Mohamed Soufiane Jouini

Numerical estimation of carbonate rock properties using multiscale images

Characterizing the pore space of rock samples using three-dimensional (3D) X-ray computed tomography images is a crucial step in digital rock physics. Indeed, the quality of the pore network extracted has a high impact on the prediction of rock properties such as porosity, permeability and elastic moduli. In carbonate rocks, it is usually very difficult to find a single image resolution which fully captures the sample pore network because of the heterogeneities existing at different scales. Hence, to overcome this limitation a multiscale analysis of the pore space may be needed. In this paper, we present a method to estimate porosity and elastic properties of clean carbonate (without clay content) samples from 3D X-ray microtomography images at multiple resolutions.We perform a three-phase segmentation to separate grains, pores and unresolved porous phase using 19 μm resolution images of each core plug. Then, we use images with higher resolution (between 0.3 and 2 μm) of microplugs extracted from the core plug samples. These subsets of images are assumed to be representative of the unresolved phase. We estimate the porosity and elastic properties of each sample by extrapolating the microplug properties to the whole unresolved phase. In addition, we compute the absolute permeability using the lattice Boltzmann method on the microplug images due to the low resolution of the core plug images. In order to validate the results of the numerical simulations, we compare our results with available laboratory measurements at the core plug scale. Porosity average simulations for the eight samples agree within 13%. Permeability numerical predictions provide realistic values in the range of experimental data but with a higher relative error. Finally, elastic moduli show the highest disagreements, with simulation error values exceeding 150% for three samples.

Simulation of elastic properties in carbonates

Predicting the elastic properties of carbonate rocks is crucial for the oil industry. However, the standard models that estimate effective elastic properties in porous media have many limitations in carbonate rocks. One main reason is highly complex pore-space structures, produced in carbonates by diagenesis and other geological processes, which create heterogeneities at several scales. Recently developed image acquisition systems, based on X-ray computed tomography, allow description of the spatial distribution of grains and pores in scanned samples at high resolution. Numerical simulations can then predict the elastic properties using the geometry of each phase (grains matrix and pore space). In this paper, we apply a new efficient automatic segmentation technique based on bi-level thresholding to separate grains and pores phases in 3D X-ray CT scans. Then we assess the ability of a finite-element simulation technique commonly used on sandstones to estimate the elastic properties of carbonate rocks unde...

Pore-Scale Modeling of Non-Newtonian Fluid Flow Through Micro-CT Images of Rocks

Most of the pore-scale models are concerned with Newtonian fluid flow due to its simplicity and the challenge posed by non-Newtonian fluid. In this paper, we report a non-Newtonian numerical simulation of the flow properties at pore-scale by direct modeling of the 3D micro-CT images using a Finite Volume Method (FVM). To describe the fluid rheology, a concentration-dependent power-law viscosity model, in line with the experimental measurements of the fluid rheology, is proposed. The model is first applied to a single-phase flow of Newtonian fluids in 2 benchmark rocks samples, a sandstone and a carbonate. The implemented FVM technique shows a good agreement with the Lattice Boltzmann Method (LBM). Subsequently, adopting a non-Newtonian fluid, the numerical simulation is used to perform a sensitivity study on different fluid rheological properties and operating conditions. The normalized effective mobility variation due to the change in polymer concentration leads to a master curve while the flow rate displays a contrast between carbonate and sandstone rocks.

The Effect of Heat Transfer and Polymer Concentration on Non-Newtonian Fluid from Pore-Scale Simulation of Rock X-Ray micro-CT

Most of the pore-scale imaging and simulations of non-Newtonian fluid are based on the simplifying geometry of network modeling and overlook the fluid rheology and heat transfer. In the present paper, we developed a non-isothermal and non-Newtonian numerical model of the flow properties at pore-scale by simulation of the 3D micro-CT images using a Finite Volume Method (FVM). The numerical model is based on the resolution of the momentum and energy conservation equations. Owing to an adaptive mesh generation technique and appropriate boundary conditions, rock permeability and mobility are accurately computed. A temperature and concentration-dependent power-law viscosity model in line with the experimental measurement of the fluid rheology is adopted. The model is first applied at isothermal condition to 2 benchmark samples, namely Fontainebleau sandstone and Grosmont carbonate, and is found to be in good agreement with the Lattice Boltzmann method (LBM). Finally, at non-isothermal conditions, an effective mobility is introduced that enables to perform a numerical sensitivity study to fluid rheology, heat transfer, and operating conditions. While the mobility seems to evolve linearly with polymer concentration in agreement with a derived theoretical model, the effect of the temperature seems negligible by comparison. However, a sharp contrast is found between carbonate and sandstone under the effect of a constant temperature gradient. Besides concerning the flow index and consistency factor, a master curve is derived when normalizing the mobility for both the carbonate and the sandstone.