Research On The Paleogene Saline Lacustrine Clastic Rock Reservoir Characteristics And Main Control Factors In The Western Qaidam Basin

The Paleogene and Neogene are the main oil-generating layers in the western Qaidam basin.The characteristics of the clastic rock reservoir of Xiaganchai formation in the Paleogene are as follows: fine granularity,poor physical properties,small pore throat radius,large diagenetic differences and have strong heterogeneity.Based on the theories of reservoir sedimentology and petroleum geology,physical work such as field geological surveys,core descriptions,log interpretation and analysis tests were conducted,in which the analysis tests mainly include thin-section observation,X-ray diffraction,porosity permeability testing,high-pressure mercury intrusion and so on.The thesis researched the petrological characteristics,reservoir space characteristics and physical properties of the clastic rock reservoirs of Xiaganchaigou formation in Paleogene of the western Qaidam basin.Combined with the factors affecting the physical properties,the target reservoir was classified and evaluated,and the favorable reservoir areas were selected finally.By using the core description,X-ray diffraction and microscope observation,the result shows that the content of three-terminal detrital components of quartz,feldspar and debris in the sandstone reservoir of Xiaganchaigou formation in the western Qaidam basin are equivalent,and the main rock types are feldspar detrital sandstone and lithic feldspar sandstone.The content of interstitial matter is relatively high,mainly composed of cement sunch as calcite,anhydrite and siliceous.The sandstone structure is mainly fine sand-silt fine grained,medium-good sorting,and basement cemented.Reservoir porosity and permeability values are small and its physical properties are poor.The pore types of clastic rock reservoirs are mainly residual intergranular pores,dissolved pores and microfractures are also visible.The shape of throat is mainly lamellar and curved.The connectivities of the throat are quite different.The capillary curves are mainly type II and type III.The types of reservoir diagenesis mainly include compaction,pressure dissolution,cementation,and metasomatism.Among them,compaction reduces the porosity of the reservoir by 20%,cementation reduces the porosity by 12%,and dissolution improves reservoir physical properties.Reservoir is presently at the middle diagenetic stage A-B.Through high-pressure mercury intrusion experiment,combined with five methods including empirical statistical method,physical property test,pore-permeability crossplot method,minimum flow pore throat radius method and mercury pressure curve method,the lower limit of the physical properties of effective reservoirs were comprehensively analyzed.The sandstone of Xiaganchaigou formation are typical low porositypermeability reservoirs.The lower limits of reservoir porosity and permeability are respectively 4% and 0.15 m D.The analyses showed that tectonics,sedimentary environment,diagenesis,pore throat structure and salinity all have effects on the physical properties of the reservoir.Sedimentary environment is the basis for determining the nature of the reservoir.Compaction is the main reason for the reduction of primary pores in clastic reservoirs.Pore throat structure and degree of salinity are important factors for controlling reservoir properties.There are three types of reservoirs developed in the study area.Among them,type II and III are the main types.The type II reservoirs have good physical properties and can have great significance to the exploration and development of the study area.