257 research outputs found
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Matrix/fracture transfer function during counter-current spontaneous imbibition in naturally fractured reservoirs
Naturally fractured reservoirs are abundant in the earth’s crust and host a substantial percentage of oil reserves globally. The main mechanism of oil recovery during waterflooding of these types of reservoirs is through spontaneous imbibition of water into the matrix and simultaneous counter-current flow of oil out of the matrix. Understanding the predominate recovery mechanism enhances reserves estimates, accurate simulation forecasts and overall sound development plans. Dual-porosity and dual-permeability simulations are used in the industry to simulate waterfloods in naturally fractured reservoirs.
One of the key parameters in these simulations is the matrix-fracture transfer term, which is not well understood and modeled, especially in mixed-wet reservoirs. The same transfer term is used for primary, secondary and tertiary recovery processes, though it should change depending on the mechanisms of oil recovery. The key mechanism during primary recovery is depressurization, not spontaneous imbibition. The main goal of this research is to develop an accurate representation of the matrix-fracture transfer term in waterflooding for dual-porosity simulators.
The analytical and semi-analytical solutions for 1D counter-current imbibition were studied for defining the exact solution in fractured porous media. Fine-grid, single-porosity numerical solutions were developed that are consistent with the 1D analytical solutions, in conjunction with coarse-grid single-porosity conceptual models. Both single-porosity models are used as reference against dual-porosity conceptual models to address the built-in matrix-fracture transfer terms through recovery of the matrix element. The error in simulation was defined as the difference in recoveries between the fine-grid single-porosity solution and the dual-porosity solutions. A detailed investigation of both rock and fluid inputs affecting transfer terms in dual-porosity was made in an effort to match the transient solution obtained from fine-grid single-porosity models. The inclusion of transient effect in dual-porosity requires optimizing the following inputs which are shape factor, capillary exponent and oil relative permeability exponent. Two main processes were proposed for optimization. Firstly, an accuracy-based Latin Hyper Cube sampling method was utilized that converged to the solution quickly. Secondly, utilizing a machine learning algorithm (specifically an Artificial Neural Net model) that predicts recovery accuracy based on the aforementioned chosen inputs. The machine learning model needed many iterations to converge to a solution.Petroleum and Geosystems Engineerin
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Estimation of fluid-transport properties of rocks based on X-ray radiography and numerical simulation of two-phase immiscible fluid displacement
Heterogeneity and anisotropy of fluid-bearing rocks remain a challenge of central importance in the quantification of subsurface energy resources. Borehole geophysical measurements are the principal source of data used to quantify in situ rock properties, but they are often riddled with uncertainty resulting from the combined effects of rock heterogeneity/anisotropy and mud-filtrate invasion. This uncertainty often persists in geological formations deemed homogeneous. Accurate interpretation of borehole geophysical measurements requires modeling of multiphase flow resulting from invasion of mud filtrate into porous and permeable rocks. For the specific case of spatially complex rocks, there is a need for experimental and numerical methods that integrate all pertinent information about the interactions between fluids (including mud filtrate) and rocks to develop realistic models of fractional flow, i.e., saturation-dependent relative permeability and capillary pressure in the near-wellbore region.
This dissertation combines new laboratory measurements with numerical simulations to estimate fluid-transport properties of spatially complex rocks subjected to two-phase immiscible fluid displacement. At the heart of these experimental procedures is a new high-resolution imaging technique based on X-ray radiography that uses a microfocus computed tomography scanner and thin rectangular rock samples to (a) capture and quantify fluid displacement patterns, (b) provide time-lapse images of fluid distribution, and (c) visualize external and internal mudcake deposition. The work also includes the development of a new method to appraise the quality of nuclear magnetic resonance measurements used to quantify rock-pore structure.
