A Research Of Comprehensive Reservoir Prediction To The E₂d₁ Stratum Of Dai Nan Formation In The Duntong Area Of The Jinhu Depression

The Jinhu sag in the North Jiangsu Basin is a faulted basin developed in the Late Cretaceous.It is located in the western part of Dongtai depression from the northern part of Jianhu uplift,south to Tianchang uplift and Lingtang Bridge low rise,connected with the western part of Zhang Baling uplift,east to Wubao low rise.It is a major oil and gas producing area.Its section of the Dainan Formation is dominated by deltas,fan deltas,and lacustrine deposits.Besides most of the area is subfacies deposits in the delta plains and delta fronts.The Duntong area is located in the South West of the Bian Minyang structure belt in the Duntong area.It is near the West of the Longgang Sub-Concave and the Lingtang Bridge low rise.Its section of the Dainan Formation is dominated by delta frontal subfacies and the reservoir is a lithological reservoir controlled by structure.The mudstone in this area does not have the ability to produce oil.The oil source is the Funing Formation E₁f₄ and E₁f₂'s source rock.In the early development process,the focus of exploration and research in the industrial area is mainly in the Funing Formation,and research in the Dainan Formation is little.With the continuous improvement of processing and interpretation technique for three-dimension seismic,the work of rolling development becomes more fine.Because of this reason,people find that the oil source of the E₂d₁ layer is from the Funing Formation.In addition,the capping condition of the reservoir benefits from the upper part of the sand mudstone.What's more,because of the unconformity surface as oil and gas migration channel,the E₂d₁'s sand can become reservoir.Therefore,many good displays of the oil and gas or oil layers were seen many times when drilling in the bottom of sandstone in the working area.In order to deepen the understanding of the working area,increase rolling development efforts and the use of reserves,with the actual production and logging,seismic and geological data,the department developped actual practice of reservoir comprehensive prediction.Firstly,the structural characteristics of the work area were determined through the layer calibration and the fine structural interpretation;Secondly,the 90°phase transformation technique is applied to the seismic section of the area to let the seismic reflection have the significance of stratigraphic lithology,so as to explain the seismic sedimentation,and to analyze the sedimentary evolution process by observing the geochronological profiles at different periods;Thirdly,extracted a variety of seismic attributes for comparison and preferred instantaneous frequency attribute to analyze the sand distribution of the work area;Finally,combining previous analysis results,characterized the sand by the high-precision seismic inversion technology.The study concluded that the overall structure of the E₂d₁ layer have the character of“south rise and north slope”in the Duntong Area.In the early deposition of the E2d1layer,affected by the North-West source system,the strata mainly showed the pattern of development from the north-west to the south-east;but in the middle and late deposition,the strata gradually developed from south to north,and these were mainly controlled by southern source.The combination of seismic attribute analysis results and inversion results can indicate that the east and south-west of the work area are favorable parts.By grading and evaluating these parts,determined as two favorable goals.These results could provide reference for exploration and development of oil and gas fields in the future.