Formation Mechanism And Distribution Of Sand Bodies In The Central Low Uplift Belt Of Dongpu Sag

The Shahejie Formation in the central low uplift belt of the Dongpu Sag has always been the key target for oil and gas exploration.Industrial oil and gas flows have been produced in the northern Puwei and Wenliu areas,as well as in the southern Qiaokou,Xuji,Machang and Sanchunji areas.Although the study area has undergone many years of exploration,it has not been drawn a clear conclusion on the source direction,formation mechanism and distribution rules of the sand bodies in the central low uplift belt,which also hinders the oil and gas exploration direction.Based on the theory of clasisical sequence stratigraphy,this paper uses seismic interpretation,logging data,laboratory analysis data and other kinds of data to establish a sequence stratigraphic framework for the Shahejie Formation in the Dongpu Sag.This paper analyzes the paleogeomorphology,archaeological source and paleoenvironmental characteristics,and studies the distribution characteristics of the sedimentary system during the Shahejie Formation period.Based on these works on the whole basin,this paper focuses on the the central low uplift belt and studies the source directions,types,controlling factors and formation mechanism of the sand bodies,and also analyzes the distribution rules of the favorable sand bodies.The study shows that the climate of the period of the third member of the Shahejie Formation in the Dongpu Sag is hot and humid,and the paleo-geomorphic features are mainly affected by fault activities.The central low uplift belt,which is now located on the high structure areas,was sometimes located on the low part of the sedimentary topography during sedimentary periods.The source of the central low uplift belt mainly cames from the north and the south margins of the basin,along the long axis directions of the basin.The central low uplift belt mainly develops delta deposits,forming fine-grained sediments characterized by thin interbedded layers of sandstone and mudstone,and develops rock salt in the northern part.The types of sand bodies of the central low uplift belt mainly conclude the delta plain distributary channel sand body,the delta front mouth bar sand body,the delta front underwater distributary channel sand body,the beach bar sand body and the gravity flow sand body.These different sand bodies are vertically stacked and laterally connected.The formation of sand bodies in the central low uplift belt is mainly affected by frequent changes of lake level,matching of accommodation and sediment supply,fault activities and paleo-geomorphology.The formation of sand bodies in the central low uplift belt is mainly affected by frequent changes of the lake level,matching of accommodation and sediment supply,fault activities and paleo-geomorphology.According to frequent changes of the lake level,sedimentary periods are further divided into drought periods and flood periods.During the drought periods,sediment supplies from the north and the south of the basin advance along long axis direction into the center of the basin on the central low uplift belt,forming long-distance delta deposits.During the flood periods,the lake level expands,and the delta sand bodies deposited in the early stage are transformed by the lake wave to beach bar sand bodies.Caused by the influence of fault activities,the gravity flow sands are widely developed.The "long-axis source" feature is the result of the difference in accommodation between the central low uplift belt and adjacent sub-sag belts,caused by faults activities,and the long-axis source supply.The sedimentary models of sand bodies in the central low uplift belt in the drought periods and flood periods are established respectively.It is considered that the central low uplift belt is the favorable exploration area for channel sand body,mouth bar sand body and beach bar sand body,while the drown side of the faults in the adjacent sub-sag belts are favorable exploration areas for gravity flow sand body and are targets for lithologic reservoir exploration.