Sedimentary And Reservoir-caprock Association Characteristics Of Lower Paleozoic In Huanghua Depression

Taking the Lower Paleozoic in Huanghua Depression as the research subject,under the guidance of sedimentology,logging geology,reservoir geology and paleogeomorphology,based on survey of surrounding geological sections,core observation and microscopic identification,logging information,seismic data,detailed analysis on the strata and sedimentary facies' division and distribution,reservoir-caprock association types,favorable area forecast of Lower Paleozoic in Huanghua Depression.Lithology in the study area including limestone,dolomite,gyprock and mudstone etc.The limestone can be divided into micrite,argillaceous limestone,banded limestone,leopard limestone,bioclastics,oolitic limestone and calcirudite.The dolomite includes putty-powder crystal dolomite and fine crystal dolomite.The common sedimentary structures include cross-bedding,horizontal bedding,block structure,stromatolitic structure and stylolite,etc.Four types of sedimentary facies are identified,including tidal flat,open-platform,restricted platform and beach.Tidal flat can be divided into mud flat,limestone flat,dolomite flat,mud-limestone flat and gyprock flat according to the characters of lithology.Beach includes oolitic beach and storm beach.Through the study of sedimentary characteristics,we find that transgression began in the sedimentary period of Fujunshan Formation and the transgression direction from south to north.Restricted platform developed in the south area and the tidal flat were typical in the north area in sedimentary period of Fujunshan Formation.In the sedimentary period of Mantou Formation,sea level dropped and the main subfacies was mud flat.Transgression got strong in the sedimentary period of Maozhuang Formation and the restricted platform facies covered most of the study area.The sedimentary period of Xuzhuang Formation is similar to that of Mantou Formation.Transgression was strongest and beach was the most typical sedimentary facy in Zhangxia Formation.During the sedimentary period of Changgu Formation,the sea level dropped and restricted platform developed in south area and tidal flat was widespread in north area.During the sedimentary period of Fengshan Formation,the transgression was strengthened again,which was characterized by open-platform.Affected by Huaiyuan Movement,the south area was uplifted and the sea water receded towards north in sedimentary period of Yeli-Liangjiashan Formation.During this period,the south area developed tidal flat and the north area became restricted platform.Two transgressive and regressive cycles were observed in the sedimentary period of Xiamajiagou Formation and Shangmajiagou Formation.Under the transgressive action,the Xiamajiagou Formation developed from the tidal flat to restricted platform,Shangmajiagou Formation devolved from the tidal flat to the open-platform.The sedimentary period of Fengfeng Formation was the last transgressive and regressive cycle of Ordovician.In the early sedimentary period of Fengfeng Formation,there was mainly limestone flat and in the late sedimentary period,there was restricted platform under the background of slow regressive.Based on the known reservoir-caprock association and related data,there are successive and interrupted two types of reservoir-caprock association in study area.The reservoir space mainly includes caves,fracture,pore and stylolite.The development of reservoir is controlled by sedimentation,structure,ancient landform and other factors.Based on the study of the influencing factors of reservoir development and the distribution of caprock,three favorable reservoir-caprock association zones are preliminarily divided.