bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Three-Phase Multicomponent Compositional Model for Asphaltene Precipitation Using CPA-EOS
Authors: Nasrabadi Hadi , Moortgat Joachim , Firoozabadi Abbas 
Published: February 2013

Abstract
Numerical modeling of asphaltene precipitation in petroleum reservoirs is important in relation to precipitation around the wellbore and in the reservoir domain. Production from some reservoirs results in asphaltene precipitation in the wellbore region, leading to production loss and need for cleanup. Fluid injection can also lead to injectivity loss due to asphaltene precipitation. There are also desirable processes in which precipitation of asphaltene can lead to "in-situ" upgrading of heavy oil recovery.
Reservoir compositional models that are currently in use rely on cubic equations of state for asphaltene precipitation. The cubic equations, despite their relative reliability in describing reservoir fluids phase behavior, become unreliable in asphaltene-rich phase description. A number of non-cubic equations of state have been introduced to overcome the shortcomings of cubic equations. The cubic-plus-association equation of state (CPA-EOS) is perhaps the method of choice in modeling asphaltene precipitation in compositional modeling. When there is no asphaltene precipitation, the CPA-EOS becomes the standard cubic equation.
In this work we implement the CPA-EOS in compositional modeling and introduce a simple technique to speed up considerably the root finding. Our efficient algorithm makes the additional cost from CPA-EOS insignificant. We also derive the basic equations for the total compressibility and total potential molar volume in our implementation of the CPA-EOS compositional modeling. Our new algorithm is introduced in a simple finite difference code. This work introduces a general framework for widespread use of the CPA-EOS in compositional modeling.
A Black-Box Stencil Interpolation Method to Accelerate Reservoir Simulations
Authors: Chen Han , Klie Hector , Wang Qiqi 
Published: February 2013

Abstract
The present work aims at predicting space-time pressure solutions via a novel non-intrusive reduced order simulation model. The construction of low- dimensional spaces entails the combination of the Discrete Empirical Interpolation (DEIM) method with a suitable regressor such as artificial neural network to accurately approximate the pressure solutions arising in an IMPES formulation. Two basic assumptions are key in the present work: (a) physics invariance and, (b) stencil locality. The first one allows for coping with the curse of dimensionality associated with the training of a lower- dimensional surrogate model. The second assumption enables to significantly reduce the input parameter space and therefore, infer the global solution from local mass conservation principles. These assumptions are inspired in the discretization of PDEs governing the flow in porous media and serve as a powerful vehicle to generate physics-based surrogate models at a low computational cost. Hence, without explicit or little knowledge of simulation equations and numerical schemes, a sequence of pressure solutions or initial guesses can be obtained from inexpensive solutions of reduced order models (ROMs). Numerical examples are provided to illustrate the potentials of the present approach.
Reservoir Modeling for Flow Simulation Using Surfaces, Adaptive Unstructured Meshes and Control-Volume-Finite-Element Methods
Authors: Jackson M. D. , Gomes J. L. , Mostaghimi P. , Percival J. R. , Tollit B. S. , Pavlidis D. , Pain C. C. , El-Sheikh A. H. , Muggeridge A. H. , Blunt M. J. 
Published: February 2013

Abstract
We present new approaches to reservoir modeling and flow simulation that dispose of the pillar-grid concept that has persisted since reservoir simulation began. This results in significant improvements to the representation of multi-scale geological heterogeneity and the prediction of flow through that heterogeneity. The research builds on 20+ years of development of innovative numerical methods in geophysical fluid mechanics, refined and modified to deal with the unique challenges associated with reservoir simulation.
Geological heterogeneities, whether structural, stratigraphic, sedimentologic or diagenetic in origin, are represented as discrete volumes bounded by surfaces, without reference to a pre-defined grid. Petrophysical properties are uniform within the geologically-defined rock volumes, rather than within grid-cells. The resulting model is discretized for flow simulation using an unstructured, tetrahedral mesh that honors the architecture of the surfaces. This approach allows heterogeneity over multiple length-scales to be explicitly captured using fewer cells than conventional corner-point or unstructured grids.
Multiphase flow is simulated using a novel mixed finite element formulation centered on a new family of tetrahedral element types, PN(DG)-PN+1, which has a discontinuous Nth-order polynomial representation for velocity and a continuous (order N+1) representation for pressure. This method exactly represents Darcy force balances on unstructured meshes and thus accurately calculates pressure, velocity and saturation fields throughout the domain. Computational costs are reduced through (i) automatic mesh adaptivity in time and space and (ii) efficient parallelization. Within each rock volume, the mesh coarsens and refines to capture key flow processes, whilst preserving the surface-based representation of geological heterogeneity. Computational effort is thus focused on regions of the model where it is most required.
Having validated the approach against a set of benchmark problems, we demonstrate its capabilities using a number of test models which capture aspects of geological heterogeneity that are difficult or impossible to simulate conventionally, without introducing unacceptably large numbers of cells or highly non-orthogonal grids with associated numerical errors. Our approach preserves key flow features associated with realistic geological features that are typically lost. The approach may also be used to capture near wellbore flow features such as coning, changes in surface geometry across multiple stochastic realizations and, in future applications, geomechanical models with fracture propagation, opening and closing.
A Soft and Law-Abiding Framework for History Matching and Optimization under Uncertainty
Authors: Hajizadeh Yasin , Nghiem Long , Mirzabozorg Arash , Yang Chaodong , Li Heng , Costa Sousa Mario 
Published: February 2013

