Study On The Enrichment Law Of Chang 4+5 Oil Reservoirs In Yanchi Area,Ordos Basin

The Yanchi area is located in the central and western part of the Ordos Basin and belongs to the Ningxia Hui Autonomous Region.Its structural location spans the Tianhuan depression and the Yishaan slope.The area is one of the key development blocks in recent years.The thickness of the sand body of the main oil reservoir of the Chang 8 and Chang 9 oil reservoirs in the study area is large,the reservoir property is good,and the output is high,at present,large-scale production has been established.At the same time,non-main reservoirs such as Chang 4+5 reservoir are constantly appearing.Therefore,research on non-main reservoirs can further clarify the prospects of oil and gas exploration in this area.The Chang 4+5 oil-bearing strata have good development potential,but at the same time there are many problems such as complex geological conditions,difficult oil reservoir identification and complex reservoir formation mechanism.Therefore,this paper intends to develop oil and gas enrichment rules from the Chang 4+5 reservoirs.The study aims to become the theoretical basis for the development of the Chang 4+5 reservoirs in the region.In response to these problems and research purposes,firstly carry out literature research and regional geological surveys in the study area,and then collect the research basic materials such as logging data and production test data,and carry out core observation and reservoir test experiments in the study area.Finally,based on the collected basic data and core observation description data,as well as the thin section data,SEM,image size,pore image and high pressure mercury intrusion obtained through reservoir testing,the characteristics of stratigraphic structures,sediments,reservoir and oil reservoirs in the Chang 4+5 strata of the study area were studied.On the basis of the above research,the research on the enrichment of Chang 4+5 reservoirs is carried out from four aspects: hydrocarbon source rock distribution,transport system,sedimentary reservoir and structural characteristics.The final study concluded that the distribution characteristics of the source rock,the sand body of the Chang 6 stratum and the length of the 6 and the 4+5 formation fractures are the characteristics of the transport system and the characteristics of sedimentary reservoirs are the main factors controlling the accumulation of the Chang 4+5 reservoirs.The structural characteristics of the Chang 4+5 oil reservoirs enrichment control is weak,not the main factorcontrolling oil reservoirs enrichment.The source rock widely developed in the Chang 7stratum provides an important material basis for the Chang 4+5 oil reservoirs.The extent and thickness of the distribution control the overall distribution of the Chang 4+5 oil reservoirs,It is the main factor.The main controlling factors are the well-connected sand bodies in the Chang 6 stratum and the high-inclination and near-east-west cracks developed by the Chang4+5 and the Chang 6 strata.Their spatial distribution and configuration relationship it affects the distribution of Chang 4+5 oil reservoirs;the high-quality reservoir “dessert” transformed by sedimentation and reservoir diagenesis is beneficial to the enrichment of Chang 4+5 oil reservoirs.Based on the study of enrichment law,the accumulation model of the Chang 4+5oil reservoirs in Yanchi area can be summarized as follows: The Chang 7 source rock provides a material basis for the Chang 4+5 oil reservoirs,when the oil and gas is discharged from the source rock.After that,the transport system enters the Chang 4+5 stratum through the combination of well-connected sand bodies and formation fractures.When the oil and gas enters the Chang 4+5 stratum,the reservoir near the transport system is favorable for preferentially accumulating oil and gas.It is eventually enriched in a well-developed reservoir“dessert” in the Chang 4+5 formation.Applying the theory of Chang 4+5 reservoir enrichment law,the favorable area prediction is carried out in the study area,and 8 favorable areas are finally selected.The total geological reserves are predicted to be 4.952 million tons,which provides a theoretical basis for subsequent exploration and development.