6-cm diameter plugs revealed that, on the pore scale, halite appeared to be pore filling. Pores were either completely filled with halite or did not contain any halite at all. It was also observed that halite preferentially occurred in the larger pores associated with larger grain sizes. The porosity and permeability results, both measured experimentally on the core plugs and calculated by segmentation of the MXCT images, demonstrated the obstructive effect of halite on storage and flow as well as the decline of both properties with increasing salt saturation. Comparison of calculated and measured values showed that the measured porosity could be up to 6 porosity units (p.u.) higher than the calculated one, while the measured permeability of core plugs after salt removal was an order of magnitude lower than the one obtained by lattice Boltzmann simulation. One possible reason for this discrepancy may be the stratified nature of the samples. While the fully salt-saturated plugs appeared homogeneous in MXCT images, post-flood MRI images revealed that the plug was composed of layers with different MRI intensities, i.e., different amounts of water-filled porosity. Consequently, the petrophysical parameters calculated for the miniplugs may only be representative for a section of the core plug. The results of the MRI-assisted core floods emphasized the importance of considering different scales when interpreting and applying the results of digital rocks analysis.