bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Polymers on the Structure and Deposition Behavior of Waxy Oils
Authors: Tinsley Jack F. , Prud'Homme Robert K. , Guo Xuhong , Adamson Douglas H. , Shao Susan , Amin Devang , Callahan Scott , Dettman Heather D. , Kriegel Robert , Saini Rajesh 
Published: December 2007

Abstract
Recent deposition studies have elucidated much of the underlying physics of wax deposition in crude oil pipelines. However, the physics behind polymer additives used to combat wax deposition has not been thoroughly studied. To this end, three types of polymers that have proved effective in reducing the yield stresses of waxy gels have been tested in yield closed-loop laboratory deposition cell. Tests with a multi-component wax solution with polymer additions of 0.1wt% showed that the thickness of the deposit could be estimated from calculations of the height of the cloud point above the cold surface. Such was the case with addition of poly(ethylene butene) polymers (PEB) and the wax solution with no polymer. Conversely, two maleic anhydride co-polymers (MAC) decreased the cloud point and prevented deposition unless the temperature of the cold surface was lowered below the cloud point. However, predictions of the deposit thickness based on cloud point did not hold if erosion occurred. Erosion was always associated with degradation of the microscopic crystal structure, in terms of shape and/or size. The most effective polymers, the MACs, produced the largest change in crystal structure and the most significant erosion. The polymers also produced deposits with the lowest wax contents and the smallest fractions of high molecular weight n-paraffins. However, one EVA polymer that led to thinner, eroding deposits also significantly increased the deposit wax contents, creating hard deposits that would be more difficult to remediate by pigging. Polymers that increased the wax content did not lower the cloud point, even though they may degrade the crystal structure. Thus the importance of both cloud point reduction and degradation of crystal structure was shown. Tests indicated that inhibition of nucleation kinetics may be important for some polymers. Although all polymers reduced the yield stress of the waxy oil when gelled, they did not all decrease deposition. Efficacy in both yield stress reduction and decreasing deposition could be grouped according to polymer type.
Fracture Propagation in High-Permeability Rocks: The Key Influence of Fracture Tip Behavior
Authors: Entov V. M. , Chekhonin E. M. , Detournay E. , Thiercelin M. 
Published: December 2007

Abstract
Pressure distribution at the tip of a hydraulic fracture is a key element for controlling fracture propagation. In low-permeability formations, under downhole reservoir conditions, a severe pressure drop occurs at the tip of the fracture and a lag zone develops due to fluid cavitation. Properly taking into account the controlling parameters of tip behavior has resulted in more accurate and robust fracture propagation models. However, the situation is still unclear in high permeability formations, because the formation fluid can invade the tip zone where the pressure drops below the far-field pore pressure. Moreover, the assumptions of the Carter leak-off model do not apply in this zone.
This work presents a fundamental study of fracture tip behavior in high permeability formations. We consider a steadily propagating fracture, taking into account the flow within the fracture, filtrate leak-off across the fracture faces, and kinetics of filter cake growth. The flow within the reservoir due to leak-off is described by the 2D pressure diffusion equation. The formation is elastic and fracture growth is based on Linear Elastic Fracture Mechanics.
Results show that the tip zone can be either a recirculation zone, in which the formation fluid enters the fracture and then get expelled back into the formation, or is completely filled with fracturing fluid. When the pressure at the tip is higher than the far-field pore pressure, a pressure wave propagates ahead of the tip with severe consequences on fracture propagation. Finally, the total energy consumption (which determines the net pressure) is primarily dissipated in viscous flow within the fracture, leak-off flow across the filter cake, and seepage flow induced by leak-off in the reservoir.
The flow within the reservoir due to leak-off is described by the 2D pressure diffusion equation. The formation is elastic and fracture growth is based on linear elastic fracture mechanics.
This work provides new insight for fracture propagation in highly permeable sandstones and allows us to understand some previously unexplained field and laboratory observations.
Effect of Sampling Strategies on Prediction Uncertainty Estimation
Authors: Erbas D. , Christie M. A. 
Published: December 2007

Abstract
Generating multiple history-matched reservoir models by stochastic sampling to quantify the uncertainty in oil recovery predictions has recently aroused interest in the industry. Coupling a stochastic sampling algorithm with a Bayesian analysis potentially allows incorporation of all sources of uncertainties including data, simulation and interpolation errors. However, the accuracy of the uncertainty estimations strongly depends on the sampling performance. In order to improve the robustness of the coupled Bayesian methodology, the factors that affect the accuracy of the estimations must be examined.
This paper investigates how different sampling strategies affect the estimation of uncertainty in prediction of reservoir production. The sampling strategy involves the choice of algorithm and selection of algorithm parameters in sampling the high-dimensional parameter space. We present examples of using both the Neighbourhood Algorithm (NA) and a Genetic Algorithm (GA) to generate history-matched reservoir models for a real field case from the North Sea.
A Method To Improve the Mass Balance in Streamline Methods
Authors: Kippe Vegard , Hægland Håkon , Lie Knut-Andreas 
Published: December 2007

