Membrane separation technology has recently emerged as a potential alternative technique for removing higher hydrocarbons (C₃₊) from natural gas. For economic reasons, membranes for this application should be organic vapor selective materials such as poly(dimethylsiloxane) (PDMS) or poly(1-trimethylsilyl-1-propyne) (PTMSP). These polymers, often called solubility selective polymers, sieve penetrant molecules based largely on relative penetrant solubility in the polymer. The sorption and transport properties in such polymers have been reported previously. However, most studies present only pure gas sorption and transport properties. Mixture properties, which are important for estimating membrane separation performance, are less often reported. In addition, mixed gas sorption and diffusion data in such polymers, to the best of our knowledge, have never been investigated before. This research work provides a fundamental database of mixture sorption, diffusion, and permeation data in solubility selective polymers. Two solubility selective polymers were studied: poly(dimethylsiloxane) (PDMS) and poly(1-trimethylsilyl-1-propyne) (PTMSP). The vapor/gas mixture was n-C4H10/CH4. CH4 partial pressures ranged from 1.1 to 16 atm, and [subscript n-]C₄H₁₀ partial pressures ranged from 0.02 to 1.7 atm. Temperatures studied ranged from -20 to 50 oC. The pure and mixed gas [subscript n-]C₄H₁₀ and CH₄ permeability and solubility coefficients in PDMS and PTMSP were determined experimentally using devices constructed specifically for these measurements. The pure and mixed gas diffusion coefficients were calculated from permeability and solubility data. In rubbery PDMS, the presence of [subscript n-]C₄H₁₀ increases CH₄ permeability, solubility, and diffusivity. On the other hand, the presence of CH₄ does not measurably influence [subscript n-]C₄H₁₀ sorption and transport properties. The [subscript n-]C₄H₁₀/CH₄ mixed gas permeability selectivities are lower than those estimated from pure gas measurements. This difference is due to both lower solubility and diffusivity selectivities in mixtures relative to those in pure gas. Plasticization of PDMS by [subscript n-]C₄H₁₀ does little to n-C4H10/CH₄ mixed gas diffusivity selectivity. Increases in mixed gas permeability selectivity with increasing [subscript n-]C₄H₁₀ activity and decreasing temperature were mainly due to increases in solubility selectivity. Unlike PDMS, the presence of [subscript n-]C₄H₁₀ decreases CH₄ permeability, solubility, and diffusivity in PTMSP. The competitive sorption and the blocking effects significantly reduce CH₄ solubility and diffusion coefficients in the polymer, respectively. However, similar to PDMS, the presence of CH₄ has no measurable influence on [subscript n-]C₄H₁₀ sorption and transport properties. [subscript n-]C₄H₁₀ /CH₄ mixed gas permeability selectivities in PTMSP are higher than those determined from the pure gas measurements. This deviation is a result of higher solubility and diffusivity selectivities in mixtures relative to the pure gas values. Mixed gas permeability, solubility, and diffusivity selectivities in PTMSP increased with increasing [subscript n-]C₄H₁₀ activity and decreasing temperature. The partial molar volumes of [subscript n-]C₄H₁₀ and CH₄ in the polymers were determined from sorption and dilation data. The dilation isotherms of PDMS and PTMSP in mixtures agree with estimates based on pure gas sorption and dilation measurements. The partial molar volumes of n-C4H10 and CH4 in PDMS are similar to those in liquids. In contrast, the partial molar volumes of [subscript n-]C₄H₁₀ and CH₄ in glassy PTMSP are substantially lower than those in liquids. Several models were used to fit the experimental data. For instance, the FFV model, the activated diffusion model, and the Maxwell-Stefan model were employed to describe the mixture permeability data in PDMS. Based on the Maxwell-Stefan analysis, the influence of coupling effects on permeation properties in PDMS were negligible. The dual mode sorption and permeation models were used to describe the mixed gas data in PTMSP. The dual mode permeability model must be modified to account for [subscript n-]C₄H₁₀ -induced reductions in CH₄ diffusion coefficients (i.e., the blocking effect). The FFV model provides poor correlations in PTMSP. There seems to be other factors, besides FFV per se, contributing to the temperature and concentration dependence of diffusion coefficients in PTMSP.

