bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel Multiple Resolutions Design of Experiment/Response Surface Methodology for Uncertainty Analysis of Reservoir Simulation Forecasts
Authors: Li B. , Friedmann F. 
Published: December 2007

Abstract
Response surfaces (RS) are useful and simple proxies to simulators, which relate in a closed form output variables (oil recovery factor, oil rate, etc.) of a simulator to input parameters over the entire parameter space. These proxies can then be used to compute production forecast uncertainty profiles with Monte Carlo calculation, instead of relying on time consuming reservoir simulation.
Typically, design of experiment (DOE) and response surface methodologies (RSM) are used to both identify statistically significant factors and to generate RS. RS are usually low order polynomials, which are generated by using the regression method. These methodologies work well if response surfaces are smooth with weak non-linearity. However, when these polynomials fail to meet reasonable accuracy criteria, adding more points to the design will only marginally improve RS accuracy. Response surface methodology can be adapted for such cases by using interpolation methods (Kriging, Spline, etc.) instead of regression method. But, most interpolation methods tend to smooth out non-linearity. These interpolated proxies can become substantially inaccurate, if: Non-linear effects are very strong;The non-linearity is not uniformly distributed throughout the parameter space.
In this paper, we introduce a novel RSM and its supporting DOE methodology to construct response surfaces as proxies of a simulator when input factors of the simulator such as faults cause strong non-linear effects. These methodologies are used to generate RS of arbitrary shapes by iteratively interpolating on a multilevel grid in the experimental space, which allows the local subdivision of the parameter domain. New partitions and interpolation points are added adaptively in the selected parameters regions, if local errors of the constructed response surface exceed a pre-selected threshold. The art of these methodologies consists in: Splitting the whole domain into sub-domains of multiple scale levels, where the components of a RS can be accurately modeled with ‘thin plate’ spline interpolants. The resultant RS is obtained by combining its global and local components.Achieving adequate RS accuracy with the minimum number of simulation runs.
We modify the SPE9 Benchmark problem to investigate the method's validity and efficiency. We compare it with traditional DOE and RSM methodologies. Finally, we perform Monte Carlo simulation using the RS proxies to assess uncertainty of the production forecasts. Results show that the presented methodologies work accurately and efficiently for problems with strongly non-linear effects, especially when the non-linear effects are non-uniformly distributed.
Implementation of Adjoint Solution for Optimal Control of Smart Wells
Authors: Sarma P. , Aziz K. , Durlofsky L. J. 
Published: December 2007

Abstract
Practical production optimization problems typically involve large, highly complex reservoir models, thousands of unknowns and many nonlinear constraints, which makes the numerical calculation of gradients for the optimization process impractical. This work explores a new algorithm for production optimization using optimal control theory. The approach is to use the underlying simulator as the forward model and its adjoint for the calculation of gradients. Direct coding of the adjoint model is, however, complex and time consuming, and the code is dependent on the forward model in the sense that it must be updated whenever the forward model is modified.
We investigate an adjoint procedure that avoids these limitations. For a fully implicit forward model and specific forms of the cost function and nonlinear constraints, all information necessary for the adjoint run is calculated and stored during the forward run itself. The adjoint run then requires only the appropriate assembling of this information to calculate the gradients. This makes the adjoint code essentially independent of the forward model and also leads to enhanced efficiency, as no calculations are repeated. Further, we present an efficient approach for handling nonlinear constraints that also allows us to readily apply commercial constrained optimization packages. The forward model used in this work is the General Purpose Research Simulator (GPRS), a highly flexible compositional/black oil research simulator developed at Stanford University.
Through two examples, we demonstrate that the linkage proposed here provides a practical strategy for optimal control within a general-purpose reservoir simulator. These examples illustrate production optimization with conventional wells as well as with smart wells, in which well segments can be controlled individually.
Effect of Grid Deviation on Flow Solutions
Authors: Wu X. H. , Parashkevov R. R. 
Published: December 2007

Abstract
The two-point flux, finite volume method (FVM-2P) is the most widely used method for solving the flow equation in reservoir simulations. For FVM-2P to be consistent, the simulation grid needs to be orthogonal (or K-orthogonal if the permeability field is anisotropic). It is well known that cornerpoint grids can introduce large errors in the flow solutions due to the lack of orthogonality in general. Multi-point flux formulations that do not rely on grid orthogonality have been proposed, but these methods add significant computational cost to solving the flow equation.
Recently, 2.5D unstructured grids that combine 2D Voronoi areal grids with vertical projections along deviated coordinate lines have become an attractive alternative to corner point gridding. The Voronoi grid helps to maintain orthogonality areally and can mitigate grid orientation effects. However, experience with these grids is limited.
In this paper, we present an analytical and numerical study of these 2.5D unstructured grids. We focus on the effect of grid deviation on flow solutions in homogeneous but anisotropic permeability fields. In particular, we consider the grid deviation that results from gridding to sloping faults. We show that FVM-2P does not converge to the correct solution as grid refines. We further quantify the errors for some simple flow scenarios using a technique that combines numerical analysis and asymptotic expansions. Analytical error estimates are obtained. We find that the errors are highly flow dependent and they can be global with no strong correlation with local non-orthogonality measures. Numerical tests are presented to confirm the analytical findings and to show the applicability of our conclusions to more general flow scenarios.
Spatial Error and Convergence in Streamline Simulation
Authors: Jimenez E. , Sabir K. , Datta-Gupta A. , King M. J. 
Published: December 2007

