Experimental Study On The Impacts Of Oil Shale In-situ Pyrolysis On Groundwater Hydrochemical Characteristics

Oil shale, one of the most important potential crude oil substitute resource, is widespread in the world. The ex-situ and in-situ pyrolysis are the two main treatment technologies of oil shale. The development of the ex-situ is limited as the wasting of water and destroying of the environment. Compared with ex- situ pyrolysis, the in-situ pyrolysis can be applied into the deep buried and large thickness oil shale layer. The in-situ pyrolysis wins its favor of human because of lots of advantages compared with ex- situ pyrolysis such no air pollution and greener to ecological environment. But large amounts of toxic organic matter can be formed during in the pyrolysis, so the impacts of oil shale in-situ pyrolysis on groundwater hydrochemical characteristics can not be ignored. The in-situ pyrolysis of oil shale has not been applied at large scale at present. Only small-scale pilot experiments are carried out, and there are rarely reporting about the environmental impact assessment and environmental protection measures of the in-situ pyrolysis.The indoor experiments are carried out in order to find out what kind of and the quantity of the pollutants exist in the oil and gas which formed during the in-situ pyrolysis. The oil shale became loose, permeable layer as the pyrolysis. The gas will volatilize into unconfined aquifer and the oil will flow into the confined aquifer. As the water- rock interaction the groundwater quality will be polluted. Based on the research of the geological, hydrogeological conditions of the five regions where are Nongan, Fuyu, Huadian, Fushun and Meihekou, the indoor pyrolysis experiment and immersion test are carried out by using the oil shale samples of the five region. The impact of oil shale in-situ pyrolysis on groundwater chemical characteristics is analyzed. The main results are as follows:(1) The structural relationship of oil shale layer and aquifer is anylyzed. The oil shale layer can be devided into cretaceous stratum and palaeogene. Cretaceous stratum: groundwater is storage in Quaternary unconsolidated strata and the cretaceous silty sand rock and mud rock. The oil shale is between in the unconfined and confind aquifer. Palaeogene: groundwater is storage in Quaternary unconsolidated strata and the palaeogene sand rock, mud rock and cretaceous conglomerate. The oil shale is between in the unconfined and confind aquifer.(2) There are many oganic matters in the pyrolysis oil and gas, and the result shows that the major organics of gas products are small molecules of alkanes, alkenes and benzenes; and the alkanes and olefins, benzenes, naphthalene, alcohol are present in the collected shale oils. The percentage of the produced water, oil and gas in total protolith of the five samples are 12.88%,7.74%,39.79%,19.53%,38.39%. The results show that the pollutants like hydrocarbons, benzene, pyridine, quinoline, phenol, aniline and naphthol are transfored from the mixture of shale oil shale gas into the water. And pollutants like hydrocarbons, benzenes are through residue into the water.(3) The pores and permeability of the oil shale increased greatly and the suface of the spent oil shale became loose. Large gap and organic solution pores appear at last. The increased pores and fractures became good water flowing channel, and make the oil shale layer permeable. The water from the overlying and underlying aquifer can flow into the oil shale layer, at the same time, the oil and gas can infiltrate into it, these will pollute the aquifer. The concentration of the hydrocarbons, benzene series will increase as the oil and gas contained in the residue.(4) The in-situ pyrolysis will change the characteristic of the groundwater. During the processing of the Kerogen pyrolysis, large amount of oganic acids, 2H S and 2 4H SO formed, this changed the pH value from alkaline to acidity. At the same time, the concentration of 2-4SO increased. The percent of ash content became large as the porolysis of Kerogen, this lead to the increase of the conductivity. The enrichment of heavy metals from fresh oil shale to spent oil shale during in the process of pyrolysis will effect the concentration of the microelements. The concentration of aliphatic hydrocatbons increased firstly and then decreased and the BETX continue to rise with the heating temperature due to the broken of the C-H bond.(5) The impact of oil shale in-situ pyrolysis on groundwater hydrochemical characteristicsis is analyzed by using the provenance analysis, the route of contamination entrance, the releasing rule of the contaminants and groundwater chemical kinetics.In this thesis, the indoor pyrolysis experiments above would finally provide a scientific theory basis for the impacts of oil shale in-situ pyrolysis on groundwater hydrochemical characteristics. And this study has a significance of pioneering. Hope this research can provide a new idea of the impacts of oil shale in-situ pyrolysis on groundwater environment.