Three-dimensional Deformable Pore Networks

Porous structures in materials play a part in many areas of research and development. A couple of examples of this are extraction of water through aquifers and oil through fracking processes. Current understanding of the small scale fluid-fluid interactions in the structure of these porous materials stops at data of the two dimensional interface between the two fluids. This experiment aimed to create three dimensional, transparent, deformable micro-models which are expected allow us to obtain three dimensional data sets of the capillary pressure–saturation–interfacial area per volume relationship. The micro-models were synthesized using a grain deposition technique. Grains were formed using the polymerization of a 5% (v/v) solutions of Irgacur 1173 initiator in poly (ethylene glycol) diacrylate when the solution is exposed to patterns of ultraviolet light (in the range of 435nm to 485nm). These grains are layered in a pre-made plain channel micro-model to create a complex but transparent porous structure. Initial imaging using laser confocal microscopy shows that these micro-models can be used to study three dimensional interactions between fluids in porous structures. Through the creation of these three dimensional micro-models we now have a better way to experimentally model porous materials found in nature which offers many topological possibilities for applications in rock, biology, oil, water, and even food science research

Particle Swarm Transport in Porous Media

In recent years, interest in particulate transport in the subsurface has increased with the increased use of micro-particulates in consumer products. In this research, we study particulate swarm transport through porous media that depends on the complexity of the flow paths, on the size and shape of the particles and on the physical interactions among the particles, fluids, and matrix. Specifically, we investigate the effect of pore geometry and grain wettability on swarm evolution under gravity. Swarms were composed of 3 micron polystyrene beads in either water or water with KCL (%). Two types of grains are used to simulate a porous medium: (1) hydrogel spheres that are hydrophyllic and (2) 3D printed PMMA spheres that are hydrophobic. We found that a hydrophillic matrix resulted in a wider transport path and caused an increase in bifurcations when compared with the hydrophobic PMMA. We also observed that as the swarms increased in volume the number of bifurcations increased. Bifurcations occurred around the beads creating a more widespread dispersed transport path. The potential spread of particulate contaminants by swarms will depend on the hydrophobicity or hydrophilicity the grains, yielding either increased dispersion or more highly localized concentrations

Hedberg Research Conference on Fundamental Controls on Flow in Carbonates: Request for Travel Support for Post-Doctoral Fellows

Carbonate reservoirs pose a scientific and engineering challenge to geophysical prediction and monitoring of fluid flow in the subsurface. Difficulties in interpreting hydrological, reservoir and other exploration data arise because carbonates are composed of a hierarchy of geological structures, constituents and processes that span a wide spectrum of length and time scales. What makes this problem particularly challenging is that length scales associated with physical structure and processes are often not discrete, but overlap, preventing the definition of discrete elements at one scale to become the building blocks of the next scale. This is particularly true for carbonates where complicated depositional environments, subsequent post-deposition diagenesis and geochemical interactions result in pores that vary in scale from submicron to centimeters to fractures, variation in fabric composition with fossils, minerals and cement, as well as variations in structural features (e.g., oriented inter- and intra layered - interlaced bedding and/or discontinuous rock units). In addition, this complexity is altered by natural and anthropogenic processes such as changes in stress, fluid content, reactive fluid flow, etc. Thus an accurate geophysical assessment of the flow behavior of carbonate reservoirs requires a fundamental understanding of the interplay of textural and structural features subjected to physical processes that affect and occur on various length and time scales. To address this complexity related to carbonates, a Hedberg conference on “Fundamental Controls on Flow in Carbonates” was held July 8 to 13, 2012, to bring together industry and academic scientists to stimulate innovative ideas that can accelerate research advances related to flow prediction and recovery in carbonate reservoirs. Participants included scientist and engineers from multiple disciplines (such as hydrology, structural geology, geochemistry, reservoir engineering, geophysics, geomechanics, numerical modeling, physical experiments, sedimentology, well-testing, statistics, mathematics, visualization, etc.) who encompass experience as well as the latest advances in these multi-faceted fields. One of the goals was to include early career scientists and engineers (post-doctoral fellows, assistant professors, etc.). With this grant 10 early career scientists and engineers were supported to attend the conference. This reports contains a brief overview of the conference and the list of support participants supported by this grant. Full details of the outcomes of the conference are given in the publication found in the Attachment section of this report

Fracture aperture reconstruction and determination of hydrological properties: a case study at Draix (French Alps)

