bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Modification of the Dykstra-Parsons Method for Inclined Stratified Reservoirs
Authors: El-Khatib Noaman A.F. 
Published: November 2012

Summary
The Dykstra-Parsons method (Dykstra and Parsons 1950) is used to predict the performance of waterflooding in noncommunicating stratified reservoirs. Much interest has been shown recently in the application of the method to chemical flooding, particularly for the case of polymer injection used for mobility control. The original method assumes that the reservoir layers are horizontal; however, most oil reservoirs exhibit a dip angle, with water being injected in the updip direction. Therefore, it is important to account for the effect of inclination on the performance of the method.
A modification of the Dykstra-Parsons equations is obtained to account for reservoir inclination. The developed model includes a dimensionless gravity number that accounts for the effect of the dip angle and the density difference between the displacing and displaced fluids. The derived equation that governs the relative locations of the displacement fronts in different layers is nonlinear, includes a logarithmic term, and requires an iterative numerical solution. This solution is used to estimate the fractional oil recovery, the water cut, the injected pore volume, and the injectivity ratio at the time of water breakthrough in successive layers.
Solutions for stratified systems with log-normal permeability distribution were obtained and compared with horizontal systems. The effects of the gravity number, the mobility ratio, and the Dykstra-Parsons permeability-variation coefficient (VDP) on the performance were investigated. Cases of updip and downdip injection are discussed.
It was found that for a positive gravity number (updip water injection), performance is enhanced in terms of delayed water breakthrough, increased fractional oil recovery, and decreased water cut as compared with horizontal layers. This occurs for both favorable and unfavorable mobility ratios but is more evident in unfavorable mobility ratios and more-heterogeneous cases. For the case of a negative gravity number (downdip water injection or updip gas injection), the opposite behavior was observed.
The results were also compared with the performance of inclined communicating reservoirs with complete crossflow. The effect of communication between layers was found to improve fractional oil recovery for favorable and unit mobility ratios and decrease recovery for unfavorable mobility ratio.
Numerical Studies on Two-Way Coupled Fluid Flow and Geomechanics in Hydrate Deposits
Authors: Kim J.. , Moridis G.J.. J. , Yang D.. , Rutqvist J.. 
Published: November 2012

Summary
Coupled flow and geomechanics play an important role in the analysis of gas-hydrate reservoirs under production. The stiffness of the rock skeleton and the deformation of the reservoir, as well as porosity and permeability, are directly influenced by (and interrelated with) changes in pressure and temperature and in fluid-(water and gas) and solid-(hydrate and ice) phase saturations. Fluid and solid phases may coexist, which, coupled with steep temperature and pressure gradients, result in strong nonlinearities in the coupled flow and mechanics processes, making the description of system behavior in dissociating hydrate deposits exceptionally complicated.
In previous studies, the geological stability of hydrate-bearing sediments was investigated using one-way coupled analysis, in which the changes in fluid properties affect mechanics within the gas-hydrate reservoirs, but with no feedback from geomechanics to fluid flow. In this paper, we develop and test a rigorous twoway coupling between fluid flow and geomechanics, in which the solutions from mechanics are reflected in the solution of the flow problem through the adjustment of affected hydraulic properties. We employ the fixed-stress split method, which results in a convergent sequential implicit scheme.
In this study of several hydrate-reservoir cases, we find noticeable differences between the results from one- and two-way couplings. The nature of the elliptic boundary value problem of quasistatic mechanics results in instantaneous compaction or dilation over the domain through loading from reservoir-fluid production. This induces a pressure rise or drop at early times (low-pressure diffusion), and consequently changes the effective stress instantaneously, possibly causing geological instability. Additionally, the pressure and temperature regime affects the various phase saturations, the rock stiffness, porosity, and permeability, thus affecting the fluid-flow regime. These changes are not captured accurately by the simpler one-way coupling. The tightly coupled sequential approach we propose provides a rigorous, twoway coupling model that captures the interrelationship between geomechanical and flow properties and processes, accurately describes the system behavior, and can be readily applied to large-scale problems of hydrate behavior in geologic media.
Combining the Ensemble Kalman Filter With Markov Chain Monte Carlo for Improved History Matching and Uncertainty Characterization
Authors: Emerick A.A.. A. , Reynolds A.C.. C. 
Published: November 2012

