| As a potential energy, Oil shale is an ideal supplement and alternative energy resources of natural oil, which has become a kind of practical significance resources. Oil shale is emphasis of energy development at many countries. On the one hand, oil shale development can solve the needs of countries for oil resources, on the other hand to reduce dependence on imported oil. In this paper, take noting heat in situ of oil shale as the research background, and the pyrolysis characteristics, porosity, pore structure characteristics connectivity, permeability characteristics and mechanical properties under high temperatures effects were researched in the combining ways of microscopic and macroscopic experimental study. The main contents and results of this paper as follows:(1) We can draw the block sample weightlessness law as by means of muffle furnace for oil shale heating, at the same time, powder oil shale samples weight loss curve can be obtained by means of thermal gravimetric analysis, according to the two test results, pyrolysis characteristics of oil shale passed through three phases:The first phase from room temperature to300℃, weight loss is mainly caused by precipitation of the water at this stage;300～600℃is the second stage, organic matters converting to produce shale oil and pyrolysis gas.(2) CT scan produces a series of2D images, which were reconstructed to create3D images using the CT image analysis system developed by research group. It can be seen from3D images, as the temperature rose, solid particles in the specimen obviously reduced. The number of pixels corresponding to different attenuation coefficients of the rectangular prism area at the temperature increments can be counted, pyrolysis character of solid particles in the specimen is obtained. From20℃to100℃, the pyrolysis rate was3.18%; from100℃to200℃, the pyrolysis rate of solid particles rose to18.94%; from200℃to500℃, the pyrolysis rate of solid particles was5.84%; from500℃to600℃, the pyrolysis rate of solid particles rose to39.80%.(3) The true distribution of pore inside the oil shale samples was obtained by way of combine of Micro-CT and mercury intrusion method. Porosity of Fushun oil shale mainly measured by mercury intrusion method, porosity of Daqing oil shale mainly measured by Micro-CT. The opening ratio of oil shales increased with temperature, percentage of close area decreased, which indicated that the pores gradually get connected as pyrolysis, then the Daqing oil shale, percentage of close area is greater than the opening ratio at400℃, which indicated that, the oil product of oil shale pyrolysis not fully leak from the sample, remaining in the open pores at this temperature. (4) Mercury intrusion method was used to analysis the pore structure characteristics of Fushun oil shale samples under high-temperature, the results showed:1) With temperature increasing, the total pore volume, porosity, average pore size and critical aperture showed an increasing trend; There was different in pore volume of different diameter pores inside oil shale at different temperatures; tortuosity of pores inside oil shale decreased, which indicated that with the process of pyrolysis, the bend degree of the pore channels was reduced. The low bend degree of the pore channels was benefit to infiltration and transport of oil and gas products, especially after a lot of oil and gas output, the tortuosity of oil shale pore channels showed a significant downward trend.2) The lagged effects of mercury in the testing process arising from the contact angle was to be corrected, which indicated that the receding contact angle of mercury retreat decreased when temperature increased, the lag factor increasd with temperature. The results illustrated that pore structure of oil shale get more and more complicated and pore surface get more and more roughness as the temperature increased.3) It can be obtained from the second mercury test of Fushun oil shale:the pore of oil shale forming constantly as the temperature increased, ink-bottle pore formed mainly, the increase of effective pore volume was small.(5) Mercury intrusion method was used to analysis the pore structure characteristics of Fushun oil shale samples under high-temperature and triaxial stress, the results showed:With temperature increasing, the total pore volume, porosity, average pore size and critical aperture showed an increasing trend; At the same temperature, oil shale porosity parameters are larger compared with samples without penetration test, which indicated that the pore volumes of oil shale increased under pore fluid.(6) Using equation Kozeny-Carman calculate permeability k1, by using the equivalent pipe model calculate the penetration k2. The variation of k1And k2has the same trend with temperature. The permeability showed an increasing trend with temperature,400℃was the threshold temperature of penetration, when the temperature increased higher than400℃, the permeability began to increase substantially.(7) High temperature triaxial stress penetration system was used to test permeability of oil shale specimens under temperature and triaxial stress. The results showed:oil shale sample having no permeability at room temperature and100℃;when the temperature rised to200℃, permeability was low; at the temperature ranges of200℃to300℃, permeability is increased, but the increase is small; when the temperature rised to350℃, permeability of the sample appeared decreasing tendency; At the temperature in the range of350℃to600℃, organic was softened and generated to bitumen, then generated oil shale oil and gas. The penetration was influenced by two factors at350～450℃, On the one hand bitumen and shale oil clogging the permeation path of oil shale sample, on the other hand clay minerals have adsorption on bitumen, at this temperature stage, pore channel was blocked. When the temperature raised to 450℃pore channel was unobstructed as the effect of pyrolysis gas and steam from mineral release, permeability of oil shale samples showed an increasing trend.(8) Uniaxial compression test was carried to oil shale samples experienced pyrolysis under different temperatures.The results showed:1) The compressive strength of oil shale samples decreased with temperature, at different temperatures oil shale uniaxial compressive strength and temperature has exponential relationshiσ=74.987e0.0024T)。2) The average elastic modulus of oil shale samples with temperature tended to decrease at20℃to600℃. From room temperature to600℃, the average elastic modulus and temperature has logarithmic decay law(E=-544.381n(T)+4943.5).3) From room temperature to600℃, the average Poisson of oil shale samples with temperature showed decreasing trend, the average Poisson and temperature has linear decay law(ν=-0.0005T+0.4653). |
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