Abstract
During the last decades, streamline methods have emerged as highly efficient simulation tools that are well-suited for e.g., history matching and simulation of large and complex reservoir models. Streamline methods are based on a sequential solution procedure in which pressure and fluid velocities are computed by solving a pressure equation on a grid in physical space and the fluid transport is computed by solving 1-D transport problems along streamlines. The sequential Eulerian-Lagrangian procedure is the key to the high computational efficiency of streamline methods. On the other hand, it necessitates mapping of saturations (or fluid compositions) back and forth between the Eulerian pressure grid and the Lagrangian streamlines. Unfortunately, this introduces mass-balance errors that may accumulate in time and in turn yield significant errors in production curves.
Mass-balance errors might be reduced by considering higher-order mapping algorithms, or by increasing the number of streamlines. Since the computational speed scales linearly with the number of streamlines, it is clearly desirable to use as few streamlines as possible. Here we propose a modification of the standard mapping algorithm that: (i) improves the mass-conservation properties of the method and (ii) provides high-accuracy production curves using few streamlines.
Mass conservation is improved by changing quantities in the transport equation locally, and we show that these modifications do not significantly affect the global saturation errors as long as a sufficient number of streamlines is used. Moreover, we propose an adaptive strategy for ensuring adequate streamline coverage. The efficiency and accuracy of the modified streamline method is demonstrated for Model 2 from the Tenth SPE Comparative Solution Project. Highly accurate production curves (compared to reference solutions) are obtained in less than ten minutes using one processor on a standard (Intel Core 2 Duo) desktop computer.
Development of a Methodology for Hydraulic Fracturing Models in Tight, Massively Stacked, Lenticular Reservoirs
Authors: Green Christopher A. , Barree Robert D. , Miskimins Jennifer L. 
Published: December 2007

Abstract
This paper describes and critically assesses a common methodology currently used to model hydraulic fractures in geologically complex, fluvial, tight gas reservoirs. A planar 3- D fracture simulator is used with a fully coupled fluid/solid transport simulator. The model incorporates a unique data set from the Piceance basin, Colorado, which produces hydrocarbons from the Cretaceous-age Mesaverde formation. Initially, vertical variations in geo-mechanical rock properties (Young’s modulus, Poisson’s ratio and Biot’s constant) were calculated from well logs. The results were then compared with previous work undertaken on the Mesaverde formation and carried out at the DOE/GRI MWX site. From this analysis, specific correlations were developed for rock properties derived from well logs on a foot-by-foot basis to be used in the hydraulic fracture model. Diagnostic mini-frac injection tests of individual sandstone reservoirs were used to confirm model inputs and develop a valid stress model.
Previous attempts to model hydraulic fracture growth in the Mesaverde have been hampered by a lack of detailed input data sets and the inability to accurately determine horizontal rock property variations. This paper outlines a method which uses micro-seismic/tiltmeter data to constrain and verify the model inputs. The resulting frac model is shown to have not only matched the fracture containment but also pressure matched the actual net surface pressure data in this extremely geologically complex area. From these results it is possible to get a better understanding of how fracs grow and interact with complex fluvial reservoirs, allowing operators to better optimize field well performance and completion methods in these geologic settings. Additionally, the minimum critical data required to develop such a model has been identified and will aid operators in developing their data acquisition programs. Although developed in the Rocky Mountain region, the presented technique can be extrapolated to other similar geologically complex reservoirs world-wide.
Implications of Geomechanical Analysis on the Success of Hydraulic Fracturing: Lesson Learned from an Australian Coalbed Methane Gas Field
Authors: Rahman Khalil , Khaksar Abbas 
Published: December 2007

