Research On Experiment Of Refrigeration System Of Underground Frozen Wall In Situ Mining Of Oil Shale

Oil shale (oil forming shale) is a kind of solid combustible organic sedimentaryrock and oil shale resources are plentiful in the world. Around the world there aremore than100oil shale deposits are found in36countries. The shale oil resourcesamount to410billion tons, which is3times of the proven recoverable reserves atpresent of the world’s natural crude oil. The age limit of oil exploitation in China is atmost40years. The per capita recoverable reserves of natural in China is only4.33percent of the world average, and according to the current level of exploitation, theage limit of extraction is less than60years. In northeast, Xinjiang, Inner Mongoliaand other regions of China, the winter is long, the temperature is low, and naturalenergy is very rich.During Oil shale in high-temperature situ exploitation, underground freezingmethod is needed, which is commonly known as frozen wall. Domestic is lack ofrelated research reports, and foreign relatively mature technology is Shell’s ICP. Inorder to prevent the flow of groundwater and the loss of underground oil and gas,Shell has used underground freezing technology, namely frozen wall technology, toestablish frozen wall and prevent the flow of groundwater and the loss of oil and gasof in situ exploitation, then ensure the success of in situ exploitation.The frozen wall technology is mainly to pump low-temperature freezing liquidinto the frozen well. In the well heat exchange happens between the soil and thefreezing liquid to realize the soil freeze. In the freezing process, the soil near the wellis rapidly frozen. With the depth of the freeze, the range of freezing will continue toexpand. Finally, frozen region is connected together to form the frozen wall.The frozen wall technology is mainly used refrigeration units, but in NortheastChina, winter is long and cold. Heat exchanger can directly use the condition ofnatural low temperature in Northeast, to refrigerate the circulation fluid in frozen well,thereby reducing equipment power and the whole project investment. And throughoutthe trial, the main problem is observing the natural low temperature conditionswhether can reduce the temperature of circulate fluid low enough to meet theconditions for further trials under natural conditions. At the same time the experimentresearch the change law of the temperature field around in such experimentalconditions.The finite element analysis software——ANSYS is used to establish thesimulation model of natural freezing cold source’s heat transfer. The temperaturechange rule of the underground freezing process is analyzed. From the analysis, theaverage temperature changes of pile center, pile edge are respectively0.13℃/h,and0.12℃/h. Then the analyses of the temperature change rule and the thermalphysical parameters is made under different freezing time, different velocity, differentinitial temperature to determine the influence on the underground temperature field.From the simulation experiment of ground freezing wall refrigeration system, itis known that the natural cold source changes with the climate temperature.Theaverage declining temperature of1.5m away from pile center, pile ridge is respectively0.11℃/h and0.10℃/h, slightly lower than the results of thesimulation analysis, but the change process of underground temperature field is thesame with the simulation results of analysis.The natural cold source in northeast of China is very rich. The simulationexperiment platform uses this natural cold source to simulate the frozen wall.Comparing with the conventional method of refrigeration to form freezing wall, theinvestment of refrigeration equipments is reduced by36.6%, the operation cost isreduced by43.7%, and the total investment underground freezing wall is reduced by42.3%.From the above analysis, if the natural low temperature can be made full use andthe method is used to exploit oil shale in high-temperature situ exploitation, it willreduce the energy consumption, the initial investment of the frozen wall built andmaintenance costs. And the use of ammonia will be also reduced. It is benefit forprotecting the environment and promoting the further development of the oil shale.