bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Flow Based Lumping Approach for Compositional Reservoir Simulation
Authors: Rastegar Reza , Jessen Kristian 
Published: February 2009

Abstract
In this paper, we present a new and automatic lumping methodology to improve the accuracy and CPU efficiency of compositional reservoir simulation. Typical equation of state (EOS) based models for prediction of PVT experiments employ a large number of components. Such detailed EOS models are subsequently lumped into a reduced number of pseudocomponents for use in compositional reservoir simulation. Traditional lumping approaches do not include any information regarding the mixture compositions will form during a gas injection process. These mixture compositions can differ significantly from those investigated by standard PVT and swelling test experiments. Here we demonstrate the benefit of including displacement characteristics obtained from semi-analytical displacement calculations in the selection of pseudo-components for compositional reservoir simulation and propose an automated scheme for grouping/lumping.
Components with close proximity in terms of specific velocities and composition space are lumped subject to the observed variation in equilibrium K values as defined by displacement dynamics. Lumping is performed starting from the most detailed fluid description in a sequential manner to gauge the quality of the fluid description as we reduce the number of components in the fluid description. Examples are provided for multicomponent reservoir fluids and CO2 injection where a substantial amount of data is available (PVT, swelling test and slimtube MMP). We demonstrate that the proposed lumping strategy provides for additional control of the predictive quality of the reduced EOS model that may not be possible with currently available lumping approaches.
A majority of oil fields currently under production are candidates for EOR processes such as tertiary gas floods. The work presented in this paper is directly applicable to the study and design of such EOR processes. In addition, this is to our best knowledge the first paper that combines displacement dynamics from the analytical theory of gas injection processes with reservoir fluid characterization towards improved accuracy/efficiency of compositional reservoir simulation.
Efficient General Formulation Approach For Modeling Complex Physics
Authors: Cao H. , Crumpton P. I. , Schrader M. L. 
Published: February 2009

Abstract
This paper describes a general formulation for phase-component partitioning that can accommodate any number of phases and components, any component existing in any phase, and requires no special ordering of phases or components. This type of formulation is desirable for flexibility in reservoir simulation but has not previously been used in commercial simulators due to its complexity and inefficiencies in both memory and speed. Here we describe an efficient natural-variable-based general formulation approach, which handles general partitioning of phase-component, consumes no extra memory, and only has a small amount of CPU overhead. This general formulation approach was developed as part of a next generation reservoir simulation project (DeBaun et al., 2005), for "next generation" is the ability to accommodate fluid models currently used in reservoir simulation as well as models that will be developed in the future. With this general formulation approach, we can model most reservoir physics with a single, unified code base, rather than custom one-off extensions of a more limited one. Currently we have tested and validated our approach on standard black-oil and compositional models, thermal steam model, and 4-phase 4-component Todd-Longstaff model.
We describe our natural variable based nonlinear system which incorporates general phase-component partitioning. We analyze the complexity of our model and explain implementation details required to minimize, and in some cases eliminate, CPU and memory overheads. We conclude with the validation of our approach and performance comparisons and analysis (all against standard implementations) for various types of field case studies.
Phase Equilibrium Computations Are No Longer the Bottleneck in Thermal Compositional EoS Based Simulation
Authors: Iranshahr A. , Voskov D. V. , Tchelepi H. A. 
Published: February 2009

