Differential Mechanism Analysis Of Chang 9-Chang10 Reservoir Characteristics Of Yanchang Formation In Longdong Area

Longdong area is located in the southwest of Ordos Basin,which is the main oil and gas producing area of Ordos Basin.Chang 9 and Chang 10 Members of Triassic Yanchang formation are the key alternate replacement Layers of the exploration and development of Changqing oilfield,while the reservoir lacks systematic research.Based on core observation,logging data,casting thin section,cathodoluminescence,scanning electron microscopy,X-ray diffraction,physical property analysis,heavy minerals,rare earth elements and other analytical tests,the reservoir petrology,diagenesis,physical properties and differential mechanism of Chang 9 and Chang 10 Members in Longdong area were studied.Finally,the reservoir classification and favorable zone prediction are carried out for Chang 9 and Chang 10 Member in the research area.The provenance direction of the study area is mainly from the north Qinling mountains in the southwest direction,and the secondary provenance is the north Yin mountains,the west Longxi ancient land and the northwest Alashan ancient land.In the study area,there are braided river delta front subfacies,subaqueous distributary channel,mouth bar and interdistributary bay microfacies.The center of the lake basin is located to the east of Kangcha-Huachi-Huashuzhuang forest field,and gravity flow deposits are developed.The lithology of Yanchang Formation Chang 9 and Chang 10 reservoirs of Longdong area is mainly medium-fine grained lithic feldspathic sandstone,feldspathic sandstone and feldspathic lithic sandstone.The lithic content is generally high,mainly primary pores with a few dissolution pores which mainly consist of feldspathic dissolved pores and turbid zeolite dissolved pores.The reservoir is of poor physical property,which mainly consists of low porosity and low permeability-ultra-low porosity and ultra-low permeability reservoir.The structure of the pore throat is mainly the fine pore fine throat type.At present,most of the reservoirs belong to stage A of the middle diagenesis phase and a small part in stage B of the middle diageneses phase.Strong compaction and cementation have a great effect on reservoir physical property destruction,while dissolution has little effect on the improvement of reservoir property.The favorable diagenetic facies are weakly compacted and strongly dissolved facies.It has the characteristics of enhanced compaction,the cementation varies from medium to weak and then to strong,the dissolution enhances from the provenance to the center of the lake basin.The main controlling factors of reservoir development are sedimentation and diagenesis,and the main channel of subaqueous distributary channel and mouth bar sand bodies are favorable sand bodies,the next is gravity-flow genetic sand bodies.Based on reservoir classification and in combination with oil enrichment regularity,the favorable area of Chang 9-Chang 10 Members in Longdong area was predicted with an area of 3344.75km~2.