Micro-CT and mercury intrusion porosimetry characterization of the fabric of roofing slate

The petrological fabric of roofing slate determines the main properties of the slate as a construction material, such as durability and waterproofing. Roofing slates are rocks derived from the low-grade metamorphism of lutites, with a characteristic lepidoblastic fabric. However, little attention by petrologists has been paid to the role of this fabric in the behaviour of roofin slates. This work characterizes the fabric and pore system of two roofing slate varieties from Spain, using two different techniques, each with its advantages and disadvantages: X-ray microtomography, useful to find heterogeneities and mineral inclusions on the slate bulk,and mercury intrusion porosimetry, which defines the pore system. The differentiation of mineral inclusions is very useful for predicting the weathering of a slate, while the definition of the pore system may help to understand how the slate will behave during its service life

A multi-scale, image-based pore network modeling approach to simulate two-phase flow in heterogeneous rocks

Despite the large interest in the multi-phase flow properties of rocks with broad pore size distributions, most digital rock physics approaches struggle with the presence of multiple pore scales. In this work, we present a method to estimate relative permeability (Kr) and resistivity index (RI) curves of such heterogeneous rocks during drainage. In our dual pore network model (DPNM), macropores are represented as pores and throats , while unresolved microporosity is treated as a continuous porous medium. The scales are coupled by including microporosity as symbolic network elements in the DPNM, based on 3D image analysis. The validity of the method is investigated by treating two carbonate rocks (Estaillades and Savonnières limestone). We present a sensitivity analysis of the drainage behaviour of these networks on the microporosity’s petrophysical properties, which are provided as input. While a number of challenges persist, the presented examples show how DPNM can help increase the understanding of two-phase flow in complex carbonate rocks

Multi-scale, image-based pore network models to simulate two-phase flow in heterogeneous rocks

Over the last couple of years, algorithms have been developed to extract pore network models directly from 3D images of a rock’s porosity. These models can be used to simulate capillary pressure curves, (relative) permeabilities and electrical properties during drainage/imbibition cycles. However, heterogeneous rocks with very broad pore-size distributions remain difficult to simulate with these models, as it is difficult to acquire and incorporate information on the different pore scales which are present. Nonetheless, the understanding of the multi-phase flow behaviour of such materials (e.g. many carbonates and tight gas sandstones) is of crucial economic and scientific importance. We build two-scale network models which incorporate microporosity information without taking every individual micropore into account. We start from a micro-CT scan which is segmented into 3 phases (pore, solid and microporous voxels), and extract a maximal ball network [1] from the porous voxels. The microporosity is clustered into 3D connected regions. Pores touching the same microporous cluster are connected by a new type of network element called micro-connections. These connections are assigned conductances based on the local contact surface areas between pores and microporous clusters, as well as on the continuum petrophysical properties of the microporosity it represents. We attempt to assess these properties with mercury intrusion and FIB/SEM experiments. This study shows results of resistivity curves and relative permeability curves calculated from networks based on micro-CT datasets of carbonate rocks. We also show the comparison of results obtained with our networks with averaged microporosity properties to results from a network with individual micropores, described in [2]. The results suggest that our method is a promising tool to simulate core-scale multi-phase flow behaviour of rocks with complex, multi-scale porosities. REFERENCES [1] H. Dong and M. Blunt, “Pore-network extraction from micro-computerized-tomography images,” Phys. Rev. E, vol. 80, no. 3, p. 036307, Sep. 2009. [2] A. Mehmani and M. Prodanović, “The effect of microporosity on transport properties in porous media,” Adv. Water Resour., vol. 63, pp. 104–119, Jan. 2014

Data fusion of High Resolution X-ray CT and SEM/EDS for pseudo-3D elemental and structural characterization of the Vosges sandstone

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