[1] We use pore network modeling to study the impact of wettability and connectivity on waterflood relative permeability for a set of six carbonate samples. Four quarry samples are studied, Indiana, Portland, Guiting, and Mount Gambier, along with two subsurface samples obtained from a deep saline Middle Eastern aquifer. The pore space is imaged in three dimensions using X-ray microtomography at a resolution of a few microns. The images are segmented into pore and solid, and a topologically representative network of pores and throats is extracted from these images. We then simulate quasi-static displacement in the networks. We represent mixed-wet behavior by varying the oil-wet fraction of the pore space. The relative permeability is strongly dependent on both the wettability and the average coordination number of the network. We show that traditional measures of wettability based on the point where the relative permeability curves cross are not reliable. Good agreement is found between our calculations and measurements of relative permeability on carbonates in the literature. This work helps establish a library of benchmark samples for multiphase flow and transport computations. The implications of the results for field-scale displacement mechanisms are discussed, and the efficiency of waterflooding as an oil recovery process in carbonate reservoirs is assessed depending on the wettability and pore space connectivity.Citation: Gharbi, O., and M. J. Blunt (2012), The impact of wettability and connectivity on relative permeability in carbonates: A pore network modeling analysis, Water Resour. Res., 48, W12513,
We investigate the characteristic properties of porous media that influence the entrapment of carbon dioxide (CO2) by capillary forces. It is known that different geological formations can trap different quantities of CO2 but the relationship between formation properties and trapping is poorly understood at present. Advances in micro computed tomography (µCT) techniques now allow the porous media and trapped CO2 clusters therein to be visualised and characterised on the micro meter scale. The context of this work is the geological storage of CO2 where the entrapment of injected CO2 by capillary forces on the pore scale is proposed as a fast and safe method to store injected CO2.
We analyse a series of saturated and unsaturated porous media using µCT; four glass bead packs, a sand pack and a sandstone. In the saturated images the pore space contains brine and residual CO2 (Sr) at subsurface storage conditions. We quantify Sr and cluster size distributions and determine characteristic properties of the porous media through image analysis and the extraction of representative networks. We show that media with narrower pore throats, such as sandstones, trap more CO2 than media with wider pore throats. Numerical simulations performed on the extracted networks do not accurately predict the measured residual CO2 saturations. We discuss the important implications of these results for CO2 storage site selection, containment security assessments, and storage capacity appraisal.
Carbonate rocks have a very complicated and heterogenous porous structure in comparison with sandstone reservoir rock. To understand the transport processes in any porous medium, we need to enhance our knowledge of the geometry and topology of the porous media. Therefore, in this work we present advances with different multi-scale imaging techniques to obtain 2D and 3D images from core-scale (1mm) using Medical CT scanning to pore scale (1-10µm) using Confocal Laser Scanning Microscopy (CLSM) and Micro CT imaging. First, we have developed a novel technique of CLSM to obtain 2D images with a large field of view, which is advantageous for scanning heterogenous carbonate rocks. We have obtained statistical data about total, macro and micro-porosity from 2D large field of view CLSM images and have validated the results using mercury intrusion capillary pressure (MICP) data. Second, we have obtained initial results using our Medical CT scanner for spontaneous imbibition of water in carbonate cores and measured the water saturation as a function of time. Also we have observed and compared the capillary heterogeneity in a simple sandstone core with a heterogeneous carbonate core sample. Finally, we have obtained 3D pore scale images of carbonate samples using our Micro CT scanner at different resolutions. By using image processing techniques for different phase segmentations, we study the effect of resolution on the measured porosity and permeability using Lattice Boltzmann simulations and pore network models. This gives valuable information about pore-throat connection and pore-throat sizes. Finally, we correlate the data for porosity and permeability for different carbonate rock samples taken at different resolutions.
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