Micro-tomographic Characterization of Dissolution-induced Local Porosity Changes including Fines Migration in Carbonate Rock

Abstract

The microstructure of carbonate rocks experiences substantial changes under reactive processes, in particular chemical dissolution and deposition including dissolution-released fines migration occurring during acidizing. A better understanding of such changes at the pore scale and their influences on rock properties is of great value for the effective design and implementation of reactive processes in carbonate reservoirs. In this work, we demonstrate the use of X-ray micro-computed tomography (μ-CT) to quantitatively investigate the local porosity changes in a meso/microporous carbonate core sample during chemical dissolution. A reactive flooding experiment in a core sample by a non-acidic solution is designed such that changes in pore space from before to after the reactant injection could be imaged in exactly the same locations using μ-CT at resolution of less than 5μm. A methodology based on three-phase segmentation and 2D intensity histograms of images is used to quantify distributions of the evolution of each image voxel. This technique allows the incorporation of microporosity into the calculation of the evolution regions including the migration of fines in order to accurately quantify the evolution scenarios. The µ-CT images reveal a quasi-uniform dissolution pattern and allow characterizing the accompanying migration of fines within the core sample. 3D pore networks are derived from the image data, which quantify changes in network structure and the pore geometry. 2D histograms of image intensity derived from the pre-and post-dissolution images quantitatively show how macro and micropores are enlarged by dissolution close to the inlet while deposition of fines mainly occurs in pores far from the inlet boundary. These results can explain why permeability of the sample initially decreases and then increases as injection time increases. Based on the spatially resolved voxel evolution scenarios, pore surface area between each region is computed. This allows calculation of local distribution of reactive surface area which in turn will assist in the prediction of local reaction rates in reactive flow simulators.

Qualitative and Quantitative Changes of Carbonate Rocks Exposed to SC CO2 (Basque-Cantabrian Basin, Northern Spain)

“…In general, the processes and the overall effect of particle migration on the hydrodynamic properties of the rock vary depending on characteristics of the rock and the circumstances. Some authors [60][61][62][63][64] have studied the importance of fine particle migration in CO 2 storage and during brine disposal demonstrating its significance on flow pathways and engineered water injection. For more detailed studies, migration of fine particles should be considered.…”

Effect of supercritical CO2 on carbonates: Savonnières sample case study

“…The independent measurements such as, for example, a mercury injection capillary pressure (Qajar et al, 2013) will be particularly beneficial at this stage of the research providing quality control of the segmentation routine and characterization of micro-porosity. These two different segmentation algorithms are indispensable.…”

“…The CO 2 injection/residence is also shown to increase the mean radii of pore throats. The independent measurements such as, for example, a mercury injection capillary pressure (Qajar et al, 2013) will be particularly beneficial at this stage of the research providing quality control of the segmentation routine and characterization of micro-porosity. In order to test how all the reported changes in microstructure affect the elastic moduli of the carbonate rock we run numerical simulations for both samples.…”

“…Effective medium models (EMMs), bounds, or empirical relationships are traditionally used to estimate effective elastic properties (e.g., Mavko, Mukerji, and Dvorkin (2009)). Recently, with the tremendous progress of micro-CT techniques and high-performance computing, the digital rock physics (DRP) approach is shown to be a promising method for predicting effective rock properties directly from microtomograms of small rock samples (e.g., Qajar et al, 2013;Ringstad et al, 2013;Shulakova et al, 2013;Kalam et al, 2011;Madadi et al, 2009;Arns et al, 2002). A typical DRP routine starts with data acquisition, followed by data processing and segmentation into a finite number of model phases and, finally, numerical simulation of the sought physical properties.…”

Numerical computations of rock dissolution and geomechanical effects for CO2 geological storage

“…At the same time, they emphasize that the increase of permeability noticed after a long time can be explained mainly by dissolution process of a solid phase. On the other hand, some investigations showed the decrease of permeability at the beginning of injection of fluid into rock samples [16,19]. The authors relate this phenomenon with the closing of pore throats by solid particles disconnected from the solid skeleton near to the inlet of injection.…”