Technologies considered for separating CO₂ from flue gas and injecting CO₂ into saline aquifers are energy intensive, costly, and technically challenging. Production of dissolved natural gas and geothermal energy by extraction of aquifer brine has shown the potential of offsetting the cost of CO₂ capture and storage along with other technical and environmental advantages. The key is to recognize inherent value in the energy content of brine in many parts of the world. Dissolved methane in brine and geothermal energy are two of the sources of energy of many aquifers. For example, geopressured-geothermal aquifers of the US Gulf Coast contain sheer volume of hot brine and dissolved methane. For the same reason, the capacity of these geopressured-geothermal aquifers for storage of CO₂ is remarkable. In this study, various reservoir models were developed from data of Texas and Louisiana Gulf Coast saline aquifers. A systematic study was performed to determine the range of uncertainty of the properties and the prospective of energy production from saline aquifers. Two CO₂ injection strategies were proposed for storage of CO₂ based on the results of simulation studies. Injection of CO₂-saturated brine showed several advantages compared to injection of supercritical CO₂. An overall energy analysis was performed on the closed-loop cycles of capture from power plants, storage of CO₂, and production of energy. The level of cost offset of CCS technology by producing energy from target aquifers strongly depends on the applications of the produced energy. The temperature of the produced brine from geopressured-geothermal aquifers is higher than the temperature of amine stripper column. Calculations for the strategy of injecting CO₂-saturated brine show that the amount of extracted thermal energy from geopressured-geothermal aquifers exceeds the amount of heat required for capturing CO₂ by amine scrubbing. In the process of injecting dissolved CO₂, compressors and pumps should run to pressurize the CO₂ and brine to be transported and achieve the required wellhead pressure. The preliminary estimations indicate that the produced methane provides more energy than that required for pressurization. In the regions where the temperature gradient is normal, the temperature of the produced brine may not be high enough for using in the chemical absorption processes. Separation mechanisms driven by pressure difference are the alternatives for chemical absorption processes since the produced methane can be burned for running the compressors and pumps. Membrane process seems to be the leading technology candidate. The preliminary estimations show that the produced power by extracted methane and geothermal energy exceeds the power needed for membranes, compressors, and pumps. Neither storage of greenhouse gases in saline aquifers nor production of methane and/or geothermal energy from these aquifers are profitable. However, designing a closed looped system by combining methods of capture, storage and production may pay off the whole process at least from the energy point of view. / text

