Bitumen is common in the pores of Chang 8

1

pay zone of the Triassic Yanchang Formation in Huaqing area of the central part of Ordos Basin

and the oil-water relationship is very complicated.According to the analysis on the geochemical characteristics of reservoir extracts and crude oil

combining with comparative test on the reservoir physical property of cores containing bitumen before and after washing oil and the reservoir fluorescence analysis

authors studies in detail the reservoir bitumen genesis and its impact on reservoir physical property and hydrocarbon migration and accumulation in this area.The results show that the genesis of reservoir bitumen and crude oil are different

and the bitumen has lower maturity with strong biodegradation.Base on the experiment of washing oil

it is found that both the post-washing porosity and permeability of cores containing bitumen increase significantly

and the oil formed in late stage mainly distributes in the residual pore filled with bitumen.It is pointed out that bitumen has an important control on reservoir physical property and hydrocarbon migration and accumulation at late stage.The Chang 8

1

formation experienced hydrocarbon two accumulation stages

the first stage happened in Middle-Late Jurassic and the second in Early Cretaceous.The early accumulated crude oil with low maturity suffered from strong biodegradation and were turned to bitumen

which filled in the pores of reservoir together with chlorites and ferrocalcites

making the reservoir tighter.The mature oil generated from the source rocks in late stage could only accumulate in the residual pores filled with bitumen or in pores of reservoir with less bitumen.