bluuebunny/crossref_metadata_2025_split huggingface dataset:
Event-Targeting Model Calibration Used for History Matching Large Simulation Cases
Authors: Selberg Stig , Schulze-Riegert Ralf , Stekolschikov Konstantin 
Published: December 2007

Abstract
Large simulation models with excessive simulation time are traditionally a challenge for the reservoir engineer. This paper introduces a new concept of Event Targeting Model Calibration used for History Matching and Uncertainty Quantification in Reservoir Simulation. It is shown that the history matching process of large reservoir simulation models can be significantly improved by coupling different experimental design, optimization and analysis techniques.
Assisted history matching techniques using stochastic and direct search methods have already proven to outperform manual workflows on small and moderate size simulation models. The application of the same techniques and methodology when confronted with the largest simulation models (defined by long simulation times) have proven challenging. A more sophisticated use of the assisted history matching tool box is necessary to utilize CPUs for multiple simulation models as efficient as possible even if distributed computing capabilities are available.
The paper describes a workflow employing assisted history matching techniques to handle ‘monster’ simulation models. An Event Targeting Model Calibration work process is introduced which focuses on key historical events and divides the production history into main time periods. The optimization algorithms usually used in assisted history matching studies are replaced by experimental design methods to investigate the different time periods. Analysis techniques like a newly implemented cluster analysis is used to identify alternative history matched models in a multi-objective optimization formulation. Optimization algorithms are finally used for fine-tuning purposes. In this framework, a remarkable improvement of both the history matching process and uncertainty quantification is possible. This is a significant break through, improving the capability of understanding reservoir uncertainties for large field developments.
This paper summarizes experiences from several different complex history matching studies and outlines guidelines to apply state-of-the-art optimization techniques in combination with experimental design methods to the problem of History Matching and Uncertainty Quantification of large simulation cases.
The Mythical Second Fracture and Its Optimal Placement for Maximizing Production
Authors: Surjaatmadja Jim B. 
Published: December 2007

AbstractPlacing a fracture in a formation is obviously well understood in our industry and has been practiced successfully for quite some time. Recently this capability was refined to enable initiation of a fracture into a specific direction through the introduction of super-high-energy jetting. Despite the developments and experience in fracturing technology and know-how, it has still not been possible to know where a far-field fracture goes—we know it will go to the local minimum stress direction—but we do not know what direction that will be. It is most probable that the far-field fracture will go to a less-than-desired area in the formation and result in only an "acceptable" improvement in production.Recently, it has been shown that refracturing actually creates new fractures in the formation, rather than simply reopening old fractures, as was commonly thought. Even reopened fractures are now known to result in new areas being reached by the fractures. It is the opinion of this paper that these new fractured areas are not substantially different from the areas reached by the first fracture because local depletion enhances the effects of the original stress regime.This paper discusses the generation of multiple, consecutive fractures created in a way that enables them to reach formations in a manner not reached before using conventional means. In this scheme, the first fracture achieves "acceptable" production goals. If the process stopped at that point, the expense for this "mediocre" production increase would be high. However, in the new process, a second fracture is quickly initiated to take advantage of the stress modification created from the first fracture, allowing the second fracture to reach more productive rock not accessible to the first fracture. This paper will present field data that supports the feasibility of this concept. Various situations where this approach could reap substantial benefits are also presented.
Parallelization on Unstructured Grids
Authors: Usadi Adam , Mishev Ilya , Shaw Jason , Wiegand Klaus 
Published: December 2007

Abstract
We describe experiences with parallelizing real models using an unstructured reservoir simulator on shared memory machines. Using ExxonMobil's proprietary reservoir simulator, EMpowerTM, which contains an object oriented data hierarchy which describes a fully unstructured mesh, a fully integrated well and surface facility network, and a highly flexible, user specified well management capability, we will show how parallelization is performed at a high level through several variants of data partitioning adapted to the specific algorithmic needs. Property calculations, Jacobian construction, matrix solution methods, and well management may use a variety of different data structures, partitioning, and parallel execution schemes. We discuss mechanisms for addressing problems encountered.
Staircase Lifting of Oil Using Venturi Principle: A New Artificial-Lift Technique
Authors: Gupta Siddhartha 
Published: December 2007

