Comprehensive Study On Chang 8 Reservoir Of Yanchang Group Of Zhangjiashan-Gengwan Area, Ordos Basin

Zhangjiashan-Gengwan area is located at the central area of Tianhuan depression and western margin of Yishan slope. Chang 8 reservoir is important oil bearing layer of ordos basin in exploration and development in recent years, and one of important objects of next oil field reserves growth, therefore, the study on Chang 8 reservoir of Zhangjiashan-Gengwan area is very important.Comprehensive study of Chang 8 reservoir in Zhangjiashan-Gengwan area was done in different scales. Reservoir characteristics and its controlling factors of ordos basin were analyzed simply in big scale; sedimentary facies, sand-body distribution and diagenism facies of the study area were studied in middle scale; petrologic characteristics, diagenesis, pore structure and hererogeneities of Chang 8 reservoir were studied in small (micro) scale.Different from craton basins, study area have nearer provenance, strong activity surrounding. The face of Chang 8 reservoir is mainly shallow front-delta, rich sand bodies is deposited from deltaic front subaques distributary channel, containing quite flexible components as continental clastic muscovite and volcanic rock. Maturity of composition is lower, and texture maturity is quite higher. The main rock type of Chang 8 reservoir is medium-fine grain lithic arkose sandstone, secondly feldspthic lithic sandstone. Constructive diagenesis are anti-compaction, dissolution, metasomatism and fracture diagenesis. Destructive diagenesis are mainly carbonate and continental matrix cementation.Using casting thin sections, sem, X-ray diffraction, physical property experiment, pressured-mercury testing and relative permeability curve analysis, combined with the division standard of diagenetic stages in clastic rocks, I obtained that Chang 8 reservoir is in the late A to early B of middle diagenetic stage. Beneficial diagenism facies are the face of chlorite film surplus hole between grains, the face of feldspar dissolution, the face of kaolinite cementation and the face of fracture porosity.Disadvantageous diagenism facies are the face of carbonate cementation and the face of iron and shale cementation.Surplus pristine hole between grains and dissolution hole are mainly reservoir space. Micro-fine throat way, pore structure lever is lower, belong to extra-low hole and extra-low permeability reservoir. Favorable reservoir is primary in the channel sand body of surplus pristine hole between grains. Overall, Chang 8; is better than Chang 8.After studing seepage characteristic and heterogeneity of the reservoir, I know micro heterogeneity is stronger.