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Characterizing Natural Fractures and Their Interactions with Hydraulically Induced Fractures
Get PDFNatural fractures are preexisting micro-cracks and fissures that can have a critical impact on hydraulic fracture treatments in shales. Most shale formations contain natural fractures, but the characteristics of these natural fractures can vary significantly. For example, the natural fractures in the Barnett Shale are mostly narrow, long, and sealed with calcite cement. The natural fractures in the Wolfcamp Shale are much more heterogeneous as a whole, but tend to be clustered in similar groupings based on the lithology of certain areas of the formation. The creation and development of natural fractures prior to any hydraulic fracturing treatments is primarily a function of mineralogy, total organic carbon, and in-situ stresses. During hydraulic fracturing treatments, certain characteristics, such as the relative angle between the natural and hydraulic fractures, the length of the natural fractures, the differential stress of the formation rock, and certain completion design variables, will determine how the natural and induced fractures interact and create a fracture network. The creation of a natural fracture network can have a positive effect on the ultimate hydrocarbon recovery in some cases. Natural fractures provide accumulation space and travel pathways for hydrocarbons, which is critical in low porosity and low permeability shales. However, natural fractures can result in higher rates of fluid leakoff, which will result in less efficient hydraulic fracture treatments overall. Also, natural fractures can provide an undesirable connection to water accumulations, which can negatively impact the economics of a well because of the disposal costs associated with water production. This thesis seeks to characterize natural fractures and also to describe the author's work on a hydraulic fracture simulation software that takes the impact of natural fractures into account.Petroleum and Geosystems Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Dielectric Properties of Fluid Saturated Rocks
No full textThe objective of this dissertation is to study the effect of wettability, clay content, water saturation and salinity on the electrical properties of hydrocarbon bearing rocks. The frequency range of interest is 10 Hz to 10 MHz. Measurements were made for the impedance of both fully and partially saturated rocks using the four-electrode method and for fully saturated rocks using the two-electrode method. These measurements include both clean and shaly sand samples. For fully saturated rocks, the dielectric constant is found to increase with the clay volume fraction, the cation exchange capacity and the electrochemical potential of the rock samples. It is found to decrease with increasing salinity, frequency, permeability, and porosity. Neither stress, nor wettability appear to significantly influence the dielectric constant of fully brine saturated Berea cores. Empirical correlations between the dielectric constant, frequency, permeability, cation exchange capacity, and porosity are presented for tight gas sands used in this study. These correlations provide a means of estimating important petrophysical parameters such as the permeability and the clay content from a non-destructive complex impedance sweep of tight gas sands fully saturated with brine. A lower critical frequency is found to characterize the geometry of the pore space. For partially saturated rocks, the dielectric constant appears to depend linearly on water saturation above 0.1 MHz and to have a power law dependence on water saturation below 0.1 MHz. This frequency appears to be the limit below which the resistivity index was invariant to frequency and at which all experimental runs displayed a peak in the reactivity index. Wettability effects were pronounced below 10 KHz. The effects observed experimentally are explained on the basis of the Generalized Maxwell-Wagner Theory. It is shown that the model presented by Lima and Sharma agrees quantitatively with the measured effects of porosity, clay content, saturation, grain size, and frequency. The Lima-Sharma theory for modeling the complex impedance of partially saturated shaly sands has been inverted. This inversion allows a log analyst to use low ( < lKHz) and high (> lMHz) complex impedance data from well logs to calculate reservoir petrophysical parameters such as water saturations in the virgin formation and in the flushed zone, porosity, clay volume fraction, clay surface charge density, and grain size.Petroleum and Geosystems Engineerin
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A Model for Particle Deposition and Filter Cake Buildup in Granular Media
No full textThe objective of this work is to develop a general technique for a better quantitative understanding of particle deposition that can be applied for studying particle deposition under as few assumptions, regarding the nature of the deposition i.e. external or internal deposition, as possible. A major objective of this study is to also include the effect of long range hydrodynamic interactions on particle deposition. The optimum form of the mobility tensors for hydrodynamic interactions was identified. The Stokesian Dynamics approach was used as a basis for constructing a model for particle deposition in granular media. A model was developed for the study of particle deposition on a granular medium. A separate model for studying 'deep bed' deposition within a granular medium was constructed by using the Ewald summation method for unequal sized particles. The results from these models indicate that the particle size and the structure of the granular medium play a very important role in particle capture and bridging. The 'deep bed' filtration model showed reasonable agreement with experimental data. Additional work needs to be done to incorporate multibody interactions and higher order multi.poles into this model. The use of a simpler lattice based model was also investigated. Results from this model indicate that the size of the particle relative to the grain size is one of the most important parameters for particle bridging. The model also showed reasonable agreement with experimental data.Petroleum and Geosystems Engineerin
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Stability of Thin Aqueous Films on Solid Surfaces
No full textThe objective of this work is to gain insight into the influence of aqueous wetting films on reservoir wettability and on the transport and distribution of the wetting phase in porous media. Theoretical and experimental studies were conducted to identify the effect of factors such as brine composition, pH, oil composition, surfactant concentration and capillary pressure on the stability of thin films. A rigorous charge regulation model was developed to study how film thinning and destabilization is affected by electrostatic parameters. Ellipsometry was used to measure the thickness of thin aqueous films as a function of the applied capillary pressure. A comparison between theoretically computed and experimentally measured disjoining pressure isotherms shows reasonable agreement. It was found that electrostatic and structural forces play a key role in determining equilibrium film thicknesses. Additional work needs to be done for the theoretical calculation of hydration forces. Experiments were also designed to detect destabilization of such films. Such experiments allowed us to identify conditions under which wettability · alteration occurs due to the destabilization of the thin aqueous films.. In systems where films destabilize, these results allow determination of the time .scale over which this. occurs. Useful insight is provided into the. generation of mixed wettability states in hydrocarbon reservoirs.Petroleum and Geosystems Engineerin
