Surrounding Rock Deformation And Fracture Developing Numerical Simulation Study For Underground Coal Gasification Coupling Carbon Dioxide Storage

Injecting carbon dioxide to improve the space utilization rate of underground coal gasification fired zone while carrying out geological storage,not only can realize the effective use of the fired area,but also alleviate the global greenhouse effect.It is one of the main means of coal clean utilization and slowing greenhouse effect.Although there are many benefits for carbon dioxide storage coupled with underground coal gasification,the risk of carbon dioxide leakage along cracks cannot be ignored.Therefore,this paper mainly uses theoretical analysis and numerical simulation to analyze the development and evolution law of underground gasification water flowing fractured zone.The main research results are as follows:1)Based on the analysis and research on the physical properties of supercritical carbon dioxide,the basic characteristics of reservoirs and caprocks that can satisfy the underground coal gasification coupled with carbon dioxide storage are proposed,and explained the supercritical carbon dioxide trap mechanism.Finally,according to the requirements of reservoirs and caprocks,the author proposed the basic site selection conditions for UCG-CCS(Underground coal gasification coupling carbon dioxide storage).2)Considering the long-term coal pillar stability,a model of secondary peeling of the coal pillar was established,and the widths of the two peelings on one side were calculated to be 3.18 m and 3.84 m respectively.And the coal pillar width after stripping was calculated to be 6.37 m.At this time,the coal pillar stability coefficient is 1.3.So it can be considered the coal pillar should have sufficient stability after undergoing the second stripping model.And then,the arch depth was introduced into the calculation of the numerical model.By comparing the results of the six groups of stripping models,it was found that when the arch depth of the isolated coal pillar reached 0.8,the maximum stripping on the side of the coal pillar was 4.0m,which was bigger than the secondary stripping width.In this case,the coal pillar instability occurs.3)Combined with the UCG-CCS coal pillar stress distribution,a UCG-CCS coal pillar stress distribution model is established.And then,it is considered that the reduction trend of the coal pillar actual bearing stress changes linearly as 26.7%,27.6%,28.9% and 30% with the storage stress increasing.It shows that the greater the storage stress,the faster the coal pillar stress decreases.The reason for coal pillars carrying capacity reducing why that the overlying rock layer is bent upward by external forces,resulting in coal pillars and rock layers effective contacting area reduced under the increasing storage stress.4)The AHP was used to determine the weights of influencing factors on the UCGCCS water flowing fractured development height.Combining geological mining conditions and storage conditions,the author was proposed an empirical formula for judging water flowing fractured development height of UCG-CCS.And the empirical formula was successfully applied in Ulanqab coal underground gasification test area.The empirical formula is in good agreement with the numerical simulation results.The research results will directly provide a decision basis for judging the UCG-CCS water flowing fractured development height.The paper has 37 drawings,15 tables and 95 references...