Study On Reservoir Developmental Model And Hydrocarbon Accumulation Conditions In The Baxigai Formation In The Yingmaili Area Of The Tabei Uplift

As an important exploration target,the Baxigai Formation in the Yingmaili Area contains abundant oil and gas resources,which is the key reservoir of the Tabei Uplift.However,at present,there is a lack of systematic research on the developmental model of reservoir and distribution of reservoirs of the Baxigai Formation.In this paper,the sandstone samples from Well YM467,Well YM46-1,Well YM903,Well YD701 and Well YD710 were observed and analyzed under microscope,physical properties,SEM,rock size,X-ray diffraction,inclusions and high pressure mercury intrusion.The rock samples form Well YN2,outcrops and oil samples from the Baxigai Formation were analyzed by gas chromatography-mass spectrometry(GC-MS).As a result,the reservoir developmental model of the Baxigai Formation was established,the hydrocarbon accumulation conditions of the Baxigai Formation were analyzed,and the main controlling factors of reservoir were identified.Through the analysis of sandstone samples,the main rock type of the Baxigai Formation reservoirs,with characteristics of medium compositional maturity and medium structural maturity,was identified as fine-grained feldspar lithic sandstone and followed by lithic feldspar sandstone.On the whole,the Baxigai Formation is divided into three types of reservoirs.The first type is massive sand at the bottom of the Baxigai Formation,which is stably developed in the whole area and develops in underwater distributary channel microfacies and interdistributary bay microfacies.The physical property is medium porosity and medium permeability,and the diagenesis intensity is medium compaction-weak cementation.The second type is thin sand body,which is confined to near Well YM46 block and develops in underwater distributary channel microfacies.The physical property,with strong reservoir heterogeneous,is mianly low porosity and low permeability.The diagenesis intensity is medium compaction-medium cementation.The third type is the reservoir developed in channel mouth,represented by sandstone in Well YD7 Area,which is developed in underwater distributary channel microfacies and estuary bar microfacies.The physical property,with strong heterogeneity,is mainly low porosity and low permeability,medium porosity and medium permeability.The diagenesis intensity is medium compaction-medium cementation.Based on the reservoir developmental model of the Baxigai Formation,and comprehensive analysis of hydrocarbon accumulation conditions,it is clear that the hydrocarbon in the study area has the contribution of two sets of source rocks that are source rocks of the Huangshanjie Formation and the Qiakemake Formation.The former has one stage of hydrocarbon charging,with a time of 5-2.5Ma.The latter has two stages of hydrocarbon charging,the first stage was crude oil charging,with a time of 4-3Ma,and the second stage was natural gas charging,with a time of 3.5-2Ma.In the hydrocarbon charging period,the reservoir porosity,with good reservoir forming conditions,was more than 15%.And the reservoir can be charged by largescale hydrocarbon.Combined with the detailed dissection of typical wells(Well YD7 and Well YM46 Areas),it is considered that the main controlling factors of the Baxigai Formation reservoirs are the source rocks and the configuration relationships of reservoir developmental character and unconformity surface and fault.The source rocks controls the distribution characteristics of hydrocarbon.Moreover,the configuration relationships of reservoir developmental character and unconformity surface and fault determine the distribution law of the Baxigai Formation reservoirs.It provides new ideas for the further exploration and development of reservoirs in the Baxigai Formation.