This paper analyzes the geologic conditions of hydrocarbon accumulation in the Chang-9 reservoir of Ordos Basin.The oil in the Chang-9 reservoir is mixed oil sourced from both the overlying Chang-7 and Chang-9 itself.However

oil in the Chang-9 reservoir in Zhidan area is only sourced from Chang-9 source rocks

without any contribution from the Chang-7 source rocks.The oil mainly occurs in the first segment of Chang-9 oil reservoir.Reservoirs are mainly of distributary channel sandstone of braided river delta plain facies and underwater distributary channel sand of delta front facies

with some turbidites of semi-deep lake facies.Lithology of Chang-9 reservoir is dominated by lithic arkose with well-developed primary inter-granular pores

low porosity and permeability.The physical properties of the Chang-9 oil reservoirs show great lateral variation.In Jiyuan area

the sandstone feature in coarse grain

well-developed inter-granular pores and good poroperm characteristics.In contrast

in Luochuan area

the carbonate cemented sandstone has poor poroperm characteristics due to poor development of pores.According to the relationship between source rocks and reservoirs

two source rock-reservoir combination patterns were identified in Chang-9 oil reservoirs

i.e."upper sourcing" pattern and "indigenously sourcing" pattern.Jiyuan area is the most favorable for further exploration based on comprehensive analysis.