Micro-computed tomography pore-scale study of flow in porous media: Effect of voxel resolution

A fundamental understanding of flow in porous media at the pore-scale is necessary to be able to upscale average displacement processes from core to reservoir scale. The study of fluid flow in porous media at the pore-scale consists of two key procedures: Imaging - reconstruction of three-dimensional (3D) pore space images; and modelling such as with single and two-phase flow simulations with Lattice-Boltzmann (LB) or Pore-Network (PN) Modelling. Here we analyse pore-scale results to predict petrophysical properties such as porosity, single-phase permeability and multi-phase properties at different length scales. The fundamental issue is to understand the image resolution dependency of transport properties, in order to up-scale the flow physics from pore to core scale. In this work, we use a high resolution micro-computed tomography (micro-CT) scanner to image and reconstruct three dimensional pore-scale images of five sandstones (Bentheimer, Berea, Clashach, Doddington and Stainton) and five complex carbonates (Ketton, Estaillades, Middle Eastern sample 3, Middle Eastern sample 5 and Indiana Limestone 1) at four different voxel resolutions (4.4 µm, 6.2 µm, 8.3 µm and 10.2 µm), scanning the same physical field of view. Implementing three phase segmentation (macro-pore phase, intermediate phase and grain phase) on pore-scale images helps to understand the importance of connected macro-porosity in the fluid flow for the samples studied. We then compute the petrophysical properties for all the samples using PN and LB simulations in order to study the influence of voxel resolution on petrophysical properties. We then introduce a numerical coarsening scheme which is used to coarsen a high voxel resolution image (4.4 µm) to lower resolutions (6.2 µm, 8.3 µm and 10.2 µm) and study the impact of coarsening data on macroscopic and multi-phase properties. Numerical coarsening of high resolution data is found to be superior to using a lower resolution scan because it avoids the problem of partial volume effects and reduces the scaling effect by preserving the pore-space properties influencing the transport properties. This is evidently compared in this study by predicting several pore network properties such as number of pores and throats, average pore and throat radius and coordination number for both scan based analysis and numerical coarsened data

Pore-Scale Modeling of Drainage Displacement Patterns in Association With Geological Sequestration of CO2

©2020. The Authors. We investigate the immiscible displacement (drainage) of a wetting fluid in a porous medium by a nonwetting fluid using multi–graphics processing unit (GPU) lattice Boltzmann simulations with the aim of better understanding the pore-scale processes involved in the geological sequestration of CO2. Correctly resolving the dynamics involved in multiphase flow in permeable media is of paramount importance for any numerical scheme. Generally, the average fluid flow is assumed to be at low Reynolds numbers Reav. Hence, by neglecting inertial effects, this immiscible displacement should be characterized by just two dimensionless numbers, namely, the capillary number Caav and the viscosity ratio, which quantify the ratio of the relevant forces, that is, the viscous and capillary forces. Our investigation reveals that inertial effects cannot be neglected in the range of typical capillary numbers associated with multiphase flow in permeable media. Even as the average Caav and Reav decrease away from the injection point, inertial effects remain important over a transient amount of time during abrupt Haines jumps, when the nonwetting phase passes from a narrow restriction to a wider pore space. The local Rel at the jump sites is orders of magnitude higher than the average Reav, with the local dynamics being decoupled from the externally imposed flow rate. Therefore, a full Navier-Stokes solver should be used for investigating pore-scale displacement processes. Using the Ohnesorge number to restrict the parameter selection process is essential, as this dimensionless number links Caav and Reav and reflects the thermophysical properties of a given system under investigation

Multidimensional observations of dissolution-driven convection in simple porous media using X-ray CT scanning