Abstract
Thermodynamic equilibrium computations are usually the most time consuming component in compositional reservoir flow simulation. A Compositional Space Adaptive Tabulation (CSAT) approach has been developed as a preconditioner for Equation of State (EoS) computations in isothermal compositional simulation. The compositional space is decomposed into sub- and super-critical regions. In the sub-critical region, we adaptively parameterize the compositional space using a small number of tie-lines, which are assembled into a table. The critical surface is parameterized and used to identify super-critical compositions. The phase equilibrium information for a composition is interpolated as a function of pressure using the tie-line table. We extend the CSAT approach to thermal problems. Given an overall composition at a fixed temperature, the boundary between sub- and super-critical pressures is represented by the critical tie-line and the corresponding minimal critical pressure. A small set of sub-critical tie-lines is computed and stored for a given temperature. This process is repeated for the pressure and temperature ranges of interest, and a coarse (regular) tie-line table is constructed. Close to the critical boundary, a refined tie-line table is used. A combination of regular and refined interpolation improves the robustness of the tie-line search procedure and the overall efficiency of the computations. Several challenging problems, including an unstructured heterogeneous discrete fracture field model with 26 components, are used to demonstrate the robustness and efficiency of this general tie-line based parameterization method. Our results indicate that CSAT provides very accurate treatment of the near-critical region. Moreover, the computational efficiency of the method is at least an order of magnitude better than that of standard EoS-based reservoir simulation approaches. We also show the efficiency gains relative to standard techniques as a function of the number of gridblocks in the simulation model.
Influence of Mechanical Constitutive Model on the Coupled Hydro– Geomechanical Analysis of Fault Reactivation
Authors: Guimarães L. J. N. , Gomes I. F. , Valadares J. P. V. 
Published: February 2009

Abstract
Injection and production of fluids cause changes of pressure, temperature and saturation that affect the state of stress in oil reservoirs, resulting in porosity and permeability variations. It is therefore a coupled hydro-geomechanical problem. The fault reactivation problem considers that shear (with dilatancy), tension or compression of filling material may cause changes in hydraulic properties. Reservoir simulation with geomechanical coupling allows realistic modeling of fault reactivation, that can influence in the production of oil due to pressure and fluid loss in the reservoir. A finite element procedure is presented that models fluid flow in a deformable reservoir crossed by a geological fault in a coupled and totally implicit manner. Whether the fault is activated or not is governed by the hydro-mechanical boundary conditions of the problem and by the modeling of the constitutive behavior of involved materials. Two alternative mechanical constitutive models were adopted to represent the behavior of the filling material of the fault: elastoplastic Mohr-Coulomb (dilatancy considered) and continuum isotropic damage model (micro-cracking considered), that lead to different responses of the reservoir-fault system. It was observed that when the continuum damage model is used reactivation chiefly tends to occur inside reservoir. On the other hand, when the Mohr-Coulomb model is used activation propagates through reservoir and adjacent rocks. Simulation of constitutive behavior of sealing faults is essential to the prediction of the possibility of reactivation especially during waterflooding with reservoir pressurization, which may cause economic as well as environmental damages. In oil reservoirs with fault reactivation possibility, definition of maximum bottom hole pressure of the injectors during waterflooding can only be safely conducted based on a coupled hydro-geomechanical analysis tool with realist modeling of the constitutive behavior of the materials.
A General Unstructured Grid, Parallel, Thermal Simulator and its Application for Large Scale Thermal Models
Authors: Shi Xundan , Chang Yih-Bor , Muller Mathieu , Obi Eguono , Lim Kok-Thye 
Published: February 2009

Abstract
We describe the contruction of a general unstructured grid, parallel, fully-implicit simulator for complex physics associated with heavy oil thermal recovery. The primary focus of the simulator is on the physics associated with steam injection and Steam Assisted Gravity Drainage (SAGD) and to simulate such models efficiently using parallel processing. The simulator solves component material balance, energy balance and mass equilibrium equations for component mole fractions, saturation, temperature and pressure using the Newton-Raphson method. External heat sources and sinks are included in source terms to model the energy interaction with over-burden and under-burden rocks. The solution procedure and the treatment of phase transition to achieve stable non-linear iterations are discussed.
The simulator is verified by comparing results from problem No. 3 of the Fourth SPE Comparative Solution Projects and a cyclic steam injection case with other commercial simulators. We also demonstrate the performance and parallel scalability of the simulator via testing a large scale SAGD model with 9 horizontal well-pairs.
Scalable Multi–stage Linear Solver for Coupled Systems of Multi–segment Wells and Complex Reservoir Models
Authors: Jiang Y. , Tchelepi H. A. 
Published: February 2009