International audienceWe propose two techniques for fracture aperture reconstruction. The first one is a correlation technique that estimates the normal aperture or the tangential shift across a discontinuity whose sides present geometrical similarities. The only required material is a pair of appropriately controlled images of each side. Here, the images are maps of the corresponding side topography, obtained from laser profilometry. Assuming a purely normal opening, it is possible, from two corresponding sides of a given discontinuity in a core log, to infer the precise geometry of the in situ aperture. The second technique allows to retrieve the three-dimensional geometry of a sealed discontinuity from non-independent topography measurements of both sides. Both techniques are applied to discontinuities extracted from a core drilled down to 20 m in a fractured marl formation at Draix (French Alps). The probability density functions of the aperture of the sealed and open discontinuities are shown to be Gaussian. At the sample scale, the sealed fracture aperture is self-affine, while the open one shows a cross-over from a self-affine regime at very small scales to an uncorrelated regime at largest scales. After extrapolating those scaling laws at the scale of the whole formation, we discuss when the aperture roughness affects the hydraulic properties of the Draix fractured bedrock. The overall estimated permeability is significant (10−9 − 10−8 m2), consistently with some previous indirect inferences

Microbial-Induced Heterogeneity in the Acoustic Properties of Porous Media

It is not known how biofilms affect seismic wave propagation in porous media. Such knowledge is critical for assessing the utility of seismic techniques for imaging biofilm development and their effects in field settings. Acoustic wave data were acquired over a two-dimensional region of a microbial-stimulated sand column and an unstimulated sand column. The acoustic signals from the unstimulated column were relatively uniform over the 2D scan region. The data from the microbial-stimulated column exhibited a high degree of spatial heterogeneity in the acoustic wave amplitude, with some regions exhibiting significant increases in attenuation while others exhibited decreases. Environmental scanning electron microscopy showed differences in the structure of the biofilm between regions of increased and decreased acoustic wave amplitude. We conclude from these observations that variations in microbial growth and biofilm structure cause heterogeneity in the elastic properties of porous media with implications for the validation of bioclogging models

When do fractured media become seismically anisotropic? Some implications on quantifying fracture properties

Fractures are pervasive features within the Earth's crust and they have a significant influence on the multi-physical response of the subsurface. The presence of coherent fracture sets often leads to observable seismic anisotropy enabling seismic techniques to remotely locate and characterise fracture systems. In this study, we confirm the general scale-dependence of seismic anisotropy and provide new results specific to shear-wave splitting (SWS). We find that SWS develops under conditions when the ratio of wavelength to fracture size (λS/d) is greater than 3, where Rayleigh scattering from coherent fractures leads to an effective anisotropy such that effective medium model (EMM) theory is qualitatively valid. When 1<λS/d<3 there is a transition from Rayleigh to Mie scattering, where no effective anisotropy develops and hence the SWS measurements are unstable. When λS/d<1 we observe geometric scattering and begin to see behaviour similar to transverse isotropy. We find that seismic anisotropy is more sensitive to fracture density than fracture compliance ratio. More importantly, we observe that the transition from scattering to an effective anisotropic regime occurs over a propagation distance between 1 and 2 wavelengths depending on the fracture density and compliance ratio. The existence of a transition zone means that inversion of seismic anisotropy parameters based on EMM will be fundamentally biased. More importantly, we observe that linear slip EMM commonly used in inverting fracture properties is inconsistent with our results and leads to errors of approximately 400% in fracture spacing (equivalent to fracture density) and 60% in fracture compliance. Although EMM representations can yield reliable estimates of fracture orientation and spatial location, our results show that EMM representations will systematically fail in providing quantitatively accurate estimates of other physical fracture properties, such as fracture density and compliance. Thus more robust and accurate quantitative estimates of in situ fracture properties will require improvements to effective medium models as well as the incorporation of full-waveform inversion techniques

Sequential approach to joint flow-seismic inversion for improved characterization of fractured media

Seismic interpretation of subsurface structures is traditionally performed without any account of flow behavior. Here we present a methodology for characterizing fractured geologic reservoirs by integrating flow and seismic data. The key element of the proposed approach is the identification—within the inversion—of the intimate relation between fracture compliance and fracture transmissivity, which determine the acoustic and flow responses of a fractured reservoir, respectively. Owing to the strong (but highly uncertain) dependence of fracture transmissivity on fracture compliance, the modeled flow response in a fractured reservoir is highly sensitive to the geophysical interpretation. By means of synthetic models, we show that by incorporating flow data (well pressures and tracer breakthrough curves) into the inversion workflow, we can simultaneously reduce the error in the seismic interpretation and improve predictions of the reservoir flow dynamics. While the inversion results are robust with respect to noise in the data for this synthetic example, the applicability of the methodology remains to be tested for more complex synthetic models and field cases.Eni-MIT Energy Initiative Founding Member ProgramKorea (South). Ministry of Land, Transportation and Maritime Affairs (15AWMP-B066761-03