bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adjoint-Based Well Trajectory Optimization in a Thin Oil Rim
Authors: Vlemmix S. , Joosten G. J. P. , Brouwer D. R. , Jansen J. D. 
Published: June 2009

Abstract
The selection of optimal well locations and trajectories is a challenging and important step in a field development plan. Selecting the optimal trajectory of a deviated well is an arduous task, which is usually done manually. In this study we demonstrate the use of a new technique to assist the determination of the optimal well trajectory with the aid of a gradient-based search method. Our approach is based on surrounding the well trajectory with side tracks to all adjacent grid blocks. These side tracks have such a small perforation and thus production rate that they hardly influence the production through the main well bore. The gradients of the side track contributions to the net present value (NPV) of the well with respect to their positions are approximated using a reservoir simulator equipped with adjoint functionality. Using the approximate gradients of the side track contributions, coordinates for a new trajectory are selected, and with these a new well trajectory is constructed. The curvature of the trajectory is restricted to stay within predefined drillability constraints expressed in terms of dog-leg severity. The process is repeated until a location with a maximum NPV is reached. The reservoir model to demonstrate the optimization technique represents a 3-dimensional heterogeneous reservoir located in a tilted anticline cut off by a fault running through the top of the anticline. It contains a thin oil rim drained by a single deviated well with a given kick-off point and a trajectory that has to be optimized within drillability constraints. The optimization results show a significant improvement in NPV of the well. Depending on the value that is assigned to the reservoir fluids (gas, oil and water) in the cost function, the well will seek a path in the reservoir that leads either away from the gas cap (in case of gas disposal), or towards the gas cap (in case of gas sales).
Azimuthal Wave Resistivity Opens a Window on the Geology Away from the Wellbore Path
Authors: Chemali Roland , Bittar Michael , Calleja Bronwyn , Hawkins Donald , Manrique Carlos 
Published: June 2009

Abstract
Deep azimuthal wave resistivity sensors yield a new type of electrical images. Although traditional micro-electrical images are limited to the surface of the wellbore, the new deep resistivity images span a volume of several cubic feet around the borehole. This new window on the geology helps to geosteer with more confidence than a series of discrete non-azimuthal curves.
Deep azimuthal images feature frowning and smiling patterns similar to their micro-images counterparts, except for two important distinctions. First, they make it possible to recognize approaching boundaries long before they intersect the well path. Because they emanate from several feet away from the wellbore, deep electrical images effectively enable proactive geosteering. They guide proper and timely evasive actions before the well exits the reservoir into shale or an underlying water-bearing interval. Second, the deep propagation images feature a characteristic bright spot that appears when drilling through a reservoir and approaching an exit into a less resistive formation. Various spacings and frequencies generate images with differing depths of field that provide a sense of 3-dimensional view away from the wellbore. This important information is unavailable from micro-images limited to the wellbore surface.
New interpretation methods specific to deep electrical images are illustrated on modeled data and on real logs where the primary objective is often to steer near a boundary, while staying clear of it. To quantify the distance to nearby beds, deep images are supplemented by Geosignal, a new real-time electromagnetic log that is very sensitive to the distance to the nearest boundary. By integrating multiple deep images with multiple depths of field, electrical Geosignals, and quantitative azimuthal resistivity data, a real-time inversion software helps the geosteering engineer to locate the well precisely with respect to the geological layers.
Joint Structural and Petrophysical History Matching Leads to Global Geological Stochastic Reservoir Models
Authors: Schaaf Thomas , Coureaud Bertrand , Labaune François 
Published: June 2009

Abstract
History matching is an integral part of reservoir production forecasting, risk analysis and uncertainties quantification workflows. One has to cope with the non-uniqueness issue as history matching is an ill-posed inverse problem, due to a lack in constraints and data. Dealing with several history matched models is therefore critical and assisted history matching tools are of great interest to speed up the process.
In practise, structural as well as petrophysical, PVT, SCAL, etc. data may be highly uncertain and the history matching process rarely tackles all these parameters in a single step. Classically, some of these parameters are considered as known while others are updated. This constitutes the ‘by default’ approach as all these parameters are interdependent and it may lead to sub-optimal history matched models.
This manuscript presents an original history matching workflow that picks uncertain structural and petrophysical parameters anywhere in the &quot;geomodeling to simulation?? workflow, using a popular geomodeling software. Efficient parameterization technique of the geological model allows both geological and simulation models to be updated at the same time, preserving the consistency between each other. Using a versatile assisted history matching software, any external software such as a geomodeling software, may be automatically launched in batch mode from the constructed workflow. Background scripts then control each building step of the geological and simulation models, possibly capitalizing on an existing geomodel. This joint structural and petrophysical history matching leads to a more robust integrated geological stochastic reservoir model, as all uncertainties are simultaneously tackled and reduced.
The results obtained on a 3D faulted synthetic waterflooding scenario demonstrate that this history matching approach is efficient since horizon depths, throw and transmissivity of faults as well as facies distribution, petrophysical and SCAL properties are simultaneously updated to explain the production history.
Understanding Compositional Grading in Petroleum Reservoirs Thanks to Molecular Simulations
Authors: Galliero G. , Montel F. 
Published: June 2009