Abstract
Wellbore flow and interactions between wells and the reservoir can be complex. Accurate modeling of these behaviors is especially important for advanced (multi-lateral) wells. This paper describes a new scalable linear solver for flow simulation of detailed unstructured models with coupled multi-lateral multi-segment wells. The linear solver accommodates systems associated with both the fully implicit approach and the adaptive implicit method (AIM).
A general-purpose research simulator (GPRS) serves as the computational platform, in which reservoir flow is described with a thermal-compositional AIM formulation, and a multi-segmented well (MsWell) model is used to describe wellbore flow. In the MsWell model, the wellbore is discretized into segments; pressure, velocity, and phase fractions are computed for each segment. Multi-lateral multi-segment wells add a large number of equations and unknowns, which are coupled to the reservoir model.
The new linear solver is a generalized two-stage constraint pressure residual (CPR) preconditioner. The first stage is a global pressure system of equations, where the pressure coupling between the reservoir and the complex wells is represented accurately. This coupled pressure system is obtained algebraically, where the multi-segment wells are reduced to a form similar to that of standard wells. The two-stage scheme serves as the inner loop of a generalized minimum residual (GMRES) iterative solver. Algebraic multigrid (AMG) is used to compute the first-stage pressure solution; a special block-based incomplete lower-upper (ILU) preconditioner with arbitrary levels of fill-in is used for the second stage. This multi-stage solution algorithm was implemented using multi-level, sparse, block-based (MLSB) data structures specially designed for AIM computations on unstructured grids. We demonstrate the superior performance of this new solver compared with state-of-the-art methods using a variety of compositional problems for highly detailed reservoir models with unstructured grids and complex multi-segment wells.
Multiscale Finite Volume Formulation for the Saturation Equations
Authors: Zhou H. , Lee S. H. , Tchelepi H. A. 
Published: February 2009

Abstract
Recent advances in multiscale methods have shown great promise in modeling multiphase flow in highly detailed heterogeneous domains. Existing multiscale methods, however, solve for the flow field (pressure and total-velocity) only. Once the fine-scale flow field is reconstructed, the saturation equations are solved on the fine scale. With the efficiency in dealing with the flow equations greatly improved by multiscale formulations, solving the saturation equations on the fine scale becomes the relatively more expensive part. In this paper, we describe an adaptive multiscale finite-volume (MSFV) formulation for the nonlinear transport (saturation) equations. A general algebraic multiscale formulation consistent with the operator based framework proposed by Zhou and Tchelepi (SPEJ 13:267-173) is presented. Thus, the flow and transport equations are solved in a unified multiscale framework. Two types of multiscale operators, namely restriction and prolongation, are used to construct the multiscale saturation solution. The restriction operator is defined according to the local sum of the fine-scale transport equations in a coarse gridblock. Three adaptive prolongation operators are defined according to the local saturation history at a particular coarse block. The three operators have different computational complexity, and they are used adaptively in the course of a simulation run. When properly used, they yield excellent computational efficiency while preserving accuracy. This adaptive multiscale formulation has been tested using several challenging problems with strong heterogeneity, large buoyancy effects, and changes in the well operating conditions (e.g., switching injectors and producers during simulation). The results demonstrate that adaptive multiscale transport calculations are in excellent agreement with fine-scale reference solutions, but with a much lower computational cost.
Quasi-Positive Multi-Family Continuous Darcy-Flux Approximations With Full Pressure Support on Structured and Unstructured Grids in 3-D
Authors: Zheng Hongwen , Edwards Michael G. 
Published: February 2009