The gas transport properties of side-chain crystalline poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends are determined as a function of temperature for varying side-chain lengths, n and m, and blend compositions. The side chains of poly(n-alkyl acrylate)s crystallize independently of the main chain for n [is greater than or equal to] 10 which leads to an extraordinary increase in the permeability at the melting temperature of the crystallites. The compatibility of these polymers are examined and macroscopic homogeneity is observed for a small range of n and m when the difference /n - m/ is between 2 - 4 methylene units. Thermal analysis shows that the blend components crystallize independently of one another; at the same time, the crystallization of each component is hindered by the presence the other component. The permeation responses of these blends show two distinct permeation jumps as the crystallites from each component melt at their respective melting temperatures. Blends with continuous permeation responses are found to have higher effective activation energies than observed for common polymers. Thermal analysis proved to be a useful tool to help predict the permeation response for poly(alkyl acrylates); thus the thermal behavior of poly(n-alkyl acrylate) blended with n-aliphatic materials and random copolymers of poly(n-alkyl acrylates) are briefly examined. A bulk modified atmospheric storage design is proposed where produce is stored in a rigid chamber that is equipped with both selective and non-selective membrane modules that help regulate the oxygen entering and the carbon dioxide leaving the produce compartment. The design enables control of the atmosphere inside the chamber by modulating gas flow, i.e. the gas flow rate and composition, through the non-selective membrane by delivering fresh air upstream of the non-selective membrane. The model shows that the choice of materials for the selective and non-selective membranes dictate the range of concentrations achievable; however, the air flow rate allows the control between these ranges. The method to design a practical chamber from this model is also described.

Thermal stimulation of geothermal wells is a production enhancement technique that is an attractive option to operators of geothermal fields as a way to enhance and revitalize well performance capabilities through injection of cold water into the geothermal reservoir. This thesis presents a review of thermal stimulation procedures that have been carried out at various geothermal fields worldwide, and then sets out to demonstrate through laboratory experiments the effects of thermal stimulation on typical reservoir rocks. Thermal damage to crustal rocks is important in many fields of practical engineering applications. Thermal fractures have been discussed in many studies, however their formation under fully water saturated conditions as a result of rapid quenching is not fully understood. In this study, a new methodology is designed to replicate thermal stimulation in such an environment, using an apparatus that allows rocks to be heated to 350°C at up to 22 MPa confining pressure and rapidly quenched with cold water to ambient temperature while maintaining system pressure. The results indicate that through thermal cycling in the apparatus, porosity was increased, density decreased, acoustic velocities attenuated and mechanical properties significantly altered. Maximum damage occurred during the first thermal cycle, a product of the thermo-mechanical Kaiser effect such that rocks should not experience additional damage unless a previous maximum stress is surpassed. The thesis details a comprehensive evaluation of the Rotokawa Andesite sourced from the Rotokawa Geothermal field located in the Taupo Volcanic Zone, New Zealand. The importance of microstructural fabrics on the physical properties of this reservoir lithology is demonstrated. The mineralogical and petrological fabrics of the rocks are coupled with detailed studies of the microstructural fracture networks, including measurements of porosity, density and permeability. Acoustic wave velocities and dynamic elastic moduli were determined. Uniaxial compressive strength testing coupled with acoustic emission have helped to determine the behavior of the rock under deformation and provided data to characterize the static elastic moduli of the rocks. These data are then utilized to build empirical, micromechanical and geometric relationships. To better constrain important engineering concerns such as wellbore stability, reservoir forecasting and stimulation procedures, thermal property measurements were carried out on samples recovered from the Rotokawa Andesite. In particular, measurements of linear thermal expansion, thermogravimetric analysis, and differential scanning calorimetry were measured utilizing varied experimental heating rates of 2, 5 and 20 K/min. The property analyses were carried out to determine if heating rates influenced the measurement of thermal properties, specifically thermal expansion coefficients and strain rate in the samples. Results indicate that thermal expansion is not heating rate dependent within the range investigated though the strain rate is significantly dependent on heating rate, with higher strain rates observed in conjunction with higher heating rates. By