Abstract
An accurate knowledge of the initial state of a petroleum reservoir is crucial in order to optimize its development plan. Such knowledge relies on a correct description of the spatial distribution of the fluid components. The compositional variations are mainly due to gravitational segregation and thermo-diffusion phenomena. Usually, a good estimation of the steady state spatial distribution of the components is obtained by thermodynamic modeling based on an Equation of State (EoS). This heuristic approach is unable to yield any knowledge on the time required to establish a segregated profile and it needs correlation for the thermodiffusion coefficients which is not readily available. One way to provide further information, both on the dynamic of the segregation and on the thermodiffusion process is to use Molecular Dynamics (MD) simulations. In this paper, Both EoS and MD simulations were applied for the calculation of the fluid distribution in reservoirs.
MD results provide insights on time evolution/stability of the fluid distribution and the calculated profile were used to tune the parameters of the EoS model for current applications.
On systems, for which an analytical solution of the thermo-gravitational problem exists, it is shown that the molecular simulations results are consistent with expected profiles. The MD simulations confirmed a non negligible impact of thermodiffusion phenomenae on the concentration profiles. In addition, simulations have shown that the transient behavior of both isothermal and non-isothermal segregation follows a diffusion process dynamic based on the mutual diffusion coefficient.
Comparison of MD results and EOS based model were made for various systems to evidence the limitation and the relevance of the thermodynamic approach. Gravity segregation calculations are widely used for the reservoir fluid evaluation and for the initialization of the reservoir model. This paper gives an in depth investigation of the underlying physics and direct validation of EoS modeling through molecular simulations.
Validating Workflows with Pore-Scale Modelling and Fine-Scale Geology for Water Saturation Interpretation
Authors: Berland Håvard , Børset Kari , Nordahl Kjetil , Rennan Lars , Rustad Alf B. 
Published: June 2009

Abstract
Future workflows for water saturation interpretation in heterogeneous intervals, should take the heterogeneity into account in a robust manner. We want fine-scale geology to be modelled realistically, down towards mm-scale when appropriate, and populate these models with properties from pore-scale modelling. The geologically realistic models can then be upscaled for effective properties for different rocktypes. Accordingly, Archie's law can be used for water saturation interpretation without breaking its assumptions. The work presented is a study in which we want to validate such a workflow, and assess the predictivity to be expected. Two core plugs from a heterogeneous reservoir have been studied in a steady-state flow experiment while simultaneously measuring both resistivity and in-situ saturation in 3D by CT-imaging. Resistivity was measured in a 4-electrode set-up connected to a multi frequency impedance meter. The experimental design yielded data where now resistivity, relative permeability and fine-scale saturation are all coupled. 3D digital models of the plugs have subsequentially been constructed from CT porosity and populated with properties from pore-space modelling. This enables us to compare the fine scale saturation modelling, which is a difficult task for this type of sedimentary rocks, to the measured water distribution in the plug. Fine-scale saturation also determines upscaled resistivity, which we can model digitally using pore-space models and compare with the measurements. Our findings indicate that the workflow is viable, and that we are able to obtain predictive power from pore-scale modelling and fine-scale geological modelling.
Integration of Production, Pressure Transient and Borehole Images in Horizontal Wells Drilled in Cambrian Sandstone Reservoirs of Hassi Messaoud Field, Algeria
Authors: Ogunyemi Taofeek , Montaggioni Philippe , Azzouguen Atmane , Kourta Mourad , Kodja Said , Madani Messaoud 
Published: June 2009

