Browsing by Subject "Compressibility"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Compressibility and permeability of Gulf of Mexico mudrocks, resedimented and in-situ(2014-05) Betts, William Salter; Flemings, Peter Barry, 1960-Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior.Item Experimental Study on Kinematics and Dynamics of Breaking Waves in Deep Water(2011-10-21) Lim, Ho JoonA new measurement technique called fiber optic reflectometer (FOR) was developed to investigate multiphase flows. The principle and setup of the FOR technique were introduced and applied to various experiments. Based on the coherently mixed signal between the Fresnel reflection off the fiber-liquid interface and the scattered signal off the object, such as a gas bubble, and a solid particle, this single probe technique is capable of simultaneously measuring the velocity of the object with a high accuracy and the phase of the fluid. In addition, bubble diameter, velocity, and void fraction were measured directly. By means of a simple modification of the FOR technique, solute concentration and refractive index change were measured with a greatly improved accuracy. This modified technique was used for measuring of a NaCl concentration in deionized water to validate a new normalization technique. In the second part of this thesis, a plunging breaking wave in deep water has been studied. Using the wave focusing method, a strong plunging breaker was generated with accuracy in the deep water condition in a two-dimensional wave tank. It was possible to describe the breaking process in detail using a high speed camera with a frame rate of 500 or 1000 fps. Four kinds of experimental techniques were employed or developed to investigate the plunging breaker. Bubble image velocimetry (BIV) and particle image velocimetry (PIV) were used to measure the velocity fields. The velocity fields of the highly aerated region were obtained from the BIV measurements. In addition, the modified PIV technique is capable of measuring the velocities in the entire flow field including the aerated region. Mean and turbulent properties were obtained by the ensemble average. The mean velocity, mean vorticity, and mean kinetic energy were examined over the entire flow field. In addition, the Reynolds stresses and turbulent kinetic energy were calculated with high temporal and spatial resolutions. Free surface elevation was obtained from wave gauge measurements. BIV and PIV images were also used to obtain the free surface elevation and the boundary of the aerated region for more accurate results. The FOR technique was used to obtain the void ratio at each splash-up region. Compressibility of the plunging breaker was considered. Mass flux, momentum flux, kinetic energy, and Reynolds stresses at each FOR station were recalculated using the void ratio obtained from the FOR measurements. All terms at the first splash-up region were highly overestimated more than 100 percent unless the void ratio was applied to the calculation of fluxes and energies. Compared with the fully developed first splash-up region, the overestimation at the second and third splash-up was less significant. However, most terms were overestimated by 20~30 percent when the void ratio was not considered.Item Leak-off test (LOT) models combining wellbore and near-wellbore mechanical and thermal behaviors(2015-08) Gandomkar, Arjang; Gray, Kenneth E., Ph. D.; Daigle, Hugh CConsiderable efforts to model leak-off test (LOT) and leak-off behaviors have been carried out in the past. Altun presented a model to estimate leak-off volume by dividing the wellbore system into four sub-systems: mud compression, casing expansion, fluid leakage, and borehole expansion (Altun 2001). The volume response from each sub-system is then combined to represent the total volume pumped during a LOT. Most existing leak-off models do not account for mechanical behavior of cement and rock formations around the wellbore. While their compressibilities are small, the cement and rock formation volume changes can be significant. In this research, a mechanical expansion model has been developed, based on a linearly elastic, concentric cylinder theory developed by Norris (Norris 2003). The model is an extension of Lamé equations for multi concentric cylinders and assumes the horizontal stresses on the system’s boundary are applied equally in all directions, i.e., the horizontal, far-field stresses around the system are isotropic. The resulting model simulates the compound radial displacements of casing, cement, and formation along the cased hole, based on pressures inside the wellbore and in the far-field stress region. The volume generated from concentric cylinder expansion is then combined with Altun’s model to simulate the total volume pumped during a LOT. One use of the model is the estimation of minimum horizontal far field stress. Since the model consists of concentric cylinders, the pressure on the outside boundary can approximate the minimum horizontal far field stress, which in turn is related to overburden pressure. The pressure inside the most inner cylinder is calculated from known mud weight. With an initial estimation for the far field stress and iterative methods, the minimum horizontal stress can be estimated. The developed models were then applied to field LOT data from Gulf of Mexico. The results show that leak-off volume along the cased hole should be analyzed as a compound expansion of casing, cement, and formation.Item Models for acoustically driven bubbles in channels(2008-08) Atkisson, Jianying Cui, 1972-; Hamilton, Mark F.; Wilson, Preston S.A model is developed for the dynamics of an acoustically driven bubble in a channel. The bubble is assumed to be smaller than the transverse dimension of the channel and spherical in shape. The channels considered are infinite in length and formed by either parallel planes or tubes with triangular, rectangular, or hexagonal cross sections. For surfaces that are rigid or pressure release, the boundary conditions on the channel walls in each of these geometries can be satisfied using the method of images. Effects due to confinement by the channel walls are thus determined by an analysis of coupled bubble interactions in line and plane arrays. An existing model for the coupled dynamics of spherical bubbles provides the basis for the model. Liquid compressibility is an essential feature of the model, both in terms of radiation damping and the finite propagation speed of acoustic waves radiated by the bubble. Solutions for the frequency response are obtained analytically by perturbation for low drive amplitudes and weak nonlinearity, and by numerical