bluuebunny/crossref_metadata_2025_split huggingface dataset:
Disproportionate Permeability Reduction Due to Polymer Adsorption Entanglement
Authors: Al-Sharji H. H. , Grattoni C. A. , Dawe R. A , Zimmerman R. W. 
Published: December 2007

Abstract
Polymers in the form of either solutions or gels are being used to control water production, especially when oil bearing and water zones cannot be isolated. Results of field treatments have varied widely, but often no obvious reason can be given for the success or the failure of the treatment. The lack of understanding of the basic mechanisms by which polymers influence the flow of water and oil hinders a wider application of this process. The achievement of a disproportionate permeability reduction (DPR - reducing the water permeability while producing minimum reduction in the oil permeability) is crucial, and several mechanisms have been proposed to explain this effect. Among those mechanisms, polymer adsorption and lubrication effect are being thought as the main reason for DPR when polymers (without cross-linker) are used.
This paper presents a mechanistic study of the effect of polymer injection on single and two-phase flow. Experiments have been performed in glass micromodels, under both water-wet and oil-wet conditions. The oil and water end-point permeabilities have been obtained, before and after the injection of a cationic polyacrylamide, while observing the fluid distribution and flow patterns. During polymer injection, under water-wet conditions, polymer layers were seen to form and build-up on the crevices between the grains. This mechanism is known as adsorption-entanglement. Data on this phenomenon are scarce, and this paper presents the first visualization study of this phenomenon in porous media.
In water-wet models there was a significant permeability reduction to water, while there was no significant reduction in oil permeability. The entanglement of polymer reduces the area available for water to flow, whereas the oil, occupying the centre of the larger pores, was nearly unaffected by the polymer entanglement. In oil-wet models, where polymer layers were not observed, the oil and water effective permeability before and after polymer injection remained unchanged. Our results confirm that adsorption-entanglement for water-wet media, which produces the build-up of the polymer layers on the grain crevices, is a basic mechanism by which polymers can modify the flow characteristics and thus preferentially reduce the water relative permeability.
In-Depth Filtration of Macromolecules Induced by Bridging Adsorption in Porous Media
Authors: Zitha Pacelli L. J. 
Published: December 2007

Abstract
Previously, we developed a microscopic model for the bridging adsorption of flexible chains, during non-inertial flow of polymer solutions through granular porous media. Owing to its local character, that model does not take into account the filtration of the largest polymer molecules, while this filtration appears to be one of the essential features of bridging adsorption, from both fundamental and practical standpoints. During polymer placement for water control, for instance, polymer propagates over distances of several inches enabling filtration of polymer to take place.
In this paper, we develop a macroscopic model for layer and bridging adsorption during polymer flow through porous media. Our emphasis is on the filtration of the largest chains induced by bridging adsorption. In order to describe this effect, we introduce for the first time a space and time dependent probability (or fraction) of the largest chains. Our model condenses in a non-linear system of four partial differential equations describing polymer and the largest mass conservation and layer and bridging adsorption kinetics. The model appears to be relevant, beyond the description of bridging adsorption, to several in-depth filtration processes induced by flow and retention.
By physical arguments based upon previous experimental observations, we reduce the general equations to a simpler formulation for which we were able to derive an approximate analytical solution. We prove that, in one simple case, the concentration and the bridging adsorption probability profiles in the core decrease exponentially as a function of the distance from core inlet. The influence of the determinant parameters (velocity gradient, adsorption energy, etc.) is discussed. We show that the model is in good agreement with previous experiments conducted under well-controlled conditions.
Prediction of Polymer Viscosity Reduction in Pores Using an Exact Depletion Profile
Authors: Zitha Pacelli L. J. 
Published: December 2007

Abstract
The modeling and numerical simulation of processes such as polymer placement for water control, fluid loss control during drilling, polymer based chemical flooding and the interpretation of the related laboratory studies need a correct quantification of the apparent viscosity of polymers in porous media.
Past experimental and theoretical studies have shown that, in the absence of adsorption, the viscosity of polymer solutions decreases in porous media due to polymer depletion near pore walls. The proposed models considered pores that are relatively large with respect to the thickness of the depletion zones and assumed Newtonian flow. The two fluid model, in particular, is based on a discontinuous concentration profile. These characteristics give rise to limitations in the estimation of the apparent viscosity in porous media with very small pores.
In this paper we provide new insights on the depletion effect and develop a new model for the apparent viscosity, taking into account an exact polymer depletion concentration profile and the Non-Newtonian character of the polymer solutions. In this way we are able to predict the lowering of the apparent viscosity in pores over entire ranges of pore radii. Using analytical and numerical hydrodynamic calculations, we investigate the influence of the parameters (polymer concentration, ratio between the thickness of the depletion layer and effective pore radius, velocity gradient, etc.). Model predictions are found to be in good agreement with experiments available in the literature.
Disproportionate Permeability Reduction when a Silicate Gel is Formed In-Situ to Control Water Production
Authors: Grattoni C. A. , Jing X. D. , Zimmerman R. W. 
Published: December 2007

