Patrice Creux

Highlights• Origin of the spontaneous surface charge at the oil / water interface• Role and interaction of the cationic surfactants at the oil/water interface• IEP of oil droplets immersed in aqueous solutions• Zeta potential changes with cationic surfactants at the oil / water interface

Digital Rock Physics (DRP) analysis is a widely employed technique for predicting transport parameters from 3D images of core samples. However, the effects of image resolution and spatial discretization of the DRP mesh grid have rarely been systematically studied in detail. To address this issue, we examine a generic sand pack, representing a homogeneous porous medium. This sample was imaged using X-ray micro-tomography at three different spatial resolutions (6, 3, and 1.5 microns/voxel). Permeability is then numerically evaluated by solving the Stokes flow equations using a finite volume method. The processed meshes for converged macroscopic evaluations consist of 105 million to 58 billion cells, necessitating the alternative use of a two-step upscaling method. By employing both methods, this study analyzes the respective influences of image resolution and spatial discretization. Significant effects are observed from both image resolution and spatial discretization, the analysis of which can contribute to identifying optimal strategies for enhancing the accuracy of permeability evaluation.

Scientists are continuously seeking new methods to identify and predict multiphase flows in porous media using experimental characterization, modeling, and numerical simulations to improve the efficiency of subsurface industry processes for extraction and storage processes

Despite the advantageous resolution of electron tomography (ET), reconstruction of three-dimensional (3D) images from multiple two-dimensional (2D) projections presents several challenges, including small signal-to-noise ratios, and a limited projection range. This study evaluates the capabilities of ET for thin sections of shale, a complex nanoporous medium. A numerical phantom with 1.24 nm pixel size is constructed based on the tomographic reconstruction of a Barnett shale. A dataset of 2D projection images is numerically generated from the 3D phantom and studied over a range of conditions. First, common reconstruction techniques are used to reconstruct the shale structure. The reconstruction uncertainty is quantified by comparing overall values of storage and transport metrics, as well as the misclassification of pore voxels compared to the phantom. We then select the most robust reconstruction technique and we vary the acquisition conditions to quantify the effect of artifacts. We find a strong agreement for large pores over the different acquisition workflows, while a wider variability exists for nanometer-scale features. The limited projection range and reconstruction are identified as the main experimental bottlenecks, thereby suggesting that sample thinning, advanced holders, and advanced reconstruction algorithms offer opportunities for improvement.

Characterization of microscopic details of the fabric of mudstones and shales (i.e., structure and composition) is important to understand their storage and transport properties. Current characterization methods struggle to probe reliably multiple scales of interest (e.g., pore and fracture) and measure properties at the finest resolution under representative in situ conditions. Micro X-ray fluorescence (μXRF) is a high-performance imaging technique that produces elemental images at sub-10 μm spatial resolution and could offer insight into a diversity of shale properties, such as mineral composition, porosity, and in situ pressure gradients. This study designed and carried out a porosity mapping protocol using model and real-rock microfluidic devices and contrast fluids. Etched silicon micromodels with real-rock pore network patterns served as ideal models to establish a proof of concept. Measurements were performed on a novel μXRF microscope not powered by synchrotron radiation. We registered the μXRF datasets with the binary rock masks used for micromodel fabrication and applied segmentation algorithms to compare porosities. We assessed expected advantages and limitations through a sensitivity analysis and beam study. μXRF is an important new imaging technique for microfluidic applications.

Estimating porous media properties is a vital component of geosciences and the physics of porous media. Until now, imaging techniques have focused on methodologies to match image-derived flows or geomechanical parameters with experimentally identified values. Less emphasis has been placed on the compromise between image processing techniques and the consequences on topological and morphological characteristics and on computed properties such as permeability. The effects of some of the most popular image processing techniques (filtering and segmentation) available in open source on 3D X-ray Microscopy (micro-XRM) images are qualitatively and quantitatively discussed. We observe the impacts of various filters such as erosion-dilation and compare the efficiency of Otsu’s method of thresholding and the machine-learning-based software Ilastik for segmentation.

A new experimental triaxial cell for in situ synchrotron X-ray micro-computed tomography aimed at imaging small samples of (6 mm × 19 mm) at high temperatures (up to 400°C) and pressures (up to 24 MPa confining) is presented. The system has flow-through capabilities, independent axial and radial pressure control, and has been developed and tested at the 8.3.2. beamline at the Advanced Light Source. The characteristics of this new experimental rig are described, along with the challenges, mainly concerning the combination of X-ray transparency with vessel strength at high temperature, and solutions found during the development stage. An experiment involving oil shale pyrolysis under subsurface conditions, highlighting the importance of a device able to operate in this pressure and temperature range, is also introduced. The availability of this cell enables an unprecedented range of experiments in the Earth Sciences, with a special focus on subsurface geothermal processes.