Mechanical Stratigraphy of the Mississippian in Osage County, Oklahoma

The Mississippian formation of Oklahoma and Kansas has recently developed as a world class unconventional reservoir with wells producing up to 800 bbl/day. The Mississippian is composed of multiple distinct lithologic zones including limestone, hard chert, and soft tripolitic chert. These zones are difficult to discern with traditional log correlation, but mechanical stratigraphy has the potential to improve previous correlations of the Mississippian. This study uses full wave sonic logs from Osage County, OK to analyze the elastic properties of the Mississippian. Our work computes isotropic elastic parameters in an effort to partition the Mississippian section into units that may be correlated between wells. Raw material for this study consists of P-sonic, S-sonic, and density logs in two wells. From sonic log data we compute metric P- and S-wave velocities, then calculate the two independent isotropic elastic parameters (Lame\u27s constant and shear modulus) at every log depth through the Miss and a short section above and below. Young\u27s modulus, a key parameter related to brittleness and fracability, is shown to vary vertically and laterally in the Mississippian. Through our work to separate the Mississippian into multiple distinguishable units, we may be able to better correlate logs in this area as a guide for oil exploration mapping and completion

Application of the Variational Fracture Model to Hydraulic Fracturing in Poroelastic Media

Hydraulic fracturing has persisted through the use of simple numerical models to describe fracture geometry and propagation. Field tests provide evidence of interaction and merging of multiple fractures, complex fracture geometry and propagation paths. These complicated behaviors suggest that the simple models are incapable of serving as predictive tools for treatment designs. In addition, other commonly used models are designed without considering poroelastic effects even though a propagating hydraulic fracture induces deformation of the surrounding porous media. A rigorous hydraulic fracturing model capable of reproducing realistic fracture behaviors should couple rock deformation, fracture propagation and fluid flow in the both the fracture and reservoir. In this dissertation, a fully coupled hydraulic fracturing simulator is developed by coupling reservoir-fracture flow models with a mechanical model for reservoir deformation. Reservoir-fracture deformation is modeled using the variational fracture model which provides a unified framework for simultaneous description of fracture deformation and propagation, and reservoir deformation. Its numerical implementation is based on a phase-field regularized model. This approach avoids the need for explicit knowledge of fracture location and permits the use of a single computational domain for fracture and reservoir representation. The first part of this work involves verification of the variational fracture model by solving the classical problem of fracture propagation in impermeable reservoirs due to injection of an inviscid fluid. Thereafter, the developed reservoir-fracture model is coupled to the mechanical model. Iterative solution of the variational fracture model and the coupled flow model provides a simplified framework for simultaneous modeling of rock deformation and fluid flow during hydraulic fracturing. Since the phase field technique for fracture representation removes the limitation of knowing a priori, fracture direction, the numerical solutions provide a means of evaluating the role of reservoir and fluid properties on fracture geometry and propagation paths. First, the proposed approach is validated for simple idealized scenarios for which closed form solutions exist in the literature. Further simulations highlight the role of fluid viscosity and reservoir properties on fracture length, fracture width and fluid pressure. Numerical results show stress shadowing effect on multiple hydraulic fracture propagation. Finally, the effect of in situ stress on fracture propagation direction is reproduced while the role of varying reservoir mechanical properties on fracture height growth is investigated

Feasibility of conventional control techniques for large highly coupled elastic boost vehicles Final report

Control techniques for large highly-coupled elastic boost vehicles with elastic and fuel slosh mode frequencies close to desired control frequencies - motion equation

Comprehensive Analysis of Acid Stimulation in Carbonates

Most wells in conventional carbonate reservoirs are stimulated with acid, either by acid fracturing or by matrix acidizing. Both methods can result in effective stimulation in carbonate reservoirs, but currently there is no published scientific criterion for selecting one technique or the other. The objectives of this study are to define ways to estimate the well performance that can be obtained from each of these treatments, and finally to define a decision criterion to select the best acid stimulation technique for a given scenario. Improvements in the modeling of both matrix acidizing and acid fracturing are proposed in this study. A new upscaled global model of wormhole propagation is proposed, based on experimental results and simulations using the Two-Scale Continuum Model. The proposed model represents experiments in different scales and field treatments. The wormhole propagation in anisotropic formations and in limited entry completions was also studied, and new analytical equations to calculate the post-acidizing skin factor for these cases were presented. In terms of acid fracturing modeling, a productivity model was developed for acid fractures, coupled to an in-house acid fracturing simulator. A leak-off model accounting for efficient wormholing was also developed, improving the prediction of high leak-off observed in acid fracturing treatments. Comparing the predicted productivity of matrix acidized and acid fractured wells, this study proposes a criterion for selection of the acid stimulation technique that results in the most productive well, for a given scenario and volume of acid. For all scenarios studied, there is a cutoff permeability above which a matrix acidized well is more productive than an acid fractured well. The value of this cutoff permeability, however, changes significantly for different scenarios. For example, in shallower reservoirs with small horizontal stresses, the cutoff permeability is much higher than in deeper reservoirs subject to high horizontal stresses. For hard rocks, the cutoff permeability is higher than for softer rocks. Concise analytical decision criteria were proposed to select the best acid stimulation method for both vertical and horizontal wells

