The Detailed Description And Quantitative Characterization On Single Sand Body In Meandering River Of QHD32-6 Oilfield

The development status of large well spacing and thin well pattern in offshore oil fields leads to great uncertainty in the prediction of single sand-body boundary between Wells.Although the offshore oilfield has relatively high quality 3D seismic data,only some layer or some area have high well-seismic coincidence and single sand-body cannot be identified using seismic data in the whole area.How to make the best use of the limited well data and seismic data to delineate the range and boundary of the single sand body in the whole region more accurately becomes the key to reservoir description in offshore oilfield development.Taking QHD32-6 oil field as the study object,the use of core,logging,seismic data,on the basis of the fine stratigraphic correlation and sedimentary environment analysis,the lithofacies types,genetic sequences,logging facies characteristics and combination patterns in the single sand body are discussed,and from the perspective of the core and logging identification of single sand body internal sequence of lithofacies types,causes,electrofacies features and combination detailed anatomy,from the perspective of the well logging and seismic recognition of single sand body of key size parameters quantitatively characterized,and the quantitative parameters of single sand body were characterized.Finally,the study result are used in areas of low seismic resolution and poor well seismic correlation.It provides a new technical method and theoretical basis for the description of oil reservoir in offshore with large well spacing.This thesis mainly obtains the following understanding and conclusion:(1)In stratigraphic of fluvial reservoirs,different methods are discussed in different reservoir scales and different accommodation.Because the fluvial reservoir often lacks the marker layer,when dividing the oil group in the study area,based on the recognition of the limited marker layer,the oil group is divided according to the changes of the net to gross rate,river channel size and stacked pattern,facies sequence,logging curve and seismic reflection characteristics among the oil groups.When dividing the thin layer of the study area,the distribution and stacking characteristics of the channel are significantly different in the oil formation(medium-term cycle)under different accommodation,so different thin correlation methods should be used with different sedimentary origin.(2)In view of the current dispute between meandering river and shallow water delta in the study area,the sedimentary characteristics and sedimentary environment of the study area are analyzed and confirmed,and the facies type of meandering river is expounded.The composition type of sandstone in the study area and the sorting and rounding indicate that the sediment transport distance in the study area is short and has the characteristics of accumulation near the source area.The mudstone color and palynology data indicate that the sedimentary period in the lower Ming section of the study area was warm and dry,and the salt-tolerant and drought-tolerant grassland vegetation was widely distributed.Most of the time and most of the area of sediments expose to the surface.At the same time,seasonal dry and wet alternations,breach,overflow events occur frequently;and some small flood plain lakes or oxbow lakes occurs in some areas.The probabilistic accumulation curve,lithofacies type and sedimentary sequence of the study area are all shown as meandering river sediments.(3)This paper introduces the Bridge theory and the theory of crevasse splay to analyze the types of lithofacies,sediment sequence,log facies in the sand body of single point bar and crevasse splay,and discusses a new log identification method for single sand body in meander river reservoir.In terms of subdivision and combination of point bar sequences,there are four sediment sequences of point bar sand bodies in the study area.Bridge’s theory states that the maximum flow velocity occurs near the bar head and the minimum occurs away from the bar tail,so the sediment sequences in well logs are generally box-like at the bar head and bell-like at the bar tail.This describes in plan view the stretches of river in fluvial reservoirs.In terms of reservoir characterization of crevasse splay,the sedimentary characteristics and identification criteria of crevasse splay in the Lower MingHuazhen Formation of the study area are expounded,and it is considered that the crevasse splay in the study area has good reservoir potential.(4)The method of seismic geomorphology is used to describe the well-preserved river reach with good well-seismic coincidence,the key parameters are measured and compared,the quantitative relationship of the key parameters in the study area is expounded,and the formula of width to thickness ratio is established based on the analysis of 95% confidence level.The comparison results show that in the width-thickness ratio chart,all data points in the study area are under the Collinson formula and above the Fielding formula,but they are quite different from the Bridge formula.Comparison with Flielding chart shows that all data points in the study area are below line 2A and above line 2B.The comparison results with the Gibling map show that all data points in the study area are close to the 100:1 width-to-thickness ratio line,and the consistency with the sample of Australia’s quaternary Riverina in the Gibling map is high.In addition,the plane size parameter of the point bar in the study area increases proportionally,that is,when the size of the point bar increases,the width,length,arch height and arc length of the corresponding reach of the point bar increase proportionally.However,the curvature of point bar in the study area is not necessarily related to the plane size parameters,which is mainly related to the suspended load.(5)The application detailed description and quantitative characterization on single sand body in meandering river in the stratum with poor seismic resolution and low well seismic coincidence is discussed,and the corresponding development suggestions are put forward.It is suggested to adjust the relationship of injection well and production well within the single point bar in the main stratum to ensure that there is production and injection in the single point bar,so as to prevent the inrush of injected water in one bar from causing poor efficiency or in the adjacent point bar.For a thin sand thicness less than 3m,its predicted width is usually close to or less than a well spacing,resulting in different single-point bar sand bodies drilled by adjacent injection and production wells within a small layer.The sand bodies are separated by abandoned channels,resulting in poor inter-well connectivity and ineffective production wells.For this kind of thin sand body,it is suggested to ensure that the sand body of a single point have both injection and production wells.