Abstract
Streamline models are routinely used for waterflood optimization and management, and are being extended to more complex processes, e.g., compositional simulation. Despite these new developments, no systematic study has examined the underlying numerical spatial and temporal discretization errors in streamline simulation and their convergence. Such studies are a prerequisite to determining the optimal density of streamlines during simulation and ensuring the resulting accuracy of the solution.
In this paper we first examine transverse spatial errors, e.g., errors due to the number or placement of streamlines. We provide an analytic proof and a numeric demonstration of the order of spatial convergence of the mass balance discretization error. Both global and local calculations are performed, and demonstrate the impact of stagnation regions on the order of convergence. A second transverse error arises for faulted grids, where lack of flux continuity at cell faces can lead to incorrect trajectories. These trajectory errors are of zeroth order, and can only be resolved by introducing additional degrees of freedom into the streamline velocity model. Longitudinal spatial errors also arise, and are associated with the inaccurate calculation of time of flight across cells.
We show that the commonly used algorithm for corner point cells leads to inaccurate time of flight calculations for stratigraphic grids, depending upon aspect ratio. We provide a simple and exact means of calculating the time of flight for arbitrary corner point cells, or unstructured grids, in two or three dimensions, for either compressible or incompressible flow. Finally, using this new time of flight formulation, we analyze a series of cross-sectional finite difference simulations to identify grid orientation errors in the numerical calculation of flux and spatial error.
Optimizing Wellbore Design Using Solid Expandable Tubular and Bi-Center Bit Technologies
Authors: Morrison W. , Baggal Z. , Baxendale B. , Boudreaux R. 
Published: December 2007

Abstract
Throughout the oil and gas industry a need exists to reduce hole size and subsequent casing strings to reach the pay zone in a safe manner with appropriate zonal isolation of the various formations. Benefits in achieving such well design can be economically advantageous to the operator.
In certain fields of Saudi Arabia, a relatively thin gas cap exists at the top of the Arab-D oil-producing zone. Isolating this gas cap is necessary to prevent future production from the gap.
In wells where a gas cap is expected, 300 to 400 ft of high angle 8-1/2 in. hole is drilled and cased off with a 7 in. liner. A 6-1/8 in. production hole is then drilled horizontally to total depth (TD).
Experimental and Numerical Studies of Gas/Oil Multicontact Miscible Displacements in Homogeneous Porous Media
Authors: Al-Wahaibi Y. M. , Muggeridge A. H. , Grattoni C. A. 
Published: December 2007

Abstract
Both vaporizing and condensing miscible gas floods are being conducted in a large number of reservoirs worldwide. The performance of these gas floods is usually determined via a combination of laboratory analysis and compositional simulation. However the ability of numerical simulation to correctly predict the progress of a multi-contact miscible displacement has not been fully verified
This paper investigates the physical processes occurring during multi-contact miscible displacementthe ability of the Coats correlation to model the changes in gas-oil relative permeabilities with interfacial tension (IFT) and the associated inaccuracies in predicted oil recoverythe importance of gas/oil disequilibrium on the prediction of oil recovery and gas-oil ratio
These objectives are achieved by using a commercial compositional simulator to predict the behaviour of multicontact miscible (MCM) floods in well-characterised, bead-pack experiments. Both condensing and vaporizing drives are investigated using a ternary liquid system that exhibits an upper critical point at ambient conditions. Relative permeabilities as a function of IFT were obtained independently from displacement experiments. Glass bead-packs permitted the visualisation of the displacements whilst the effluent profiles in terms of composition and phase volume versus time were measured using a calibration with refractive index of the fluids.
Condensing and vaporizing gas-drive displacements were very efficient with about 90% of the oil in place recovered at one pore volume injected. Compared to immiscible displacements, breakthrough and total recoveries were increased by 8% and 20% respectively. However, in both condensing and vaporising drives, the compositional simulation (that assumes equilibrium conditions) over-predicted oil recovery. Further simulations identified that these errors are due to inaccuracies in Coats’ correlation describing the behaviour of relative permeabilities as miscibility is approached and/or the fact that the produced fluids were not in compositional equilibrium.
A New Technique in Acquiring High Quality Image Logs in Deviated & Horizontal Wells: Case History
Authors: Talabani S. , Efnik M. , Baradi A. , Salim B. 
Published: December 2007