Binary Decision Diagrams and Composite Classifiers for Analysis of Imbalanced Medical Datasets

oai:journal.ub.tu-berlin.de:article/1227Imbalanced datasets pose significant challenges in the development of accurate and robust classification models. In this research, we propose an approach that uses Binary Decision Diagrams (BDDs) to conduct pre-checks and suggest appropriate resampling techniques for imbalanced medical datasets as the application domain where we apply this technology is medical data collections. BDDs provide an efficient representation of the decision boundaries, enabling interpretability and providing valuable insights. In our experiments, we evaluate the proposed approach on various real-world imbalanced medical datasets, including Cerebralstroke dataset, Diabetes dataset and Sepsis dataset. Overall, our research contributes to the field of imbalanced medical dataset analysis by presenting a novel approach that uses BDDs and composite classifiers in a low-code/no-code environment. The results highlight the potential for our method to assist healthcare professionals in making informed decisions and improving patient outcomes in imbalanced medical datasets

Three essays on the effects of natural resources rents, institutions and demographic factors on economic growth

This thesis consists of three distinct but interrelated essays on the implications of resources rents, institutions and demographic indicators for economic growth. Chapter two utilises timeseries data to investigate the impacts of oil rents, institutions, and diversification on the Nigerian economy's growth. Chapter three applies panel data to determine the effects of oil rents and institutions on OPEC economies' growth. Chapter four uses extensive panel data of 216 economies and extends our study to consider the implications of demographic factors, political institutions, and natural resource rents on economic growth. Given the potential for endogeneity in regression analysis of the drivers of growth, we draw our main results from estimators that consider possible endogeneity. For the Nigerian economy, oil rents positively impact economic growth, contingent on good institutions. Our findings suggest that the quality of democratic institutions in Nigeria is significant for economic growth. Diversification of the economy also shows a positive effect on growth. For the OPEC economies, oil rents have negative implications for its economic growth. We find empirical evidence that institutional qualities: the legal, anticorruption and government effectiveness qualities positively impact OPEC economic growth. Chapter four shows that the population size and growth rate have an asymmetric impact on economic growth. This thesis contributes to the literature by developing varying institutional qualities for Nigeria and OPEC. Furthermore, we develop a model for the OPEC oligopoly power and demonstrates that countries' population growth rates and size are crucial drivers of growth. We observe that whilst democracy promotes economic growth; it does not necessarily follow that those states that are not democratising will lag in growth. The main conclusions of the thesis are that the existence of strong institutions is crucial for resource-producing countries. Demographic factors are significant for growth, and diversification of the economy is vital for economic growth.This thesis consists of three distinct but interrelated essays on the implications of resources rents, institutions and demographic indicators for economic growth. Chapter two utilises timeseries data to investigate the impacts of oil rents, institutions, and diversification on the Nigerian economy's growth. Chapter three applies panel data to determine the effects of oil rents and institutions on OPEC economies' growth. Chapter four uses extensive panel data of 216 economies and extends our study to consider the implications of demographic factors, political institutions, and natural resource rents on economic growth. Given the potential for endogeneity in regression analysis of the drivers of growth, we draw our main results from estimators that consider possible endogeneity. For the Nigerian economy, oil rents positively impact economic growth, contingent on good institutions. Our findings suggest that the quality of democratic institutions in Nigeria is significant for economic growth. Diversification of the economy also shows a positive effect on growth. For the OPEC economies, oil rents have negative implications for its economic growth. We find empirical evidence that institutional qualities: the legal, anticorruption and government effectiveness qualities positively impact OPEC economic growth. Chapter four shows that the population size and growth rate have an asymmetric impact on economic growth. This thesis contributes to the literature by developing varying institutional qualities for Nigeria and OPEC. Furthermore, we develop a model for the OPEC oligopoly power and demonstrates that countries' population growth rates and size are crucial drivers of growth. We observe that whilst democracy promotes economic growth; it does not necessarily follow that those states that are not democratising will lag in growth. The main conclusions of the thesis are that the existence of strong institutions is crucial for resource-producing countries. Demographic factors are significant for growth, and diversification of the economy is vital for economic growth

