LOGGING EVALUATION OF THE LOWER LIMIT OF PHYSICAL PROPERTIES OF TIGHT SANDSTONE RESERVOIRS IN YANCHANG FORMATION, ORDOS BASIN

The core of the evaluation of terrestrial tight sandstone reservoir properties is the evaluation of the lower limit of physical properties. In this paper, taking the tight sandstone oil reservoir of the Chang 6 Member of Yanchang Formation in Block A of the Ordos Basin as an example, the effective reservoir lower limit parameters of the tight oil reservoir have been systematically evaluated based on a large amount of lithology, physical property data, logging data, and mercury injection data. The results showed that the lithology of the tight oil reservoir of Chang 6 Member in the study area is feldspar sandstone, and the main pore types include intergranular pores, intergranular dissolved pores, lithic dissolved pores and feldspar dissolved pores. The porosity is concentrated in 6%-12%, and the permeability is concentrated in 0.02-1 mD. Core observations, experimental analysis and comprehensive interpretations of logging parameters showed that the lower limit of lithology of tight sandstone reservoirs in this area is fine sandstone, which corresponds to the oil trace level. The lower limits of the physical and electrical parameters are: porosity 6%, permeability 0.15 mD, oil saturation 43%, resistivity 8.5 Ω•m, and acoustic time difference 214.5 us/m. In addition, the thickness of the sandstone has a positive correlation with the effective thickness, and the effective thickness also has a positive correlation with the porosity. When the reservoir physical properties are better and the sand layer thickness is larger, the oil layer thickness is larger; on the contrary, when the reservoir physical properties are poor and the sand layer thickness is small, the poor oil layer is mainly developed.