Abstract
Water production from oil and gas reservoirs is increasing world-wide, as more reservoirs are becoming mature. In order to control water production, polymers or gels are injected into production wells to either block the flow, or to reduce water permeability. In the latter case the polymers/gels are known as relative permeability modifiers. In these treatments, a gel is often formed in-situ through a chemical reaction, creating a semi-solid material that is capable of modifying the permeability.
To visualise the processes that occur during the flow of water and oil through a porous rock containing gel, experiments were conducted in transparent glass models in which the flow events can be observed. To form the gel in-situ, a novel alkyl silicate gelant was used, which is soluble in the oil phase, and which, when in contact with water, reacts to convert the water phase into a gel. From the flow observations, the underlying physics can be extracted and the basic mechanisms understood (reduction in effective pore size distribution, gel-bounded water, wetting films of free water, etc.). These mechanisms were used to develop a conceptual model, which consists of three main elements: pore space (bundle of capillary tubes), occupancy of the phases (fluid and gel distribution), and flow equations.
The output from the conceptual model is the capillary pressure as a function of total water saturation and end-point relative permeability. The results from this model successfully represent the disproportionate permeability reduction observed in micromodels and core experiments, verifying the mechanisms included in the model. This model may be quickly and easily used to study the influence of pore size distribution, gelant concentration, and initial water saturation, before undertaking laboratory or more complex modelling studies.
A Fractal Model for the Vertical Distribution of Sands in the Perales Oil Fields in the Basin of Golfo San Jorge (Argentina)
Authors: Hlebszevitsch Julio C. , Breda Eduardo 
Published: December 2007

Abstract
The irregularity and discontinuity that the sands present in the vertical sections of the Bajo Barreal Formation lead us to the concept that these sands present a difficult and chaotic distribution. The tuning effects and lack of resolution of the seismic information leads us on a search for new models and methodologies to find a model for the distribution of these sands. The objective of this work is to demonstrate the fractal behavior of the sets of sands, and the need to keep this property in mind for any type of geostatistical analysis, since these types of analysis generally assume a normal distribution of the data population in opposition of the fractal concept.
The term fractal was first defined in 1975 by Benoit Mandelbrot to describe the geometry of those objects which have an extremely irregular shape, interrupted and fragmented, and continue being so at any scale chosen for study. The fractal dimension (D) allows us to quantify the degree of irregularity of a geometrical set or of a natural object. An important consequence of this scale exponent is that a population of objects that respond to a fractal distribution will not have average values of its properties, being able to speak only of the distribution of sizes, of which a specific object or phenomenon occurs within a specific interval of time or space. An important concept is that the fractal behavior only occurs within a range of scales in nature, and no natural object is indefinitely fractal.
The punctuated behavior of the sedimentation brings, as a consequence, the distribution of the sands presented in a discontinuous form, and for that reason describable from a fractal viewpoint. Based on these observations, there is a need to characterize the population of sands in the Bajo Barreal Formation as a fractal set. Likewise, these results of the subsurface have been verified with data from outcroppings, having obtained similar results. The fractal vision has contributed to the discrimination of parasequences, the recognition of a distribution model of the sands, and the conclusion that the most important problems in these oil fields are the pathways of migration and trapping of hydrocarbons and not the presence of sands as was previously assumed.
Selection of Proper EOR Method for Efficient Matrix Recovery in Naturally Fractured Reservoirs
Authors: Babadagli T. 
Published: December 2007