SummaryIt is well known that when applied to reservoir history-matching problems, the ensemble Kalman filter (EnKF) can lead to a large underestimation of uncertainty in the posterior probability-density function (PDF) for reservoir-model parameters. Here, we demonstrate that, regardless of whether covariance localization is used, EnKF also can lead to an overestimation of the uncertainty in future predictions of reservoir performance. This overestimation occurs because, even though the data matches obtained with EnKF tend to appear reasonable, these matches are significantly worse than those that can be obtained when history matching dynamic data with a gradient-based method. The relatively poor data match obtained with EnKF means that the ensemble of states generated by assimilating data with EnKF are of relatively low probability (low value of posterior PDF). Under reasonable assumptions, a Markov Chain Monte Carlo (MCMC) algorithm will theoretically generate an accurate sampling of the posterior PDF conditional to dynamic data. However, standard implementations of MCMC are not computationally feasible because each proposed state in the chain requires a run of the forward model (reservoir simulator). In this work, the EnKF and MCMC methodologies are combined to obtain a relatively efficient algorithm for sampling the posterior PDF for reservoir-model parameters. In this algorithm, a symmetric square root of the state vector's posterior covariance matrix is calculated from an ensemble of state vectors obtained from EnKF. It is shown that this square root can be used both to propose new states in the Markov chain and to evaluate the probability of accepting the state without running the simulator, which results in an efficient algorithm. In order to improve sampling, we also propose to generate multiple ensembles with EnKF and multiple Markov chains, which are then combined and resampled based on the normalized objective function. We tested the proposed EnKF-MCMC algorithm on a small 3D two-phase-flow reservoir example. The problem is sufficiently small that by using MCMC only, we are able to generate a long chain based on 2 million proposed states. The posterior PDF calculated from this long chain is assumed to be accurate. The posterior PDFs for predicted cumulative oil and water production generated with the new EnKF-MCMC algorithm provide results that are in reasonable agreement with the posterior PDFs for the cumulative oil and water production obtained from the long Markov chain, whereas the corresponding PDFs obtained using EnKF with and without covariance localization exhibit a significantly higher variance (i.e., overestimate uncertainty in the predicted cumulative reservoir production).
Advanced Casing Design With Finite-Element Model of Effective Dogleg Severity, Radial Displacements, and Bending Loads
Authors: McSpadden A.R.. R. , Coker III O.D.. D. , Ruan G.C. C 
Published: November 2012

Summary
A purpose-built finite-element model (FEM) is applied to simulate radial displacement of a casing string constrained within an outer wellbore. The FEM represents a fully stiff-string model wherein the casing is approximated by general-beam elements with six degrees of freedom at each node to account for all possible physical displacements and rotations. Results predicted include deflection of the casing centerline from the wellbore centerline, effective dogleg curvature, bending deformation, wall-contact forces, and bending-stress magnification. These results will provide for a more-accurate assessment of well integrity in terms of casing-stress safety factors and centralization before cementing, as well as more accurate prediction of running loads during the drilling phase.
In critical-well-casing design, accurate assumptions regarding bending stiffness may be necessary to avoid overly conservative as well as nonconservative analysis. Challenging finite high-pressure/ high-temperature (HP/HT) and extreme-temperature wells are opportunities for increased design efficiency by avoiding overly conservative and costly designs, which can be crucial. Alternatively, design for extreme loads such as overpull loads in long deviated wells may be nonconservative if severe bending stresses are not considered.
A realistic case study is presented that demonstrates the possibility to achieve cost efficiency by means of optimized casing design. A case study also is presented in which a nonconservative design may result if severe bending loads are not modeled. The purpose-built FEM code is in many ways preferable to the use of commercial finite-element-analysis (FEA) packages because of the time-consuming effort required to build up the detailed model.
In typical casing and tubular-stress design, a soft-string model assumes casing strings are coincident with the wellbore centerline. The known or assumed wellbore curvature is applied directly to the casing string. Any effect of casing-string stiffness and allowable radial displacement within the outer wellbore is ignored. In many cases, this results in an overly conservative analysis. Likewise, the impact of bending-stress magnification is typically ignored, along with the effects of centralizer placement. This may also be nonconservative for critical overpull situations, such as in extended-reach-drilling (ERD) and horizontal wells.
Enhanced-Velocity-Multiblock Method for Coupled Flow and Reactive-Species Transport Through Porous Media: Applications to Bioremediation and Carbon Sequestration
Authors: Thomas S.G.. G. , Wheeler M.F.. F. 
Published: November 2012