Abstract
Current frameworks for optimization and assisted history matching lack the ability to control and guide the sampling engine and to incorporate geo-engineering knowledge. Defining the interactions between uncertain parameters and handling multiple constraints are also arduous tasks. Despite recent advances in adaptive population-based sampling algorithms and other gradient and ensemble-based methods, these specific drawbacks have left engineers with several history-matched models that are inconsistent with the physical and geological knowledge of the field.
We introduce a novel rule-based framework based on fuzzy reasoning to integrate engineering knowledge with optimization and assisted history matching workflows. The system can handle multiple complex constraints both in parameter and objective function space. The use of fuzzy set theory in this workflow is a natural way to address uncertainty arising from imprecision of definition. This type of uncertainty is important in expressing the parameters of interest; however, it has been less addressed in existing workflows. The proposed system can be coupled with any algorithm used for assisted history matching, including gradient-based, population-based and particle filter approaches.
The framework is coupled with differential evolution algorithm and is tested for three cases. The results show that fuzzy rule-based engine preserves the computational efficiency of the sampling engine, while allowing for definition of flexible rules in history matching and optimization that honor engineering knowledge.
A Novel Approach for Incorporation of Capillarity and Gravity Into Streamline Simulation Using Orthogonal Projection
Authors: Tanaka Shusei , Datta-Gupta Akhil , King Michael J. 
Published: February 2013

Abstract
The effective use of streamline simulators for flow simulation of multi-million cell detailed 3D models relies on the ability to take large simulation time-steps with few pressure solutions. For processes that are convective, the streamline approach works quite well while for flow simulation with compressibility, strong capillarity or strong gravity terms, the maximum time step size may be substantially reduced, limiting the utility of streamline simulation. This is the case when applying the conventional streamline operator-splitting approach, where the nonlinear terms associated with capillarity and gravity limit the time step. Earlier studies have shown the importance of an "anti-diffusive" correction in which numerical dispersion from the convective solution must be removed before capillary pressure can be accurately modeled. Evaluation of the anti-diffusive term involves the solution of a local Riemann problem which, unfortunately, is difficult to determine in full field multi-dimensional problems with heterogeneity, and spatially variable viscosity, fluid velocity, and saturations. The alternative approach is to perform the operating splitting calculation with very small time-steps to minimize the numerical dispersion, but this is not an effective simulation strategy.
In our approach, the equations are reformulated so that all of the flux terms including capillarity and gravity forces are solved simultaneously with the streamline convection equations. We utilize an orthogonal projection method in which the fluxes of capillary and gravity are separated into components parallel and orthogonal to the total velocity. Fluxes parallel to total velocity are included within the solution of the convective flow equations on streamlines. The remaining terms are calculated on the underlying three dimensional grid. With the introduction of this orthogonal-projection, there is no longer a need for an anti-diffusive correction. This formulation still uses an operator splitting approach, but the size of the remaining transverse flux correction terms are reduced, allowing for large time steps.
We demonstrate the utility and validity of our approach using a series of increasingly complex numerical experiments in 1D and 2D including the 3D SPE10 reservoir model. We compare our results to a commercial finite difference simulator, and to a streamline simulator using a conventional operator splitting approach, but without the anti-diffusive correction. We obtain a good match to the saturation distribution and production profile using large time steps, compared to the small time steps required for conventional operator splitting. The 2D and 3D examples clearly demonstrate the effectiveness of the orthogonal projection approach in minimizing the transverse flux allowing for the larger time steps. It also provides a systematic means of including additional displacement mechanisms in the future.
Developement of Algebraic Multigrid Solvers Using GPUs
Authors: Liu Hui , Yu Song , Chen Zhangxin 
Published: February 2013

