Study On Microscopic Characteristics Of In-situ Pyrolysis Oil Shale And Oil Gas Exploration Through Superheated Steam

In Chinese energy structure,The proportion of coal resources is decreasing,and the proportion of clean energy is gradually increasing,so diversified energy development is a general trend of events.The oil shale is unconventional oil and gas resources,and reserves of oil shale deposits in China is rich,so the development and utilization of resources to alleviate the tensions in the oil and gas energy demand in China has important practical significance.At present,In-situ mining technology of oil shale has been widely used.This paper takes Fushun oil shale as the research object,based on in situ extract oil shale simulation test through superheated steam,Through the combined method of scanning electron microscope,mercury injection test and infrared spectrum analysis,The microstructure and pyrolysis law of pyrolytic seam were carried out.The main research results are as follows:(1)The morphology and microstructure of Fushun oil shale and Xinjiang oil shale under different temperature were analyzed by SEM method,so as to provide the experimental basis for in situ steam injection exploitation technology of oil shale.The Research shows,The distribution of minerals in Fushun oil shale is dominated by scattered distribution of kaolinite and sheet quartz,and the distribution of minerals in Xinjiang oil shale is dominated by scaly montmorillonite and massive quartz;With the increase of temperature,the thermal fracture process occurred in the clay mineral layer,such as dehydration,interlaminar fracture and layer stretch brittle fracture,On the surface,it shows the characteristics of adhesion,softening and melting.Thermal rupture energyconsumption of Fushun oil shale is lower than that of Xinjiang oil shale,the process of fracturing fracture is more obvious,and pyrolysis of organic matter is more efficient.(2)In the process of in situ pyrolysis oil shale through superheated steam,oil shale seam is influenced by steam pressure and stress.By the mercury method,The characteristics of the inner cavity of the oil shale after pyrolysis of superheated steam is studied,The pore structure,porosity and pore width of the direction of parallel to main fracture and vertical to main fracture are obtained: The porosity of oil shale is more than 26.5% in each position of main fracture,which showed that the porosity of oil shale has changed qualitatively under steam injection;The porosity of seam close to roof rock is lower,The pyrolysis of the position is dominated by heat conduction;In each position of the main fracture,the percentage of the different types of pores are as follows:Middle pore > small pore>large pore > micro pore,The contribution of mesopore to porosity variation is the most obvious;The statistics of oil shale seam porosity in different positions showed,The percentage of oil shale seam fully pyrolysis reached 81.6846%,which fully proved the feasibility and efficiency of in-situ pyrolysis oil shale and oil and gas exploration through superheated steam.(3)Permeability and fractal characteristics of oil shale after pyrolysis of superheated steam were analysed.Research shows that the effective porosity of seam in situ mining of oil shale is lower than that of direct carbonization and pyrolysis,which is mainly due to the influence of in-situ stress;The pore tortuosity of parallel to main fracture is between 2.15~2.17,and the pore tortuosity of vertical to main fracture is between 2.145~2.165,Tortuosity of pyrolysis seam is smaller on the whole;Through multiple regression analysis method,The quantitative relationship between the ratio of surface area,porosity,tortuosity,pore throat ratio and permeability was obtained,while the effects of different factors were further compared.(4)Through infrared spectroscopy,The chemical structure evolutionlaw of oil shale after pyrolysis of superheated steam at different positions were analysed.With the continuous pyrolysis of oil shale kerogen,on the one hand,functional groups of aliphatic compounds occurred continuously pyrolysis,on the other hand,with the continuous injection of superheated steam,the strength of C=C bond is weakened,the electronic key between unstable residual bond is transfered,thereby producing a new bond and improving the degree of aromatization;Steam of high temperature and pressure not only plays a role of pyrolysis of oil shale,but also complex chemical reaction occurs between the vapor and oil shale carbonate at high temperature.The conclusions obtained in this paper provide some guidance for the development of in situ pyrolysis oil shale technology.