Abstract
Artificial lift systems are now being considered of extreme importance as the reserves across the globe are depleting and the wells are unable to flow naturally. Over the years a number of artificial lift techniques have evolved as a result of extensive research and ground work. All the systems have proven their worth by increasing the productivity of the field by many folds. But each of these artificial lift systems has economic and operating limitations that eliminate it from consideration under certain operating condition. However all the conventional artificial lift systems have a common feature. The energy added to the lift the fluid from the wellbore is lost in the process and cannot be utilized for some other operation. This paper describes a new technique of artificial lift which uses the concept of venturi to lift the fluid to the surface. A high velocity power fluid is used to create drawdown at the throat of a surface venturi and this pressure drawdown is transmitted downhole by pressure tappings. The drawdown lifts the fluid through the production tubular in a stepwise manner. The power fluid coming out from the other end of the venturi is used to drive a turbine which generates power as a result. This power is used to operate the inlet compressor thus the cycle being completed. After startup, effectively, no energy is used up to keep operating the system.
The system is of immense economic benefit as the operating expenditures are low. Also this system uses zero-cost air as power fluid. It is a space efficient package which can be used on offshore locations as well.
The paper describes the individual components of the system and the calculations involved therein. The economic and technical comparison of this system with the conventional methods is also enlisted.
The Importance of Hole Quality for Effective Image Log Interpretation Clearly Demonstrated in an Eight Well Program in Kuwait
Authors: Jumah Saud , Saleh Khaled , Al-Mayyan Haitham I. , Turner Mike 
Published: December 2007

Abstract
The objective of supplying real time LWD or FE information (Logging While Drilling and Formation Evaluation) should be to enable the client to make quick, accurate decisions on the formations being drilled, thus reducing and minimizing the geological uncertainty and maximizing or increasing the well bore exposure in the desired structure. During the course of drilling an 8 well Horizontal drilling program for the Kuwait Oil Company (K.O.C.) in the Burgan Field, Kuwait it became apparent that there was a need for clearer and better quality real time log information to enable the Drilling team to make quick decisions on were to place the well within the structure. This short paper will show the step change bought about in 3 of the wells drilled and the success and benefits realized by using long gauge PDC bits combined with a specialized short bearing pack motors, not only in the quality of the real time and recorded logs but in the over all bore hole quality as well.
Effects of Frictional Geological Discontinuities on Hydraulic Fracture Propagation
Authors: Zhang X. , Jeffrey R. G. , Thiercelin M. 
Published: December 2007

Abstract
This paper presents numerical results for a hydraulic fracture interacting with a frictional geological discontinuity in layered sedimentary rocks. A 2D hydraulic fracture model has been developed that can consider the details of the interaction and includes elastic rock deformation coupled to both fluid flow and frictional slippage. The interaction can result in fracture blunting, crossing or entering the interface, depending on modulus and stress contrasts, as well as the shear strength of the discontinuity. The numerical results are compared to experimental and field observations. When hydraulic fractures interact with long geological discontinuities, fracture growth can be stopped or retarded by the process. Treating pressure is increased by the large pressure gradients generated at offsets in the fracture path. Proppant transport can be impeded by such offsets because of the associated narrowing of fracture width. In some cases, the hydraulic fracture cannot easily enter frictional discontinuities when the interfaces have low frictional strength. In addition, pre-existing flaws are likely to serve as sites for re-initiation, allowing further hydraulic fracture growth into the intact side of the discontinuity. A higher closure stress acting in the intact rock favors arrest of the hydraulic fracture at the discontinuity, e.g., when a fracture attempts to cross a soft-to-stiff bedding plane. As a part of the interaction, the main hydraulic fracture will typically also lose fluid into cross-cutting frictional discontinuities.
Efficient and Robust Reservoir Model Updating Using Ensemble Kalman Filter With Sensitivity-Based Covariance Localization
Authors: Devegowda Deepak , Arroyo-Negrete Elkin , Datta-Gupta Akhil , Douma S. G. 
Published: December 2007

Abstract
Recently Ensemble Kalman Filtering (EnKF) has gained increasing attention for history matching and continuous reservoir model updating using data from permanent downhole sensors. It is a sequential Monte-Carlo approach that works with an ensemble of reservoir models. Specifically, the method utilizes cross-covariances between measurements and model parameters estimated from the ensemble. For practical field applications, the ensemble size needs to be kept small for computational efficiency. However, this leads to poor approximations of the cross-covariance matrix, resulting in loss of geologic realism. Specifically, the updated parameter field tends to become scattered with a loss of connectivities of extreme values such as high permeability channels and low permeability barriers, which are of special significance during reservoir characterization.
We propose a novel approach to overcome this limitation of the EnKF through a ‘covariance localization’ method that utilizes sensitivities that quantify the influence of model parameters on the observed data. These sensitivities are used in the EnKF to modify the cross-covariance matrix in order to reduce unwanted influences of distant observation points on model parameter updates. In particular, streamline-based analytic sensitivities are easy to compute, require very little extra computational effort and can be obtained using either a finite difference or streamline-based flow simulator.
We show that the effect of the covariance localization is to increase the effective ensemble size. But key to the success of the sensitivity-based covariance-localization is its close link to the underlying physics of flow compared to a simple distance-dependent covariance function as used in the past. This flow-relevant conditioning leads to an efficient and robust approach for history matching and continuous reservoir model updating, avoiding much of the problems in traditional EnKF associated with instabilities, parameter overshoots and loss of geologic continuity. We illustrate the power and utility of our approach using both synthetic and field applications.
Successful Breaker Optimization for Polyacrylamide Friction Reducers Used in Slickwater Fracturing
Authors: Carman P. S. , Cawiezel K. E. 
Published: December 2007

