| Lijin sag of the Binnan Area is one of the important oil generation sag in Dongying depression,also is the key area with great exploration potential.Since 2006 beach bar sandstone reservoirs were found,this area had produced thousands of tons of oil,which has proven reserves of more than four hundred ten thousand tons.However,due to the development characteristics and sedimentary background of the beach bar sand body,there is still no more breakthrough in the exploration and development of the beach bar reservoirs in this area.Among them,the understanding of sedimentary facies and sedimentary patterns in this area are important factors restricting the progress of exploration.During the Upper Fourth Member of Paleogene Shahejie Formation,the area was the lacustrine environment.The area had experienced the period of lake area shrunk,the period of the lake area expansion and the highstand period of the lake area,and the general trend of lake level was on the rising.In sequence,the key strata in the study area,the Upper Fourth Member of Paleogene Shahejie Formation,could be summed into a whole Sequence.According to the lithology and superimposed features from bottom to top,this sequence can be further divided into lowstand system tract,transgressive system tract,highstand system tract.Tripartite is the feature of the strata sequence.Through the observation of the wells and the analysis of the seismic data in the study area,it can be found that in the western part of the area,the sedimentary body developed along the slope to the basin was coarse-grained in the grainage character with a large number of erosion surface,mud pebbles,graded bedding,deformation structure and other sedimentary structures.In the vertical,the typical Bouma sequence could be seen in the core.Meanwhile,the convergence-downlap seismic reflection characteristic could be seen.Therefore,it could be judged as the slope fan and the basin-floor fan deposit.The overall grain size of the eastern part in the study area is fine,sediments with pebbles only developed on the slope belts.In the cores,erosion surfaces,mud pebbles,low-angle cross bedding could be observed,which possessed with features of the Bouma sequence in the vertical.Downward to the deep lake area,fine sandstone and siltstone mainly developed.In the core,hummocky cross bedding,sunken cross bedding,truncated structures,and channel mold could be observed which showed the storm seiche effect.Therefore,it was determined as the slope fan and storm-seiche beach bar deposits.In the lowstand period,sand body widely deposited in the area and effected by storm.The gravity flow sedimentary system of the slope fan – deep floor fan developed in the west part.Sediments from Binxian Bulge flow into the lake basin under the action of gravity along the northern slope zone,formed the typical slope fan.Then,the sediments cut through the slope fan into deep basin area and formed deep floor fan.In the east part,effected by the storm,a set of slope fan – storm seiche beach bar system developed.With the terrigenous debris pouring into the basin and forming the slope fan,it also received the transported and reconstruction by the storm action,and then deposited in the deeper and more distal area forming the isolated beach bar.However,during the transgressive and highstand period,the overall depth of water rose,and disturbance range of the storm wave was limited,thus the storm seiche deposits did not develop any more.Only the slope fan and deep floor fan still developed.Basing on the sedimentary characteristics and sedimentary model,the typical seismic characteristics were identified and summarized.According to the unique characteristics of storm seiche beach bar,4 un-drilled sand bodies were found in the east part of the study area,which with the acreage of 10.75 square kilometers in total. |
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