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The extraction of geothermal heat can cause precipitation of the minerals dissolved in geothermal fluid. Their deposition on the walls of wells and above-ground plant and in pores near reinjection wells, also known as mineral scaling, is one of the main obstacles to increasing the effectiveness of utilization of the limited geothermal resources. If not controlled properly it can result in accumulation of a significant amount of scale which obstructs pipes and reinjection wells and reduces the efficacy of heat exchangers. The most abundant mineral in geothermal fluid is silica and thus its precipitation can cause the highest scaling rate. While this dissertation is devoted to the study of silica scaling the results obtained may be applicable to other minerals with similar deposition mechanism. Oversaturated silica is known to precipitate from aqueous solution either by the direct chemisorption of single silicic acid molecules (monomers) or by forming colloidal particles suspended in the solution. These particles can subsequently be transported to, and attach onto, a wall. This process of colloidal silica deposition was previously recognised to cause much faster scaling than the direct deposition of silica monomers under typical geothermal plant conditions. While the chemical kinetics of silica polymerization and colloid formation are relatively well understood, transport of these colloids and their stability, which control their aggregation and attachment rates, on the other hand are not. Previous studies of the silica scaling process have identified prominent effects of geothermal brine hydrodynamics on the scaling rate. It was found to increase with the flow rate and particle size, thus suggesting the dominance of the advective (inertial) deposition of colloidal silica. However, this conclusion contradicted the present theory of particle transport in turbulent flows which argues the dominance of the diffusive transport for the relevant range of particle sizes (<1 μm). The development and continuing improvement of the anti-scaling measures required deeper understanding of the complex combination of the phenomena involved in the process of silica scaling. This was pursued in the present study using theoretical and experimental methods. First, the rate of colloidal silica transport from a turbulent flow onto the internal surface of a circular pipe, a cylinder and a flat plate were calculated using available analytical and numerical methods. The obtained theoretical transport rate was found to be about four orders of magnitude higher than the corresponding experimental scaling rate. The latter was determined in the previous studies to be 4.2·10-8 kg/s/m2 for silica colloids of 125 nm in diameter which corresponded to the dimensionless deposition velocity (the dimensionless deposition velocity is the scaling rate normalised by the particle mass concentration and friction velocity) of 1.2·10-6 for the dimensionless particle relaxation time of 2·10-4. Next, based on the standard DLVO theory of particle interactions and in the framework of the Smoluchowski approach the probability of colloidal silica particle attachment to a wall was found to be 10-6. Therefore, the theoretical scaling rate, calculated as a product of this probability and the above-mentioned transport rate was two orders of magnitude lower than the experimental scaling rate. This suggested that the implemented theoretical approach either underestimated particle transport rate or overestimated particle stability. Both possibilities are explored in this dissertation. In addition, the silica scaling rate was measured for a range of conditions: particle size from 20 to 60 nm, particle concentration 1600-10000 ppm, friction velocity from 0.09 to 0.18 m/s (Re = 9-50·103) and ionic strength from 30 to 80 mM, pH 8.1-9.5 and temperature from 25 to 44 °C. For this, laboratory experiments were designed and progressively modified in order to improve the repeatability of the results and to study the scaling process. In these experiments colloidal silica deposition onto the walls of mild steel pipe sections was studied with a recirculating flow rig with variable (but controllable) particle size, concentration, flow rate, pH and ionic strength of the solution. In addition, a parallel plate flow test section was designed and built which will provide better capabilities for the control over the hydrodynamic and test surface conditions in future experiments. The control over the chemical conditions was achieved by the use of the synthetic colloidal solutions. Two methods of their production – hydrolysis of either sodium metasilicate or active silicic acid – were employed. The influence of the synthesis conditions, ion content and pH on the long term behaviour of these colloidal solutions was investigated. The particle size data, obtained using dynamic light scattering (DLS) and verified by electron microscopy, was analysed and compared against the predictions of the current models of nanoparticle growth and stability. The kinetic aggregation was identified to be the dominant particle growth mechanism. Experimental data collected during the long-term observations of the particle growth allowed relationships between the aggregative stability and such parameters as the particle size, ion concentration and pH of the solution to be elucidated. In particular, the aggregative stability of 10-20 nm particles was found to be 108-1010 which is 7-9 orders of magnitude higher than the corresponding DLVO stability. It was also found to decrease with the increase of the particle size. This agreed with the theory of the colloid stabilization by steric interactions. Moreover, the model of the “gel” layer was used to explain the observed “anomalies” of the colloidal silica behaviour. The deposition experiments conducted with these synthetic colloidal solutions showed that the scaling rate increased with the particle size, flow rate and ionic strength (IS) of the solution. Thus, it was measured to be 9.7·10-9 kg/s/m2 for the 45 nm particles in a solution with IS = 0.05 M, which corresponded to the dimensionless deposition velocity of 6.6·10-8 for a dimensionless particle relaxation time of 2.2·10-6. The scaling rate was calculated for these conditions by multiplying the corresponding transport rate and the actual attachment probability determined as an inverse of the experimental stability. It was found to agree with the experimental value within an order of magnitude. In addition, the observed increase of the scaling rate with the increase of particle size was explained by the compensation of the decreased rate of the particle transport by faster decrease of actual particle stability (increase in attachment probability). Therefore the contradiction between the theory and the experiment was resolved for the particles of 20 to 60 nm in diameter. Moreover, the observations of the dimensions and distribution of the scale elements formed in some of the present experiments strongly suggested the significance of the advective (inertial) mechanism of particle deposition. This and comparative analysis of other experimental and theoretical data suggested that the present theory may underestimate the convective transport of the particles onto a rough wall. Therefore, the hypothesis of the parallel-to-wall advective deposition of the nanoparticles onto the roughness/scale elements (not accounted in the current theory) was proposed. The corresponding mass transfer problem was solved analytically using experimentally found dimensions of the scale elements. The additional transport was found to decrease the above-stated discrepancy between the theoretical and experimental scaling rate for large (125 nm) particles by one order of magnitude. The remaining difference of one order of magnitude was speculated to be due to the underestimation of these particles attachment probability derived with the standard DLVO theory. The actual aggregative stability of the silica colloids larger than 60 nm in diameter and for a wider range of IS values is of interest for future experimental studies. An improved understanding of the interrelation between the chemical and hydrodynamic phenomena in the process of silica scaling and its dominant mechanisms was achieved in this dissertation. This allowed optimization of the present anti-scaling practices aimed to minimize the negative effects of mineral scaling on the operation of geothermal power stations. Besides the practical recommendations, which may ultimately help to increase the efficiency of geothermal power stations, the results of the present study may be of value in the fields of mass transfer and colloid science.

Thesis (M.S. - Mechanical Engineering)--University of Arizona. / Includes bibliographical references.

