Research On The Chlorite Coating Of The Chang 9 Oil-bearing Of The Yanchang Formation In Zhenjing Area,Ordos Basin,China

By selecting the chlorites rim of sandstone reservior in Yanchang formation in Zhenjing area,Ordos Basin as the research object,this paper is based on the scientific research project of North China branch of Sinopec and the open foundation subject of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation: the research on the clay coated of reservoir sandstone in Yanchang formation,Ordos Basin.On the basis of the researches made by scholars both at home and abroad,this paper is guided by multidisciplinary theory,the integration of field research and laboratory analysis,the macroscopic observation and microscopic test,and the theory and practice.It intends to research the characteristics of sandstone petrology of Yanchang formation in this area,the main diagenesis and diagenetic stage by analyzing the field data and the indoor slices observation,physical properties,scanning electron microscope and gamma-spectrometric data.This paper discuss the sedimentary environment,material composition and diagenetic background of authigenic chlorite rim,also,the occurring state of chlorite rim,the relations between chlorite rimand carbonate cements and that of between chlorite rim and authigenic quartz formation are included.Finally,the relations between the authigenic chlorite rim and the space types of reservoir rocks,reservoir pore evolution and the physical characters are explored.Some relative knowlege is obtained in the following:The sedimentary environment of developmental authigenic chlorite rim is mainly for distributary channel,mouth bar of delta which has humid climate,hydrodynamic conditions and strong underwater.The forming stages of chlorite rim should belong to the A-B period of precocious rock stage.By scanning electron microscopy,a large number of intergranular holes exist in the development chlorite rim,hence the anti-pressure ability of such chlorite should be low.The slices indicate that the sandstone pore is mainly preserved by the support of particles for each other.In other words,it is because particles undertake the overlying pressure instead of chlorite to increase the mechanical strength and ability to resist the compaction of the rock.The overgrowth of quartz in reservoir sandstone would be prevented by chlorite rim.But if authigenic quartz formation is finished before chlorite rim formation,its formation will not be affected by authigenic chlorite rim.Chlorite rim has begun to grow before calcite cementation,but during the process of calcite cementation,the growth of chlorite rim does not stop.It is because that the supply of calcite cement is adequate that the outpouring pores prevent the growth of chlorite rim,which leads to the stopped growth of authigenic chlorite rim.There is a certain corelation between porosity and chlorite rim while it has less corelation with permeability.Chlorite rim does not have obvious function for protecting sandstone porosity and improving the sandstone reservoir.The reason that sandstone has good reservoir is the result of the development of primary intergranular pores.The existence of chlorite rim is the indication for the development of sandstone promary intergranular pores.