The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on January 15, 2010). Thesis advisor: Dr. Peter Nabelek. Includes bibliographical references.

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Over the past decade, patterns of horizontal crustal motion observed along the Cascadia subduction zone (CSZ) from Global Positioning System (GPS) measurements have been used to derive locked subduction zone models with varying geometry and coupling factors. Although vertical crustal deformation estimates have been less abundant and less accurate than horizontal component observations, they provide key constraints to the models for estimating the extent of rupture for the next subduction thrust earthquake. In order to provide updated model constraint estimates, the contemporary vertical deformation pattern across the northern Cascadia margin was investigated through the combined application of GPS, repeated leveling, precise gravity, and monthly mean sea level measurements across southern Vancouver Island and repeated leveling on the mainland. To the first order, these estimates are consistent with across-margin tilt predictions from current dislocation models for the region. In their details, however, they reflect a more complex system than suggested by the simple models. Minor landward tilt across the margin at Tofino determined from the re-analyses of -8 years of continuous vertical GPS positions, -40 years of monthly mean sea levels and long-term time (decadal) intervals of repeat leveling surveys is distinctly different than the -3 mm yr'l of landward tilt observed at Neah Bay. While this difference may be minimized by allowing for a small amount of tilt induced at the southern stations from northward migration of the Cascadia forearc, differences in tilting of 3-4 mm yr'l between short- and long-term estimates of repeat leveling at Bamfield are attributed to transients. To a lesser degree, elevation changes across the margin at Tofino may also illustrate transients. As well, distinct differences in the magnitude of vertical deformation for stations to the north and south of Barkley Sound suggest that differential deformation may be occurring along the margin. Similarly, while repeat relative gravity measurements across the margin at Tofino indicate 3-7 mm yr-' of seaward tilt (at odds with results from all other methods), a temporal dependence of vertical deformation might also be evident from the long-term versus short-term tilt rates. However, although repeat absolute gravity estimates between 1995 and 2002 indicate little across-margin tilt, consistent with continuous GPS results, differences between the time series at the Ucluelet absolute gravity and GPS stations indicate that gravity observations could be influenced by episodic mass redistribution beneath western Vancouver Island. This suggests that gravity results might not be directly comparable to estimates from other geodetic methods in determining uplift rates. Extension of the vertical deformation profile eastward into the backarc using repeat leveling surveys indicates a broad region of uplift in the Pemberton area with respect to the coast, which is consistent with the vertical component at the continuous GPS station WSLR. Current dislocation models cannot account for the observed deformation. Therefore, modification of one model was attempted in which a weaker crustal zone, coincident with high heat flow near the Garibaldi Volcanic Arc, was included. A poor fit to the observed deformation rates indicates that further refinements must be made to such a model. Nonetheless, these results suggest a complex system of strain accumulation in the northern CSZ, which may result from a greater 3- dimensionality of the tectonic controls than current dislocation models of the region employ.

Problems involving coupled thermo-poro-chemo-mechanical processes are of great importance in geothermal and petroleum reservoir systems. In particular, economic power production from enhanced geothermal systems, effective water-flooding of petroleum reservoirs, and stimulation of gas shale reservoirs are significantly influenced by coupled processes. During such procedures, stress state in the reservoir is changed due to variation in pore fluid pressure and temperature. This can cause deformation and failure of weak planes of the formation with creation of new fractures, which impacts reservoir response. Incorporation of geomechanical factor into engineering analyses using fully coupled geomechanics-reservoir flow modeling exhibits computational challenges and numerical difficulties. In this study, we develop and apply efficient numerical models to solve 3D injection/extraction geomechanics problems formulated within the framework of thermo-poro-mechanical theory with reactive flow. The models rely on combining Displacement Discontinuity (DD) Boundary Element Method (BEM) and Finite Element Method (FEM) to solve the governing equations of thermo-poro-mechanical processes involving fracture/reservoir matrix. The integration of BEM and FEM is accomplished through direct and iterative procedures. In each case, the numerical algorithms are tested against a series of analytical solutions. 3D study of fluid injection and extraction into the geothermal reservoir illustrates that thermo-poro-mechanical processes change fracture aperture (fracture conductivity) significantly and influence the fluid flow. Simulations that consider joint stiffness heterogeneity show development of non-uniform flow paths within the crack. Undersaturated fluid injection causes large silica mass dissolution and increases fracture aperture while supersaturated fluid causes mineral precipitation and closes fracture aperture. Results show that for common reservoir and injection conditions, the impact of fully developed thermoelastic effect on fracture aperture tend to be greater compare to that of poroelastic effect. Poroelastic study of hydraulic fracturing demonstrates that large pore pressure increase especially during multiple hydraulic fracture creation causes effective tensile stress at the fracture surface and shear failure around the main fracture. Finally, a hybrid BEFEM model is developed to analyze stress redistribution in the overburden and within the reservoir during fluid injection and production. Numerical results show that fluid injection leads to reservoir dilation and induces vertical deformation, particularly near the injection well. However, fluid withdrawal causes reservoir to compact. The Mandel-Cryer effect is also successfully captured in numerical simulations, i.e., pore pressure increase/decrease is non-monotonic with a short time values that are above/below the background pore pressure.

