Abstract: The terrestrial pulveryte of Da'anzhai Member in Yuanba Area of Sichuan Basin is different from that in other areas in the Basin, and the physical properties of the reservoirs are quite different, so it is necessary to study the physical properties of the pulveryte reservoirs in the target member in this area. The physical properties, reservoir space, pore structure and permeability of rocks in the study area were analyzed by means of microscopical observation, porosity and permeability measurement with helium, low-temperature nitrogen adsorption, scanning electron microscope, FIB, etc. The results showed that the pulveryte reservoir space type in the study area was classified as pore and fracture, including organic matter pore, intergranular pore, dissolved pore, intercrystalline pore and micropore among clay minerals, as well as tectonic fracture, shale bedding fracture and diagenetic shrinkage fracture; the average porosity was 3.35% and the average permeability was 1.54 mD, so this reservoir was a pore-fracture reservoir with ultra-low porosity and low permeability; the pulveryte reservoir was dominated by micropores and mesopores with a size of mainly 3 to 7 nm; the organic-rich shale and shell shale were the most favorable reservoir lithology in the second sub-member, and the organic-rich pulveryte section in the lower and middle layers of the Da'anzhai Member was the favorable reservoir interval. The analysis of reservoir characteristics is helpful to discover the formation mechanism of terrestrial tight reservoirs with ultra-low porosity and low permeability in the Da'anzhai Member, and also provides support and reference for the genesis analysis and of distribution rule prediction of such reservoirs.

Key words: terrestrial shale gas, pulveryte, reservoir physical properties, micropore, Yuanba Area, Da'anzhai Member