using a one dimensional stress model, a failure criterion can be established for the Rotokawa Andesite when subject to thermal stressing. The importance of this study is to further understand the critical heating and cooling rates at which thermal stress causes cracking within the Rotokawa reservoir. This can enhance permeability but can also affect wellbore stability, so constraining these conditions can be beneficial to resource utilization. To test effects of thermal stimulation in the laboratory, Rotokawa Andesite core was heated to 325ºC at pressure of 20 MPa and quenched rapidly to 20ºC while maintaining a pressure of 20 MPa. Permeability increased by an order of magnitude over original pre-treatment values. Ultrasonic velocities also reflected a significant change after stimulation testing. Scanning electron microscopy showed significant microstructural change to samples and supplemented physical property investigations. The results imply that thermal stimulation can be successfully repeated in the laboratory and is coupled with both thermal and chemical components. The results of these investigations are of profound importance for effective utilization and maintenance of the Rotokawa Geothermal field and the results also have implications for geothermal fields worldwide.

A three-dimensional stochastic numerical inverse model has been developed for characterizing the properties of unsaturated fractured medium through analysis of singleand cross-hole pneumatic tests. Over 270 single-hole [Guzman et al., 1996] and 44 cross-hole pneumatic tests [Illman et al., 1998; Inman, 1999] were conducted in 16 shallow vertical and slanted boreholes in unsaturated fractured tuffs at the Apache Leap Research Site (ALRS), Arizona. The single-hole tests were interpreted through steady-state [Guzman et al., 1996] and transient [Illman and Neuman, 2000b] analytical methods. The cross-hole tests were interpreted by analytical type-curves [Illman and Neuman, 2000a]. I describe a geostatistical analysis of the steady-state single-hole data, and numerical inversion of transient single-hole and cross-hole data. The geostatistical analysis of single-hole steady-state data yields information about the spatial structure of air permeabilities on a nominal scale of 1 m. The numerical inverse analysis of transient pneumatic test data is based on the assumption of isothermal single-phase airflow through a locally isotropic, uniform or non-uniform continuum. The stochastic inverse model is based on the geostatistical pilot point method of parameterization [de Marsily, 1978], coupled with a maximum likelihood definition of the inverse problem [Carrera and Neuman, 1986a]. The model combines a finite-volume flow simulator, FEHM [Zyvoloski et al., 1997], an automatic mesh generator, X3D [Trease et al., 1996], a parallelized version of an automatic parameter estimator, PEST [Doherty et al., 1994], and a geostatistical code, GSTAT [Pebesma and Wesseling, 1998]. The model accounts directly for the ability of all borehole intervals to store and conduct air through the system; solves the airflow equations in their original nonlinear form accounting for the dependence of air compressibility on absolute air pressure; can, in principle, account for atmospheric pressure fluctuations at the soil surface; provides kriged estimates of spatial variations in air permeability and air-filled porosity throughout the tested fractured rock volume; and is applied simultaneously to pressure data from multiple borehole intervals as well as to multiple cross-hole tests. The latter amounts to three-dimensional stochastic imaging, or pneumatic tomography, of the rock as proposed by Neuman [1987] in connection with cross-hole hydraulic tests in fractured crystalline rocks near Oracle, Arizona. The model is run in parallel on a supercomputer using 32 processors. Numerical inversion of single-hole pneumatic tests allows interpreting multiple injection-step and recovery data simultaneously, and yields information about air permeability, air-filled porosity, and dimensionless borehole storage coefficient. Some of this cannot be accomplished with type-curves [Inman and Neuman, 2000b]. Air permeability values obtained by my inverse method agree well with those obtained by steady-state and type-curve analyses. Both stochastic inverse analysis of cross-hole data and geostatistical analysis of single-hole data, yield similar geometric mean and similar spatial pattern of air permeability. However, I observe a scale effect in both air permeability and air-filled porosity when I analyze cross-hole pressure records from individual monitoring intervals one by one, while treating the medium as being uniform; both pneumatic parameters have a geometric mean that is larger, and a variance that is smaller, than those obtained by simultaneous stochastic analysis of multiple pressure records. Overall, my analysis suggests that (a) pneumatic pressure behavior of unsaturated fractured tuffs at the ALRS can be interpreted by treating the rock as a continuum on scales ranging from meters to tens of meters; (b) this continuum is representative primarily of interconnected fractures; (c) its pneumatic properties nevertheless correlate poorly with fracture density; and (d) air permeability and air-filled porosity exhibit multiscale random variations in space.

