Study On The Law Of Pollutant Migration During In-situ Heat Injection To Exploit Oil Shale

Based on the background of pollutants produced by in-situ heat injection extraction of oil shale,the characteristics of pore structure evolution,deformation and permeability of oil shale and mudstone were studied by the method of combining theoretical research with physical experiments.The decay and migration of pollutants in the surrounding strata was analyzed with the experimental data achieved.The main research results of this paper are as follows:(1)The pore structure evolution of Jimusar oil shale from room temperature to 600°C was studied.Porosity increases with temperature.It is roughly divided into two stages: from room temperature to 300°C,the porosity increases slowly.From 300 to 600°C,the porosity of oil shale is raised rapidly.(2)The pore structure evolution of Jimusar mudstone from room temperature to 600°C was analyzed.It is roughly classified into two stages: from room temperature to 300°C,the porosity generally remains constant with increasing temperature.Between 300°C and 600°C,the porosity of mudstone increases linearly with temperature.(3)The evolution deformation law of Jimusar oil shale under in-situ conditions of 200 m and 500 m was studied.The results indicate that the axial deformation of Jimusar oil shale with 200 m depth generally shows expansion with increasing temperature.Axial deformation can be divided into two phases: Low temperature expansion deformation stage from room temperature to 300 °C and high temperature expansion deformation stage from 300°C to 600°C.The axial deformation of Jimusar oil shale with 500 m depth is similar to that of 200 m depth.(4)Permeability characteristics of oil shale of 200 m and 500 m depth was also analyzed The results showed that the permeability of Jimusar oil shale of 200 m depth can be divided into three stages with increasing temperature: At low temperature stage,from room temperature to threshold temperature 200℃-250°C,permeability is very low and nearly 0;At media temperature stage from 200℃-250°C to 350℃-400°C,the permeability increased slowly with the rising temperature and the raised changes is small;At high temperature stage the permeability rises quickly between 350℃-400°C and 600°C.The permeability of 500 m depth is similar to that of 200 m depth but it is different at high temperature stage.(5)The permeability characteristics of Jimusar mudstone from room temperature to 400°C were studied by steady-state method.The results show that the permeability of mudstone first increases,then decreases and then increases with the rising temperature.It can be divided into four stages.In the first stage,there was no permeability from room temperature to 100℃;In the second stage of 100℃-200℃,the permeability of mudstone appears and the value is small;In the third stage it decreases with increasing temperature from 200℃ to 250℃;In the fourth stage of 250℃-400℃,it increases with increasing temperature.(6)The law of pollutants migration in surrounding strata during producing period of 0-2.5 years and the stagnation period of 0-20 years of was studied by numerical simulation method.The results showed that: In production period 0-2.5 years,the horizontal pollutant concentration decays with the increasing distance,the velocity of horizontal pollutant migration is 2-4 times of that of vertical pollutant migration.;In the stagnation period of 0-20 years,the horizontal pollutant concentration decays with the increasing distance,the velocity of horizontal pollutant migration is the same as that of vertical pollutant migration;The peak of vertical pollutant concentration appears at the junction between the oil shale layer and the roof or floor.The vertical pollutant concentration decays with the increasing distance.