Experimental Research On The Formation And Distribution Of Methane Hydrate In The Layered Quartz Sand

As a clean energy source,natural gas hydrate(NGH)is widely found in permafrost area and deep seabed.According to drilling data in a lot of NGH occurrence areas all over the world,it shows that the stratigraphic structure of NGH occurrence area has the characteristics of vertical stratification distribution,and it has different NGH occurrences in different vertical geological strata.In order to research on the formation and distribution of methane hydrate in identical size of quartz sand and the layered quartz sand which is made up of different quartz sand.This thesis used the natural medium-quartz sand which has four particle sizes,and combined them of two into a double-deck structure.Under the same conditions of initial temperature and pressure,the methane hydrate is formed in this quartz sand structure.The contents and the results in this study show that:In layered quartz sand,which have the same quartz sand size as the overlying layer and different size as lower layer.The quartz sand sizes have a significant influence on the formation of hydrate in the overlying layer.The layered quartz sand which made the 0.5~1mm quartz sand as overlying layer,whose quartz sand size in lower layer has the most significant influence on the overlying layer.And it is favorable for the occurrence of hydrate in the overlying layer with 0.5~1mm.However,the quartz sand with 0.075~0.5mm as the overlying layer,the quartz sand size in lower layer has a minor effect on the overlying layer,and it is unfavorable for the formation of hydrate in the overlying layer.After that,the lower layer is regard as the research object.The quartz sand with 2~3mm as the lower layer,the quartz sand size of overlying layer has a significant influence on the formation of hydrate in the lower layer,and it is favorable for the occurrence of hydrate in the lower layer.The quartz sand size with 0.075~0.5mm as the overlying layer which is unfavorable for the occurrence of hydrate in the lower layer,and when 1~2mm quartz sand as the lower layer,the quartz sand size of overlying layer has the minor effect to the formation of hydrate in the lower layer.It is found that there are more experimental groups have a higher rate of methane hydrate formation which has 0.5~1mm quartz sand.According to this,it is thought that the quartz sand in the particle size range has a positive impact.In the quartz sand with an identical size,there may have a special size,it is 0.5~1mm.When the quartz sand size bigger or less than this special size,they are all unfavorable for the occurrence and formation of methane hydrate.And in the quartz sand with an identical size,the saturation of methane hydrate is decrease as the increase of quartz sand sizes,expect for the 0.5~1mm quartz sand.However,the quartz sand with 0.5~1mm has the most hydrate occurrence,because there are lots of methane hydrate formed above the quartz sand.In this experiment,the saturation of methane hydrate in the lower layer and overlying layer is compared in the double-deck sand layer,the results show that: the saturation of methane hydrate in the layer is much more than another whose particle size less than it,when there has no lots of methane hydrate occurs above the quartz sand.When the particle size of quartz sand in the lower layer is smaller than that in the overlying layer,this system is much more favorable for the formation of hydrate.It is found that methane hydrate has different morphology in different layer in the double-deck quartz sand.Methane hydrate is dispersed among the quartz sand particle in the layer who has smaller particle size,and methane hydrate is flaky in the surface of quartz sand which has a larger particle size.According to this research,it is expected that this experiment research will have reference for the distribution and reserves in the natural gas hydrate occurrence in the nature.