M. Tech. Polymer Technology. / The gas permeability of composite epoxy resins formulated with graphene platelets and glass flakes was investigated. The purpose of researching the gas permeability of the composite resins was to develop a possible coating system that could prevent or limit the release of radioactive gases like tritium from irradiated graphite waste which may accumulate in underground repositories. Helium was used as a substitute gas to simulate the diffusive properties of tritium gas.

<p>The adaptive response of vascular endothelial cells to shear stress alteration induced by global hemodynamic changes is an essential component of normal endothelial physiology in vivo; and an understanding of the transient regulation of endothelial phenotype during adaptation will advance our understanding of endothelial biology and yield new insights into the mechanism of atherogenesis. The objective of this study was to characterize the adaptive response of arterial endothelial cells to acute increases in shear stress magnitude and frequency in well-defined in vitro settings. Porcine endothelial cells were preconditioned by a basal level shear stress of ±15dynes/cm^2 at 1 Hz for 24 hours, and an acute increase in shear stress magnitude (30 ±15 dynes/cm^2) or frequency (2 Hz) was then applied. Endothelial permeability to bovine serum albumin was measured and gene expression profiling was performed using microarrays at multiple time points during a period of 6 hours after the shear stress alteration. The instantaneous endothelial permeability was found to increase rapidly in response to the acute increase in shear stress magnitude. Endothelial permeability nearly doubled after 40 minutes exposure to the elevated shear magnitude, and then decreased gradually. However, less dependency of endothelial permeability on shear stress frequency was observed. Endothelial permeability increased slowly from 120 minutes to 6 hours after exposure to the elevated shear frequency, but the increase was not statistically significant and was relatively small (1.2 fold increase at 6 hours). The transcriptomics studies identified 86 genes that were sensitive to the elevated shear magnitude and 37 genes sensitive to the elevated frequency. A significant number of the identified genes are previously unknown as sensitive to shear stress. The acute increase in shear magnitude promoted the expression of a group of anti-inflammatory and anti-oxidative genes; while the acute increase in shear frequency upregulated a set of cell-cycle regulating genes and angiogenesis genes. The adaptive response of global gene expression profile to the elevated shear magnitude is found to be triphasic, consisting of an induction period, an early adaptive response (ca. 45 minutes) and a late remodeling response. However, no apparent temporal regulation pattern of global gene expression was found during the adaptation to the elevated shear frequency. The results from this dissertation suggest that endothelial cells exhibit a specific phenotype during the adaptive response to changes in shear stress; and the transient phenotype is different than that of fully-adapted endothelial cells and may alter arterial atherosusceptibility.</p> / Dissertation

Unconventional natural gas resources, particularly tight gas sands, constitute a significant percentage of the natural gas resource base and offer abundant potential for future reserves and production. The premise of this research is that several unique characteristics of these rocks are the consequence of post depositional diagenetic processes including mechanical compaction, quartz and other mineral cementation, and mineral dissolution. These processes lead to permanent alteration of the initial pore structure causing an increase in the number of isolated and disconnected pores and thus in the tortuosity. The objective of this research is to develop a pore scale model of the geological processes that create tight gas sandstones and to carry out drainage simulations in these models. These models can be used to understand the flow connections between tight gas sandstone matrix and the hydraulic fractures needed for commercial production rates. We model depositional and diagenetic controls on tight gas sandstones pore geometry such as compaction and cementation processes. The model is purely geometric and begins by applying a cooperative rearrangement algorithm to produce dense, random packings of spheres of different sizes. The spheres are idealized sand grains. We simulate the evolution of these model sediments into low-porosity (3% to 10%) sandstone by applying different amount of ductile grains and quartz precipitation. A substantial fraction of the original pore throats in the sediment are closed by the simulated