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Simulation Of Temperature Field And Experiment Of In-situ Oil Shale Pyrolysis

Posted on:2013-02-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q LiFull Text:PDF
GTID:1110330371977494Subject:Geological Engineering
Abstract/Summary:PDF Full Text Request
Energy is closely linked to the human society. Tracing back to the history, thereplacement of energy applications always runs through each development stage ofthe human society. With gradual deepening of industrialization across the globe, theincrease of energy consumption becomes a necessity, and energy security has beenone of the most important factors affecting future development of human society.Fossil fuels are not renewable energy, and will be exhausted one day. Finding anddeveloping alternative energy sources have become atop priority. China is the largestdeveloping country in the world today, as China's economy has entered a stage ofrapid growth, demands for energy is increasing rapidly, the energy supply-demandgap is also growing. By2011, more than55percent of the oil depends on foreignimports in China, the strategic petroleum reserve can only use for four months, andpose a serious threat to national energy security. In order to reduce China'sdependence on external oil and gas, and to meet the needs of national construction,exploration and development on unconventional oil and gas resources must beaccelerating.The oil shale is combustible organic sedimentary rock, which contains morethan40%ash. Oil can be obtained by pyrolysis; oil content can reach between3.5to18%, and organic content is high. Its reserves are huge; the shale oil extracted fromoil shale resources through the world is about411billion tons, equivalent to threetimes of the remaining recoverable reserves of world's proven crude oil andcondensate. China's oil shale resources can extract about47.6billiontons ofshale oil,equivalent to1.5times ofconventionaloil resources, which are ranking the4th in theworld. But only2.7billion tons resources are identified, accounting for only5.67%of the shale oil resources, exploration potential is huge. So, as long as webreakthrough the technology bottleneck in oil shale mining, and control the cost in a reasonable range through using new technologies, the oil shale resource extractionwill be promising. From the economic analysis, the costsof surface carbonization oilshale are about1500Yuan/tons (30U.S dollars/barrel), which seemed higher in thepast, but become very economical now. Large-scale development of oil shale hasbecome a very urgent task.Development and application of oil shale have nearly200years of history.Comparing oil shale, natural oil has been widely used, because of high quality,simple processing technology, and relatively low cost. With the1970's energy crisis,oil shale exploration flourishes again. Now, two ways are used to operate oil shale,burned to generate electricity or dry distillation refinery, two ways are only suitablefor lowly buried deposits. But whether it is burned to generate electricity or drydistillation refinery, there are disadvantages-pollution, low efficiency; limitedadaptation to stratigraphic and high maintenance cost. In order to prevent theseshortcomings, in situ dry distillation heating technology of oil shale has beendeveloped; although in situ mining has obvious advantages, there are many technicalproblems as well. So it is still no large-scale promotion. The article starts with thebasic physical properties of oil shale, researching pyrolysis characteristics of oilshale, development of cracks and pores, thermal permeability of oil shale, theinternal heat transfer law. By building oil shale pyrolysis test stand, laws of gas oroil-producing in oil shale pyrolysis are obtained, and then the thermal properties andcharacteristics of cracks development are verified. Besides, establishingthermosetting coupling model of oil shale in situ heating, the model boundary withmeasured parameters in test experimentally are set.And by using finite element, heatmigration patterns of heating oil shale are studied once again.Oil shale pyrolysis is defined that, the process of series physical reactions andchemical reactions occurred in pyrolysis temperature without contacting to outsideair. Pyrolysis process can be seen as a weight loss of oil shale. In-Depth study ofweight loss in pyrolysis actually analyzes the dehydration and oil precipitation in oilshale pyrolysis process at different stages, which is the basis of researching oil shalethermal cracking, pore structure changing, bulk density, and seepage characteristics, and has very important significance. Pyrolysis of oil shale is a pattern, which can bedivided into four phases: oil shale desiccation stage; the kerogen softening stage;kerogen pyrolysis stage and thermal decomposition stage of other minerals in oilshale.In situ permeabilityof oil shale in the pyrolysis process revealed a decrease firstand then an increase. And it can be divided into three phases: the first phase at roomtemperature~250℃, oil shale permeability rises rapidly, water precipitation inthe form of steam promote liquid penetration; the second phase of250℃~450℃, the permeability drastically reduced. This section is the softening process ofkerogen, softening kerogen block the cracks, penetration properties reduced. thethird phase of450℃~520℃, the penetration rate begins a slow increase,kerogen in this stage almost pyrolysis, a large number of pores and cracks in the oilshale promotes the penetration of liquid.Oil shale thermal conductivity, specific heat capacity show the step-down trendas the pretreatment temperature rises, while the thermal diffusivity is indeed firstincreased and then decreased. Thermo physical parameters are affected by themoisture content of rock sample, the factors of porosity, fracture size, theprecipitation of chemical substances.Producing oil and gas in oil shale pyrolysis is a macroscopic process, while thepyrolysis process itself is a microscopic process, which involves many subtlechemical and physical changes, such as kerogen decomposition, phase transition, oiland gas seepage, pores, cracks change and so on. To make in-depth study of theinternal material traits in pyrolysis process, you need to observe morphologycharacteristics and internal material changes in oil shale pyrolysis by precision zoominstruments on full temperature range. The scanning electron microscope can takethis role.As the temperature increases, the pores in oil shale increase, as well as thewhole area ofa single. While the process ofpores increased is mainly due to physicaland chemical changes in substances, such as kerogen. Before350℃, the kerogencheese do not pyrolysis, the porosity changes slowly. After350℃, the kerogen pyrolysis produces oil and gas, and precipitates along the seepage channel, resultingin explosive growth of pores. In the process of heating, cracks length, width andnumber increase, not only connected with thermal stress, but also significantlyaffected by series of chemical physical changes.In the pyrolysis process, heating energy transferred in the internal oil shale,resulting in chemical and physical changes. Due to the complexity of changingprocess, energytransfer process is caused quite complex. The heat transfer process inthe oil shale follows the Fourier thermal conductivity basic laws.Study of oil shale nature can lay a solid foundation for oil shale in situ mining,by using the oil shale quasi-situ pyrolysis bench developed by Jilin University. I havedone some pyrolysis laboratory studies on Hua Dian oil shale at different heatingrates and different particle characteristics. According to the laboratory researches,heat mechanism of action is analyzed, output effects of oil and gas are evaluated,chromatographic analysis of production and gas composition analysis on differenttemperature have been made, and the oil shale pyrolysis equation is summed up:In situ heating thermosetting coupling model ofoil shale has been established toanalysis temperature changes and energy migration patterns. Conclusions have beenobtained that, the greater heating power is, the quicker steady state heat transfer willbe reached. Steady state temperature and reaching time are directly related to thedistance between heat wells and frozen wall. If freeze wall is farther away, thereaching time to steady state is longer, and the steady state temperature is higher.When we design in situ dry distillation oil-producing system, heating power andlayout borehole must be taken into full account.
Keywords/Search Tags:Oil shale, in situ dry distillation, thermal physical properties, microscopicmorphology, heat transfer law, finite element numerical simulation
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