Thesis (M.A.)--Oregon State University, 1986. / Typescript (photocopy). Includes bibliographical references (leaves 174-191). Also available via the World Wide Web.

The magnetotelluric method has been used in the determination of the electrical conductivity structure of the Pemberton area of British Columbia: Meager Mountain, which is at the junction of the Garibaldi volcanic belt and the Pemberton volcanic belt, is the focus of a detailed geothermal resource evaluation. The aim of this project is to determine whether there is a resistivity structural change across the Pemberton volcanic belt. A knowledge of this will give some information about the structural control. This will aid in the investigation of any correlation between the electrical conductivity structure and the hot springs which almost circumscribe Meager Mountain. The temporal variations in the electric and magnetic components of the earth's field were recorded at Alta Lake (ALT), Pemberton (PEM) arid D'Arcy (DAR) from July to September 1975. This profile runs across the Pemberton volcanic belt. Selected sections of the analogue data were converted to digital form and power spectral analyses were made on the latter. The computed apparent resistivity curves show a discrepancy between the EX/D and EY/H which indicates the presence of a resistivity anisotropy/inhomogeneity in the region. Since there is some power in the vertical magnetic component (Z) in the region, it can be concluded that there is inhomogeneity in the conductivity structure. Also the computed Z power attenuation ratios between stations infer that any lateral conductivity change does not persist to large depths. It is also deduced that Z power increases slightly from ALT towards DAR. Some of the difference between the EX/D and EY/H apparent resistivity curves may be due to near surface inhomogeneities and the physical topography of the region. However, the bulk of this difference can be explained by considering a vertical fault zone near PEM, with ALT and PEM on the up-fault and DAR on the down-fault structure. The wider displacement between the EX/D and EY/H curves at DAR as compared to ALT can then be due to the fact that ALT is nearer the fault zone than DAR. On the basis of this interpretation one would expect a more pronounced change in the vertical magnetic component than observed. Apparent resistivity type curves for several theoretical layered earth models were computed and matched with the experimental curves. The results thus obtained indicate that the electrical resistivity structure in the Pemberton area fits the following layered earth model. The upper crustal layer has a resistivity of the order of 300 ohm-m and a thickness of about 40 km under ALT and PEM and about 60 km under DAR. At ALT and PEM, this layer is underlain by a more conductive material of resistivity about 30 ohm-m and a thickness of approximately 20 km. There is no trace of this layer at DAR. The resistivity value of this second layer is of the same order of magnitude as those usually reported from regions of geothermal investigations. The next layer at all the stations is highly resistive (greater than 2000 ohm-m) and has a thickness of about 500 km. This is underlain by a highly conductive basement having a resistivity of about 10 ohm-m or less. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Geothermal energy can make an important contribution to the U.S. energy portfolio. Production areas require seismic monitoring tools to develop and monitor production capability. This paper describes modifications made to a prototypical seismic tool to implement improvements that were identified during previous tool applications. These modifications included changing the motor required for mechanical coupling the tool to a bore-hole wall. Additionally, development of a closed-loop process control utilized feedback from the contact force between the coupling arm and bore-hole wall. Employing a feedback circuit automates the tool deployment/anchoring process and reduces reliance on the operator at the surface. The tool components were tested under high temperatures and an integrated system tool test demonstrated successful tool operations. / Master of Science

The optimal design of geothermal power plants across the entire spectrum of meaningful geothermal brine temperatures and climates is investigated, while accounting for vital real-world constraints that are typically ignored in the existing literature. The constrained design space of both double-flash and binary geothermal power plants is visualized, and it is seen that inclusion of real-world constraints is vital to determining the optimal feasible design of a geothermal power plant. The effect of varying condenser temperature on optimum plant performance and optimal design specifications is analyzed. It is shown that condenser temperature has a significant effect on optimal plant design as well. The optimum specific work output and corresponding optimal design of geothermal power plants across the entire range of brine temperatures and condenser temperatures is illustrated and tabulated, allowing a scientifically sound assessment of both feasibility and appropriate plant design under any set of conditions. The performance of genetic algorithms and particle swarm optimization are compared with respect to the constrained, non-linear, simulation-based optimization of a prototypical geothermal power plant, and particle swarm optimization is shown to perform significantly better than genetic algorithms. The Pareto-optimal front of specific work output and specific heat exchanger area is visualized and tabulated for binary and double-flash plants across the full range of potential geothermal brine inlet conditions and climates, allowing investigation of the specific trade-offs required between specific work output and specific heat exchanger area. In addition to the novel data, this dissertation research illustrates the development and use of a sophisticated analysis tool, based on multi-objective particle swarm optimization, for the optimal design of geothermal power plants.