庆城地区长8致密砂岩储层含油性影响因素分析OA

To address the big difference in sandstone oil-bearing property in Chang 8 of Qingcheng Area and the un-clear controls on oil layer distribution,drilling,logging and experimental data were integrated by using porosity in-version,pore-throat restoration,overlays of geological factors,investigations were conducted on the relationships with oil bearing property concerning sedimentary microfacies,pore throat characteristics,structure and caprock condi-tions.The results show that the Chang 8 sandstones in the study area were deposited in delta-front environments,in-cluding three microfacies:underwater distributary channels,mouth bars and lateral splays of underwater distributary channels.Among them,the single sand bodies in the underwater channel facies ranged between 2～15 m in thick-ness,with well-developed coarse pore throats that were tightly clustered-these facies were most favorable for hydro-carbon accumulation.The mouth bar facies had single sand bodies between 2～8 m in thickness with relatively con-centrated pore throat sizes.The channel-splay facies had thinner(2～3 m)sand bodies with finer pore throats;their reservoir quality and oil-bearing property were poorer than the other two facies.The late Early Cretaceous experi-enced large-scale hydrocarbon migration and accumulation,and the movable-fluid saturation of the Chang 8 reser-voir was generally high(mostly above 70%),which is favorable for hydrocarbon charging.In late diagenesis,the channel splay sand bodies were further compacted and strongly cemented,which resulted in finer pore throats and reduced movable-fluid saturation.After the reservoir formation,there were possible redistribution of hydrocarbons for the oil layer distribution was not closely controlled by anticlines but was strongly associated with fault zones.Hydrocarbon accumulation tended to be enhanced where the overlying mudstone seal exceeded 10 m in thick-ness.This study provides a theoretical basis for identifying geological"sweet spots"in Qingcheng Area and offers insights for understanding hydrocarbon accumulation in analogous areas.