Digital Rock Reconstruction And Property Calculation Of Fractured Shale Rock Samples

As the preferential flow channels in the shale reservoir, the fracture systems including the natural micro-cracks and hydraulic fractures have received great attention from the whole energy industry worldwide. However, it is challenging to quantify the fracture systems in the shale rocks precisely because most of well-developed “histogram-based” image processing techniques cannot handle the case of small target segmentation. Because the fracture apertures are very thin, the over-segmentation or insufficient segmentation would lead to significant error in the quantification, including the fracture porosity, aperture, length, tortuosity etc., which would lead to serious mistakes to the property calculation. In this research, two novel image processing methods are proposed. The self-adaptive image enhancement method employs incomplete beta function and simulated annealing algorithm to modify the grayscale intensity histogram. The contrast between the target and the background of the transformed gray image reaches the maximum. Also, “self-adaptive” means the enhancement process is specified by the input images. The comparison of segmentation results before and after the image enhancement show that the target becomes more obvious to the naked eyes and the precise fracture porosity of the test image is 4.02 %. The multi-stage image segmentation (MSS) method combines the global and local information of the image to finish the segmentation. The generated three-dimensional model provides visualization of the fracture systems existing in the core. Also, the important parameters of the fractures can be obtained, including aperture, length, tortuosity, and porosity. Compared with the real permeability from the core-flooding experiments, the permeability calculated from the MSS method has the minimum error of 22.1 %. The results show that the proposed methods in this research can be effective tools for the precise quantification of the thin fracture systems

Tortuosity of porous media: Image analysis and physical simulation

Tortuosity is widely used as a critical parameter to predict transport properties of porous media, such as rocks and soils. But unlike other standard microstructural properties, the concept of tortuosity is vague with multiple definitions and various evaluation methods introduced in different contexts. Hydraulic, electrical, diffusional, and thermal tortuosities are defined to describe different transport processes in porous media, while geometrical tortuosity is introduced to characterize the morphological property of porous microstructures. In particular, the rapid development of microscopy imaging techniques has made digital microstructures of porous media increasingly accessible, from which geometrical and physical tortuosities can be evaluated using various image analysis and numerical simulation methods. These tortuosities are defined differently and can differ greatly in value, but in many works of literature, they are used interchangeably. To address this situation, we systematically examine geometrical, hydraulic, electrical, diffusional, and thermal tortuosities from the viewpoints of the definition and evaluation method. For the same porous medium, visible discrepancies are found in the evaluated geometrical and physical tortuosities, depending on the specific definition and the evaluation method adopted. This observation makes it questionable to directly use the geometrical tortuosity as a substitute for physical tortuosities, a common practice in the literature. Thus, the correlations between geometrical and physical tortuosities are further analyzed, which also takes into account the influence of both image size and resolution. From the correlation analysis, phenomenological relations between geometrical and physical tortuosities are established, so that the latter can be accurately predicted by using the former which is much cheaper to evaluate from digital microstructures

Impact Of Fines On Gas Relative Permeability Through Sand Using Pore Networks From 3d Synchrotron Micro-Computed Tomography

Fines migration and transport in sand systems have huge influence on vital applications, including the storage and recovery of water and energy resources from the subsurface. Multi-phase flow of gas through saturated unconsolidated media takes place between the pores of sediments, physical phenomenon at the pore-scale control the flow properties. Given a sandy sediment media, gas permeability is highly affected by fine particles due to migration, clogging and bridging reducing gas flow or causing sand particles to displace creating fractures. There is a knowledge gap of fines effects on gas production from sandy sediments, especially at the pore-scale. Therefore, there is a need to model and quantify effects of fines in multi-phase flow using pore networks to better understand gas recovery systems. Three-dimensional, synchrotron micro-computed tomography images of sand sediments were obtained at Argonne National Laboratory at a resolution of 3.89 micron per voxel. Kaolinite and Montmorillonite fine particles were added in varied concentrations in six soil specimens, each system was scanned at four stages with varied saturations of brine and CO2, resulting in 20 systems. Micro-computed tomography images were processed for 3D visualization, quantification and pore network modeling. Pore Network Models were generated, and relative permeability properties were then computed for each system. Findings revealed that fines accumulate at sand-brine and brine-gas interfaces. As fines concentration increased, gas percolation decreased. Further increase in fines concentrations resulted in blocking local gas flow causing pressure variations enough to create fractures that allows gas to escape and permeability to increase back. Pore Networks and Computer-Based Two-Phase Flow Simulations can effectively be used to characterize flow in porous media. In unconsolidated media the pore space geometry will change due to sand grains movements. At high concentrations, different fines type produces altered gas flow regimes, Kaolinite resulted in fractures while montmorillonite resulted in detached gas ganglia. Generally, increasing fines reduces gas percolation and further injection of gas reduced permeability. The finds herein are critical in understanding the impact of fines migration during gas flow in sand, they can be applied to characterizing and predicting two phase properties of unconsolidated sediments