Summary
This paper presents a multiblock-discretization method—the enhanced-velocity mixed-finite-element method (EVMFEM) (Wheeler et al. 2002)—for coupled multiphase flow and reactive-species-transport modeling in porous-media applications. The method provides local mass balance and a continuous approximation of fluxes across interfaces of elements and subdomains. It can treat nonmatching grids, allowing for a flexible choice of grid refinements. Further, by distributing the blocks among processors such that each block has approximately the same number of elements, this method can be implemented efficiently in parallel, thereby offering further reductions in computational cost.
The paper also presents recent application of EVMFEM to challenging problems such as compositional flow simulations of CO2 sequestration. Tests with EVMFEM suggest that it is advantageous to apply grid refinements around wells and to areas in which dynamics of chemical-species concentration is highest. Allowing for variable grid refinements greatly reduces the simulation cost, while preserving overall accuracy of the solution. For completeness, a few significant analytic results on convergence of the method are stated and referenced, omitting proof.
This work is significant in advancing the discretization and application of EVMFEMs in reservoir-simulation development. Problems such as transport of chemical species in multiphase flow and CO2 sequestration have begun to assume significant importance in decisions regarding the preservation of our environment and in the safe and reliable means of delivering energy. This paper offers useful methods and some innovative future directions to address the huge computational costs involved in solving such complex problems.
Accurate and Efficient Simulation of Multiphase Flow in a Heterogeneous Reservoir With Error Estimate and Control in the Multiscale Finite-Volume Framework
Authors: Hajibeygi H.. , Lee S.H.. H. , Lunati I.. 
Published: November 2012

Summary
The multiscale finite-volume (MSFV) method is designed to reduce the computational cost of elliptic and parabolic problems with highly heterogeneous anisotropic coefficients. The reduction is achieved by splitting the original global problem into a set of local problems (with approximate local boundary conditions) coupled by a coarse global problem. It has been shown recently that the numerical errors in MSFV results can be reduced systematically with an iterative procedure that provides a conservative velocity field after any iteration step. The iterative MSFV (i-MSFV) method can be derived with an improved (smoothed) multiscale solution to enhance the localization conditions, with a Krylov subspace method [e.g., the generalized-minimal-residual (GMRES) algorithm] preconditioned by the MSFV system, or with a combination of both. In a multiphase-flow system, a balance between accuracy and computational efficiency should be achieved by finding a minimum number of i-MSFV iterations (on pressure), which is necessary to achieve the desired accuracy in the saturation solution. In this work, we extend the i-MSFV method to sequential implicit simulation of time-dependent problems. To control the error of the coupled saturation/pressure system, we analyze the transport error caused by an approximate velocity field. We then propose an error-control strategy on the basis of the residual of the pressure equation. At the beginning of simulation, the pressure solution is iterated until a specified accuracy is achieved. To minimize the number of iterations in a multiphase-flow problem, the solution at the previous timestep is used to improve the localization assumption at the current timestep. Additional iterations are used only when the residual becomes larger than a specified threshold value. Numerical results show that only a few iterations on average are necessary to improve the MSFV results significantly, even for very challenging problems. Therefore, the proposed adaptive strategy yields efficient and accurate simulation of multiphase flow in heterogeneous porous media.
Combining Elastic and Plastic Fatigue Damage in Steel Pipelines, Risers, and Coiled Tubing
Authors: Bridge C.D.. D. 
Published: November 2012

