In Situ Chemically-Selective Monitoring of Multiphase Displacement Processes in a Carbonate Rock Using 3D Magnetic Resonance Imaging

Abstract

Accurate monitoring of multiphase displacement processes is essential for the development, validation and benchmarking of numerical models used for reservoir simulation and for asset characterization. Here we demonstrate the first application of a chemicallyselective 3D magnetic resonance imaging (MRI) technique which provides high-temporal resolution, quantitative, spatially resolved information of oil and water saturations during a dynamic imbibition core flood experiment in an Estaillades carbonate rock. Firstly, the relative saturations of dodecane (S o ) and water (S w ), as determined from the MRI measurements, have been benchmarked against those obtained from nuclear magnetic resonance (NMR) spectroscopy and volumetric analysis of the core flood effluent. Excellent agreement between both the NMR and MRI determinations of S o and S w was obtained. These values were in agreement to 4 and 9% of the values determined by volumetric analysis, with absolute errors in the measurement of saturation determined by NMR and MRI being 0.04 or less over the range of relative saturations investigated. The chemically-selective 3D MRI method was subsequently applied to monitor the displacement of dodecane in the core plug sample by water under continuous flow conditions at an interstitial velocity of 1.27 × 10 −6 m s −1 (0.4 ft day −1 ). During the core flood, independent images of water and oil distributions within the rock core plug at a spatial resolution of 0.31 mm × 0.39 mm × 0.39 mm were acquired on a timescale of 16 min per image. Using this technique the spatial and temporal dynamics of the displacement process have been monitored. This MRI technique will provide insights to structure-transport relationships associated with multiphase displacement processes in complex porous materials, such as those encountered in petrophysics research.

Identification of sampling patterns for high‐resolution compressed sensing MRI of porous materials: ‘learning’ from X‐ray microcomputed tomography data

“…As already mentioned for the fully sampled acquisition, a shift of 4 echoes was found to give a good balance between the SNR and the sharpness of the image. A sampling fraction of 0.25 was chosen as it gives significant reduction in the acquisition time compared to the fully sampled acquisition, which in this case is from 20 to 5 h, and still provides high‐quality images (Ramskill et al ., , ).…”

“…oil and water), which can potentially alter the properties of the system. Although the routinely used spatial resolution of MRI is lower (a few hundred µm), it offers a range of different noninvasive contrast mechanisms, based on, for example, fluid type via the MR chemical shift (Ramskill et al ., ), wetting properties via MR relaxation time constants (Reci et al ., ), and fluid mobility via MR measurements of molecular self‐diffusivity, flow dispersion and velocity (Mitchell et al ., ; Colbourne et al ., ; de Kort et al ., , b). Thus, the high spatial resolution MRI acquisitions enabled by the present work are of particular relevance in studying structure‐flow correlations, imaging displacement processes and mapping spatial variation in fluid‐surface interactions in rocks.…”

“…Rapid 3D MRI acquisition methods, such as Rapid Acquisition with Relaxation Enhancement (RARE) (Hennig et al, 1986), can alleviate this problem by significantly reducing the acquisition time (from weeks to days). The acquisitions of 3D MRI can be further sped up by combining these rapid imaging techniques with compressed sensing (CS) techniques (Lustig et al, 2007;Ramskill et al, 2016Ramskill et al, , 2018de Kort et al, 2018a) which can reduce the total image acquisition time to a few hours, which is comparable to scan times of 3D X-ray microcomputed tomography (µCT). This is achieved by acquiring only a subset of the data that would be acquired in conventional MRI.…”

Acquisition of spatially-resolved displacement propagators using compressed sensing APGSTE-RARE MRI

“…In this paper, CS reconstructions with a single regularisation term are considered, and the effectiveness of two different regularisation functionals, the total variation (TV) and the nuclear norm (NN), for the reconstruction of spatially-resolved propagators is explored. Total variation regularisation aids in the reconstruction of sharp edges and has already been shown to work well for MR images of heterogeneous porous media [14][15][16] and the present work explores whether it also performs well for the reconstruction of spatially-resolved propagators of flow through porous media. Nuclear norm regularisation is a relatively novel approach [21][22][23] that helps to reconstruct a domain wherein only a limited number of shapes or features exist.…”

“…To accelerate the acquisitions of multi-dimensional data such as spatially-resolved propagators, we have previously demonstrated the use of interpolation of under-sampled qspace data to reconstruct a 1D spatially-resolved displacement propagator [13], and the use of k-space under-sampling and compressed sensing (CS) to acquire velocity maps in porous media [14] and 3D images of porous media using Rapid Acquisition with Relaxation Enhancement (RARE) MRI [15,16]. Further, Paulsen et al have demonstrated the use of compressed sensing to accelerate the acquisition of a multi-dimensional diffusive propagator in an anisotropic porous medium [17].…”