Pore network modeling of thin water film and its influence on relative permeability curves in tight formations

Acknowledgments We acknowledge the Beijing Natural Science Foundation of China (No. 2204093), Science Foundation of China University of Petroleum, Beijing (No.2462018YJRC033) and financial support from China Scholarship Council ((No. 201906440134). Dr. Yingfang Zhou would like to acknowledge the support from State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University), PLN201602.Peer reviewedPostprin

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

Experimental investigation on the micro damage evolution of chemical corroded limestone subjected to cyclic loads

Micro damage evolution in chemical corroded limestone samples subjected to cyclic loads is investigated using Nuclear Magnetic Resonance (NMR) system. Based on the experimental data of Magnetic Resonance Imaging (MRI), T2 values and porosity, the micro damage evolution process is visualized and analyzed. It is found that the porosity and micro cracking of the corroded limestone samples increase with the cyclic loading, and the micro damage evolution process consists of three distinct stages: micro crack emergence stage, micro damage development stage and damage development accelerated stage. Chemical erosion is found to have a significant influence on the propagation of micro cracks and accelerate the damage development of the limestone samples under cyclic loading. With the same number of load cycles, the chemical corroded samples always have lower peak strength than that of the water softened samples. Before the inflection point in the micro damage-loading cycles curve, the main damage is caused by new micro cracks increase inside the limestone; while after this point, the new micro crack emergence is being restrained, and the existed micro cracks connect into rupture bands. A damage model is finally proposed to quantify the damage evolution of the chemical corroded rocks subjected to cyclic loads

ALERT Doctoral School 2012: advanced experimental techniques in geomechanics

The twenty-second session of the European Graduate School 2012 (called usually ALERT Doctoral School) entitled Advanced experimental techniques in geomechanics is organized by Cino Viggiani, Steve Hall and Enrique Romero.Postprint (published version

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected

Microstructure evolution during sintering of multilayer ceramic capacitors: nanotomography and discrete simulations