Abstract
Well bore images become increasingly important in identifying formation features and their possible extent.There are two different tools that acquire image data, acoustic and micro-resistivity.Both tools faced difficulties and challenges in acquiring quality data over the deviated and horizontal section of a well.
To perform quality image data in deviated and horizontal section of a well is difficult because of; firstly, drilling rogues, deviated and horizontal section, and these results in poor pad-wall contacts.Therefore, the quality of the resistivity image data is highly affected by the drilling fluid, along with the acoustic data.Secondly, poor mud properties that behaves as a blocking medium to acquire quality data.
A new technique requires modifying in both drilling and mud properties has been applied in different fields with high success.This new technique requires certain bottom hole assembly and drilling parameters, along with drilling fluid properties to better drill smooth holes.
The new technique resulted in smooth horizontal section and better in the deviated section, therefore, better pad-wall contact.Images from both; resitivity and acoustic modes provided high quality data acquisition.As a result, geological features were very clear by the image logs after the implementation of this new technique.
In this paper, the new technique is explained along with case histories from three different fields of the image logs are presented and compared to previous poor quality logs.
Integrated Approach for Improving Development of a Mature Field
Authors: Xiaoguang L. , Xuewen Z. , Sincock B. , Handono B. W. , Mayanullah F. 
Published: December 2007

Abstract
Makmur Field, South Sumatra, Indonesia, is a faulted anticlinal rollover with its major mutli-layer reservoir of distributary mouth bar, delta front sheet, and sub-aqueous channel sand. The field reached its production peak at end of 2001. In order to hold back the bottom or peripheral water encroachment, arrest promptly production declining, and ensure the maximum final recovery, integrated reservoir characterization including detailed microfacies and structure mapping, 3D geostatistic modeling, and subsequent reservoir simulation coupled with routine drainage radius analysis have been conducted. Meanwhile, pressure build-up test and production monitoring were optimized and selected performed.
The effective reservoir management including development infilling, optimized well sidetracking, dual string well completion, gas lifting, active workover operation, as well as drilling of injector and optimization of facility utilization for water injection enhancement has been implemented, which provided a road map for improving the field development. Application of the integrating reservoir management techniques resulted in substantial added reserve and mitigated pressure dropping. The successful infilling and water shut in workover have obviously arresting production declining rate.
Evaluation and Field Applications of Water Treatment Residue as a Profile Control Agent
Authors: Tianjiang H. , Huating Z. , Zongtian L. , Bin Y. , Puchun Z. 
Published: December 2007

Abstract
A great amount of residue from water treatment process in water-flooded oilfields has gradually accumulated and thus caused serious environmental pollution. The water treatment residue is a grey suspension with its density of 1.08g/cm3, and mainly contains over 65% light CaCO3, MgCO3, CaSO4, Fe2S3 and Ca(OH)2, etc. We made laboratory tests, such as microphotograph and the comparison of the core permeability to kerosene, cast model image analysis parameters, mercury injection capillary pressure curve parameters and scanning electron microscope porosity variation before and after profile control. The results indicate that the water treatment residue is of strong profile control and plugging capability, resistance to erosion and long effective period, and thus can be used as a cheap raw material for profile control. In the past 8 years, totally 60164m3 water treatment residue has been used for profile control of 151 wells, with the success ratio of 98% and effectiveness ratio of 83.2%. The field tests show that the starting pressure and injection pressure of the injection wells increased, the apparent injectivity coefficient decreased, the injection profile was obviously improved, and the injection wells achieved long average service life. Thus, more 28381 tons of oil was recovered from the corresponding oil wells, with 3069.55×104 Yuan benefits and a remarkable input output ratio of 1:8.6. The successful application of the water treatment residue as a profile control agent both reduces environmental pollution and converts bane into boon.
Quantification of Asphaltene and Wax Sludge Build-up in Crude Oil Storage Facilities
Authors: Leontaritis K. J. 
Published: December 2007