Injection experiments were performed to study the impact of connate fluid properties, drilling fluid properties, and rock petrophysical properties on two-phase flow taking place during mud-filtrate invasion, injection, or production. Experimental and numerical results indicate that the spatial distribution of fluids (both connate fluids and mud filtrate), flow patterns, and mudcake deposition resulting from mud-filtrate invasion depend heavily on the nature and degree of rock heterogeneity, bedding plane orientation, and anisotropy during both drainage and imbibition. In rocks considered homogeneous, fluid displacements approach piston-like behavior, as predicted by the Buckley-Leverett theory of fractional flow, while in spatially complex rocks, high-resolution time-lapse images uncover preferential flow paths along high-permeability sections of the rock, hence giving rise to low sweep efficiency. At late experimental times, both the spatial distribution of fluids and sweep efficiency are significantly influenced by variations in capillary pressure and transmissibility across the rock sample. Laboratory experiments also emphasize the impact of viscous and/or capillary forces on two-phase flow behavior during mud-filtrate invasion. It is found that mud properties dominantly control both invasion rate and mudcake thickness growth, independently of rock properties.
The new hybrid laboratory-simulation approach is effective for examining the time evolution of fractional flow, as it offers an alternative to the laborious and time-consuming traditional steady-state laboratory methods used for measuring relative permeability and capillary pressure. Furthermore, the new laboratory methods introduced in this dissertation are fast and reliable to simultaneously assess flow-related petrophysical properties of spatially complex rocks and to examine competing fluid displacement mechanisms. Overall, the combination of experimental and numerical results improves our understanding of two-phase immiscible flow in heterogeneous rocks and of the various effects that mud-filtrate invasion can have on borehole geophysical measurements during or after drilling operations. This new approach foreshadows new interpretation methods for production-oriented formation evaluation.Petroleum and Geosystems Engineerin
Chapter 34 - Biocompatibility of nanocellulose: Emerging biomedical applications
Nanocellulose already proved to be a highly relevant material for biomedical
applications, ensued by its outstanding mechanical properties and, more importantly, its biocompatibility. Nevertheless, despite their previous intensive
research, a notable number of emerging applications are still being developed.
Interestingly, this drive is not solely based on the nanocellulose features, but also
heavily dependent on sustainability. The three core nanocelluloses encompass
cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). All these different types of nanocellulose display highly interesting biomedical properties per se, after modification and when used in
composite formulations. Novel applications that use nanocellulose includewell-known areas, namely, wound dressings, implants, indwelling medical
devices, scaffolds, and novel printed scaffolds. Their cytotoxicity and biocompatibility using recent methodologies are thoroughly analyzed to reinforce their
near future applicability. By analyzing the pristine core nanocellulose, none
display cytotoxicity. However, CNF has the highest potential to fail long-term
biocompatibility since it tends to trigger inflammation. On the other hand, neverdried BNC displays a remarkable biocompatibility. Despite this, all nanocelluloses clearly represent a flag bearer of future superior biomaterials, being
elite materials in the urgent replacement of our petrochemical dependence
A posteriori error estimation and modeling of unsaturated flow in fractured porous media
This doctoral thesis focuses on three topics: (1) modeling of unsaturated flow in fractured porous media, (2) a posteriori error estimation for mixed-dimensional elliptic equations, and (3) contributions to open-source software for complex multiphysics processes in porous media.
In our first contribution, following a Discrete-Fracture Matrix (DFM) approach, we propose a model where Richards' equation governs the water flow in the matrix, whereas fractures are represented as lower-dimensional open channels, naturally providing a capillary barrier to the water flow. Therefore, water in the matrix is only allowed to imbibe the fracture if the capillary barrier is overcome. When this occurs, we assume that the water inside the fracture flows downwards without resistance and, therefore, is instantaneously at hydrostatic equilibrium. This assumption can be justifiable for fractures with sufficiently large apertures, where capillary forces play no role. Mathematically, our model can be classified as a coupled PDE-ODE system of equations with variational inequalities, in which each fracture is considered a potential seepage face.