diagenetic alteration. Thus, the pore space in typical tight gas sandstones is poorly connected, and is often close to being completely disconnected, with significant effect on flow properties. The drainage curves for model rocks were computed using invasion percolation in a network taken directly from the grain-scale geometry and topology of the model. The drainage simulations show clear percolation behavior, but experimental data frequently do not. This implies that either network models based on intergranular void space are not a good tool for modeling of tight gas sandstone or the experiments are not correctly done on tight gas samples. In addition to reducing connectivity, the porosity-reducing mechanisms change pore throat size distributions. These combined effects shift the drainage water relative permeability curve toward higher values of water saturation, and gas relative permeability shifts toward smaller values of gas. Comparison of simulations with measured relative permeabilities shows a good match although same network fail to match drainage curves. This could happens because the model gives the right fluid configuration but at the wrong values of curvature and saturation. The significance of this work is that the model correctly predicts the relative permeabilities of tight gas sandstones by considering the microscale heterogeneity. The porosity reduction due to ductile grain deformation is a new contribution and correctly matches with experimental data from literature. The drainage modeling of two-phase flow relative permeabilities shows that the notion of permeability jail, a range of saturations over which both gas and water relative permeabilities are very small, does not occur during drainage. / text

Chemical treatments using solvents and surfactants can be used to increase the productivity of gas-condensate wells with condensate banks. CMG’s compositional simulator GEM was used to simulate such treatments to gain a better understanding of design questions such as how much treatment solution to inject and to predict the benefits of such treatments. GEM was used to simulate treatments in vertical wells with and without hydraulic fractures and also horizontal wells. However, like other commercial compositional simulators, the flash calculations used to predict the phase behavior is limited to two phases whereas a three-phase flash is needed to accurately model the complex phase behavior that occurs during and after the injection of treatment solutions. UTCOMP is a compositional simulator with three-phase flash routine and attempts were made to use it to simulate such well treatments. However, this is a very difficult problem to simulate and all previous attempts failed because of numerical problems caused by inconsistent phase labeling (so called phase flipping) and the discontinuities this causes in the relative permeability values. In this research, a new relative permeability model based on molar Gibbs free energy was developed, implemented in a compositional simulator and applied to several difficult three-phase flash problems. A new way of modeling the residual saturations was needed to ensure a continuous variation of the residual saturations from the three-phase region to the two-phase region or back and was included in the new model. The new relative permeability model was implemented in the compositional reservoir simulator UTCOMP. This new relative permeability model makes it is unnecessary to identify and track the phases. This method automatically avoids the previous phase flipping problems and thus is physically accurate as well as computationally faster due to the improved numerical performance. The new code was tested by running several difficult simulation problems including a CO2 flood with three-hydrocarbon phases and a water phase. A new framework for doing flash calculations was also developed and implemented in UTCOMP to account for the multiple roots of the cubic equation-of-state to ensure a global minimum in the Gibbs free energy by doing an exhaustive search for the minimum value for one, two and three phases. The purpose was to determine if the standard method using a Gibbs stability test followed by a flash calculation was in fact resulting in the true minimum in the Gibbs free energy. Test problems were run and the results of the standard algorithm and the exhaustive search algorithm compared. The updated UTCOMP simulator was used to understand the flow back of solvents injected in gas condensate wells as part of chemical treatments. The flow back of the solvents, a short-term process, affects how well the treatment works and has been an important design and performance question for years that could not be simulated correctly until now due to the limitations of both commercial simulators and UTCOMP. Different solvents and chase gases were simulated to gain insight into how to improve the design of the chemical treatments under different conditions. / text

