Simulation Experiment And Numerical Simulation Of In-situ Sub-critical Water Extraction Of Organic Matter In Oil Shale

In recent years,Chinese demand for energy further increases as the developing of economy and the improving of technology.However,the scarcity of traditional non-renewable resources in China leads to the increasing dependence on foreign crude oil.Oil shale is a kind of unconventional oil and gas resources,which is regarded as an important supplementary and alternative energy source of traditional energy resources,and it is becoming more and more popular in China and even globally.Chinese oil shale resources are abundant and second in the world,and the oil shale reserves in Jilin Province are equal to 80% of the total reserves of Chinese oil shale.Therefore,seeking an effective and low-cost method for exploiting and utilizing oil shale resource is of great significance to alleviate the shortage of traditional non-renewable resources.Because the oil shale reservoirs in China are always deeply buried and low-grade,some researchers put forward the concept of in-situ converting and extracting the organic matter in oil shale by using sub-critical water.In this paper,the simulation experiment of in-situ sub-critical water extraction of organic matter in oil shale has been designed and studied firstly.Then,pore evolution of oil shale during simulated in-situ sub-critical water extraction has been researched.Finally,the physical model and the numerical simulation of in-situ sub-critical water extraction of organic matter in oil shale has been established and carried out,respectively.The following results has been obtained:(1)Firstly,the simulation experiment of in-situ sub-critical water extraction of organic matter in oil shale has been designed and studied.With the increase of extraction time or extraction temperature,the extract yield of bitumen and the total converted amount of organic matter increased during the sub-critical water extraction experiment,while the content of Bitumen 2 increased firstly and then decreased.This is probably because that the organic matter in the oil shale began to convert and some of the pore channels were blocked at the beginning of the extraction experiment.As the extraction continued,the content of Bitumen 2 decreased because the organic matter was extracted and the pore channels opened gradually.The evolution of gas yield with the increasing extraction time or extraction temperature is roughly opposite to that of Bitumen 2.This indicates the conversion processes of gas and Bitumen 2 during sub-critical water extraction are basically synchronous.(2)After comparing analysis results of the extracts obtained after 350 ? extraction with that obtained after 150 h extraction,we found the components of bitumen,Bitumen 2 and gas in the two extraction experiment are similar,while the content change of them is different.The main components of bitumen are n-alkanes,n-alkenes,n-alk-2-one,n-alkanoic acid,a small amount of isoprene and little aromatic compounds.In Bitumen 2,n-alkane is the most important ingredient.The main components of the gas are carbon dioxide,n-alkanes,hydrogen and little number of n-alkenes.(3)In this paper,higher extraction temperature or longer extraction time was needed when the bitumen extract yield obtained in my extraction experiments was becoming similar to that gotten by predecessors.This is because the breaking phenomenon often occurs,especially vertical to the bedding plane,when the oil shale is in free state during the sub-critical water extraction.This phenomenon effectively enlarges the contact area between the sub-critical water and the oil shale,and then,it caused the rising of the extraction efficiency.The evolution of fractures is different when the oil shale is in the simulated in-situ state during sub-critical extraction.This means that with the increasing extraction time and the extraction temperature,the evolution of extract yield found in this paper may be closer to the reality,and these results can provide some reference to researching and developing of the in-situ sub-critical water extracting technology.(4)After researching pore evolution,we found that the apparent pore and microcosmic pore in the raw oil shale sample were not developed.The raw sample contain a small number of intergranular pores,organic pores and fractures.With the increase of extraction time and extraction temperature,pores in spent samples extended to the inner part of the shale matrix,and their size gradually increased from the nano-to micron-scale.At the same time,the evolution of the mesopore volume,the specific surface area,the quantity of macrospores(especially distributed in 100~1600nm),and the porosity of spent shale samples was similar with that of bitumen extract yield.This is probably because of the secondary organic matter pores' formation which is caused by the converting and releasing of the organic matter during the sub-critical water extraction.It is also suggested that the diameter of kerogen distributed in Huadian oil shale may ranges from 100 to 1600 nm.(5)The deformation of the samples in vertical bedding direction is restrained by using special clamps during the sub-critical extraction.It caused that the evolution of fractures in oil shale which is under a confining pressure is different from that in free state during sub-critical water extraction because the fractures probably propagated parallel to the bedding plane in this study.After a certain amount of organic matter was released,inner support from organic matter was weakened,resulting in fractures strongly compacted by pressure from sub-critical water.This effect might become more significant when the pressure increased.(6)The simulation results showed that the heating effect of single direction heat injecting was poor.It can be seen from the simulation results,such as the evolution of temperature field,bitumen extract yield and porosity,the oil shale can be heated to the ideal temperature by exchanging the working well and the production well at intervals.The ideal heating effect can be obtained after 80 days by replacing of the working well and production well every 30 days during heat injecting.When the heat injection has been lasted for 80 days,the organic matter in the oil shale was almost completely converted and extracted.(7)In this simulation process,the change of some parameters during the sub-critical water extraction is considered.In particular,the evolution of bitumen extract yield and oil shale porosity as the increasing extraction time and extraction temperature were simulated according to the experimental results,and then,were calculated through the UDF program during the numerical simulation.Therefore,the simulation results were more practically for predicting the extract yield and the porosity.Due to the high injection quantity and ignoring the conversion of organic matter in the numerical simulation,it may take longer time to get the ideal heating effect and bitumen extract yield during in-situ extracting engineering compared with the numerical simulation results.These above results can provide theoretical guidance for developing the technology of in-situ sub-critical water extraction of organic matter in oil shale.