Our second contribution deals with error estimation for mixed-dimensional (mD) elliptic equations, which, in particular, model single-phase flow in fractured porous media. Here, based on the theory of functional a posteriori error estimates, we derive guaranteed upper bounds for the mD primal and mD dual variables, and two-sided bounds for the mD primal-dual pair. Moreover, we improve the standard results of the functional approach by proposing four ways of estimating the residual errors based on the conservation properties of the approximations, that is, (1) no conservation, (2) subdomain conservation, (3) local conservation, and (4) pointwise conservation. This results in sharper and fully-computable bounds when mass is conserved either locally or exactly. To our knowledge, to date, no error estimates have been available for fracture networks, including fracture intersections and floating subdomains.
Our last contribution is related to the development of open-source software. First, we present the implementation of a new multipoint finite-volume-based module for unsaturated poroelasticity, compatible with the Matlab Reservoir Simulation Toolbox (MRST). Second, we present a new Python-based simulation framework for multiphysics processes in fractured porous media, named PorePy. PorePy, by design, is particularly well-suited for handling mixed-dimensional geometries, and thus optimal for DFM models. The first two contributions discussed above were implemented in PorePy.Denne avhandlingen tar for seg tre emner: (1) modellering av flyt i umettet porøst medium med sprekker, (2) a posteriori feilestimater for blandet-dimensjonale elliptiske ligninger, og (3) bidrag til åpen kildekode for komplekse multifysikk-prosesser i porøse medier.
I det første bidraget anvender vi en Discrete-Fracture Matrix (DFM) (Diskret-Sprekk Matrise) metode til å sette opp en modell hvor Richard's ligning modellerer vann-flyt i matrisen, og sprekkene representeres som lavere-dimensjonale åpne kanaler, som naturlig virker som kapillærbarrierer til vann-flyten. Derfor vil vann i matrisen kun få tilgang til sprekken når kapillærbarrieren blir brutt. Når det inntreffer, antar vi at vannet i sprekken flyter nedover uten motstand, og at hydrostatisk ekvilibrium derfor inntreffer øyeblikkelig. Slike antakelser kan rettferdiggjøres for sprekker med tilstrekkelig stor apertur (åpning), hvor kapillærkrefter ikke har noen innvirkning. Fra et matematisk standpunkt kan modellen klassifiseres som en sammenkoblet PDE-ODE med variasjonelle ulikheter hvor hver sprekk behandles som en filtreringsfase.
Det andre bidraget tar for seg feilestimater for blandet-dimensjonale elliptiske ligninger, som modellerer en-fase flyt i porøse medier med sprekker. Her anvender vi teorien for "funksjonal a posteriori feilestimater" til å finne øvre skranker for primær og dual variablene, samt øvre og nedre skranker for primær-dual paret. Dessuten viser vi at vi kan forbedre standardresultatene fra "funksjonal a posteriori feilestimater" ved å foreslå fire måte å estimere residualfeilen basert på bevaringsegenskapene til diskretiseringen. De fire forskjellige bevaringsegenskapene er; ingen bevaringsegenskap, under- domene bevaring, lokal bevaring og punktvis bevaring. Dette fører til skarpere skranker som er mulige å beregne når masse er bevart enten lokalt, eller eksakt. Vi kjenner ikke til andre tilgjengelige feilestimater for sprekknettverk som inkluderer snitt av sprekker og sprekkrender som ligger innenfor domenets rand.
