The Underground Hot Water Circulation Mechanism And The Resource Evaluation In Xining Basin

Economic development cannot do without energy, energy shortage and environmental problem of excessive exploitation of petroleum, coal and other non renewable resources brought about by the increasingly serious, seeking for new energy imminent, but the development and utilization of geothermal resources in the economic, technical and environmental aspects are a good energy solutions. This paper mainly through the groundwater dynamic field, Xining basin groundwater chemical field, geothermal research field and isotopic analysis of underground hot water, the source or origin, and carries on the research analysis to the underground hot water circulating mechanism; simulation method through numerical groundwater flow of papers, underground water basin permit extraction volume is calculated and evaluation, model prediction to different exploitation scheme design, and analysed the present situation of mining and underground hot water, provide the foundation and scientific basis for the research results of using geothermal water resources in Xining basin exploitation. Finally, put forward to solve the problems to be encountered in the process of underground water exploitation technology. The main research contents and conclusions are as follows:(1) The underground hot water circulation:confined artesian water flow direction from the basin edge flow to the center of the basin, the basin mountain accept around all kinds of water supply, the overall supply groundwater with the center of the basin runoff, from the edge of the basin of high pressure to low head collection and excretion of discharge characteristics.(2) Features of the basin geothermal field:through the geothermal well temperature measurement results show that, with the increasing depth of underground geothermal wells, water temperature is higher. Through 100m,200m,500m, temperature 1000m and 2000m depth level show, rising from the basin edge toward the center, reflecting the heat conduction effect of deep heat from the bottom up; in the circulation process, groundwater absorption heat released to form the surrounding rock of underground hot water. The cycle of the deeper, the higher water temperature. Geophysical data show:the main source of underground water basin to as heat flow and geothermal gradient heating high.(3) The basin water chemical field characteristics:the statistics of 13 underground hot water in geothermal well water chemical data display, Xining basin salinity presented by annular horizontal edge of the basin to the center gradually increased zoning characteristics of geothermal wells, coal 12 mineralization degree up to 148.62g/L, belongs to high salinity of underground hot water. At the same time chemical type of water from basin edge to center of basin occurs in a sequence of bicarbonate type water-water-sulfate chloride type water ring shape hydrogeochemical horizontal zoning evolution trend.(4) Isotopic characteristics of the three groups of samples:hydrogen and oxygen isotope composition of basic fell on Craig precipitation line, that the underground hot water basin is the main source of the surrounding mountain precipitation recharge. Because of the different positions of the fall on a line, suggests that the three sample control recharge recharge area of groundwater recharge area location, time, formation age and migration in different systems with different rates of. According to the hydrogen and oxygen isotope curve and the content of local meteoric isotopic contrast, and the use of highly effect in precipitation, deduce the underground hot water in Xining basin recharge altitude of more than 2903m.Radioactive isotope age determination by14C analysis of underground hot water age concluded:at present, the exploitation of underground hot water in the basin and aquifers is not generated at the same time the sedimentary water. As the underground hot water circulation, underground hot water before continue to be replaced with a new water, and this slow replacement role continues.(5) Through the method of groundwater numerical simulation, simulation of groundwater level under different exploitation and drawdown condition, and choose the optimal mining plan reasonably come basin groundwater allowable withdrawal is 16079 m3/d. To determine the parameters needed by the geothermal resources evaluation, calculation of geothermal reserves basin is 4.29 · 1020J, can the exploitation of geothermal reserves of 4.29 · 1027J.