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Notes: Summary Thermal spallation is a method whereby the surface of a rock is rapidly heated causing small (100–1000 μm) flakes or spalls, to form. When applied to drilling, a supersonic, high temperature (2600 K) gas jet is directed at the rock to provide the heat source and sweep away the spalls. Previous studies of thermal spallation drilling indicate that penetration rates of up to 30 m/hr (100 ft/hr), approximately ten times greater than commonly obtained using conventional rotary mechanical methods, can be achieved in competent, non-fractured hard rock such as granite. A total direct operating cost for drilling in granite using a flame-jet spallation drill was estimated by Browning (1981) to be approximately $9/m in 1991$ (about $3/ft) compared to “trouble-free” well drilling costs for conventional rotary methods in similar rock to depths of 3 to 7 km (10000 to 21000 ft) of $300 to $900/m ($100 to $300/ft) (Tester and Herzog, 1990, 1992). The Browning estimates for spallation drilling are obviously optimistic in that they don't include capital costs for the rig and associated hardware. However, the substantially higher penetration rates, significantly reduced wear of downhole components, and the high efficiency of rock communition in comparison to rotary methods suggest that substantial cost reductions could be possible in deep drilling applications. For example, in the construction of hot dry rock geothermal power plants where rotary mechanical methods are used for well drilling to depths of (4 to 5 km), about half of the initial capital cost would be required for well drilling alone (Tester and Herzog, 1992). The current study has focused on gaining a better understanding of both the rock failure mechanism that occurs during thermal spallation and the heat transfer from the gas jet to the rock surface. Rock mechanics modeling leads to an expression for the surface temperature during spallation as a function of rock physical properties and the incident heat flux. Surface temperature measurements and heat flux determination during laser and flame-jet induced thermal spallation are used to provide appropriate values of the “Weibull parameters” that statistically describe the size-strength relationship in granite. Use of these parameters allows one to accurately estimate surface temperatures required by the numerical simulation model to calculate heat and mass transport rates occurring in the flow field above the spalling rock surface. Based on the results of this experimental study, we concluded that mechanically-determined Weibull parameters are not directly applicable to describe spallation failure phenomena caused by thermal stress. Under the extreme rapid heating conditions of flame-jet drilling, local overheating and possibly stress relief lead to higher temperatures than predicted using room temperature Weibull parameters. Nonetheless, the Weibull-based statistical model of failure can be utilized by empirically fitting them and σ0 Weibull parameters to match experimental measurements of spalling surface temperature as a function of applied heat flux. Correlations for steady state and onset spallation conditions were established with consistent results obtained for both laser and propane-oxygen flame jet heating.

Notes: Thermodynamic properties pertaining to phase equilibria in the binary-fluid hydrate systems, methylene chloride-water and chloroform-water, and the ternary hydrate system, methylene chloride-chloroform-water, were measured. Total vapor pressure data were recorded as a function of temperature over a range of -3 to + 10°C. Quadruple locus measurements of the ternary four-phase equilibrium, L1-L2-H-G, and isobaric studies of the ternary system chloroform-methylene chloride-water, support the existence of a solid solution hydrate between methylene chloride and chloroform. The addition of the nonhydrate former, hexane, to the methylene chloride-water system lowered the isobaric critical decomposition temperature of the hydrate.

Notes: Identification and characterization of coupled diffusional and electrochemical kinetics effects was achieved under potentiostatic anodic dissolution conditions. A one-dimensional artificial pit geometry with sample wire electrodes embedded in an inert support exposed to NaCl solutions was used to study the dissolution of stainless steel and highnickel Alloy 600. Multiple steady states for both materials were determined at conditions where the diffusional transport rates balanced the electrochemical rate of dissolution at the surface of the wire electrode. A theoretical transport model was developed to quantitatively explain the observed multiple steady state phenomena.

Notes: Of importance to geothermal energy development, oil, gas and mineral recovery, and waste storage is the characterization of the dissolution rate of host reservoir rock as a function of temperature, pressure and liquid-phase composition. As a major constitutive mineral in natural geologic systems, quartz was selected for study. Dissolution experiments were carried out in a continuous-flow, titanium autoclave reactor system at 100-200°C in various chemical environments. Acidification to pH 1.1 using nitric acid showed very little effect on the quartz dissolution rate. The effect of hydroxide ion concentration and ionic strength were evaluated in NaOH, NaOH/NaCl and NaOH/Na2SO4 solutions. The fractional-order dependency of the quartz dissolution rate on hydroxide ion and sodium ion (or ionic strength) concentration was determined in NaOH/NaCl solutions. The results that extend the available range of kinetic data for quartz generally agree with previous work. The observed fractional-order kinetics were qualitatively described using classical adsorption isotherms. No significant variation in the apparent reaction order of the hydroxide ion with increasing temperature could be determined due to the scatter in the data. Quartz dissolution rates were slower by about 40% in NaOH/Na2SO4 solutions than in NaOH/NaCl solutions at sodium concentrations higher than 0.01 molal. The apparent activation energy from 100 to 200°C in NaOH/NaCl solutions up to 0.01 molal hydroxide ion and 0.1 molal sodium ion was estimated to be 72 (±6) kJ/mol.