An Experimental Study On The Effect Of Water Content On Permeability Of Granular Shale

Permeability is a crucial physical parameter of rock formation,especially for shale.Shale is a very tight,low-permeability,ultra-low-permeability rock formation,with a tiny permeability,usually at the nanoscale,and is a good cover.The compactness of shale makes it a vital choice for the geological reservoir of high radioactive nuclear waste.With the commercial exploitation of shale gas,shale has turn into an important gas reservoir rich in shale gas,and the shale permeability has become a key parameter to evaluate the production and capacity prediction of shale gas.As a cover,the permeability of shale itself directly determines the size of the breakthrough pressure which also affects the exploitation of shale gas resources to some extent.In actual formation,shale contain certain moisture content.The existence state of shale and the existence state of water have extremely important impact on studying the migration law and occurrence of gas in shale.So the visible water permeability of shale under the research has very important practical significance.In this paper,we carried out the pressure attenuation experiments of 4 groups of Carboniferous shale samples from ChaiYe 2 Well in the eastern Qaidam Basin with the help of the self-designed laboratory equipment and calculated the permeability under different water content.At the same time,we conducted low temperature carbon dioxide adsorption,low temperature nitrogen adsorption and high pressure mercury injection for rock samples,which qualitatively analyzed the pore size distribution characteristics and obtained the important parameters of pore structure.Finally,the effect of water content on permeability was studied combining with organic matter content and mineral composition in detail and significant conclusions were drawn.It is concluded that the permeability decreases with the increase of water content,and it is influenced by the three stages of the migration channel of the gas.The permeability increases with the increases of porosity of the three test methods and decreases with the increases of water content.When the water content is relatively small,the permeability increases with the increases of pore ratio of micropores and macropores.However,this increase is not obvious.In view of the complex and variable pore structure of water-bearing shale,this paper presents the need to analyze the influence of pore structure on the permeability of water-bearing shale.When the water content is not equal to zero,the relationship between permeability and the content of quartz is very poor,and clay content and total organic carbon in the water content of 0.2%,0.4% and 0.6% respectively have strong correlation.At this point,the permeability increases with the content of clay minerals and the total organic carbon content,respectively.When the water content reaches 0.8%,the correlation is extremely poor.The mineral composition of water-bearing shale influences its permeability by changing its pore structure.The permeability and clay mineral content have a good correlation in low water content.With the increase of water content,the correlation becomes weaker and weaker.And the change of shale permeability with total organic carbon content can be attributed to the changes in porosity.