solution for high drive amplitudes and strong nonlinearity. The perturbation solutions for the radial motion at the drive frequency and its second harmonic are obtained in closed form for a bubble between parallel planes. The response of a bubble between rigid parallel planes is found to be mass controlled, whereas for a rigid tube it is found to be radiation damping controlled. The dynamics of a bubble located near the center of a tube are found to depend on the area but not the specific geometry of the cross section. At drive amplitudes below which subharmonic generation occurs, the numerical solutions for high drive amplitudes reveal the same general properties as the perturbation solutions for low drive amplitudes. All of the solutions can be extended to tubes with arbitrary wall impedance if the radiation impedance on the bubble is known, for example calculated by normal mode expansion.Item Reliability Analysis of Settlement Using an Updated Probabilistic Unified Soil Compression Model(2012-02-14) Ambrose, AverySettlement of a structure is a matter of great concern. Both excessive and differential settlement can cause expensive damage to buildings and must be avoided. Most methods used to estimate settlement are both deterministic in nature and are based on elastic analysis of soils. To better estimate settlement, a probabilistic estimate that uses a more in depth analysis of the behavior of soil is required. This thesis develops a new probabilistic model for estimating settlement based on a probabilistic unified soil compression model. The model is then used to estimate the settlement of an embankment. Lastly, a reliability analysis of settlement is carried out on the settlement estimate of the embankment. The new probabilistic unified soil compression model used in this thesis was developed based on a previously developed probabilistic unified soil compression model, accounting for further uncertainties into the model and correcting for errors in the model calibration. This model was calibrated using data from a site on the Venice Lagoon using a Bayesian approach. The model to estimate settlement was developed based on this probabilistic soil compression model and is unbiased in nature. Using this model, unbiased settlement estimates were obtained for an embankment also located in the Venice Lagoon. Using the developed probabilistic model for settlement, reliability analysis was carried out. This reliability analysis involved assessing the conditional probability that, for a specific load and given soil properties, a specified settlement threshold would be reached or passed. Sensitivity and importance analysis were carried out, determining which parameters and random variables have the largest impact on the fragility estimates. Lastly, a closed-formed approximation based on the Central Limit Theorem was developed to allow for easier fragility estimation.Item Short timescale Brownian motion and applications(2015-08) Mo, Jianyong; Raizen, Mark G.; Downer, Mike; Fiete, Gregory A; Bengtson, Roger D; Kumar, PawanThis dissertation details our experiments and numerical calculations on short timescale Brownian motion and its applications. We test the Maxwell-Boltzmann distribution using micrometer-sized spheres in liquids at room temperature. In addition to that, we use Brownian particles as probes to study boundary effects imposed by a solid wall, viscoelasticities of complex fluids, slippage at solid-fluid interfaces, and fluid compressibility. The experiments presented in this dissertation relies on the use of tightly focused laser beams to both contain and probe the Brownian motion of microspheres in fluids. A dielectric sphere near the focus of a laser beam scatters some of the incident photons in a direction which depends on the particle's position. Changes in the particle's position are encoded in the spatial distribution of the scattered beam, which can be measured with high sensitivity. It is important to emphasize that the Brownian motion in this dissertation is exclusive for translational Brownian motion. We have reported shot-noise limited measurements of the instantaneous velocity distribution of a Brownian particle. Our system consists of a single micron-sized glass sphere held in an optical tweezer in a liquid in equilibrium at room temperature. We provide a direct verification of a modified Maxwell-Boltzmann velocity distribution and a modified energy equipartition theorem that account for the kinetic energy of the liquid displaced by the particle. Our measurements con rm the distribution over a dynamic range of more than six orders of magnitude in count-rate and five standard deviations in velocity. We have reported high-bandwidth, comprehensive measurements of Brownian motion of an optically trapped micrometer-sized silica sphere in water near an approximately at wall. At short distances, we observe anisotropic Brownian motion with respect to the wall. We find that surface confinement not only occurs in the long time scale diffusive regime but also in the short time scale ballistic regime, and the velocity autocorrelation function of the Brownian particle decays faster than that of particle in a bulk fluid. Furthermore, at low frequencies the thermal force loses its color due to the reflected flow from the no-slip boundary. The power spectrum of the thermal force on the particle near a no-slip boundary becomes at at low frequencies. We have numerically studied Brownian motion of a microsphere in complex fluids. We show that Brownian motion of immersed particles can be dramatically affected by the viscoelastic properties of the host fluids. Thus, this fact can be used to extract the properties of complex fluids via observing the motion of the embedded particles. This will be followed by two experimental demonstrations of obtaining the viscosities of water and acetone. We also study Brownian motion with partial and full slip boundary conditions both on the surface of a sphere and a boundary. We show that the motion of particles can be significantly altered by the boundary condition of fluid flow on a solid surface. We suggest that this fact can be used to measure the slippage, namely the slip length. Lastly, I will discuss the efforts to study fluid compressibility and nonequilibrium physics using a short duration pulsed laser. We expect to increase the postion sensitivity from current 10⁻¹⁵ m/[square root of Hz] to about 10⁻¹⁹ m/[ square root of Hz] by using a pulsed laser with a peak power of 10^8 W. With such a high position sensitivity, we expect to be able to resolve the compressibility of fluids. We will also discuss a few future experiments studying non-equilibrium physics.