Abstract
To pump a high-rate fracture stimulation with fresh water or brines, a friction reducer must be employed. Most friction reducers used in slickwater fracture stimulation are high-molecular-weight polyacrylamide emulsions. Since these friction reducers are typically pumped at low concentrations (0.5 to 2 gpt), the industry belief has been that these polymers are causing minimal damage to the formation. There has also been a perception that the polyacrylamide polymer is difficult to degrade. However, fracture stimulations in areas such as the Barnett Shale use very large quantities of water with several stages per well which introduces large volumes of friction reducer into the formation. Because these large treatments are now widely used, several production companies have recently expressed concerns about the possible fracture and formation damage caused by these friction reducers. For this reason, a study was undertaken to find suitable breakers to effectively reduce the size (or molecular weight) of the polyacrylamide polymer chains and, therefore, reduce fracture and formation damage. Several conventional oxidizers were chosen and screened to determine if they could effectively reduce the viscosity of the polyacrylamide polymer. The molecular weight degradation of the polymer was then measured using a molecular weight cut-off (MWCO) filtration technique to determine the size and percentage of polymer fragments. Surprisingly, most of the breakers tested showed some reduction in viscosity and in molecular weight. Additional laboratory testing was then conducted to ensure that the addition of breaker to the friction reducer did not adversely affect polymer hydration or friction-reduction performance. This study reports on the results of the testing and shows which breakers were most effective in reducing the molecular weight of the polyacrylamide polymers used as slickwater friction reducers.
A New Approach to Automatic History Matching Using Kernel PCA
Authors: Sarma Pallav , Durlofsky Louis J. , Aziz Khalid , Chen Wen H. 
Published: December 2007

Abstract
Efficient history matching of geologically complex reservoirs is important in many applications, but it is central in closed-loop reservoir modeling, in which real-time model updating is required. Within the context of closed-loop reservoir modeling, the two approaches receiving the most attention to date are ensemble Kalman filtering and gradient-based methods using Karhunen-Loeve representations (eigen-decomposition) of the permeability field. Both of these procedures are technically appropriate only for random fields (e.g., permeability) characterized by two-point geostatistics (multi-Gaussian random fields). Realistic systems are much better described by multipoint geostatistics, which is capable of representing key geological structures such as channels. History matching algorithms that are able to reproduce realistic geology provide enhanced predictive capacity and are therefore more suitable for use with field optimization. In this work, we apply a new parameterization, referred to as a kernel principal component analysis (kernel PCA or KPCA) representation, to model permeability fields characterized by multipoint geostatistics. Kernel PCA enables preserving arbitrarily high order statistics of random fields, thereby providing the capability to reproduce complex geology. The KPCA representation is then combined with an efficient gradient-based history matching technique. The linkage of KPCA for modeling geology with gradient-based history matching is very natural as the KPCA representation is differentiable and gradients with respect to geological parameters can be readily computed. The overall procedure is then applied to several example cases, including synthetic models and a model of a real reservoir. The approach is shown to better reproduce complex geology, which leads to improved history matches and better predictions, while retaining reasonable computational requirements.
Understanding Formic Acid Decomposition as a Corrosion Inhibitor Intensifier in Strong Acid Environments
Authors: Cassidy Juanita M. , McNeil Robert I. , Kiser Chad E. 
Published: December 2007

Abstract
For many years formic acid has been used to intensify, or aid in, the performance of acid corrosion inhibitors in hydrochloric acid-based fluids used for stimulation procedures in the oilfield industry. Even so, the picture of how formic acid accomplishes this and under what conditions it functions is incomplete.
One theory for how formic acid aids in inhibition is that it undergoes a dehydration reaction to form water and carbon monoxide (CO), a known corrosion inhibitor.HCOOH→CO+H2O
This paper confirms that CO is produced by decomposition of formic acid in strong acids under downhole conditions. In addition, the conditions for the release of CO were found to be dependent on several variables, including temperature, acid strength, and alloy. Delineation of these conditions is important for effective implementation of formic acid as a corrosion inhibitor intensifier.
Simulating Gravity Drainage and Reinfiltration With a Subdomain-Dual-Permeability Hybrid Fracture Model
Authors: Rubin Barry 
Published: December 2007