Abstract
As most of the oil is stored in matrix due to its higher storage capacity than fracture network of naturally fractured reservoirs (NFR), reservoir development plans will aim at maximizing the matrix oil recovery. An enhanced oil recovery (EOR) application principally targets (a) to minimize the residual oil in matrix depleting the matrix as effective as possible and/or (b) to accelerate the recovery rate for rapid production of oil cost efficiently. For reservoirs with high recovery factor, minimizing matrix residual oil saturation is a critical issue to extend the life of the reservoir. For reservoirs with low recovery factor, accelerating the production rate is more vital. For each of these reservoir types, different EOR methods should be considered and implemented accordingly. This paper addresses and discusses these two issues and identifies selection criteria for different EOR methods in NFR, namely chemical (surfactant and polymer) and hot water injection.
The focus is specifically on matrix type (permeability and wettability), oil and water viscosities, matrix boundary conditions, transfer type (co- or counter-current imbibition), and IFT. For the different values of these properties, the most proper injection fluid type to be used as an EOR fluid is identified to obtain an effective matrix recovery. Co-current and counter-current capillary imbibition experiments at static conditions are conducted to show how effective and how useful these applications are for different rock and fluid types and matrix boundary conditions. For experimentation, strongly water wet Berea Sandstones and oil-wet carbonates (cores from an oil formation) are used. Light crude oil, kerosene and engine oil are selected as the oleic phase.
Proper project implementation (adjustment of injection rate and/or concentrations) and selection of the injection fluid for a cost efficient management are also discussed for different conditions outlined above. Finally, the selection criteria of EOR methods based on the rock and fluid properties are defined. This will provide an insight into an effective management of NFRs and reservoir depletion strategies, if the matrix oil recovery is the main target.
High-resolution Sequence Stratigraphy and Reservoir Characterization Applied to Mature Fields: Example from Eastern Venezuela Basin
Authors: Picarelli Andre , Holder Bruce , Arguello Jorge , Peron Renato , Nieves Israel , Rojas José 
Published: December 2007

Abstract
The Mata-Araibel Concession (Eastern Venezuela Basin – Mata 3, Mata 16, Mata 19, Mata 20, Mata 14, Mata 7 and Zorro Fields-) records Miocene shallow-marine sedimentation in the distal zone of the foreland basin, which was formed by the eastward migration of the Caribbean Plate in oblique convergence with the South American Plate. This work aims to integrate high-resolution sequence stratigraphy with historical production data to optimize production in this mature area, through the reactivation of abandoned reservoirs and the definition of flow units to implement secondary recovery projects. The shallow marine paleophysiography in a ramp setting, distal to the collision front of the foreland, allowed the development of multiple high frequency sequence boundaries within a broad estuarine system. The main reservoir rocks were deposited during 5th order lowstand/transgressive systems tracts, represented by estuarine (channels and tidal bars) and platform (sand ridges) sediments. Isolated transgressive sand ridges and tidal bars encased in estuarine mud constitute the main targets for by-passed oil. Higher frequency (4th and 5th order) erosional surfaces within 3rd order lowstand/transgressive systems tracts and minor extensional faulting allowed communication among different reservoirs. Based on this communication, simultaneous development of (formerly) different reservoirs is possible through the identification of hydraulic flow units. A volumetric review of each stratigraphical unit, the reallocation of the production records to appropriate units and the analysis of pressure as a function of recovery factor were completed. The results of this work, supplemented with newly acquired data, indicated the entire Oficina L sand package may be considered as one hydraulic unit (historically, the L sands in Mata were produced as 12 discrete reservoirs). Similar conclusions were reached for the Oficina S and U (Oficina and Merecure) sand packages. Additional studies have been undertaken to identify the existence of other hydraulic units as already shown in the Oritupano Area, also operated by Perez Companc SA(1). Mata wells are deep and expensive to drill or recomplete. The economic viability of producing this mature field will be greatly enhanced by allowing commingled production from identified and proven hydraulic units and from a set of reservoirs which proven to be economically unviable under individual production scheme.(2).
Application of New Generation Large Roller-Cone Bits Reduces Drilling Costs in Eastern Venezuela
Authors: Carre Leandro , McCoy Rick , Wilson Larry , Drilling Cliffs , Cockerham Jerry , Grimes Bobby , Anderson Mark , Pardo Nesny 
Published: December 2007

Abstract
An analysis of recent run data from two fields in Eastern Venezuela documents large metal seal bearing roller cone bits (16″ & 17–1/2"), with a new generation steel tooth cutting structure, can be used for a much greater number of total bit revolutions than prior generation bits. The new generation metal seal has proven its ability to significantly extend bearing life and reliability and thereby provide significant reductions in drilling costs. Penetration rates have more than doubled with total footage up 89% in some instances, with less overall cutting structure wear. Cost savings of up to $121,000 US per well have been documented.
The authors will describe the application of these new bits and present case studies that document significant performance improvement in the Santa Barbara and Mulata fields of Eastern Venezuela. They will also describe the development of the latest generation metal sealed bearing package and the metallurgical and design improvements of the new steel tooth cutting structures.
Physical and Economic Feasibility of Waterflooding of Low-Pressure Gas Reservoirs
Authors: Valjak M. , Novakovic D. , Bassiouni Z. 
Published: December 2007

