Computational and experimental pore-scale studies of a carbonate rock sample

Abstract

Carbonate rocks host several large water and hydrocarbon reservoirs worldwide, some of them highly heterogeneous involving complex pore systems. Pre-salt reservoirs in the Santos Basin off the south-east coast of Brazil, are an example of such rocks, with much attention focused on proper characterization of their petrophysical and multiphase flow properties. Since it is very difficult to obtain rock samples (coquinas) from these very deep reservoirs, analogues from north-eastern Brazil are often used because of very similar geological age and petrophysical properties. We used a coquina plug from an outcrop in a quarry in northeast Brazil to perform a comprehensive set of analyses. They included Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), and micro-computed tomography (μCT) image acquisition using a series of pixel sizes, as well as direct permeability/porosity measurements. Some of the experimental data were collected from the plug itself, and some from a small sample of the rock slab, including thin sections. Results included the carbonate rock composition and the pore system at different scales, thus allowing us to reconstruct and model the porosity and absolute permeability of the coquina using 3D digital imaging and numerical simulations with pore network models (PNMs). The experimental and numerical data provided critical information about the well-connected pore network of the coquina, thereby facilitating improved predictions of fluid flow through the sample, with as ultimate objective to improve hydrocarbon recovery procedures.

Effects of carbonated water injection on the pore system of a carbonate rock (coquina)

“…7 could be confirmed by the main percolation clusters in the coquina (Fig. 9) before and after CSW injection (Godoy et al, 2019;Hoerlle et al, 2020;Lima et al, 2020). A more detailed evaluation is presented in the following section based on the generated skeleton of the sample.…”

“…The non-destructive microCT experiments were used to investigate changes in the internal pore structure of the samples to better understand permeability changes that may occur after carbonated water injection. X-ray microtomography is now widely used for both qualitative and quantitative porescale analyses, including for pore-scale flow modeling (Godoy et al, 2019;Lima et al, 2020;Saxena et al, 2017), determination of wettability through studies of the contact angle in images (Al Ratrout et al, 2018;Andrew et al, 2014;Armstrong et al, 2021;Prodanović et al, 2004), and analyses of the distribution of immiscible fluids inside pores (Alvarado et al, 2004;Schnaar and Brusseau, 2006), among other soil and rock hydrologic applications. MicroCT results provide input for digital pore and pore network modeling (PNM) analyses to highlight the pore-scale basis of macro-scale (or continuum-scale) multiphase fluid flow and contaminant transport processes (de Vries et al, 2017;Rabbani and Babaei, 2019;Raoof et al, 2013).…”

“…We note here that pore-scale models are not necessarily a substitute for experimental methods, but rather serve as a complement to better understand the experimental data and their uncertainties, and allowing one to replicate experimental conditions (Gundogar et al, 2016). In our study, calculations were carried out using the pore-scale network module within the PoreStudio software (PoreStudio website, 2021), which is an update of the PoreFlow model (Raoof et al, 2013) used by Raoof and Hassanizadeh (2012) and Godoy et al (2019), among others.…”

Petrophysical Correlations for the Permeability of Coquinas (Carbonate Rocks)

“…The samples were subjected to X-ray microtomography imaging in order to understand the pore framework of the coquinas. Imaging was performed in three sequential steps: acquisition of high-resolution (16-bit) x-ray images using Skyscan model 1173 microtomography, image reconstruction using NRecon ® software (Skyscan/Bruker, v.1.6.9.4) as detailed by Godoy et al (2019), and image processing using Avizo Fire ® 9.5 software (ThermoFisher Scientific, Massachusetts, US). For the acquisition, we used a 1-mm aluminium filter to reduce noise in the images, while the equipment was calibrated with a voltage of 80 kV and 100 µA.…”

Transport of Solutes and Colloids in Multi-Scale Porous Media Under Single and Multi-Phase Flow

“…Average properties can be determined by averaging over a large bundle of pores. Pore network modeling has been successfully employed for reactive transport , two-phase flow (Bultreys et al, 2015;Yin et al, 2018), flow and permeability estimation (Godoy et al, 2019), solute transport (Qin and Hassanizadeh, 2015;Mahmoodlu et al, 2020), and colloid transport (Zhang et al, 2015). The computational efficiency of pore network modeling enables simulating a very large number of pores in three dimensions.…”