Summary
Coiled tubing is a continuous pipe that, having been coiled around a reel for storage, can be deployed and used as a pipeline or riser. During deployment as a riser, the coiled tubing is unspooled from the reel, run into the water, and connected to the wellhead. This process plastically strains the pipe, causing plastic (or low-cycle) fatigue damage. When the coiled tubing is connected to the wellhead, the environmental loading causes elastic-stress cycles, resulting in elastic (or high-cycle) fatigue damage.
Numerous methods are available to determine fatigue life from either plastic or elastic cycling; however, few data are available within the industry on how the fatigue damages from elastic and plastic cycles combine.
This paper presents the experimental work conducted to show the combined fatigue life of notched samples of flat steel used to manufacture coiled tubing that has been plastically and elastically cycled. The data show that the combined fatigue life can be lower than the total of the plastic and elastic fatigue damages by use of Miner's rule. Existing theory suggests that the combined fatigue life could be as low as 10% of the Miner's-rule fatigue damages; however, the experimental data indicate that a more appropriate value is closer to 75%.
Assessing Well-Integrity Risk: A Qualitative Model
Authors: Dethlefs J.C.. C. , Chastain B.. 
Published: November 2012

Summary
For successful delivery of well integrity (WI), there needs to be an understanding of the risks that can cause undesirable events such as safety hazards or loss of containment. Performing a risk assessment (RA) on a well, or type of well, will help determine and rank the potential risks and provide information that allows limited resources to be applied in the most effective manner. The main objectives of performing a risk assessment include (a) following a formal process to assess risk consistently and to enable comparison between well-barrier failure-mode scenarios; (b) qualitatively assessing well-barrier failure risk for every segment of a well; (c) documenting suggestions that are offered by the riskassessment team for mitigating well-barrier failure risk; and (d) providing a report of the methodology, failure-mode scenarios, risk ranking, and potential mitigation actions for use as a reference tool for managing WI on a routine basis.
Our WI/RA model follows a common qualitative risk-assessment process—a team-based, structured brainstorming format, using the "What-If Methodology" to identify potential hazards associated with well-barrier failure modes. In addition, the model has the following attributes: It incorporates a unique method to segment well barriers into discrete sections, successively "failing" each section for evaluation. The list of analyzed well-barrier failure modes, along with their risk ranking, becomes the risk register for the well or type of well.It is adaptable for assessing well-barrier failure modes on a single well, or a group of wells, having the same general design parameters. An entire well portfolio can be assessed quickly by analyzing types of wells rather than individual wells.It can be used to assess well-barrier failure risk for any type of well.The model can easily be modified to conform to any company's risk model.The WI/RA model has been proven toSuccessfully assess well-barrier failure risk for thousands of wellsFocus specifically on well-barrier failure modes, and as a result be an effective tool that should be incorporated into a "best-in-class" WI programBe used as a management tool to provide guidance for how limited resources can be used effectively to continuously deliver WI.
Negative-Saturation Approach for Compositional Flow Simulations of Mixed CO2/Water Injection Into Geothermal Reservoirs Including Phase Appearance and Disappearance
Authors: Salimi Hamidreza , Wolf Karl-Heinz , Bruining Johannes 
Published: November 2012