Finite element computer modeling has been compared with scale modeling of vertical block uplifts of continuous, homogeneous, and isotropic material, representing geologic structures. Gelatin was used as the standard modeling material with deformation limited to the elastic range. Computer models with dimensions identical to the gelatin were varied in boundary conditions, material constants, and uplift configuration until close approximation to the gelatin model occurred. Zero density computer cases were obtained to isolate the effects of gravity on the deformation and points of maximum shear and tensile stresses were indicated and co-roared with weighted examples.After achieving close agreement between the two techniques, additional gelatin and computer models, both with elastic properties greater than the standard., were compared and evaluated to substantiate the results. Applications to field situations are indicated and areas for additional comparisons are suggested for further investigations.Ball State UniversityMuncie, IN 47306

Wireline formation testers are widely used to measure in-situ fluid pressure, to retrieve reservoir fluid samples, and to estimate formation mobility. However, formation-tester measurements are invariably influenced by mud-filtrate invasion due to drilling overbalance pressure, thereby affecting the acquisition of uncontaminated fluid samples and the estimation of in-situ petrophysical properties. Moreover, in cases of stress-sensitive formations, rock mechanical deformation may take place due to the combined effects of in-situ stress, wellbore stress imposed by mud overbalance, and wellbore pressure exerted by the formation tester itself. The latter deformation causes near-borehole perturbations of porosity and permeability that are evidenced by pressure transients measured during build-up and shut-in stages of formation testing, especially when using dual-packer pressure probes. If unaccounted for, such perturbations can also bias the estimation of in-situ fluid and petrophysical properties. Conversely, the detection and quantification of elastic mechanical deformation effects on measured pressure transients can be used to infer the underlying rock elastic and petrophysical properties of the stressed formation. The purpose of this dissertation is twofold: (a) to quantify the relative effects of mud-filtrate invasion and geomechanical deformation on pressure-transient measurements acquired with dual-packer formation testers, with special emphasis on the appraisal of near-borehole porosity and permeability enhancement due to elastic mechanical deformation, and (b) to develop a new method to estimate elastic and petrophysical properties of rock formations from dual-packer pressure transients acquired in mechanically deformable rocks. Numerical simulations of mud-filtrate invasion are performed with an axialsymmetric two-phase (water-oil) method that enforces the specific boundary and source conditions of a wellbore that penetrates horizontal layers. Simulations are performed in a cylindrical system of coordinates using finite differences together with an implicit-pressure, explicit-saturation time-marching approach that also incorporates the dynamic conditions of immiscible mudcake growth due to filtration of solids at the wellbore. Laboratory experiments are conducted to further study pressure transients due to formation testing in the presence of invasion with water-base mud. Experiments include the effects of both mud circulation and mudcake on pressure-transient measurements and are performed on a variety of rock-core samples. Measurements are successfully validated with both the developed simulator and a commercial simulator, thereby lending credence to the assumed model of dynamic solid filtration. The developed mud-filtrate fluid-flow simulator is coupled with a finite-element code that assumes 2D axial-symmetric linear elasticity to quantify geomechanical deformation. Coupling of mechanical deformation with variations of porosity and permeability assumes a staggered-in-time, iteratively coupled volumetric model. We assume a dual-packer formation tester to quantify elastic deformation effects in stress-sensitive formations as a preamble to estimating in-situ elastic and petrophysical properties. It is shown that near-wellbore spatial variations of porosity and permeability due to mechanical deformation can bias the corresponding pressure-transient measurements acquired with the dual-packer formation-tester. The degree of biasing depends on the rigidity of the stressed formation. Finally, we develop a method to estimate in-situ petrophysical and elastic rock properties from pressure-transient measurements acquired with formation-testers in mechanically deformable rocks. Petrophysical and elastic properties will change in both time and space depending on the time evolution of the conditions that influence mechanical deformation. We use a commercial reservoir simulator to calculate pressure transients due to fluid pumpout in the presence of both invasion and mechanical deformation. A pre-stressed initial condition due to mud overbalance is assumed with incremental deformation due to surface force applied by the packers or probes, and active flow imposed by the formation-tester. In so doing, we consider pressure data sets acquired with both flow and observation probes during draw-down and build-up periods. For cases where a-priori information can be sufficiently constrained, our estimation method provides reliable and accurate estimates of petrophysical and elastic properties in the presence of moderate levels of random noise. / text

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Detailed field and petrographic study of the Precambrian Rough Ridge Formation of the Packsaddle Schist documents a more complex tectonic history for the Llano Uplift than has previously been reported. The Rough Ridge Formation was affected by two metamorphic events and four phases of deformation. Mineral assemblages in pelitic and mafic lithologies are characteristic of the amphibolite facies, and the presence of cordierite in preference to almandine indicate low pressure during part of the metamorphism. Inclusions of staurolite in a Mn-rich garnet, coupled with the absence of staurolite elsewhere in the rock suggest that pressure may have ranged from medium to low during metamorphism. Textures indicate that post-tectonic recrystallization occurred as a consequence of either slow cooling or of reheating after dynamothermal events. The first phase of deformation (D1) was a complete transposition of original sedimentary layers, with a pervasive foliation (S1) forming parallel to the axial planes of isoclinal folds. D2 is characterized by small folds and a crenulation cleavage S2. D3 formed a crenulation cleavage S3. D4 formed the prominent folds in the area, with a pervasive axial planar cleavage S4. Isolated occurrences of a pre-S1 metamorphic foliation are evidence of still earlier deformation. In one pelitic unit, oriented inclusions show that garnet growth was post-D2, while cordierite growth was post-D4. Growth and recrystallization of micas, quartz and feldspar span all the deformations. The timing of deformation events is bracketed by the pre- to syn-tectonic intrusion of the 1167 +/- 15 m.y. old Red Mountain Gneiss, and the post-tectonic intrusion of a 1080 +/- 15 m.y. old melarhyolite dike. The results of this study demonstrate that rocks of the Llano Uplift have undergone a complex tectonic and metamorphic history similar to that seen in other Grenville Age rocks of North America. / text

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