Comprehensive Analysis of Acid Stimulation in Carbonates

Most wells in conventional carbonate reservoirs are stimulated with acid, either by acid fracturing or by matrix acidizing. Both methods can result in effective stimulation in carbonate reservoirs, but currently there is no published scientific criterion for selecting one technique or the other. The objectives of this study are to define ways to estimate the well performance that can be obtained from each of these treatments, and finally to define a decision criterion to select the best acid stimulation technique for a given scenario. Improvements in the modeling of both matrix acidizing and acid fracturing are proposed in this study. A new upscaled global model of wormhole propagation is proposed, based on experimental results and simulations using the Two-Scale Continuum Model. The proposed model represents experiments in different scales and field treatments. The wormhole propagation in anisotropic formations and in limited entry completions was also studied, and new analytical equations to calculate the post-acidizing skin factor for these cases were presented. In terms of acid fracturing modeling, a productivity model was developed for acid fractures, coupled to an in-house acid fracturing simulator. A leak-off model accounting for efficient wormholing was also developed, improving the prediction of high leak-off observed in acid fracturing treatments. Comparing the predicted productivity of matrix acidized and acid fractured wells, this study proposes a criterion for selection of the acid stimulation technique that results in the most productive well, for a given scenario and volume of acid. For all scenarios studied, there is a cutoff permeability above which a matrix acidized well is more productive than an acid fractured well. The value of this cutoff permeability, however, changes significantly for different scenarios. For example, in shallower reservoirs with small horizontal stresses, the cutoff permeability is much higher than in deeper reservoirs subject to high horizontal stresses. For hard rocks, the cutoff permeability is higher than for softer rocks. Concise analytical decision criteria were proposed to select the best acid stimulation method for both vertical and horizontal wells

Managing the welfare impacts of urbanization in Zambia: A case for a composite district performance index

This paper looks at the evolution of urbanization in Zambia. The country has a population of just over 15 million people with about 35% living in urban areas. The population in the urban areas is projected to increase driven by both natural population growth and rural-urban migration. This population growth is expected to put pressure on the provision of services in urban areas. The country has been implementing a decentralization programme that is meant to devolve vital tasks to the local authority. If this happens, the local authorities will have the pressure of ensuring that people in their cities have decent standards of living. The localized city development index will assist local authorities with information to use in assessing their performance. The index adopts the Alkire Foster multidimensional measurement approach

A Study of Interwell Interference and Well Performance in Unconventional Reservoirs Based on Coupled Flow and Geomechanics Modeling with Improved Computational Efficiency

Completion quality of tightly spaced horizontal wells in unconventional reservoirs is important for hydrocarbon recovery efficiency. Parent well production usually leads to heterogeneous stress evolution around parent wells and at infill well locations, which affects hydraulic fracture growth along infill wells. Recent field observations indicate that infill well completions lead to frac hits and production interference between parent and infill wells. Therefore, it is important to characterize the heterogeneous interwell stress/pressure evolutions and hydraulic fracture networks. This work presents a reservoir-geomechanics-fracturing modeling workflow and its implementation in unconventional reservoirs for the characterization of interwell stress and pressure evolutions and for the modeling of interwell hydraulic fracture geometry. An in-house finite element model coupling fluid flow and geomechanics is first introduced and used to characterize production-induced stress and pressure changes in the reservoir. Then, an in-house complex fracture propagation model coupling fracture mechanics and wellbore/fracture fluid flow is used for the simulation of hydraulic fractures along infill wells. A parallel solver is also implemented in a reservoir geomechanics simulator in a separate study to investigate the potential of improving computational efficiency. Results show that differential stress (DS), parent well fracture geometry, legacy production time, bottomhole pressure (BHP) for legacy production, and perforation cluster location are key parameters affecting interwell fracture geometry and the occurrence of frac hits. In general, transverse infill well fractures are obtained in scenarios with large DS and small legacy producing time/BHP. Non-uniform parent well fracture geometry leads to frac hits in certain cases, while the assumption of uniform parent well fracture half-lengths in the numerical model could not capture the phenomenon of frac hits. Perforation cluster locations along infill wells do not play an important role in determining whether an infill well hydraulic fracture is transverse, while they are important for the occurrence of frac hits. In addition, the implementation of a parallel solver, PETSc, in a fortran-based simulator indicates that an overall speedup of 14 can be achieved for simulations with one million grid blocks. This result provides a reference for improving computational efficiency for geomechanical simulation involving large matrices using finite element methods (FEM)

Digital-Rock-Physics Modelling of Carbonates and Sandstones

This thesis seeks to investigate the influence of porosity and pore geometry on the macroscopic parameters of a porous rock saturated with fluid. These macroscopic parameters, also known as Biot's parameters, include the drained and undrained bulk moduli which characterize the rock’s resistance to compression (or expansion), the pressure parameter needed to increase the fluid content by a unit value at constant total dilatation, and the so-called Biot-Willis coefficient. This study also seeks to examine the effects of porosity and pore geometry on the stored solid elastic energy in the rock. To achieve these goals, I develop numerical simulations of compression tests of digital rock models. These simulations allow me to calculate Biot’s parameters for samples with known pore geometries. The numerical model results are shown to be in good agreement with an analytical model for a spherical rock sample with a single spherical pore. I investigate the variation of the macroscopic parameters as a function of the porosity and of the solid and fluid material properties. In particular, I show that, apart from the Biot-Willis coefficient, the other macroscopic parameters, as well as the total and compression solid energy densities, decrease with an increase in porosity. Whereas Biot's parameters are generally influenced by both porosity and pore geometry, the pressure parameter is only influenced by porosity but remains the same regardless of changes in pore geometry. Also, the results reveal that the carbonate pore geometries have some similarity to the simple pore geometries but are generally softer, while sandstone pore geometries are even softer than carbonate ones