Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA Mechanistic Pore-Scale Analysis of the Low-Salinity Effect in Heterogeneously Wetted Porous Media
60
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The enhanced oil recovery technique of low-salinity (LS) water flooding is a topic of substantial interest in the petroleum industry. Studies have shown that LS brine injection can increase oil production relative to conventional high-salinity (HS) brine injection, but contradictory results have also been reported and an understanding of the underlying mechanisms remains elusive. We have recently developed a steady-state pore network model to simulate oil recovery by LS brine injection in uniformly wetted pore structures (Watson et al., Transp. Porous Med. 118, 201-223, 2017). We extend this approach here to investigate the low-salinity effect (LSE) in heterogeneously wetted media. We couple a model of capillary force-driven fluid displacement to a novel tracer algorithm and track the salinity front in the pore network as oil and HS brine are displaced by injected LS brine. The wettability of the pore structure is modified in regions where water salinity falls below a critical threshold, and simulations show that this can have significant consequences for oil recovery. For networks that contain spanning clusters of both water-wet and oil-wet (OW) pores prior to flooding, our results demonstrate that the OW pores contain the only viable source of incremental oil recovery by LS brine injection. Moreover, we show that a LS-induced increase in microscopic sweep efficiency in the OW pore fraction is a necessary, but not sufficient, condition to guarantee additional oil production. Simulations suggest that the fraction of OW pores in the network, the average network connectivity and the initial HS brine saturation are key factors that can determine the extent of any improvement in oil recovery in heterogeneously wetted networks following LS brine injection. This study highlights that the mechanisms of the LSE can be markedly different in uniformly wetted and non-uniformly wetted porous media.
rate research
Read More
We study the transport of inertial particles in water flow in porous media. Our interest lies in understanding the accumulation of particles including the possibility of clogging. We propose that accumulation can be a result of hydrodynamic effects: the tortuous paths of the porous medium generate regions of dominating strain/vorticity, which favour the accumulation/dispersion of the inertial particles. Numerical simulations show that essentially two accumulation regimes are identified: for low and for high flow velocities. When particles accumulate in high-velocity regions, at the entrance of a pore throat, a clog is formed. The formation of a clog significantly modifies the flow, as the partial blockage of the pore causes a local redistribution of pressure. This redistribution can divert the upstream water flow into neighbouring pores. Moreover, we show that accumulation in high velocity regions occurs in heterogeneous media, but not in homogeneous media, where we refer to homogeneity with respect to the distribution of the pore throat diameters.
Natural convection in porous media is a fundamental process for the long-term storage of CO2 in deep saline aquifers. Typically, details of mass transfer in porous media are inferred from the numerical solution of the volume-averaged Darcy-Oberbeck-Boussinesq (DOB) equations, even though these equations do not account for the microscopic properties of a porous medium. According to the DOB equations, natural convection in a porous medium is uniquely determined by the Rayleigh number. However, in contrast with experiments, DOB simulations yield a linear scaling of the Sherwood number with the Rayleigh number (Ra) for high values of Ra (Ra>>1,300). Here, we perform Direct Numerical Simulations (DNS), fully resolving the flow field within the pores. We show that the boundary layer thickness is determined by the pore size instead of the Rayleigh number, as previously assumed. The mega- and proto- plume sizes increase with the pore size. Our DNS results exhibit a nonlinear scaling of the Sherwood number at high porosity, and for the same Rayleigh number, higher Sherwood numbers are predicted by DNS at lower porosities. It can be concluded that the scaling of the Sherwood number depends on the porosity and the pore-scale parameters, which is consistent with experimental studies.
As a typical multiphase fluid flow process, drainage in porous media is of fundamental interest in nature and industrial applications. During drainage processes in unsaturated soils and porous media in general, saturated clusters, in which a liquid phase fully occupies the pore space between solid grains, affect the relative permeability and effective stress of the system. In this study, we experimentally studied drainage processes in unsaturated granular media as a model porous system. The distribution of saturated clusters is analysed by an optical imaging method under different drainage conditions, in which pore-scale information from Voronoi and Delaunay tessellation was used to characterise the topology of saturated cluster distributions. By employing statistical analyses, the observed spatial and temporal information of multiphase flow and fluid entrapment in porous media are described. The results indicate that the distributions of both the crystallised cell size and pore size are positively correlated to the spatial and temporal distribution of saturated cluster sizes. The saturated cluster size is found to follow a lognormal distribution, in which the generalised Bond number correlates negatively to the scale parameter and positively to the shape parameter. These findings can be used to connect pore-scale behaviour with overall hydro-mechanical characteristics in partially saturated porous media, using both the degree of saturation and generalised Bond number.
In this paper, a numerical study on the melting behavior of phase change material (PCM) with gradient porous media has been carried out at the pore scales. In order to solve the governing equations, a pore-scale lattice Boltzmann method with the double distribution functions is used, in which a volumetric LB scheme is employed to handle the boundary. The Monte Carlo random sampling is adopted to generate a microstructure of two-dimensional gradient foam metal which are then used to simulate the solid-liquid phase transition in the cavity. The effect of several factors, such as gradient porosity structure, gradient direction, Rayleigh number and particle diameters on the liquid fraction of PCM are systematically investigated. It is observed that the presence of gradient media affect significantly the melting rate and shortens full melting time compared to that for constant porosity by enhancing natural convection. The melting time of positive and negative gradients will change with Rayleigh number, and there is a critical value for Rayleigh number. Specifically, when Rayleigh number is below the critical value, the positive gradient is more advantageous, and when Rayleigh number exceeds the critical value, the negative gradient is more advantageous. Moreover, smaller particle diameters would lead to lower permeability and larger internal surfaces for heat transfer.
The dissolution of porous materials in a flow field shapes the morphologies of many geologic landscapes. Identifying the dissolution front, the interface between the reactive and the unreactive regions in a dissolving medium, is a prerequisite for studying dissolution kinetics. Despite its fundamental importance, the dynamics of a dissolution front in an evolving natural microstructure has never been reported. Here we show an unexpected spontaneous migration of the dissolution front against the pressure gradient of a flow field. This retraction stems from the infiltration instability induced surface generation, which can lead to a reactive surface dramatically greater than the ex situ geometric surface. The results are supported by a very good agreement between observations made with real time X-ray imaging and simulations based on static images of a rock determined by nanoCT. They both show that the in situ specific surface area of natural porous media is dependent on the flow field and reflects a balancing between surface generation and destruction. The reported dynamics challenge many long-held understanding of water-rock interactions and shed light on reconciling the discrepancies between field and laboratory measurements of reaction kinetics.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
