| By the end of year 2015,world proven oil reserves were detected as 1.6976 trillion bbls,which could satisfy global requirements of production for only 50.7 years.As the world's largest energy consuming country,China depends highly on foreign petroleum.These factors directly threaten the national economic development and even the national security.Therefore,it is necessary to develop and utilize unconventional energy sources in our country,in order to find new alternative energy sources.As unconventional energy,oil shale,a kind of sedimentary rock rich in organic matter,possesses outstanding potential due to its large reserves.The large oil shale reserves in China can be converted to 47.644 billion tons,which ranks second in the world.Retorting above ground and in-situ pyrolysis underground are the two main development approaches of oil shale,while the later has better prospects due to several advantages such as good product quality and environmental protection.This study were based on National Pilot Project for Oil Shale In-Situ Exploitation(NPOSE).In this study,the pyrolysis temperature range of Nongan oil shale was determined to be 300~540 oC(N2 atmosphere)by analyzing the pyrolysis characteristics using thermogravimetric analyzer(TGA)(STA-449F3);Nongan oil shale was determined to be anisotropic by testing thermophysical properties of oil shale using Hot Disk thermal constant analyzer.The formula of thermal conductivity changing with temperature was finally processed.The temperature field of oil shale in-situ pyrolysis was then simulated.It's known that the thickness of Nongan oil shale formation was 7.2 m,and the distance between injection wells and exploitation wells was 5 m.Assuming that three crack models was established based on fracturing,e.g.Model 1(two cracks,6 mm in heigth),Model 2(three cracks,4 mm in heigth),and Model 3(four cracks,3 mm in heigth).The meshes were divided through ICEM CFD,The temperature field of oil shale was simulated by Fluent at different temperatures of 450? or 420?.The results show that using Model 2 and 140 Nm3/h N2 injection,the energy utilization reached 58.3%,and the oil shale in this region were completely paralyzed after heating for 47.3 days.The thermal conductivity of different insulation materials was testes in order to choose proper materials applied to heat injection strings.The critical thickness of insulation layers was calculated through theoretical calculation method.A proper insulation structure of heat injection strings was finally designed and tested.The temperature of injected gas passing heat injection strings was simulated with different gas flow at a certain initial condition.The results shows that for the heat injection string(70m in length and 32 mm in diameter)twined with 4-layered SiO2 aerogel(GR10),when the temperature of N2 injection was 500oC,the string's outlet temperature was able to reach 400oC.Finally,based on NPOSE,heat injection experiment was carried out.The cracks were formed by perforation-fracturing,and the heat injection strings were treated with insulation.The results show that when the surface temperature reached 450~500 oC,and the injection flow was 120~140 Nm3/h,thxe downhole temperature was 400~420 oC.After 10-days heating,the HC contents in products exceeded 10%,which indicated the pyrolysis of oil shale. |
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