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Impact of Injection Well Fractures on Well Injectivity and Reservoir Sweep in Waterflooding and Enhanced Oil Recovery
No full textWater injection is widely used to maintain reservoir pressure and to displace bypassed oil from unswept zones. During the water injection process, deposition of suspended solids and oil droplets at the wellbore zone leads to a decline in well injectivity. Hence, an increased injection pressure is required to maintain a given injection rate. If the increase in the injection pressure is such that it exceeds the minimum horizontal stress within the formation rock around the wellbore, fractures are initiated in the adjacent formation. If the temperature of the injected fluid is different from that of the formation, a thermal front propagates from the injection well. This change in temperature causes the rock to contract or expand, thereby altering the stresses both in the region of changed temperature and in the surrounding rock. For example, injection of cold water into a high temperature reservoir can induce thermal stresses in the near wellbore region, which facilitates fracturing. The above two processes, pore plugging and changes in the temperature of the rock, are the main mechanisms that drive injection well fractures. To maximize the oil recovery the consideration of fracture growth rate and fracture orientation is essential. The extent of fracture growth and the fracture orientation significantly affects the sweep efficiency for given well pattern. Therefore, in the reservoir with complicated well patterns, the optimum fracture growth rate and fracture orientation is essential in maximizing the oil recovery. The appropriate selection of injection rate and the knowledge of particle concentration of the water and the temperature of the water are key factors necessary to determine the optimum fracture growth rate. Therefore, the accurate oil recovery simulation should include the detailed description of the fracture growth during the water injection. However, there is no reservoir simulator which explicitly considers fracture growth during the simulation so far. The usual simulator considers just the fixed fracture in the reservoir. However, because the fracture grows continuously as the injection of water progresses, a proper consideration of the fracture growth is necessary in the process of reservoir simulation. To add the explicit accounting of the fracture growth to the reservoir simulator will be the initial focus of my thesis research, as I describe it in the method for conducting research. After completing the combination of two simulators (single-well fracture growth simulator and reservoir simulator), the optimum fracture growth rate, optimum fracture orientation and optimum properties of injected water can be obtained by a sensitivity study.Petroleum and Geosystems Engineerin
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Role of Acid-Base Interactions in Colloid Adhesion and Stability of Aqueous Thin Films
No full textExperiments were performed to evaluate the hydrodynamic force required
to detach colloidal particles from different types of substrates by fluids in simple
shear flow. The role of DL VO and acid-base interactions on the process of adhesion
and removal of colloidal particles, from model surfaces, in various fluid
environments was investigated. Particles and substrates with varying degrees of
hydrophobicity were used. The free energy of interaction between these surfaces
in a number of fluid media was calculated using the acid-base approach.
Good qualitative agreement was obtained between calculated values of
free energy of interaction using the acid-base approach and the critical
hydrodynamic force required to detach the particles if long range electrostatic
repulsion is properly accounted for. Results for a range of particles and substrates
of varying hydrophobicity and for a range of solvents can be consistently explained
using this approach.
Interactions between hydrophilic and hydrophobic surfaces in aqueous
medium at various pH and ionic strengths as well as in some organic solvents
were measured using atomic force microscopy. In hydrophilic systems the forces
observed were found to be well described by DL VO theory at large separation
distances. Very long-range hydrophobic forces were not observed in hydrophilic hydrophobic
systems. The interaction between two hydrophobic surfaces was
dominated by the long-range attraction due to hydrophobic forces. This
interaction was found to be sensitive to the type of substrate as well as to the pH
and electrolyte concentration.
Measured pull-off forces showed poor reproducibility. However, average
values showed clear trends and were used to estimate interfacial energies or work
of adhesion for all systems studied by means of the Derjaguin approximation.
These values were compared to those calculated by the acid-base approach. Good
qualitative agreement was obtained, giving support for the usefulness of this
approach in estimating interfacial energies between surfaces in liquid media. A
comparison of the measured adhesion force with hydrodynamic detachment
experiments showed good qualitative agreement.
The wetting behavior of model systems and crude oils was investigated by
means of the "extended DLVO theory". The model oil is octadecane and the
acidic or basic character of the oil is obtained by addition of a fatty acid or an
amine. Good agreement between AFM measurements and acid-base calculations
was obtained only for pure octadecane. We also applied a novel methodology to
use contact angle measurements to compute the acid-base component of
disjoining pressure in crude oil systems. The calculated disjoining pressure
isotherms were compared with experimental data. from atomic force microscopy
measurements. The method was shown to work for three crude oils tested.Petroleum and Geosystems Engineerin
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Theory for Hydration Forces in Thin Films of Aqueous Electrolytes
No full textA theory is presented to quantify the electrostatic forces in thin aqueous electrolyte films between two charge regulating surfaces. The Poisson-Boltzmann equation (PBE) is modified to include the effects of dielectric saturation of the double layer and the corresponding change in hydration free energy of ions. The results obtained agree remarkably well with the experimental data of Pashley (1981) and Israelachvili et. al. (1978) at low electrolyte concentration and pH. At higher concentration and pH, the model provides qualitative agreement with experimental observations. Finite ion sizes needs to be incorporated into the PBE to obtain quantitative agreement with experimental data in the high ion concentration range. The reduction in dielectric constant with increasing electric field increases the hydration energy of the ions in the double layer, giving rise to a repulsive hydration force. It is concluded that dielectric saturation of the double layer near a charged interface plays an important role in the electrostatic interactions in thin electrolyte films.Petroleum and Geosystems Engineerin
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