Summary
Cold mixed CO2/water injection into hot-water reservoirs can be used for simultaneous geothermal-energy (heat) production and subsurface CO2 storage. This paper studies this process in a 2D geothermal homogeneous reservoir, a layered reservoir, and a heterogeneous reservoir represented by a stochastic-random field. We give a set of simulations for a variety of CO2/water-injection ratios. In this process, often regions of two-phase flow are connected to regions of single-phase flow. Different systems of equations apply for single-phase and two-phase regions. We develop a solution approach, called the nonisothermal-negative-saturation (NegSat) solution approach, to solve efficiently nonisothermal compositional flow problems (e.g., CO2/water injection into geothermal reservoirs) that involve phase appearance, phase disappearance, and phase transitions. The advantage of this solution approach is that it circumvents using different equations for single-phase and two-phase regions and the ensuing unstable switching procedure. In the NegSat approach, a single-phase multicomponent fluid is replaced by an equivalent fictitious two-phase fluid with specific properties. The equivalent properties are such that the extended saturation of a fictitious gas is negative in the single-phase aqueous region.
We discuss the salient features of the simulations in detail. When two phases are present at the injection side, heterogeneity and layering lead to more CO2 storage compared with the homogeneous case because of capillary trapping. In addition, layering avoids movement of the CO2 to the upper part of the reservoir and thus reduces the risk of leakage. Our results also show that heterogeneity and layering change the character of the solution in terms of useful-energy production and CO2 storage. The simulations can be used to construct a plot of the recovered useful energy vs. maximally stored CO2. Increasing the amount of CO2 in the injection mixture leads to bifurcation points at which the character of the solution in terms of energy production and CO2 storage changes. For overall injected-CO2 mole fractions less than 0.04, the result with gravity is the same as the result without gravity. For larger overall injected-CO2 mole fractions, however, the plot without gravity differs from the plot with gravity because of early breakthrough of a supercritical-CO2 tongue near the caprock. The plot of the useful energy (exergy) vs. the CO2-storage capacity in the presence of gravity shows a Z-shape. The top horizontal part represents a branch of high exergy recovery and a relatively lower storage capacity, whereas the bottom part represents a branch of lower exergy recovery and a higher storage capacity.
Use of Pressure/Rate Deconvolution To Estimate Connected Reservoir-Drainage Volume in Naturally Fractured Unconventional-Gas Reservoirs From Canadian Rockies Foothills
Authors: Chen Andrew , Jones Jack R. 
Published: November 2012

Summary
Case studies are presented in this paper to demonstrate the use of the pressure/rate deconvolution-approach in estimating drainage areas for wells completed in some of the naturally fractured tight gas reservoirs of the Canadian Rockies foothills. These case studies demonstrate the application of deconvolution to two key carbonate-stratigraphical horizons in the area: the Triassic Baldonnel and the Permo-Carboniferous Taylor Flat formations. In these structural plays with significant areal formation-rock heterogeneity, the matrix-rock properties controlling the gas storativity are low, with porosity between 3 and 6%, causing low matrix-rock permeability (from 0.01 and 0.1 md). However, all of these formations have been thrusted, overturned, and subjected to reverse faulting. These diagenetic factors have created swarms of natural fractures that control flow rates and may define rock volumes connected to individual wells.
In each well, a preproduction flow test was performed with the intent of ensuring acceptable flow rates and scoping facility design. At this stage of early development, initial-gas-in-place (IGIP) estimates were derived mainly from geophysical mapping, with plans to calibrate the IGIP number through the application of gas material balance, rate-transient analysis, and/or simple late-time rate decline. The rate-history data available in the early stage of production were integrated with pressure-buildup (PBU) data collected later in the production life of the well during annual or routine shut-in periods that were relatively short. Application of deconvolution in this paper is aimed at detecting early signs of pseudosteady-state pool depletion and estimating connected drainage volume. The deconvolution procedures help calibrate and/or reconcile geosciences-defined volumetric resource sizes, map remaining reserves, and help identify possible infill-drilling opportunities.