Abstract
In this paper we describe how we have used finely gridded single porosity reference models to simulate the behavior of gravity drainage in fractured secondary gas caps/gas invaded zones with and without block to block reinfiltration.
These models were used as reference solutions in the development of the Subdomain-Dual Permeability Dual Continua model (SD-DK model). This extension of the classic Subdomain model 1 can simulate gravity drainage flow due to both direct matrix flow (capillary continuous) and matrix to matrix reinfiltration from fractures without the use of pseudo functions.
The behavior of the SD-DK model compares well with the fine grid single porosity reference models in situations where vertical oil drainage with capillary continuity between vertical matrix blocks is assumed or where vertical oil drainage is assumed to occur entirely due to reinfiltration.
In addition the model has been extended (heuristically) to allow it to model both drainage mechanisms occurring simultaneously (capillary continuous gravity drainage and reinfiltration).
The paper includes the details of the formulation as well as examples comparing the SD-DK technique to reference solutions and existing models.
Adaptive Multiscale Streamline Simulation and Inversion for High-Resolution Geomodels
Authors: Stenerud V. R. , Kippe V. , Datta-Gupta A. , Lie K. -A. 
Published: December 2007

Abstract
A particularly efficient flow solver can be obtained by combining a recent mixed multiscale finite-element method for computing pressure and velocity fields with a streamline method for computing fluid transport. This multiscale-streamline method has shown to be a promising approach for fast flow simulations on high-resolution geologic models with multimillion grid cells. The multiscale method solves the pressure equation on a coarse grid while preserving important fine-scale details. Fine-scale heterogeneity is accounted for through a set of generalized, heterogeneous basis functions that are computed numerically by solving local flow problems. When included in the coarse-grid equations, the basis functions ensure that the global equations are consistent with the local properties of the underlying differential operators. The multiscale method offers a substantial gain in computation speed, without significant loss of accuracy, when the multiscale basis functions are updated infrequently throughout a dynamics simulation.
In this paper we propose to combine the multiscale-streamline method with a recent ‘generalized travel-time inversion’ method to derive a fast and robust method for history matching high-resolution geologic models. A key point in the new method is the use of sensitivities that are calculated analytically along streamlines with little computational overhead. The sensitivities are used in the travel-time inversion formulation to give a robust quasilinear method that typically converges in a few iterations and generally avoids much of the subjective judgments and time-consuming trial-and-errors in manual history matching. Moreover, the sensitivities are used to control a procedure for adaptive updating of the basis functions only in areas with relatively large sensitivity to the production response. The sensitivity-based adaptive approach allows us to selectively update only a fraction of the total number of basis functions, which gives a substantial savings in computation time for the forward flow simulations.
We demonstrate the power and utility of our approach using a simple 2D model and a highly detailed 3D geomodel. The 3D simulation model consists of more than one million cells with 69 producing wells. Using our proposed approach, history matching over a period of 7 years is accomplished in less than forty minutes on an ordinary workstation PC.
A New Method of Calculating Water Invasion for Heavy-Oil Reservoir by Steam Injection
Authors: Dou Hongen , Chen Chuangchun , Chang Yuwen , Wang Xiaolin , Yu Jun , Wang Fenglan 
Published: December 2007

Abstract
Heavy oil production methods included the cyclic steam stimulation (CSS), steam flooding and steam assistant gravity drainage (SAGD). It is well known, when water invasion occurs in heavy oil reservoirs with edge/bottom water, for a long time, how much of the produced water comes from the steam injection process as oppose to edge/bottom water invasion? Reservoir engineers do not clearly understand the process, because after the steam condenses a part of the condensation comes to the surface and another part is stored within the reservoir itself. This is the problem that still gives reservoir engineers trouble. Through studying the production data of thermal recovery at the Liaohe oilfield, in China, for the first time, this paper reveals a new theory and calculation method that shows how to calculate water invasion from the bottom/edge water reservoir, therefore, a new concept of conversion rate was presented and a new parameter of steam-water ratio was defined, as k. new equations of calculating produced water invasion and water invasion of the remaining formation with bottom/edge water were derived according to the new parameter k. In addition, an estimation method of breakthrough time of bottom/edge is presented in this paper. The methods have been used to calculate and analyze the production performance of heavy oil with steam injection in Liaohe oilfield. The calculation results accord well with actual situation of heat-recovery reservoirs. Therefore, this method will be recommended to optimize production performance parameters of thermal recovery.