Abstract
Hydraulic fracturing is a widely used technology in the petroleum industry to increase production rates from low- permeability reservoirs. It has also been successfully applied to coalbed methane gas development in many occasions. This paper presents an Australian field case of coalbed methane gas development where expensive fracture treatments did not yield the expected benefits. A comprehensive integrated geomechanical analysis was performed to understand the underlying causes for the failure. The geomechanical model consists of the magnitude and orientation of the three principal stresses, the pore pressure, and the rock strength. Fracture treatment data were used to estimate the least principal stress, vertical stress was determined from density logs, pore pressure was derived from direct field measurements, and rock strength values were determined from well logs and core measurements. The maximum horizontal stress (SHmax) magnitude was constrained by modeling the stress and pressure conditions consistent with the observation of wellbore breakouts in image logs. The relative magnitude of principal stresses corresponds to a transition between Strike- Slip and Reverse Faulting stress regimes (SV ≤ Shmin ≤ SHmax) with an overall SHmax orientation of NE-SW. Fracture propagation simulations using boundary element modeling showed that a complex fracture growth under the influence of the current in-situ stresses could be the main reason for the fracture treatment failure. The study recommended a number of alternative configurations for well orientations and fracture treatments in the field considering the existing in situ stress and the complex fracture network. Also the interactions between the coal seam and different fracturing fluids have been studied to evaluate the formation damage aspects to recommend the formation compatible fracturing fluid. Presentation of these results in this paper is expected to give a general framework for successful hydraulic fracture treatments and example of specific implementation issues with respect to an Australian coalbed methane gas field.
Coiled-Tubing Gyro MWD Improves Kickoff Direction Accuracy for Cased-Hole CTD Re-Entry Drilling
Authors: Madarapu R. , Corson C. S. , Grant D. 
Published: December 2007

Abstract
Coiled tubing drilling (CTD) is an economical method of re-entering existing cased wells in mature fields to exploit bypassed reserves because of its versatility in accommodating a variety of candidates and its technological edge in drilling more efficiently.
In re-entry drilling, kicking off with the right bearing attenuates the single biggest issue when drilling long laterals—weight transfer problems. Correct re-entry wellbore placement from vertically cased wells has traditionally required many single-function trips. The magnetic interference from the steel casing makes the acquired magnetic tool face measurements from traditional instruments inaccurate. Verification of the kickoff direction is usually performed with a wireline multi-axis gyro instrument. This process can be time-consuming and still requires additional correctional runs or directional changes prior to beginning drilling in the desired direction toward the target.
Hence, the entire process of intervention, from setting a whipstock in the right orientation to drilling in the least tortuous direction from these vertically cased wells, requires a more efficient approach if CTD is to be a viable option in marginal projects.
This paper assesses the limitations in the current methods of kicking off and details an innovative approach to improve re-entry wellbore quality through the use of an integrated coiled tubing gyro measurement-while-drilling (MWD) instrument.
Use of Microbial DNA Probes as a Potential New Tool in Oil Exploration and Characterization
Authors: Kotlar Hans Kristian , Brakstad Odd Gunnar , Markussen Sidsel 
Published: December 2007

Abstract
There are numerous examples of microorganisms isolated from oil reservoirs, yet very little is known about the microbial ecology and in situ microbial metabolic processes of reservoirs. Such processes may have a great impact on oil quality and recovery. The oil reservoir constitutes a unique microbial habitat with respect to temperature, pressure, salinity, pH and nutrient availability. Even though oil reservoirs are considered anaerobic, also strains classified as more "aerobic" have been isolated and are thought to be of indigenous origin. Molecular methods have only recently started to be employed in exploring oil reservoir microbiology. Such analyses have mainly focused on determining the diversity of species present using 16S rDNA sequencing and other forms of direct sequence information. Through our biotech-project 16S ribosomal RNA gene libraries have been made on organisms found in different North Sea fields, fields in South America and Asia. From these libraries specific selected target organisms associated with oil and gas have been found. This has been developed into different DNA probe-like tests. It is interesting to note that similar bacteria have been isolated from different oil fields located very far from each other. This paper will focus on the use of this new non-invasive tool for finding/detection of oil. Field examples from differentiation of gas seeps and new evidence to the infill history of a North Sea reservoir will be given. This methodology can also be used for finding of new oil and gas in sensitive areas and for monitoring of existing production.
A Rigorous Pore-to-Field-Scale Simulation Methodology for Single-Phase Flow Based on Continuous Time Random Walks
Authors: Rhodes Matthew E. , Bijeljic Branko , Blunt Martin J. 
Published: December 2007

