PETROLOGICAL CHARACTERISTICS AND OIL-GAS EXPLORATION INDICATION OF THE RESERVOIRS ON NORTHERN SHAANXI SLOPE IN ORDOS BASIN: A Case Study of Chang 6 Oil Reservoir in Northern Youfangzhuang Area

To identify favorable facies belt and high quality reservoir development area in northern Youfangzhuang area and expand the proved reserves in Ordos Basin, the paper studies the clastic particle composition and interstitial component of Chang 6 oil formation reservoir through various experimental means such as core thin section observation and mineral composition analysis with detailed experimental data. On this basis, the distribution rule of heavy and light minerals in Chang 6 reservoir is analyzed, and the indication significance of provenance and oil-gas coupling relation are discussed to supplement the scientific research results of reservoir petrology and provenance analysis in the area. The results show that Chang 6 sandstone reservoir is mainly feldspar sandstone, with minor lithic arkose. The interstitial materials are various in types and contents, including clay cement, carbonate cement and siliceous cement. The grains are mainly fine sand, sub-angular and above middle-level sorted. The cementation types are mainly film-pore, pore-film, pore, film and overgrowth-pore cementation. The standard deviation vs. average grain size diagram, heavy mineral association and light mineral composition of Chang 6 sandstone reservoir all indicate that the Chang 6 oil formation is mainly affected by the provenance from northeast, therefore the multi-stage superimposed delta front underwater distributary channel sand bodies are developed. Besides, the residual intergranular pores and feldspar dissolution pores are developed due to long distance transport. The mineral assemblage of feldspar, chlorite and kaolinite improves the physical properties of reservoir in the study area and increases the permeability of low resistivity reservoir. The underwater distributary channel reservoirs in Chang 61 and 62 oil formations are high quality reservoir development areas.