Abstract
In reservoir simulation, algebraic multigrid (AMG) solvers are the most effective solvers for linear systems arising from the discretization of pressure equations. The AMG solvers are also important components for many multi-stage preconditioners. In this paper, we introduce our work on developing these solvers on NVIDIA Tesla GPUs. A classical algebraic multigrid solver is developed. Numerical experiments are performed to test the efficiency of this GPU-based parallel AMG solver. The numerical experiments show that the GPU-based algebraic solver is sped up to 12.5 times faster than the corresponding CPU-based algebraic multigrid solver.
Techniques for Effective Simulation, Optimization, and Uncertainty Quantification of the In-situ Upgrading Process
Authors: Alpak Faruk O. , Vink Jeroen C. , Gao Guohua , Mo Weijian 
Published: February 2013

Abstract
Strongly temperature-dependent compositional flow and transport, chemical reactions, delivery of energy into the subsurface through downhole heaters, and complex natural fracture architecture render the dynamic modeling of In-situ Upgrading Process (IUP) a computationally challenging endeavor for carbonate extra-heavy oil resources. Economic performance indicators for such recovery methods can be considerably enhanced via simulation or simulation-based proxy models within an optimization framework (e.g., maximizing Net Present Value through achieving an optimal compromise between hydrocarbon recovery and the number of heater wells). The IUP is endowed with uncertain subsurface parameters as in the case of other recovery mechanisms. The number of subsurface uncertainties is especially large and the impacts of these uncertainties are intricate when IUP is applied to a complex naturally-fractured carbonate reservoir. Simulation results must reflect the impacts of these uncertainties; hence they should always deliver "expected-value production functions" and their attached uncertainty ranges, in short, the "error bars". Both the optimization and the uncertainty quantification workflows require (typically multiple) multi-scenario simulations, and are therefore very compute intensive.
We describe our recent developments in simulation techniques, optimization algorithms, tool capabilities, and high-performance computing protocols that in unison form a massively parallel simulation/optimization/uncertainty-quantification workflow, in which it is almost equally easy to produce recovery time-functions with an attached uncertainty range, as it is to run a single simulation. Uncertainties are integral part of the simulation models in our dynamic modeling workflow. Our in-house simulation platform supports various optimization and uncertainty quantification methods, such as conventional as well as robust optimization using a novel Simultaneous Perturbation and Multivariate Interpolation technique, Experimental Design, and Monte Carlo simulation, that can be linked together through a unified script-based interface, to carry out optimization in the presence of subsurface uncertainties and to quantify the impact of these uncertainties on simulation results. Application of our massively parallel dynamic modeling workflow is illustrated on a proprietary IUP recovery method for a complex naturally fractured extra-heavy oil (bitumen) reservoir as example. After briefly explaining these recovery processes and the modeling approach, we show the techniques (including their accompanying application results) that (1) notably accelerate the (single-model) simulation process, (2) effectively identify the predominant subsurface uncertainties, (3) rapidly optimize heater-producer patterns under the influence of predominant subsurface uncertainties, and (4) efficiently compute expected-value production functions with error bars.
Tie-Simplex-Based Phase Behavior Modeling in an IMPEC Reservoir Simulator
Authors: Rezaveisi M. , Sepehrnoori K. , Johns R. T. 
Published: February 2013

Abstract
Numerical simulation of gas injection processes requires coupling of phase equilibrium equations with complex multiphase flow equations. Standard EOS-based phase equilibrium modeling in reservoir simulators involves computationally intensive and time-consuming calculations for stability analysis and flash calculations. Therefore, speeding up stability analysis and flash calculations is an active research area.
Recently, the tie-simplex based phase behavior modeling in reservoir simulators has been applied and investigated as a potential method for improving the computational speed of EOS-based reservoir simulators. The most promising of the tie-simplex based approaches in terms of practicality and computational efficiency is Compositional Space Adaptive Tabulation (CSAT). We implemented CSAT in UTCOMP, The University of Texas’s in-house IMPEC compositional reservoir simulator to investigate its computational efficiency compared to the phase behavior algorithm in the original UTCOMP. Several example miscible and immiscible case studies are presented.
The results show that using CSAT to generate initial estimates for flash calculations is inefficient compared to the original UTCOMP's phase behavior algorithm. Applying CSAT to only skip stability analysis does improve the computational time, but only when a significant portion of the grid blocks are in the single-phase region and no other technique for avoiding stability analysis is used. CSAT may skip as much as 99% of the stability analyses performed in the base case original UTCOMP, which may amount to about 30% improvement in total computational time in such cases. However, in most cases there is little or no computational advantage to use CSAT when the simple option in UTCOMP is used where stability analysis is skipped for blocks surrounded by single-phase regions. Thus, we see no reason to implement CSAT into an IMPEC type simulator over other simpler schemes to avoid stability analyses. We explore in detail the performance of CSAT, which depends significantly on the specific gas flood modeled, and the number of tie lines generated during adaptive tabulation. The number of tie lines generated depends on tolerances specified for tie-line detection and for acceptance of a phase stability skip.
The results shed light on applicability of CSAT in the IMPEC type compositional reservoir simulators and show that the advantages of CSAT are not as great as initially thought.
The Role of Analysts in Intra-Industry Information Transfer
Authors: Hilary Gilles , Shen Rui 
Published: February 2013