Abstract
We demonstrate a pore-to-reservoir simulation methodology and apply it to singe-phase flow. Traditional numerical methods are based on the discretization of partial differential equations with known spatially-dependent coefficients, such as porosity and permeability. However, in porous media flow we do not know a priori what the governing transport equations are − for instance, single-phase transport cannot be accurately described by an advection-dispersion equation − nor do we know the reservoir properties everywhere.
We propose a different approach that does not pre-suppose the functional form of the upscaled transport equations and which automatically accounts for uncertainty in the reservoir description. Single-phase transport is modeled as a continuous time random walk. Particles make a series of transitions between nodes with a probability ψ(t)dt that a particle will first arrive at a node from a nearest neighbor in a time t to t+dt. A top-down multiscale approach is used to find the flow field. At the micron scale, ψ(t) for particle transitions from pore to pore are found from modeling advection and molecular diffusion in a geologically representative network model. This ψ(t) is used to compute transport on the mm to cm scale. At larger scales, we represent the reservoir as a network of nodes connected by links. For each node-to-node transition, we compute an upscaled ψ(t) from a simulation of transport at the smaller scale. We account for small-scale uncertainty by interpreting ψ(t) probabilistically and running simulations for different possible realizations of the reservoir model. To make the number of computations manageable, ψ(t) is parameterized in terms of sub-scale heterogeneity and Peclet number, meaning that only a few representative simulations are required.
We demonstrate the methodology by finding ψ(t) for pore-scale flow and using it in a million-cell reservoir model. We show that the macroscopic behavior can be very different from that predicted by assuming that the advection-dispersion equation operates at the small scale. Small-scale structure does impact macroscopic transport; increasing the pore-level heterogeneity delays breakthrough and leads to longer late-time tails of the production since the solute spends more time in slow-flowing regions of the domain. We discuss extensions to multiphase flow and the development of a novel network-based probabilistic reservoir simulation approach.
Decline Analysis for Horizontal Wells of Intercampo Field, Venezuela
Authors: Dou Hong'en , Chen Changchun , Chang Yuwen , Fang Yanjun , Chen Xinbin , Liu Wei , Cai Wenxin 
Published: December 2007

AbstractIntercampo oilfield is characterized by heavy oil with mid-high permeability and high oil saturation, which is an unconsolidated reservoir driven by edge water and bottom water. This paper presents the oilfield's application of three decline analysis models to the 13 horizontal and 13 vertical wells of the oilfield respectively, as well as the comparison of the decline features between vertical and horizontal wells. The authors point out that the decline analysis models are not only applicable for vertical wells but also for horizontal wells. Although the water cut rising of horizontal wells are different from vertical wells, the authors emphasize the well type and reservoir properties are not associated with the decline analysis models. In regards to screening and comparing of decline analysis models; how to select and use the models; their application condition; and the models features are clearly presented in this paper.The paper introduces two new decline analysis models for horizontal wells. They have been applied to predict production rate of the oilfields, reservoirs, and wells, as well as their future trends. The results accord well with the actual data from the oilfield. The classical models screened out and the new models were recommended analyzing the production performance of the oilfields and reservoirs for the types of wells.
19F NMR Study of Ovalbumin Diffusion in Guar Filter Cake
Authors: Fu Lin , Pethica Brian , Prud'homme R. , Pacheco Carlos 
Published: December 2007

Abstract
Enzymatic degradation is commonly used to degrade the filter cakes formed from hydraulic fracturing fluids (guar solution). In this highly concentrated filter cake, enzymatic degradation kinetics is diffusion-controlled. It becomes crucial to understand the diffusion process of enzymes in the polysaccharide gel layer. The transport of a protein that mimics the enzyme protein (i.e. ovalbumin) in concentrated polymer solutions (hydroxylpropyl guar), including both translational diffusion and rotational diffusion, has been studied by NMR. Translational diffusion is required to degrade the filter cake over long length scales, but rotational diffusion is necessary for the enzyme to bind to the guar chains to initiate degradation. The proton NMR signal for protein/polymer systems is too complicated to be applied in practice. A CF3 group, which is chemically tagged to protein by reacting with S-ethyl trifluorothioacetate, is introduced to differentiate the protein from polymer matrix and reduce the complexity.
19F pulsed field gradient NMR is used to measure the translational diffusion coefficient, while T1 and T2 relaxation of the 19F signal is measured to obtain the rotational diffusion coefficient. Translational and rotational diffusion coefficients are compared with Stokes Einstein (SE) equation. Both diffusion coefficients deviate from Stokes Einstein (SE) equation significantly. For translational diffusion, this deviation indicates that on the length scale of the protein size the protein molecule feels inhomogeneity of the matrix polymer. This results in a 67% decrease in protein mobility when the matrix polymer concentration is only 5wt%. The rotational diffusion coefficient is found to stay relatively constant when the tracer size is much smaller than the mesh size of polymer matrix, which is consistent with the SE equation. But when the protein size is comparable to the mesh size of polymer solution, the SE model fails. In this range, proteins only feel a fraction of the hydrodynamic interaction of the polymer matrix and the relationship between the rotational diffusion coefficient and macroscopic viscosity is found to obey a power law. Further, experimental results are compared with effective medium theory and confined diffusion model, from which we can see that proteins are confined by "dynamic" polymer chains.