Abstract
The economical viability of the Cambrian sandstone reservoirs in the Hassi Messaoud field is closely linked to the presence of fractures. Natural or hydraulically induced fractures control hydrocarbon productivity due to the low porosity, low matrix permeability and heterogeneous sedimentological characteristics of these fluvial deposits.
Fracture corridors and permeable fault zones also represent a major risk of water breakthrough from the underlying aquifer in horizontal wells. The identification and characterization of open fractures and conductive faults is of critical importance for the completion decisions in this field.
Whole cores enable a comprehensive description of fractures (morphology and type) over the cored sections of the reservoir. Meso-scale fractures can also be identified, oriented and characterized (open vs. cemented) on high resolution borehole images over the entire open-hole section. When combined with pressure transient analyses and production data, borehole image logs provide invaluable information on the enhanced fracture conductivity, the completion optimization and the reservoir management for sustaining long term production in these complex reservoirs.
Wells with high fracture density usually correlate with high production rates as long as the dominant fracture strike is close to the direction of the maximum in-situ horizontal stress (σH). Wells with low fracture density or dominant fracture strike oriented oblique or perpendicular to sH generally show poor production rates.
This paper discusses case studies of fracture and fault characterization from a combination of borehole images with production and pressure transient data to provide an explanation for ambiguous production observations and well test data. Examples of completion optimization utilizing this integrated approach are also presented.
Feasibility of Using Wind Energy and CAES Systems in a Variety of Geologic Systems
Authors: Neumiller Jessica , Graves Ramona , Fanchi John 
Published: June 2009

Abstract
Renewable energy sources, such as wind energy, are expected to be sources of sustainable energy as fossil fuels are depleted. Wind energy is a promising, but intermittent energy source. Large scale energy storage such as Compressed Air Energy Storage (CAES) is needed to account for intermittency. CAES is designed to store off-peak energy to make it available for use during peak demand periods. Currently, CAES plants are located in caverns, which are uncommon in occurrence. CAES wind farms can become a more reliable energy source if other geological structures such as depleted hydrocarbon reservoirs are used for storage.
This study used a black oil simulator to model CAES in a typical cavern setting, in a hypothetical reservoir setting, and in a potential CAES wind farm area in the Greater Green River Basin (GGRB) of Wyoming. The cavern setting is modeled after the Huntorf CAES facility in Germany. Wind speed and resulting power data for GGRB models were taken from the Medicine Bow Wind Project in Wyoming. Porosity, permeability, and injectivity information from GGRB was used to construct four models of hybrid systems that combined wind energy and CAES for different geographical locations and geological properties.
The model of a cavern setting validated use of a black oil simulator for CAES applications. The study showed that CAES can be used in a variety of geologic settings, and that the GGRB has good potential for supporting wind energy and CAES systems. This talk will present details of the study and provide suggestions for future work.
Sedimentary Facies Computation and Stratigraphic Analyses Using Well Logs, Borehole Images and Cores in Triassic Fluvial Sandstones of the Algerian Sahara
Authors: Ogunyemi Taofeek , Montaggioni Philippe , Boubakeur Ibtissem , Junguito Mario , Batrina Maria Teresa 
Published: June 2009

Abstract
The Triassic reservoirs of the eastern Sahara province represent one of the main oil and gas accumulations in Algeria. This clastic succession corresponds to fluvial, estuarine and shallow marine deposits characterized by common lateral and vertical facies changes that are responsible for uncertainties in the modeling of the reservoir heterogeneities.
A realistic identification of the depositional environment is critical to the delineation and prediction of the best quality reservoir facies so that optimized exploitation of the reservoir can be achieved. This paper describes a methodology that was used to generate a depositional model in the Lower to Upper Triassic reservoirs of the Rhourde El-Khrouf field based on subsurface data from six wells including well logs, borehole images, cores and the regional knowledge of the basin.
Structural and sedimentary dip analyses were performed both on borehole images and oriented full-bore core photos that provided at least twice as many dips than borehole images. Facies logs were derived from the integration of core calibrated electrical borehole image analysis results with open-hole log data using neural network techniques. Depositional environments were then determined from correlations based on logs stacking patterns, facies associations and dip data.
These results show that the fluvial reservoirs of the Rhourde El-Krouf field are characterized by large variations from laterally extensive bodies with good interconnectedness and high net-to-gross ratios, to multi-storey ribbon bodies with poor interconnectedness and low net-to-gross ratios. This integrated approach using high resolution image logs and full-bore core photos provided a much more robust reservoir model than would be obtained from traditional approach based solely on open-hole logs.
Different Approaches to Understand Mechanism Of Wettability Alteration of Carbonate Reservoirs
Authors: Rezaei Gomari K. A. 
Published: June 2009