Abstract
At some thermodynamic conditions, asphaltenes flocculate into larger, almost spherical particles that have a specific gravity of 1.05 to 1.10. Work is cited here that indicates that asphaltene stable colloids exist in oil as very minute particles and that their pre-flocculation sizes are in the range of about 10 to 15 Å This corresponds to 334 and 1,128 molecular weight respectively, assuming asphaltene spherical colloids and an experimentally determined asphaltene density of 1.06 g/cm3. The reason for this high specific gravity of asphaltene particles compared to the rest of the molecules of oils is that they consist mostly of asphaltenes and resins, the heaviest constituents of oils. Roughly, resins have specific gravities of 0.95 to 1.0 and asphaltenes 1.1 to 1.2. Because of their high specific gravity asphaltene particles settle by the force of gravity in storage systems where the convection currents and shear forces are minimal. Some of these particles are large enough to overcome the convection currents and shear forces and settle in large separators and occasionally in large pipes due to Stoke's law effects, especially at elbows changing the direction of flow where the particles impinge against the pipe wall and are temporarily halted.
Wax precipitation often results in the formation of sub-micron wax spherical particles that also settle under the influence of gravity. Although paraffin waxes have specific gravities around 0.8 to 0.85, field waxes have higher specific gravities, usually higher than 0.9, because they usually co-precipitate with asphaltenes and resins, if present. Hence, in oils that contain asphaltenes and resins, precipitating waxes do settle by gravity. It has been shown that asphaltenes and resins are considered responsible for causing the formation of amorphous spherical wax crystal particles rather than wax needle crystals. Both flocculated asphaltene particles and crystallized wax particles agglomerate to form very large micron-level particles whose molecular weights run in the hundreds of thousands or millions. These large particles settle fairly quickly in storage systems.
This paper presents a modeling methodology for the simulation of sedimentation of asphaltene and wax particles in both onshore and offshore storage systems. The asphaltene and wax particle size distribution is usually available from microscopic observations, filtration, and thermodynamic models. The sedimentation calculation is done by assuming that the particles have settled and are at gravimetric equilibrium. Two examples are presented: one 1,000,000-barrel FPSO case and one 250,000-barrel oil storage tank case. Both the FPSO and the tank had lost a substantial fraction of their capacity due to accumulation of asphaltene and wax sludge.
Oilfield Reservoir Souring During Waterflooding: A Case Study with Low Sulphate Concentration in Formation and Injection Waters
Authors: Cavallaro A. N. , Martinez M. E. Gracia , Ostera H. , Panarello H. , Cordero R. R. 
Published: December 2007

Abstract
A case study is presented which addressed the origin of Hydrogen Sulphide (H2S) in produced gas associated with the oil in Las Heras - Cerro Grande oilfield in Gulf of San Jorge Basin, Argentina.
The reservoir was initially sweet. However, after waterflooding an increase in H2S concentration was detected in several wells. The H2S amount varies across the field with the highest values found in wells where water injection was initiated and the wells produce with a high water cut.
Knowledge of H2S origin contributes to effective control and therefore, to reduce environmental risk, minimize emissions, improve quality of produced hydrocarbons and reduce corrosion rate.
The main stages followed include, H2S measurements, H2S source identification and mitigation treatments.
The possible mechanisms of reservoir souring have been analyzed by sulphur isotope ratio analysis. These results have been integrated with geological factors and other parameters related to waterflooding.
This case is unusual because of water composition. The formation and injection waters have low salinity and are not rich in sulphate ion concentration, very different from sea water composition. Nutrients such as fatty acids are present in both formation and injection waters.
The increase in H2S production is attributed to sulphate reducing bacteria (SRB) living in the reservoir. The proposed model to explain H2S origin suggests a closed system with reactive-limited reaction where H2S production is controlled by low sulphate concentration present in waters.
A strong correlation was demonstrated between produced H2S, injection water parameters and subsequent souring. A decrease in sulphate concentration present in water production appears to correspond with an increase in H2S concentration.
At present, the produced gas is being treated with scavengers. A nitrate injection project is being analyzed to control reservoir souring. The development of a biofilter to oxidize H2S in plant treatment is in laboratory phase.
New Ultra-lightweight Cementing Technology Proven with Case Studies, Combines Benefits of Current Leading Methodologies
Authors: Kulakofsky D. , Araujo O. , Self F. , Mora A. , Hendriks P. , de Mestre P. 
Published: December 2007

Abstract
As the global demand for energy increases, operators are being forced to drill in increasingly challenging environments. Cementing across highly depleted zones and weaker formations requires a dedicated engineering focus and low-density cements that are stretching the limits of current technology. If cement cannot be successfully circulated, a large impact on the drilling cost can be experienced and delays in production delivery can occur due to the required remedial work.
Historically, the industry has relied on two primary technologies for the creation of ultra-light cement slurries - either foaming base cement with nitrogen or through the addition of microspheres to the slurry. While both of these technologies are considered premium solutions and have been used successfully for a number of years, they each have distinct advantages and also limitations when compared to one another.While ideal for certain situations, neither can be used to cover the entire spectrum of today's ever-increasing spectrum of challenges.
This paper presents case histories from Mexico and Oman showing how both technologies, foam and microspheres, have been used in the same design to stretch current lower slurry-density limits, allowing us to meet ever-challenging operational demands. Along with the case histories, guidelines are provided for how to best use these technologies. Details provided from the case histories illustrate how the advantages of both technologies were maximized, while their limitations were minimized.