Det siste bidraget omhandler utvikling av åpen kildekode. Først presenterer vi imple- menteringen av en multipunktfluks-basert modul for flyt i umettet deformerbart porøst medium som er kompatibelt med "Matlab Reservoir Simulation Toolbox"(MRST). I tillegg presenterer vi et nytt Python-basert rammeverk for simulering av multifysikkprosesser i porøse medier med sprekker, som heter PorePy. Dette rammeverket er designet for å håndtere geometrier med blandede dimensjoner og er derfor optimalt for DFM modeller. De to første bidragene i avhandlingen (nevnt over) er implementert i PorePy.Doktorgradsavhandlin
Microfluidics for Biosensing
There are 12 papers published with 8 research articles, 3 review articles and 1 perspective. The topics cover: Biomedical microfluidics Lab-on-a-chip Miniaturized systems for chemistry and life science (MicroTAS) Biosensor development and characteristics Imaging and other detection technologies Imaging and signal processing Point-of-care testing microdevices Food and water quality testing and control We hope this collection could promote the development of microfluidics and point-of-care testing (POCT) devices for biosensing
Development of Localized Diffuse Source Basis Function for Near Well Upscaling and Compressible Flow Diagnostics Applied to Reservoir Modeling
The topic of this study is the fast and accurate simulation and flow diagnostic techniques used for simulations of flow and transport in porous media, particularly petroleum reservoirs. Fast and reliable simulation and flow diagnostic techniques are becoming increasingly necessary for reservoir management and development. The geological models increase in size and level of detail and require more computational resources to be utilized. The upscaling framework is a promising approach to facilitate the simulation of detailed geological models.
The shale gas/ tight oil reservoir gradually becomes the critical exploration target for petroleum resources. This unconventional reservoir has commonly low permeability properties distribution and is explored by the multi hydraulic fractured horizontal well. The compressible flow diagnostic is a robust and flexible method to analyze the fluid flow behavior in any reservoir model. Combining the convective time of flight (resolution of flow diagnostic) and diffusive time of flight (solution of fast marching method) allows us to investigate further detail of unconventional reservoir model, particularly for the multi hydraulic fractured horizontal well.
This study's work includes developing a coupling Diffuse Source transmissibility upscaling and the novel near well upscaling method for the high-resolution geological model. The work contains the development of a new flow diagnostics that extended the previously proposed flow diagnostics to compressible flow and an application of the flow diagnostics for the field analysis of multi transverse hydraulically fractured well. The research indicates a great potential for flexibility and scalability suitable for high-fidelity simulators and fast and robust diagnostic methods
Structure-Preserving Model Reduction of Physical Network Systems
This paper considers physical network systems where the energy storage is naturally associated to the nodes of the graph, while the edges of the graph correspond to static couplings. The first sections deal with the linear case, covering examples such as mass-damper and hydraulic systems, which have a structure that is similar to symmetric consensus dynamics. The last section is concerned with a specific class of nonlinear physical network systems; namely detailed-balanced chemical reaction networks governed by mass action kinetics. In both cases, linear and nonlinear, the structure of the dynamics is similar, and is based on a weighted Laplacian matrix, together with an energy function capturing the energy storage at the nodes. We discuss two methods for structure-preserving model reduction. The first one is clustering; aggregating the nodes of the underlying graph to obtain a reduced graph. The second approach is based on neglecting the energy storage at some of the nodes, and subsequently eliminating those nodes (called Kron reduction).</p
Fundamentals of Enhanced Oil Recovery
For many years, the trend of increasing energy demand has been visible. Despite the search for alternative energy sources, it is estimated that oil and natural gas will be the main source of energy in transport for the next several dozen years. However, the reserves of renewable raw materials are limited in volume. Along with the degree of depletion, oil recovery becomes more and more difficult, even though the deposits are not yet completely empty. Therefore, it is essential to find new methods to increase oil and gas recovery. Actions aimed at intensifying oil recovery are very rational use of energy that has not yet been fully used. Usually, an increase in oil recovery can be achieved by using extraction intensification methods. However, measures to increase oil recovery can be implemented and carried out at any stage of the borehole implementation. Starting from the well design stage, through drilling and ending with the exploitation of oil and gas. Therefore, in order to further disseminate technologies and methods related to increasing oil recovery, a special edition has been developed, entitled "Fundamentals of Enhanced Oil Recovery". This Special Issue mainly covers original research and studies on the above-mentioned topics, including, but not limited to, improving the efficiency of oil recovery, improving the correct selection of drilling fluids, secondary methods of intensifying production and appropriate energy management in the oil industry
Magnetic Hybrid-Materials
Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials
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