Abstract
A volumetric gas reservoir reaches its economic limit when the reservoir pressure falls below the level needed to sustain the surface pressure necessary to move the gas through surface facilities and into a pipeline. Compression is considered when economically feasible. Waterflooding of low-pressure gas reservoirs is viable alternative to compression. Waterflooding reserves may in certain cases exceed that of compression. Water displaces gas efficiently because of extremely favorable mobility of low-pressure gas. The incremental recovery depends on the initial reservoir pressure and the pressure at which the waterflooding is implemented. This management option may also be used in conjunction with compression to maintain reservoir pressure, which ensures well unloading, and reduces need for well workover.
The economic feasibility of waterflooding depleted gas reservoirs is controlled by the amount of water needed, which is high because of the high gas compressibility. The amount of needed water increases dramatically as the reservoir pressure decreases. Managing this option as a water disposal for the field or nearby fields would be a major additional economic incentive. The injection is not a major cost component, as the water hydraulic head would exceed the reservoir pressure in most cases.
The cost of water injection can be eliminated altogether by downhole commingling of high pressure large aquifer with the depleted gas reservoir. This option would require special but simple downhole completion. Water volume supplied by the aquifer can be monitored using reservoir pressure and production data.
Studies of actual reservoirs demonstrated the technical and economic feasibility of this management option.
Extra-Heavy Crude Oil Downhole Upgrading Process Using Hydrogen Donors under Steam Injection Conditions
Authors: Ovalles Cesar , Vallejos Carlos , Vásquez Tito , Martinis Jorge , Perez-Perez Alfredo , Cotte Edgar , Castellanos Luis , Rodríguez Héctor 
Published: December 2007

Abstract
An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive (tetralin) under steam injection conditions. Using a batch laboratory reactor or a continuous bench scale plant (280-315°C and residence times between 24-64 h), physical simulation experiments showed an increase of at least 3° in API gravity of the treated Extra-Heavy Crude Oil, three-fold viscosity reduction and, approximately, 8% decrease in the asphaltene content with respect to the original crude. It was found that the presence of the natural formation (catalyst) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. Compositional-thermal numerical simulations were carried out and the results showed a good match between the calculated and experimental °API gravities of the upgraded crude oil (average relative error 1-4%) for all conditions studied. Similar results were obtained with the asphaltene contents (14-23%), percentage of conversion of the &gt;500°C fraction (12%) and tetralin (16-23%).
Progressing Cavity Pump Pattern Recognition in Heavy and Extra-Heavy Oil Cold Production
Authors: Ocanto Leonardo , Rojas Alexander 
Published: December 2007

Abstract
The large heavy oil reserves discovered in the Orinoco Belt, in Eastern Venezuela during the last ten years lead to a growing interest to raise the level of the technology used to support the exploitation of heavy and extra-heavy oil reservoirs, due to the complexity of such processes. To obtain the most of the reservoir while maintaining equipment working at top performance conditions, the use of Progressing Cavity Pumping (PCP), along with extensive use of emerging technologies for process monitoring and analysis, has proven to be a valuable tool to protect for formation damage while successfully increasing productivity.
Being Progressing Cavity pumping behavior a very complex issue, due to the inextricability of its operation (system kinematics difficult to model explicitly, interaction of elastomer with lifted fluid, among others), the use of Artificial Intelligence (AI), particularly in identifying operation and fault patterns, can be a powerful tool to gain insight of heavy and extra-heavy production processes. Some considerations regarding the use of these techniques are presented.
Analysis of a Successful Cyclic Steam Process at Cymric Field, California
Authors: Fong W. S. , Lederhos L. , Skow L. A. , Evola G. M. , Choi J. 
Published: December 2007

Abstract
A successful cyclic steam project has been implemented by Chevron USA Production Company in the Antelope Shale Formation of the Cymric 1Y Field, California. Recovery is expected to exceed 50% OOIP from this low permeability, heavy oil diatomite reservoir. The expected high recovery will be achieved through aggressive infill drilling, optimization of current steam injection operations, and favorable interaction of steam with induced fractures.
The patented cyclic steam process induces fractures by injecting steam at pressures exceeding the reservoir fracture gradient. Small, controlled injection/production cycles are applied to maximize steam efficiency. Optimizing cyclic operations in over 400 wells, which are, on average, cycled more than once per month, is a formidable task.
To follow is a description of two very different approaches for predicting and optimizing the performance of the cyclic steam process: (1) use of a very detailed, multiple-pattern simulation model, and (2) use of Design of Experiment techniques (DOE) coupled with much simpler, single-well simulation models.
While the detailed simulation model was able to capture complex operational history and provided a good history match, its use was limited due to long run times. Consequently, sensitivities to various key uncertainties are time consuming to obtain, limiting the flexibility of this approach. The DOE approach allows us to study more reservoirs and operational parameters in a relatively short time. Results from both approaches were combined to analyze and forecast field performance, and for aiding reservoir development decisions. Our combination method represents an optimal approach for cyclic thermal recovery process evaluation in heavy oil diatomite reservoirs.