Study On The Reservoir Characteristic Of The Chang-8 In The Ma Ling Region

This paper is based on study of Chang 8 sandstone reservoir within Ma Ling oilfield which belongs to Basin Ordos.The whole research has been guided by the theories like sedimentology,reservoir geology and petroleum geology and has been supported by data generated from the experiments on core,well logging,mud logging and so on.The whole process starts with systematic studies on the sedimentary background of reservoir,its distribution and occurrence,followed by its lithological composition,physical features,pore-throat structure,then the corresponding diagenesis and main control factors of reservoir property.The results of the study show that the sedimentary facies of the targetareais mainly distributary channel of fan delta front;the type of rocks are mainly lithic arkoseand feldspathic lithic sandstone(basically medium-fine,sub-edged roundness and point-line contact/line contact);intergranular pores and dissolved feldspar pores are the main reservoir space;major throats are laminated throat and curved lamellar throat,control shape throat and necking throat come next;pore-throat combinations are mainly large-middle pore with very fine throat;theporosity is in a positive correlation with its permeability,so it is a typical reservoir with low-extreme low porosity and ultra-low-low permeability.Based on the above researches,the author divided the reservoir into three categories:?(K>1mD,(?>10%),very high porosity and permeability with very thick sandstone,can be targeted as high quality reservoirs;?a(0.6mD<K(?)1mD,9%<?(?)10%),highporosity and permeability with thick sandstone,can be regarded as good reservoir;?b(0.3mD<K(?)0.6mD,7%<?(?)9%),low porosity and permeability,thinner sand body,classified as general reservoir;?(0.1mD<K(?)0.3mD,5%<?(?)7%),very low porosity and permeability,thin sand body,poor reservoir.Apart from these,the focused reservoir has been affected by sedimentary micro facies,as the result of which the proportion of sandstone has been getting higher so the physical properties also have been in a good trend.The poor reservoir,which was affected by early compactions and early cementations,are also improved due to dissolution of reservoir.Because of the same reason,the pore-throat space has larger sorting coefficients than before,so the permeability of the reservoir can be higher when sorting is poor.