Multi-Layer Ceramic Capacitors (MLCCs) are key passive components in modern electronics. MLCCs consist of alternating metal electrode and ceramic dielectrics layers. In ultrathin MLCC chips, the micrometric layers are composed of submicrometric metal and ceramic powders and nano sized ceramic additives (to retard the sintering of electrode and minimize the sintering mismatch). A number of defects such as cracks, delamination of layers and electrode discontinuity and homogeneity, may arise in the processing of these ultrathin MLCCs. The cracks and delamination result in product rejection. Electrode discontinuities (uncovered areas) and thickness homogeneity generate a number of problems including capacitance loss, electrical short, leakage current and decreased reliability. It is generally recognized that these defects are linked to the sintering kinetics mismatch between electrode and dielectric materials, during the co-firing (co-sintering) process of MLCCs. However, when it comes to the origin of these defects and to their evolution during the sintering process, little knowledge is available. Conventional post-sintering and 2-dimensional (2D) imaging methods suffer limitations. In this context, in-situ synchrotron X-ray imaging and Discrete Element Method (DEM) have been carried out to explore the origin and the evolution of defects during the co-sintering process. X-ray imaging including 2D radiography and 3-dimensional (3D) nano computed tomography (X-ray nCT) enable non-destructive in-situ observation of the microstructure change in 2D and 3D. In parallel, DEM can simulate the sintering of MLCCs by taking into account the powders’ particulate nature (particle size, packing, etc.) Synchrotron (Advanced Photon Source, Argonne National Laboratory, IL, USA) X-ray based Transmission X-ray Microscope (TXM) with spatial resolution of 30 nm was used to characterize a representative cylindrical volume of Ø 20 µm × 20 µm extracted from a 0603 (1.6 mm×0.8 mm) case size Nickel (Ni)-electrode Barium Titanate (BaTiO3, or BT)-based MLCC before and after sintering under 2H2%+Ar atmosphere. 3D tomographic microstructure imaging shows that the final electrode discontinuity is linked to the initial heterogeneity in the electrode layers. In situ X-ray radiography of sintering (heating ramp of 10 oC, holding at 1200 oC for 1 hour, cooling ramp -15 oC) of a Palladium (Pd) electrode BNT (Barium-neodymium-titanate) based MLCC representative volume was also carried out. It confirmed that discontinuities in the electrode originate from the initial heterogeneities, which are linked to the very particulate nature of the powder material. The discontinuity occurs at the early stage of the sintering cycle. At this stage, the electrode starts to sinter while the dielectric material may be considered as a constraining substrate. Correlative studies using Focused Ion Beam - Scanning Electron Microscope (FIB - SEM) tomography were conducted on green and sintered MLCC samples at high resolution (5 × 5 × 5 nm3). FIB images confirmed that the resolution of the X-ray nCT is sufficient to deal with these heterogeneity evolutions. Still, FIB tomography allows the X-ray nCT to be re-interpreted more accurately. Also, it provides detailed particulate parameters for the DEM simulations. The DEM was used to simulate the microstructure of a multilayer system during sintering. These simulations operate at the particle length scale and thus recognize the particulate nature of the multilayers at the early stage of sintering. First, the sintering of Ni matrix with BT inclusions was simulated using the dp3D codes (developed at SIMaP/GPM2, Université de Grenoble, France). The retarding effect of BT inclusions on the sintering of Nickel matrix was predicted by varying the size, the amount and the homogeneity of inclusions. It is found that the densification rate of the matrix decreases with increasing volume fraction of inclusions and with decreasing size of inclusions. For a given volume fraction and size of inclusions, a better dispersion of the inclusions results in a stronger retardation of the densification kinetics of the nickel matrix. Co-sintering of BT/Ni/BT multilayers was simulated with DEM by taking into account the particulate nature collected from the high resolution FIB nanotomography (FIB-nT) data, such as particle size, size distribution, heterogeneities, pores, and geometry. The temperature profile was also reproduced in these simulations. It is found that the electrode discontinuities originate from the initial heterogeneities in the green compact and form at the early stage of sintering under constraint, in good correspondence to the experimental observations. Parametric studies suggest that electrode discontinuities can be minimized by homogenizing the packing density and thickness of the electrodes and using a fast heating rate. Based on both experimental and DEM simulation results, a general conclusion is reached: the final discontinuity originates from the initial heterogeneity in the electrode layers and occurs at the early stage of sintering when the dielectric layers constrain the electrode layers. A defect evolution mechanism is proposed: after the lamination of BT sheets, there exist inevitably heterogeneous regions in the electrodes. Below 950-1000 oC, the nickel powder densifies except in heterogeneous zones for which desintering has been observed. At this stage, the Ni layers are under tensile stress. Tensile stresses in the thinner sections induce matter flow towards the thicker sections until the thinner sections are disrupted and discontinuities form. Once nickel is fully dense, electrodes are subjected to compressive stress at high temperature (1100 oC) due to BT densification. The compressive stress causes contraction of the viscous nickel, resulting in swelling of electrodes and hence a further increase in electrode discontinuity. Meanwhile, the nano-sized BT additives are expelled due to their unwettability with Ni at high temperature. The aggregated BT additives sinter, possibly forming percolation between two adjacent BT layers and enhancing the mechanical adhesion between Ni and BT layers in the MLCCs