We present an experimental study of dissolution-driven convection in a three-dimensional porous medium formed from a dense random packing of glass beads. Measurements are conducted using the model fluid system MEG/water in the regime of Rayleigh numbers, Ra=2000−5000. X-ray computed tomography is applied to image the spatial and temporal evolution of the solute plume non-invasively. The tomograms are used to compute macroscopic quantities including the rate of dissolution and horizontally averaged concentration profiles, and enable the visualisation of the flow patterns that arise upon mixing at a spatial resolution of about (2×2×2)mm3. The latter highlights that under this Ra regime convection becomes truly three-dimensional with the emergence of characteristic patterns that closely resemble the dynamical flow structures produced by high-resolution numerical simulations reported in the literature. We observe that the mixing process evolves systematically through three stages, starting from pure diffusion, followed by convection-dominated and shutdown. A modified diffusion equation is applied to model the convective process with an onset time of convection that compares favourably with the literature data and an effective diffusion coefficient that is almost two orders of magnitude larger than the molecular diffusivity of the solute. The comparison of the experimental observations of convective mixing against their numerical counterparts of the purely diffusive scenario enables the estimation of a non-dimensional convective mass flux in terms of the Sherwood number, Sh=0.025Ra. We observe that the latter scales linearly with Ra, in agreement with both experimental and numerical studies on thermal convection over the same Ra regime

'It's a big deal, being given a person': why people who experience infertility may choose not to adopt

This article explores why individuals and couples who experience infertility and undergo treatment through new technologies do not subsequently go on to become parents via adoption. It does this in three ways: a review of the literature; interviews with those affected; and an online survey of views on adoption among people who have experienced infertility. It was found that couples do consider adoption alongside infertility treatment but it is usually a fallback choice. If adoption is to be perceived as an equal option, agencies need to offer support and advice at an earlier stage than is usual. Couples who are emotionally exhausted by medical interventions for their childlessness can then be helped off the infertility treadmill in order to become parents

Exercise therapy after corticosteroid injection for moderate to severe shoulder pain: large pragmatic randomised trial

Objective To compare the effectiveness of subacromial corticosteroid injection combined with timely exercise and manual therapy (injection plus exercise) or exercise and manual therapy alone (exercise only) in patients with subacromial impingement syndrome

Engineering enzymes with non-canonical active site functionality

The combination of computational enzyme design and laboratory evolution provides an attractive platform for the creation of protein catalysts with new function. To date, designed mechanisms have relied upon Nature’s alphabet of 20 genetically encoded amino acids, which greatly restricts the range of functionality which can be installed into enzyme active sites. Here, we have exploited engineered components of the cellular translation machinery to create a protein catalyst which operates via a non-canonical catalytic nucleophile. We have subsequently shown that powerful laboratory evolution protocols can be readily adapted to allow optimization of enzymes containing non-canonical active site functionality. Crystal structures obtained along the evolutionary trajectory highlight the origins of improved activity. Thus our approach merges beneficial features of organo- and biocatalysis, by combining the intrinsic reactivities and greater versatility of small molecule catalysts with the rate enhancements, reaction selectivities and evolvability of proteins. Please click Additional Files below to see the full abstract

Searching for ‘relations’ using a DNA linking register by adults conceived following sperm donation

This paper considers how sperm donor-conceived adults registered with a voluntary DNA linking register, UK DonorLink, constructed identity and relatedness by examining two areas: how their identity was affected by becoming aware that they were donor-conceived; and the process of searching for their donor and donor-conceived siblings. The views and experiences of donor-conceived adults has, until recently, been a neglected area. This study is the first to consider the experiences of those searching through a DNA-based register, and contributes to the growing literature on searching. This paper presents qualitative data from a questionnaire-based study with 65 adults conceived following sperm donation. It examines emerging linkages by investigating how ideas of relatedness, kinship and identity were enacted and how narrative certainties were moved and removed by opening up new conceptions of what it means to be ‘related’. Their knowledge of being donor-conceived was both a powerful disrupter and a consolidator of family relationships. No single story of being donor-conceived emerged – with competing narratives about the effects and implications for respondents’ kinship relationships and sense of identity. This study sheds light on how kinship relationships are negotiated and managed in adulthood by those conceived following sperm donation and how this can change over the life-course