Microscopic characteristics and oil content of Chang 6 tight sandstone reservoirs in Lijiachengze area, Jingbian Oil Field, Ordos Basin

The microscopic characteristics and oil-bearing properties of the Chang 6 tight sandstones in Lijiachengze area of the Jingbian Oilfield were studied using the analysis and test data of cast thin sections, thin section fluorescence, scanning electron microscopy, pressure-controlled porosimetry (PCP) and rate-controlled mercury porosimetry (RCP). The results show that the rock type of the Chang 6 sandstone reservoir is fine feldspar sandstone, and the main composition is calcite, chlorite and turbidite. The pore type is varied, mainly with residual intergranular pores and various dissolution pores, and the average pore diameter is mainly distributed at 20-50 μm. The reservoir porosity and permeability are poor. Micro-cracks are locally developed, and pore structure is very complex. Combined PCP and RCP indicate pore throat radius extends from nanometers to micrometers, but there are mainly two peaks, and the pore radius is mainly smaller than 2 μm. The oil content of Chang 6 sandstones is poor, mainly with oil spot grade, and oil is mainly distributed in the residual intergranular pores and dissolution pores. For the oil-bearing sandstones with industrial oil flow wells, the lower limits of porosity, permeability and pore throat radius are 7.5%, 0.15×10^-3 μm² and 0.1 μm, respectively.