Study on Oil Potential of Oil Shale Based on Terahertz Time Domain Spectroscopy

Author:Li Zuo Zuo

Supervisor:zhao kun


Degree Year:2018





Oil shale is one sort of organic-rich sedimentary and a supplementary energy for petroleum,featured by wide distribution and large reserve.Complex reservoir forming conditions determine the oil potential of oil shale that will further influence the benefit of its exploration.Therefore it is of great significance to determine oil potential of oil shale in a rapid way.Terahertz time domain spectroscopy is rising as a novel optical technique and contributes to fields including material identification,component analysis and non-destruction detection.Since terahertz wave is sensitive to molecular structures,one can determine features of oil and gas resources by analyzing their optical parameters in THz range.Consequently,it is promising to study oil potential of oil shale based on terahertz time domain spectroscopy.The terahertz spectrum and optical parameters of oil shale from three regions(Huadian,Barkol,Beipiao)are studied to analyze the relationship between refractive index and oil content in this study.Oil shale from Longkou is used to verify the conclusion.It is indicated by results that oil shale with higher oil content has lower refractive index in terahertz range.The difference of refractive index for oil shale tablets with different oil content is minor compared to that for ground samples;ground oil shale may lead to major individual difference;the order of refractive index for compacted and ground oil shale from one region is uncertain.To ensure that the influence of minerals on THz response of objects is consistent,pyrolysis under various conditions were implemented to prepare semicoke.Maximal pyrolysis temperature,heating rate and ventilating rate all work on extent of pyrolysis.In the intervals concerned,lifting maximal pyrolysis temperature would benefit oil yield whereas increasing heating rate and ventilating rate would first increase the oil yield and then decrease that.Pyrolysis conditions work on absorption of THz wave by semicoke and one can determine critical conditions to control oil yield according to tendency of absorption index at multiple frequencies;the absorption index of THz wave by semicoke decrease with its oil content.Consequently,terahertz time domain spectroscopy is able to determine conversion of kerogen during pyrolysis and assists pyrolysis optimization.In order to study terahertz wave response of oil shale with different density,ZnCl solutions are prepared for float and sink experiments.The separated oil shale with different density are pulverized and compacted for tests.Refractive index of oil shale doesn’t change monotonously with the density for all intervals.For oil shale whose density is between 1.7 g/cm~3 and 1.8 g/cm~3,the refractive index is the highest.The absorption of THz wave increases with the density of oil shale,which is rigorous and especially notable for terahertz wave at around 0.8 THz according to extinction coefficient.The change of optical parameters is related to the distribution of organic matter and minerals regarding density.Regular change of optical parameters for oil shale is related to density distribution of organic and mineral materials.Enhydrite is characterized by strong molecular polarity,which may affect optical parameters of oil shale in THz range.Therefore,a mixture of gypsum and gaolinite is prepared to simulate the case in oil shale and the change of optical response with respect to component is studied.With the increasing of kaolinite,multiple peaks emerge in time domain waveform.The frequency of maximal component decreases from 0.4 THz to0.2 THz,which is probably related to stack structure of kaolinite.The refractive index,extinction coefficient and absorption index of kaolinite are all higher than those of gypsum for definite frequency.The optical parameters do not change linearly with the ratio of gypsum because of imperfect dispersity.