Study On The Characteristics Of Temperature Distribution And Its Influence On The In-situ Heating Process For Oil Shale

The energy and environment are the substance foundation for human social activities,sufficient energy and excellent environment guarantee the prosperity and long-lasting peace in the country.With the decreasing reserves in the traditional fossil energy sources(coal,crude oil and gas,etc.),the new energy sources are unable to compensate for their shortage in short term,and the utilization of unconventional energy sources gradually obtains attention,of which oil shale is a significant source to develop unconventional energy resources shale oil.With abundant oil shale resources,the converted shale oil reserves in China account for about 7% of the global oil shale reserves,and the exploiting of oil shale has become an essential guarantee for the national energy security and the stability of the oil and gas industry.Oil shale underground in-situ heating exploration technology is the crucial technology to explore and utilize oil shale economically and environmentally.Based on underground in-situ oil shale exploration technology,the characteristics of oil shale temperature distribution during the underground in-situ heating process are studied by numerical simulation,and the heating efficiency of oil shale is analyzed in three modes:underground in-situ electric heating,underground in-situ steam injection heating without fracturing and underground in-situ steam injection heating after fracturing.Analyzing the influence of oil shale physical properties,oil shale heat source supply,oil shale reservoir thickness and oil shale fracture distribution on oil shale heating efficiency,clarifying the influence of factors on oil shale underground in-situ exploration technology,and providing theoretical foundation for oil shale exploration.The main conclusions are as follows:(1)Establishing underground in-situ electric heating oil shale model and underground insitu steam injection heating oil shale model without fracturing,and analyzing the changes of temperature field and seepage field during the heating process of oil shale.In the electric heating condition,the oil shale temperature is ellipsoidal distributed with the heating well as the center,and the temperature increases faster in the lateral direction than in the vertical direction,and the temperature change shows a trend of large in the middle and small in the sides.In the 10 th year,most areas of the oil shale have reached 450°C,and the oil shale is basically pyrolyzed to produce shale oil.Without fracturing underground in situ steam injection in the condition that the temperature increases gradually outward with the heating well as the center of the circle,the pressure shows a trend of first increasing and then decreasing.The valid heating radius of oil shale is less than 4m at 3.5 years without fracturing.(2)Establishing underground in-situ steam injection fracturing model after fracturing,analyzing the changes of temperature field and seepage field of oil shale during the heating process,and comparing the heating efficiency in three modes: underground in-situ electric heating,underground in-situ steam injection heating without fracturing and underground in-situ steam injection heating after fracturing.The temperature of the oil shale is driven by the pressure in a "Y" shape,and the pressure increases and then decreases with time,and the average pressure of the oil shale reaches the highest value of 0.61 MPa in 0.8 years.The heating efficiency of steam heating after fracturing is much higher than that of steam heating without fracturing and electric heating.(3)Based on the model of underground in-situ electric heating for oil shale to analyze the effect of oil shale physical properties,oil shale heat source supply and oil shale reservoir thickness on the heating efficiency of oil shale.Oil shale density,oil shale heat transfer coefficient,oil shale reservoir thickness and oil shale heat source supply temperature have significant effects on oil shale heating efficiency.Decreasing oil shale density,increasing oil shale heat transfer coefficient,increasing oil shale reservoir thickness and increasing oil shale heat source supply temperature are conducive to improving oil shale heating efficiency.(4)Based on the model of underground in-situ steam injection heating of oil shale without fracturing to analyze the effects of oil shale physical properties,oil shale heat source supply and oil shale reservoir thickness on oil shale heating efficiency.Oil shale permeability,oil shale heat source supply and oil shale reservoir thickness have significant effects on oil shale heating efficiency.Increasing oil shale permeability and heat source supply temperature and pressure,decreasing oil shale reservoir thickness are conducive to enhancing oil shale heating efficiency.(5)Based on the model of underground in-situ steam injection heating after fracturing of oil shale to analyze the effects of oil shale physical properties,oil shale heat source supply,oil shale reservoir thickness and fracture distribution on oil shale heating efficiency.Oil shale permeability,oil shale heat source supply,oil shale reservoir thickness and fracture distribution have significant effects on oil shale heating efficiency.Increasing oil shale permeability and heat source supply temperature and pressure,decreasing oil shale reservoir thickness,increasing fracture width and the number of fracture bars,decreasing fracture and cross-section angle,increasing relative fracture angle are conducive to enhancing oil shale heating efficiency.