MULTI-SCALE METHOD OF NANO(MICRO)-CT STUDY ON MICRO PORE THROAT OF TIGHT SANDSTONE OF YANCHANG FORMATION, LACUSTRINE ORDOS BASIN IN CHINA

The distribution of pore throat in tight reservoir is characterized by relatively strong heterogeneity.The diameter of them ranges from Nano to micro level and even millimetre(300nm`40um).Based on the study of Nano - micron multi-scale CT three-dimensional imaging of tight sandstone reservoir of Yanchang Formation, Ordos Basin to represent the micro-scale pore throat structural distribution of heterogeneity in tight sandstone reservoir, finding that some differences of structure features exist in the shape, size , spatial distribution and connectivity of tight sandstone pores. The size of the micropores is different in the scale of micro-meters, and the diameter of which ranges from 5.4~26μm. The arrangement of micropores reflects malditribution in vertical and in the shape of isolated points. The part of them is well developed in banding and arranged around particles,which shows tube form in three-dimensional space with good connectivity and is the main channel to connect the relatively larger micropores. In nanometer scale, the quantity of Nanoscale micropores increases, the diameter of which ranges from 0.4-1.5um. the pore throat is arranged in the shape of tube, ball and reflects the characteristics of internaland outer mineral particles.theball-shaped micropores in nanoscale show the poor connectivity and are in the three-dimensional space as reservoir space. But the tube-shaped micropores in nanoscale show the characteristics of connectivity with micro-scale tube-shaped micropores and closely isolated ball-shaped micropoes in nanoscale. Based on the Numerical calculation, permeability is 0.843×10^-3um³ and porosity is 10%. The multiple scale evaluation method of pore throat in tight sandstone reservoir could provide basis for accurately understanding micro pore throat features of tight sandstone reservoir and be a new method to research nano hydrocarbon reservoir.