The main drawback in the utilization of geothermal resources arises from the precipitation of secondary minerals within wells, pipelines, steam separators, turbines and other surface equipment in form of scales. Scale...The main drawback in the utilization of geothermal resources arises from the precipitation of secondary minerals within wells, pipelines, steam separators, turbines and other surface equipment in form of scales. Scale formation is an outcome of the alteration of various rocks dissolved in geothermal fluids that find their way into a reservoir. Once geothermal fluids ascend to the surface, hydrostatic pressure decreases toward a phase separation level that permits the dissolved gases such as CO<sub>2</sub>, H<sub>2</sub>S and H<sub>2</sub>, and steam to separate from the liquid phase by “boiling”. Stripping of these volatiles may increase fluid pH, leading to precipitation and deposition of secondary minerals. The study sought to establish the relationship between water-rock interaction and secondary mineral precipitates at the surface and deep fluid at different temperatures during depressurisation boiling and cooling. Samples were collected from selected Olkaria wells;OW-38A, OW-910 and OW-910A. The analysis of the results outlined deep fluid Alkali-Chloride waters and surface steam-heated Alkali-Bicarbonate and acidic Sulphate-Chloride waters. Various models suggested adiabatic boiling, conductive cooling and possible mixing and dilution in the wells. Hydrothermal alteration minerals were found to be in equilibrium with the geothermal fluids at varying temperatures, and the secondary minerals controlled the chemistry of the reservoir. Silica-saturated solutions precipitated silica in OW-910 and OW-910A, which may have resulted from rapid cooling following mixing with cold surface water.展开更多
Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is prop...Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is proposed.It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels.Under the conditions of both density difference in natural circulation and narrow rectangle channels,the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established.The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels.Features of ONB in natural circulation narrow rectangle channels are as follows:heating power is the incentive of the happen of ONB;the higher the heating power is,the higher the degree of superheat is,and the earlier the ONB will appear.With the pressurizing,the appearance of ONB will be delayed.The higher the degree of supercooling is,the later the ONB appears.The ONB will happen easier when there are noncondensable gases and roughness in the channels.展开更多
文摘The main drawback in the utilization of geothermal resources arises from the precipitation of secondary minerals within wells, pipelines, steam separators, turbines and other surface equipment in form of scales. Scale formation is an outcome of the alteration of various rocks dissolved in geothermal fluids that find their way into a reservoir. Once geothermal fluids ascend to the surface, hydrostatic pressure decreases toward a phase separation level that permits the dissolved gases such as CO<sub>2</sub>, H<sub>2</sub>S and H<sub>2</sub>, and steam to separate from the liquid phase by “boiling”. Stripping of these volatiles may increase fluid pH, leading to precipitation and deposition of secondary minerals. The study sought to establish the relationship between water-rock interaction and secondary mineral precipitates at the surface and deep fluid at different temperatures during depressurisation boiling and cooling. Samples were collected from selected Olkaria wells;OW-38A, OW-910 and OW-910A. The analysis of the results outlined deep fluid Alkali-Chloride waters and surface steam-heated Alkali-Bicarbonate and acidic Sulphate-Chloride waters. Various models suggested adiabatic boiling, conductive cooling and possible mixing and dilution in the wells. Hydrothermal alteration minerals were found to be in equilibrium with the geothermal fluids at varying temperatures, and the secondary minerals controlled the chemistry of the reservoir. Silica-saturated solutions precipitated silica in OW-910 and OW-910A, which may have resulted from rapid cooling following mixing with cold surface water.
基金Supported by National Natural Science Foundation of China(No.50976033)National Key Laboratory of Bubble Physics and Natural Circulation(No.9140C7 101030905)North China Electric Power University’s 211 Project
文摘Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is proposed.It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels.Under the conditions of both density difference in natural circulation and narrow rectangle channels,the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established.The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels.Features of ONB in natural circulation narrow rectangle channels are as follows:heating power is the incentive of the happen of ONB;the higher the heating power is,the higher the degree of superheat is,and the earlier the ONB will appear.With the pressurizing,the appearance of ONB will be delayed.The higher the degree of supercooling is,the later the ONB appears.The ONB will happen easier when there are noncondensable gases and roughness in the channels.
