Oil Reservior Controlling Factors And Accumulation Regularity Of Yan'an Formation In HL Area,Ordos Basin

The Yan'an formation in HL oil area of ordos basin is weak in the study of reservoir distribution characteristics,control factors,accumulation rules and patterns,which brings great difficulties to the next exploration and development.Application field of existing data,this paper carried out the study area in geomorphology Yan'an group,structure,sedimentary facies,reservoir and hydrocarbon source rock,hydrocarbon migration channel and power,oil and gas filling period of time,and time limit factor analysis,to determine the objective layer control factors,summarizes the accumulation mode and accumulation rule,which will provide a scientific basis for late oil and gas exploration and development reasonably.The results show that:In the study area,the top surface structure of the Yan10-8 is generally presented as a number of small nose folds in the east-west direction on the background of the western-leaning anticline,and each layer has a certain inheritance;The pre-jurassic palaeogeomorphology in the study area was divided into four types of units: ancient-river,tributary river,ancient-slope and ancient-highland,the ancient-highland mainly developed in the northeast and southwest of the study area,and the ancient-river through the whole study area in the NE-SE direction;The Yan10 reservoir is the meandering river sedimentary system,and the Yan9-8 layers are the delta plain sedimentary system,and high quality reservoirs are concentrated in the sedimentary sand bodies of river channel,bank and distributary channel;The diagenesis of the 10-8 reservoirs is strong and reaches the middle diagenetic A stage,and the reservoir evaluation results show that the Yan10-8 reservoirs are all medium-low porosity and ultra-low permeability sandstone reservoirs.The oil and gas in Yan10 is comprehensively controlled by geological factors such as palaeogeomorphology,sedimentary facies,structure,reservoir physical property,etc.The palaeogeomorphology controls the distribution characteristics of the Triassic Jurassic unconformity and the development location of the nose uplift structure,providing favorable conditions for the migration and accumulation of oil and gas,On this basis,the reservoir distribution characteristics can be divided into three types of reservoir forming modes: adjacent(branch)ancient river slope,near river ancient highland and inside of ancient highland.Meanwhile,sedimentary facies and reservoir physical properties jointly control the oil and gas enrichment location and scale.Based on the above analysis,the oil and gas accumulation rules and patterns of Yan'an formation in the research area is summarized as follows:The source rocks of Chang7 in the study area reached the peak of hydrocarbon generation in the early cretaceous.Driven by the pressure difference between source and reservoir and the abnormal pressure,the oil and gas migrated upward through the superimposed sand bodies and fractures in the Yan Chang formation to the unconformity surface of the Triassic-Jurassic system.Then,driven by the edge and bottom water,the oil and gas will continue to migrate to the sand body of Fu Xian + Yan10 formations.At this time,some oil and gas will form reservoirs on the slope and at the highand,and the other part will continue to migrate upward through the overlying sand body and fractures in Yan 'an formation to form reservoirs in the trap of Yan 9 and Yan 8 formations.