| Fan-delta depositional systems have developed in most of the rift lake basins in China.However,the fan delta reservoirs have complex architecture features,and there are great differences in the stacking pattern,shape,scale and distribution of fan delta sandbodies developed under different paleotopography slopes,which lead to different reservoir heterogeneity and influence the exploitation effect of oil and gas.In this paper,taking the Dujiata oil formation of the 4th member of Shahejie formation and the Dalinghe oil formation of the 3rd member of Shahejie formation of the 3rd District of Shuguang Oilfield in the Western sag,Liaohe depression,Bohai Bay basin as an example,the differences and genetic mechanism of the sandbody architecture characteristics of the steep slope and the gentle slope fan delta front reservoir are studied by using the seismic,logging,and core data and combining the sedimentary numerical simulation.It lays a necessary foundation for the effective development of this kind of oil reservoirs.Through the research,the following results and recgnitions have been achieved mainly.1.The controlling factors of multi-stage sandbody stacking patterns in the fan delta front area are discussed.The multi-stage front sandbody of Dujiatai oil formation in the research area can be progradation,accretion or retrogradation stacking pattern by the source direction.The foreset dip angle of progradable multi-stage sandbody is about 0.51~0.57 degrees,and the sandbody can be in the lateral and vertical stacking pattern across the source direction.The multi-stage front sandbody of Dalinghe oil formation are prograding stacking pattern,with the dip angle of about 5~6 degrees,and taking on lateral stacking pattern across the source direction.The stacking pattern of multi-stage sandbody by the source direction is mainly controlled by short-term base-level cycles change,and the multi-stage sandbody are dominated by prograding stacking pattern in the short cycle dominated by the falling half cycle,and the multi-stage sandbody are dominated by retrograding stacking pattern in the short cycle dominated by the rising half cycle.Sedimentary simulation studies show that under the condition of A/S unchanged,the topographic slope controls the stacking pattern of the front sandbody,and the steep slope topographic is more likely to develop prograding stacking pattern.The larger the topographic slope,the larger the foreset dip angle of prograding stacked sandbody,the greater the thickness of stacking,the shorter the extension distance,and the topographic slope is linearly and positively correlated with the thickness of the stacked sandbody and the initial foreset dip angle(the foreset dip angle of the first stage sandbody),but has a linear negative correlation with the extension distance of the foreset sandbody.2.The distribution characteristics and differences of fan delta front sandbody in the research area are clarified.The front single layer sandbody of Dujiatai oil formation in the research area are mainly composed of interlaced striped type and discrete striped type on the plane,Isolated lenticular distributary bay sandbody is relatively developed;The single layer sandbody in Dalinghe oil formation is mainly composed of continuous type,and the development of isolated lenticular sandbody is relatively low.The plane distribution pattern of the front single layer sandbody of the fan delta is related to the sediment supply and the energy of the basin.When the sediment supply is low,the distributary channel sandbody mainly forms discrete striped sandbody after entering the lake;When the supply is medium,the distributary channel sandbody mainly forms interlaced striped sandbody;When the amount of supply is strong,the distributary channel sandbody mainly forms continuous sandbody after entering the lake.The energy of lake basin affects the development of isolated lenticular distributary bay sandbody.When the energy of the lake basin is strong,the lake wave can transform the edge of the front sandbody and forms a large number of bay sandbody distributed along the coast.3.The architecture characteristics and differences of single sandbody and single microfacies in fan delta front are studied.The fan delta front single sandbody is mainly single channel bar sandbody,which is composed of distributary channel and mouth bar.The single channel bar sandbody in Dujiatai oil formation is mainly on the plane of narrow belt and lobate,and the distributary channel more deep incised the middle of the mouth bar,and the extension distance is far away,as the distributary function of 1~3 times is more developed.The width of the mouth bar is less than 700 m,but the extension length is more than 3000 m,and the thickness of the sandbody is only 2~6m;The single channel bar sandbody in Dalinghe oil formation is mainly on the plane of wide belt and lump shape,and the distributary channel more shallow incised the middle of the mouth bar,and the distributary channel is mostly the end channel,as the extension distance is less than 1/2 of the length of the single sandbody.The width of the mouth bar is more than 700 m,but the extension length is mostly less than 2500 m,and the thickness of the sandbody is more than 10 m.The distribution characteristics of fan delta front single sandbody and single microfacies are mainly controlled by the influence of topographic slope in sedimentary period.The topographic slope of Dujiatai oil formation is only 0.5 degrees.The distributary channel continuously deep incised the mouth bar and filling the lake basin rapidly,with strong distributary function,and the single channel bar sandbody extends far,with relatively thin thickness;The topographic slope of the Dalinghe oil formation reaches about 3 degrees,and the lake basin edge water is deeper.The distributary channel shallow incised the mouth bar and the filling of the lake basin slowly,and the distributary function is weak.The extension distance of single channel bar sandbody is relatively close,with large thickness.4.The controlling factors of the internal foreset sandbody architecture characteristics of the mouth bar in the fan delta front are discussed.The thickness of the foreset sandbody of Dujiatai oil formation in the research area is 1.5~3m.The thickness of the shaly foreset is about 0.2~0.6m,and the length of the extension is between 600~1200m.The horizontal distance between the two phases of the foresets is about 300~500m,and the foreset dip angle is about 1.9 degrees.The thickness of the foreset sandbody of Dalinghe oil formation in the research area is 3.5~6m.The thickness of the shaly foreset is about 1~2m,and the length of the extension is generally more than 1200 m.The horizontal distance between the two phases of the foresets is about 600~800m,and the foreset dip angle is about 6.6 degrees.Sedimentary simulation studies show that the topographic slope controls the architecture characteristics of the foreset inner the mouth bar of the fan delta front.The greater the topographic slope,the larger the inner foreset dip angle of the mouth bar,and there is a linear positive correlation between the two.The relationship between the extension length of the foreset and the topographic slope is more complex.Below the critical slope,the extension length of the foreset is linearly and positively related to the topographic slope,and there is a logarithmic negative correlation over the critical slope. |
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