Abstract
Wettability is a key parameter when concerned with the flow of fluids in any porous medium. This paper describes the several possible mechanisms of wettability alteration of carbonate rocks using different approaches. The most crucial parameters which have severe impact on wettability alteration such as oleic phase composition, aqueous phase pH, as well as temperature are discussed.
At the oleic/aqueous interface, the interfacial tension and its variation with the structure of active surface species, partitioning of species between phases, and temperature are important signs to track the wettability alteration. The effect of the IFT on wettability alteration is revealed with the contact angle measurements on the carbonate rock surfaces.
On the other hand at rock/fluids interface, the paper presents the variations in surface tension and adsorption isotherms of surface active species on the rock surfaces which imply the strength of wettability alteration. The degree of wettability alteration and its reversibility due to influence of aforementioned parameters are explained based on desorption of active species from surfaces justifying by several thermo-gravimetric measurements.
Hybrid Optimization Coupling EnKF and Evolutionary Algorithms for History Matching: A Case Example
Authors: Schulze-Riegert Ralf , Krosche Markus , Pajonk Oliver 
Published: June 2009

Abstract
This paper discusses a hybrid extension of the Ensemble Kalman Filter (EnKF) with application to History Matching. The new approach combines the Ensemble Kalman Filter (EnKF) and Evolutionary Algorithms (EA). Key characteristics of either approach are used for data assimilation and optimization.
In a previous publication similarities between particle filter techniques (EnKF) and stochastic optimizers (i.e., Evolutionary Algorithm – EA) were analyzed. Both algorithms are population based, they have similar implementation properties but different optimization characteristics. A hybrid optimizer which couples an EnKF approach and the advantages of an Evolutionary Algorithm was introduced and applied to a synthetic test function.
In this paper the hybrid optimization approach is first applied to a history matching process of a synthetic reservoir simulation model. Production data is assimilated via a continuous update of 3D porosity and permeability fields. At the same time, additional parameter uncertainties are included in a parallel parameter estimation process guided by an evolutionary optimization method.
It is shown how an EnKF workflow can be coupled to other stochastic optimization schemes with complimentary optimization features. The EnKF formulation reduces a non-linear optimization problem in a large parameter space to a statistical optimization problem in ensemble space. An evolutionary optimization scheme modifies individual parameters and adds a focus on optimal solutions. The hybrid approach is applied to a history matching problem in reservoir simulation. The application case shows that an EnKF ensemble can be combined with a population of individual realizations from a generational update scheme using an Evolutionary Algorithm.
Roadmap to Monetization of Unconventional Resources
Authors: Vassilellis George D. 
Published: June 2009

Abstract
What has been regarded as unconventional by many has been conventional for the few that have developed viable, and in many cases, very profitable projects that succeeded in extending the envelope of recoverable hydrocarbons.
The range of recoverable hydrocarbons is bounded by physical constraints like reservoir properties, unfavorable hydrocarbon characteristics, or in many cases, hydrocarbons still captured in the formations. The methods of extraction that have been devised to address such challenges frequently combine applications of enhanced recovery, intensive stimulation, or advanced drilling. The distinction between conventional and unconventional can be reasoned not in the context of new versus old, more or less prolific accumulation attributes, or the method of extraction, but in the approach that is followed. A conventional development approach would cover the entire field with increasing intensity; an unconventional approach would pursue intensive development sequentially from the more prolific to the less prolific parts of the field.
Although it is easy to see the technical benefits of unconventional methods, their integration with economic and market parameters is necessary in order to provide a successful implementation. The purpose of this paper is to present a set of features that are found as common denominators in successful developments of such resources. These common features could be viewed as unconventional resource development principals that outline the areas where particular attention is required for their ultimate success. In that context, the influence of market pricing, cost structure and resource evaluation are examined and offer a platform for project implementation that can be viewed as a "road map". The basic premise in this reasoning is that while it is not possible to develop a universal technological solution, careful adaptation of technology to the subsurface and operational realities allow synergies to develop that improve the chance of economic success. The recognition of key risks in unconventional resource development is instrumental in addressing the reasoning in resource classification. In that sense, while geological risks are often viewed as key in conventional resources, unconventional resources carry more risks as more complex extraction methods are implemented. Once development commences, it could maintain a positive outlook with changing market conditions as the associated costs relate to some extent to fuel costs that are in turn dependent on the product prices. The long development cycle of such projects lasting more than 20 years reduces the exposure to fluctuating prices as long as a reasonable average trend is considered at the onset.
With evolving methods of extraction, the oil industry is shifting focus from exploration into intensive exploitation. Inevitably, the terms unconventional resources and a non conventional approach present a new direction for realizing the fuel sources of the future.