Multi-scale 3D Reconstruction Of Microstructural Features Of Volcanic Rock Samples In The Southern Songliao Basin

In the past decade or so,there have been many studies on conventional oil and gas reservoirs such as sandstone,including macroscopic and microscopic studies.However,with the increasing proportion of unconventional oil and gas reservoirs with low porosity and low permeability in oil exploration and production,it is more urgent to study the microscopic pore structure of low permeability rocks.In recent years,unconventional volcanic rock reservoirs have received continuous attention due to their significant commercial value.Volcanic rock reservoirs have the characteristics of strong heterogeneity,poor macroscopic reservoir quality and complex microscopic pore structure.Pore structure,that is,the geometry,size and distribution of pore throats and their connectivity,determines the macroscopic storage and migration performance of a reservoir.Due to the existence of a large number of irregular and random micro-nano pore throats and fractures,the permeability and reservoir capacity of volcanic rock reservoirs are complicated.At present,there are many achievements in the research of volcanic rock reservoirs,but the research angle is mostly two-dimensional.It is rare to study the influence of microscopic three-dimensional pore-fracture network on gas storage and transportation in volcanic rock reservoirs through three-dimensional modeling.A series of experimental results show that there is an abnormal negative correlation between the porosity,permeability and gas diffusion coefficient of volcanic reservoir rocks.In this paper,the microscopic three-dimensional pore-fracture network of Yingcheng Formation volcanic reservoir samples in the southern Songliao Basin was evaluated by CT scanning technology,and the influence of the microscopic threedimensional pore-fracture network on gas storage and transport in volcanic reservoirs was further discussed.In this paper,CL1 dacite samples and DH2 andesite samples,which are both porphyritic extrusive rocks,were selected from the Yingcheng Formation volcanic reservoir samples in the southern Songliao Basin.Using the image data obtained by CT scanning,three-dimensional reconstructions were carried out on the two wellhead samples at the micro and nano levels,respectively,and the microscopic pore structure and macroscopic and microscopic fracture characteristics of the rock samples were analyzed.Compared with DH2 samples,CL1 samples have larger average pore volume and higher porosity,higher average coordination number and the existence of microscopic fractures,resulting in better pore connectivity and better potential storage and permeability.The reason for the abnormal negative correlation between porosity,permeability and natural gas diffusion coefficient of volcanic reservoir rocks is explained,and it is further proved that there is a positive correlation between them.In addition,the effect of microscopic three-dimensional pore-fracture network on gas storage and transport in volcanic reservoirs is further discussed.The results show that the microscopic pore structure and fractures in tight volcanic rock reservoirs with strong heterogeneity have a decisive controlling effect on the storage and migration of natural gas.This has important implications for understanding the migration mechanism of natural gas in unconventional volcanic reservoirs.