Abstract
New mutli-families of flux-continuous finite-volume methods are presented for the full-tensor pressure equation with general discontinuous coefficients for any cell type in three dimensions. Full pressure continuity that is built into the new methods leads to a quasi-positive formulation that minimises spurious oscillations in discrete pressure solutions for strongly anisotropic full-tensor fields. The multi-family formulation permits maximum flexibility in quadrature yielding improved solution resolution.
Advantages of Using Vertical Stair Step Faults in Reservoir Grids for Flow Simulation
Authors: Gringarten E. , Haouesse A. , Arpat B. , Nghiem L. 
Published: February 2009

Abstract
Conventional reservoir modeling relies on the construction of 3D grids which conform to stratigraphy and whose columns are aligned with faults.
When modeling non-vertical faults, traditional "pillar technology" yields large volume distortions between cells leading to non-orthogonality problems. It is difficult or impossible to construct conventional grids in structurally complex environments: reverse, dying faults, X-, Y-, λ-faults. Modelers can spend days simplifying their model by removing or verticalizing faults. Deciding on which data to alter is cumbersome and results in inaccurate models. This affects connectivity and compartmentalization, impacting significantly reservoir management decisions.
Therefore, it is essential to construct grids that honor the integrity of the complete reservoir structure regardless of its complexity, and yet that are compatible with commercial flow simulators.
A solution, in terms of structured grids, is to consider vertical stair-step faults. They have many advantages: all types of faulting patterns can be accurately represented; columns can be (sub-) vertical; cells are less likely to be distorted and orthogonality can be ensured. These grids are ideal for reservoir flow simulation purposes. However, since it has been difficult to construct them in the past, few engineers have experience with them.
In this paper, a methodology to construct such grids that preserve the integrity of the structure and stratigraphy of reservoirs is presented. Approaches to robust reservoir property modeling and upscaling are also discussed. Test cases are presented, comparing results from conventional pillar grids with grids in which faults are defined as vertical stair-steps. The integration of this type of grid with a high-performance reservoir simulator is also highlighted.
Multi-D Upwinding for Multi Phase Transport in Porous Media
Authors: Kozdon J. , Mallison B. , Gerritsen M. , Chen W. 
Published: February 2009

Abstract
Multidimensional transport for reservoir simulation is typically solved by applying 1D numerical methods in each spatial coordinate direction. This approach is simple, but the disadvantage is that numerical errors become highly correlated with the underlying computational grid. In many real-field applications this can result in strong sensitivity to grid design for the computed saturation/composition fields, but also for critical integrated data such as breakthrough times. To increase robustness of simulators, especially for adverse mobility ratio flows that arise in gas injection and other EOR processes, it is therefore of much interest to design truly multi-D schemes for transport that remove, or at least strongly reduce, the sensitivity to grid design.
We present a new upwind biased truly multi-D family of schemes for multi-phase transport capable of handling counter-current flow arising from gravity. The proposed family of schemes has four attractive properties: applicability within a variety of simulation formulations with varying levels of implicitness; extensibility to general grid topologies; compatibility with any finite volume flow discretization; and provable stability (monotonicity) for multi-phase transport. The family is sufficiently expressive to include several previously developed multi-D schemes, such as the narrow scheme, in a manner appropriate for general purpose reservoir simulation.
A number of water flooding problems in homogeneous and heterogeneous media demonstrate the robustness of the method as well as reduced transverse (cross-wind) diffusion and grid orientation effects.
A Next-Generation Parallel Reservoir Simulator for Giant Reservoirs
Authors: Dogru Ali H. , Fung Larry S. K. , Middya Usuf , Al-Shaalan Tareq M. , Pita Jorge A. , HemanthKumar K. , Su H. J. , James C. T. Tan , Hoy H. , Dreiman W. T. , Hahn W. A. , Al-Harbi R. , Al-Youbi A. , Al-Zamel N. M. , Mezghani M. , Al-Mani T. 
Published: February 2009

