Abstract:

The Zhijing-Ansai area is an important producing area of interlayered type shale oil in Chang 7 Member in Ordos basin. The sandstone reservoir is tight and poor in physical property, and there is still no specific reservoir classification and evaluation standards. In this study, lithological analysis, physical property testing, scanning electron microscopy, mercury injection experiment, nitrogen adsorption and other methods were used to analyze the petrological characteristics, physical characteristics and pore structure of Chang 7 sandstone reservoirs in Zhijing-Ansai area, and to establish classification and evaluation criteria. The results show that: 1) The mineral composition is mainly plagioclase. The rock types are mainly arkose and lithic feldspar sandstone. The porosity is 2%-17%, the permeability is 0.001×10-3-1.486×10-3  μm2, and the sandstone reservoir is tight. 2) Favorable reservoir diagenetic facies are feldspar dissolution diagenetic facies, chlorite film cementation diagenetic facies and authigenic clay mineral dissolution diagenetic facies. 3) The main pore types are primary pores, secondary pores, and microcracks. Reservoir pore throat structures can be classified into four categories. 4) Combined with the physical property and displacement pressure, the porosity of 2% and permeability of 0.01×10-3  μm2 are taken as the lower limits of effective reservoir properties in the study area. Ultimately, integrating reservoir characteristics and pore-throat classification criteria, a classification and evaluation standard for interbedded shale oil reservoirs in the Chang 7 Member of the study area was established, and the reservoirs were categorized into four types, with type I and type II identified as favorable reservoirs.

Key words:  , Chang 7 Member,  , interlayered shale oil,  , reservoir characteristics, classification evaluation, Zhijing-Ansai area, Ordos basin