| As one of the unconventional energy development projects, in situ oil shale exploittechnology has become the forefront of energy development research.In this paper, in accordance with the project construction sequence, the formation offrozen wall and process of in situ hot drive exploit of oil shale are simulated numerically byFLUENT.In the numerical simulation of the frozen wall, a three-dimension computational model isestablished according to project. It is concluded that temperature of rock gets higher linearlywith altitude getting deeper considering experimental data. The energy change from phasetransition is also taken into consideration. Latent heat is calculated in the simulation byequivalent specific heat method. In this paper, the changing regularity of these parameters isadded into calculation by User’s Define Function of FLUENT. Changing regularity oftemperature on the cross-section along the central axis of frozen wall is computed. And eachpoint on the line of350m deep on the cross-section is observed in order to summarize thechanging regularity of temperature. The exact time to form a closed loop of frozen layer canbe clearly seen. The results show that there exits big difference of freezing rate among thethree regions due to different specific heat capacity and thermal conductivity. The uppermostpart has the least efficient. Frozen rate of rock is relatively higher than sand. A closed frozenloop formed after freezing240days, meaning this part has reached the standard of frozen wallin project. As the specific heat capacity and thermal conductivity of oil shale are all thesmallest among the three kind of rock, the frozen rate of oil shale is the highest. So it is thefirst to form a closed frozen loop.In the numerical simulation of in situ hot drive exploit of oil shale, a four fracture in oilshale layer axisymmetric flow model is designed based on actual measurements in project.The injected medium is hot air. In this paper, porosity and permeability of oil shale areespecially researched as pyrolysis occurs these two parameters also change. The changingregularity of porosity and permeability with the changing of temperature is observed.According to the data from experiment, porosity of oil shale gets piecewise-linearly biggerwith the increase of temperature, and permeability gets exponentially larger. These tworegularities are added into computation by UDF of FLUENT which makes parameter settingmore realistic for engineering environment, and the results more accurate and effective.Temperature changing pattern and regularity with time is obtained. And the change oftemperature on the center line of oil shale layer and the vertical line5meters off the injectingwell is observed to see the most productive period. The results show that heating the sametime, the closer off the injecting well, the higher temperature the formation gets and the fasterthe temperature change. As there exists four fractures and constant pyrolysis in oil shale, itsporosity and permeability get larger and larger, and the hot air infiltrated faster and fasterwhich results in temperature increasing quicker and quicker. When heated4to6years, rate ofoil shale’s temperature change is the highest. When heated8years, rate of temperature changebegins to slow down. When heated to12years, temperature of the oil shale area within18mall reaches complete pyrolysis temperature. Pressure contours at different times are obtainedfrom pressure calculating results. The nearer the area is from the injection well, the greater thepressure gradient is, and the faster the flow rate is. In the far area from the well, pressure gradient gets smaller and smaller, so the flow gets slower and steady. At the first, as there are4fractures in the oil shale area, pressure of oil shale part is significantly greater than thebedrock part. As injection proceeds, pressure difference between the two parts graduallyreduces. When heated for2years, pressure different gets small enough for the flow to bestable. |
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