Gas wells suffer a decrease in productivity because of the formation of a liquid hydrocarbon “condensate” in the near wellbore area. This "condensate" forms near producing wells when the flowing pressure is below the reservoir fluid's dew point. Several methods have been shown to temporarily alleviate this problem, but eventually the condensate bank reforms and the productivity again decreases. The use of surfactants to alter the near wellbore wettability to neutral wetting is a potential longer term solution to liquid blocking in these reservoirs. This alteration increases the gas and liquid relative permeabilities and thereby the productivity by reducing the residual liquid saturation. This enhancement allows the accumulated liquid to flow and is durable as long as the wettability alteration is persistent. This solution has been shown to be successful through core flood experiments and field trials in high permeability sandstones, but no improvements had been observed in low permeability cores. As the global demand for energy increases, the petroleum industry has begun to develop unconventional (low permeability) assets, new techniques are needed to maintain and improve their productivity. Liquid blocking in these wells can have a much larger impact on both the gas and condensate production in such low permeability formations. Applying this technique increases both gas and condensate mobility and should increase the economic producing life of these wells. Core flood experiments were conducted to investigate the ability of a chemical treatment to alter the wettability of low permeability sandstones. Previous experimentation did not find any improvement because the increased capillary forces prevented the treatment solution from being easily displaced. This concealed the benefit achieved when the wettability was altered. These experiments recorded smaller relative permeability increases compared to higher permeability core floods, so super critical carbon dioxide was tested as an alternative solvent. While the new treatment was more injectable, it was not as successful at altering wettability. Progress has been made on a solution to liquid blocking in low permeability sandstones, but additional research needs to be completed to further optimize this method. / text

I present results from quantitative evaluation of the capability of hosting and trapping CO₂ of a carbonate brine reservoir from Dickman Field, Kansas. The analysis includes estimation of some reservoir parameters such as porosity and permeability of this formation using pre-stack seismic inversion followed by simulating flow of injected CO₂ using a simple injection technique. Liner et at (2009) carried out a feasibility study to seismically monitor CO₂ sequestration at Dickman Field. Their approach is based on examining changes of seismic amplitudes at different production time intervals to show the effects of injected gas within the host formation. They employ Gassmann's fluid substitution model to calculate the required parameters for the seismic amplitude estimation. In contrast, I employ pre-stack seismic inversion to successfully estimate some important reservoir parameters (P- impedance, S- impedance and density), which can be related to the changes in subsurface rocks due to injected gas. These are then used to estimate reservoir porosity using multi-attribute analysis. The estimated porosity falls within a reported range of 8-25%, with an average of 19%. The permeability is obtained from porosity assuming a simple mathematical relationship between porosity and permeability and classifying the rocks into different classes by using Winland R35 rock classification method. I finally perform flow simulation for a simple injection technique that involves direct injection of CO₂ gas into the target formation within a small region of Dickman Field. The simulator takes into account three trapping mechanisms: residual trapping, solubility trapping and mineral trapping. The flow simulation predicts unnoticeable changes in porosity and permeability values of the target formation. The injected gas is predicted to migrate upward quickly, while it migrates slowly in lateral directions. A large amount of gas is concentrated around the injection well bore. Thus my flow simulation results suggest low trapping capability of the original target formation unless a more advanced injection technique is employed. My results suggest further that a formation below our original target reservoir, with high and continuously distributed porosity, is perhaps a better candidate for CO₂ storage. / text