ABSTRACT
When a firm issues a management forecast, analysts who have observed more forecasts from this firm since covering it (i.e., have more MF-Experience) subsequently improve their own accuracy more and provide timelier earnings forecasts for other (non-issuing) firms in the same industry. We also find that, subsequent to a management forecast, investors are more responsive to forecast revisions for non-issuing firms made by analysts with more MF-Experience. Further tests suggest that our results are not explained by endogeneity in firm coverage.
Data Availability: Data are commercially available.
Conservative Treatment of Complicated Oblique Crown-root Fractures of Molars: A Report of Five Representative Cases
Authors: Wang P , He W , Ni L , Lu Q , Sun H 
Published: February 2013

SUMMARY
The five cases presented here describe a conservative treatment procedure for complicated crown-root fractures of molars with extensive loss of tooth structure. After the mobile crown-root fragments were extracted, the remaining crowns were restored at the juxtagingival level. The follow-up time ranged from two years, seven months, to four years. At the follow-up examinations, all of the teeth were asymptomatic and had healthy clinical appearances. There was no evidence of pockets related to fractures. The results of these cases show that complete periodontal healing is possible with conservative treatment of complicated crown-root fracture of molars.
Control of T-2 Toxin in Fusarium Langsethiae and Geotrichum Candidum Co-Culture / Kontrola Toksina T-2 U Kokulturi Fusarium Langsethiae I Geotrichum Candidum
Authors: Gastélum-Martínez Elida , Compant Stephane , Taillandier Patricia , Mathieu Florence 
Published: February 2013

AbstractDue to contamination of barley grains by Fusarium langsethiae, T-2 toxin can be present in the brewing process. It has been observed that the presence of the yeast Geotrichum candidum during malting can reduce the final concentration of this mycotoxin in beer. In this work, a co-culture method was carried out for both microorganisms in order to evaluate the effect on T-2 mycotoxin concentration in comparison with the pure culture of F. langsethiae in the same conditions. The microbial growth of both microorganisms was assessed using three different methods: dry weight, DOPE-FISH, and DNA quantification. In coculture, both microorganisms globally developed less than in pure cultures but G. candidum showed a better growth than F. langsethiae. The concentration of T-2 was reduced by 93 % compared to the pure culture. Hence, the interaction between G. candidum and F. langsethiae led to a drastic mycotoxin reduction despite the only partial inhibition of fungal growth
Provenance of Paleozoic very low- to low-grade metasedimentary rocks of South Tisia (Slavonian Mountains, Radlovac Complex, Croatia)
Authors: Biševac Vanja , Krenn Erwin , Finger Fritz , Lužar-Oberiter Borna , Balen Dražen 
Published: February 2013

Abstract
Monazite age dating, detrital heavy mineral content and whole-rock geochemistry provided insight into the provenance, depositional history and paleogeological setting of the Radlovac Complex very low- to low-grade metasedimentary rocks (South Tisia, Slavonian Mountains, Croatia). Electron microprobe based Th-U-Pb dating of detrital monazite indicates a Variscan age of the protolith (330 ± 10 Ma). The detrital heavy mineral assemblages of representative metasedimentary rocks are dominated by apatite, zircon, tourmaline and rutile accompanied by minor quantity of epidote/zoisite, monazite and titanite. Judging from the heavy mineral assemblage, felsic igneous rocks served as the source material. This is consistent with the major and trace element spectrum of studied metasedimentary rocks characterized by high concentration of Th, high L + MREEs and high ratios of La/Sc, Th/Sc, La/Co, Th/Co and Th/Cr. The occurrence of magmatic monazite, zircon and xenotime and the absence of metamorphic heavy minerals suggest that granitoids, migmatites and migmatitic gneisses served as one major source for the metapsammites. Such rock types are commonly exposed in the Papuk Complex of the older surrounding complexes, while the Psunj Complex also contains metamorphic rocks. This is in good correlation with the monazite ages presented here which fits better with ages of Papuk Complex representative rocks than with those of the Psunj Complex known from the literature. Overall, data show that the Radlovac Complex represents the detritus of the local Variscan crust characterized by granitoid bodies, migmatites and migmatitic gneisses typical for the Papuk Complex.