Abstract
Giant reservoirs of the Middle East are crucial for the supply of oil and gas to the world market. Proper simulation of these giant reservoirs with long history and large amount of static and dynamic data requires efficient parallel simulation technologies, powerful visualization and data processing capabilities.
This paper describes GigaPOWERS, a new parallel reservoir simulator capable of simulating hundreds of millions of cells to a billion cells with long production history in practical times. The new simulator uses unstructured grids. A distributed unstructured grid infrastructure has been developed for models using unstructured or complex structured grids. Unconventional wells such as maximum reservoir contact wells and fish-bone wells, as well as faults and fractures are handled by the new gridding system. A new parallel linear solver has been developed to solve the resulting linear system of equations. Load balancing issues are also discussed.
A unified compositional formulation has been implemented. The simulator is designed to handle n-porosity systems. An optimization-based well management system has been developed by using mixed integer nonlinear programming. In addition to the core computational algorithms, the paper will present the pre- and post-processing software system to handle large amount of data. Visualization techniques for billions of cells are also presented.
Successful Application of MPD Technique in a HP/HT Well Focused on Performance Drilling in Southern Mexico Deep Fractured Carbonates Reservoirs
Authors: Tellez C. P. , Duno H. , Casanova O. , Colombine W. , Lupo C. , Palacios J. R. , Medina L. 
Published: February 2009

Abstract
The development field Tizon, is located west of Frontera, NE of the Palapa and Luna Fields, Municipality of Centla, in the Coastal Plain of the Southern Gulf of Mexico in Tabasco State. Historic crude oil exploitation targets the Cretaceous and Jurassic formations (5600 to 6300 m TVD). Formation pressure in these naturally fractured carbonates is close to 12000 psi and temperatures ranging between 160 and 180 °C. Managed Pressure Drilling (MPD) techniques were implemented to avoid formation influx and increase the safety of operations (H2S-bearing reservoir) and also, to avoid lost circulation, formation damage and differential sticking due to conventional drilling procedures requiring a highly overbalanced mud weight. The significant risk to drill with conventional techniques was critical enough to consider a full MPD application. This paper describes the experience gained in the planning and execution of the drilling operation of this well; using backpressure at the wellhead and the implementation of a conventional MPD package to improve performance of the operation targeting reducing the Non-Productive-Time. The paper will guide the technical, community over the design, planning and execution process, geological review, pre-engineering study, steady state flow modeling, final drilling program, training, safety and contingencies.
A New Chapter in MPD: Subsea Pumping
Authors: Hinton Andy 
Published: February 2009

Abstract
Subsea pumping systems improve the safety and efficiency of drilling operations in tophole in water depths down to 525m (1720ft). The system collects mud at the seabed and pumps it back to the rig before the rig BOP / riser has been run.
This equipment can be reconfigured to a ‘pumped riser’ mode for use after the riser is run. Drilling mud is pumped from an outlet in the marine riser with a blanket fluid, usually seawater above. Varying the level of heavy mud in the riser compensates for the Annular Pressure Loss. By dropping the level as mud circulation starts, there in no increase in the Bottom Hole Pressure (BHP). The Equivalent Circulating Density (ECD) is the same as the mud weight. There is a constant BHP when drilling, circulating, making connections, tripping, logging etc.
The system is simple to understand and doers not rely on surface pressure or pressurising the marine riser. Connections are likely to be slower than the alternative methods but this is not considered a significant problem. In some ways is reassuring to be able to change conditions slowly and steadily.
Pumped riser systems may also be used to drill surface holes, without any gas, at bottom hole pressures below seawater hydrostatic. This may be done to avoid losses into vugular formations or to improve drill rates in hard formations.
Subsea pumping has also been used in a deepwater 5000ft (1500m) field trial. This proved up deepwater RMR but is a step towards the goal of full Dual Gradient Drilling in deep water.