Research On Sandbody Architecture And Remaining Oil Of Braided River Reservoir In L80 Oil Group Of P Oil Field In Bohai Area

After decades of exploiting,the P oilfield in the Bohai area has been in a high water cut stage,and various problems in the development process have become increasingly prominent.For example,the vertical and horizontal injection and production of oil fields are not balanced,and there are differences within different levels of reservoir units.Research on the internal configuration of reservoirs is particularly important.This paper,based on the core data,logging data and related production dynamic data of the L80 oil group in the P oil field in the Bohai area,studies the architecture of the braided river reservoir and the distribution of remaining oil in the research area.Using principle of sedimentology,reservoir geology,sequence stratigraphy and theory of reservoir architecture,the paper reviews the L80 oil field reservoir stratum in the study area,establishes an elaborate isochronous stratigraphic gird framework,and confirms the different levels of constructional units of the braided river reservoir.The braided stream,the braid bar and the interlayer of the braid bar are configured,dissected and depicted meticulously.The scale of the braid bar and braided channel is confirmed.According to the study results of the architecture,the distribution of remaining oil in the study area is summarized which guides the production increasing and potential digging of remaining oil in the later stage of the oil field.The elaborate stratigraphic division and contrast of the whole area are earried out by using the method of key bed cycle contrast and the single sand layer division and contrast in the study area,to depict the vertical and lateral overlapping relationship of the single sand body inside the reservoir.Using the theory of rescervoir geology,the type of braided river in the study area is analyzed.According to the quantitative theory of the modern braided river sedimentary system,the quantitative dissection of the braided river reservoir architecture in the study area is carried out;the four-level architecture elements of the braided river of the L80 reservoir are divided into four types:braided river channel,braid bar,infralittoral deposit and flood plain;and four types of architecture space combination forms are established,which include braided channel and braid bar splicing,braided channel and infralittoral deposit splicing,braided river channels and flood plain splicing,and infralittoral deposit and flood plain splicing.The plane distribution and evolutional law of braided stream of the main sand bodies L82 and L88 in the study area are summarized.During the deposition period,the braided stream spreads in a continuous and interlaced shape,and the braided river migrates to the southwest as a whole.Using the logging response characteristics,the relative depth of the sand top and the thickness of the sand body to identify the braid bar in the study area,and determine the combination mode of the three kinds of braid bar and braided river channels,that is,the combination of muddy filling braided river channel and braid bar.The combination of semi-mud filling braided channel and braid bar and sandy filling filled braided channel and braid bar,combined with the moden braided river sedimentary theory,the scale of the core sand dam of the main sand body layer is determined,and the width of the braid bar is determined.The range is 237.01～559.09m,with an average of 339.62m,the length range is 476.4～1355.52m,the average is 690.38m,and the average aspect ratio of braid bar is 2.03.The paper analyzes distribution law of braid bar,and proposes the scale is difference.In the same way,the direction of the long axis is basically the same as that of the river channel and the lateral sand bar develops in the local area.The braided river channels are mostly distributed in a flaky and narrow strip.There are mainly three distribution patterns in the interlayer of braid bar in the study area,which are the distribution of contiguous sediments layer,the distribution of local sediments layer and the distribution of strip sediments layer.According to the analysis of reservoir architecture unit,the study combines with the formation reason of remaining oil to determine four types of remaining oil distribution in the study area.