Ordivician Lithofaces-paleographical And Reservoir Distribution In Dagang Oilfield

This thesis mainly focuses on Ordivician carbonate strata in northern Dagang Oilfield, including stratagraphic correlation, every formation's lithofaces-paleographical distribution, carbonate diagenesis, reservoir characteristics and its affecting factors, paying close attention to Qianmiqiao buried hill. The main results have been achieved as following: 1 .On the basis of many dividing schemes of Ordivician strata that have been established since the liberation of nation, we determined another scheme of the studying area: Ordivician is divided into three series: Lower, Middle and Upper. Lower Ordivician consists of Yeli and Liangjiashan formations;Upper Ordivician strata is eroded; Middle Ordivician consists of lower Majiagou, upper Majiagou and Fengfeng formations. At the same time, relationship between rock and elctronics for every formation is determined.2. There are five depositional faces in the area: open sea, restrained sea, tidal flat, salified lagoon and bank. On the basis of depositional studying of single well, concluding lithofaces-paleography of every formation: Yeli-Liangjiashan formations deposit in restrained sea; lower Majiagou formation early in tidal flat and late in restrained platform; upper Majiagou formation early in tidal flat and late in open sea; Fengfeng formation early in tidal flat and late in open sea.Main diagenesis of carbonate reservoir as following:(1). There are five types of dolomitization: evaporative pumping, seepage reflux, mixing and deep buried. Ordivician main type of dolomite of Qianmiqiao buried hill in Dagang oilfield is elogenetic micrite and microspar dolomite.(2). There are three types of karst: subaerial, gypsum dissolution and deep buried karsts., paying more attention to subaerial karst.(3). Cenmentation is the most important destructive diagenesis of karst reservoir. For Dagang oilfield, cements mainly is calcite, other and fills are mud, silicate, pyrite and organic matter, at least there are two or three stages.(4). After studying of cement stratagraphy, cementation-dissolution diagenesis is divided into four zones: phreatic, vadose, deep mixing and deep convection zones. Among them, phreatic, vadose and in the middle of convection zones undergone dissolution (especially in vadose zone). The mixing and upper convection zones undergone cementation. The lower convection zone remained unaltered. There are five stages of cements in Qianmiqiao buried hill carbonate strata. 4.There are many reservoir spaces in the studying area. After the studying of core, petrophysics, capillary, impregnated thin section, SEM and electronical characteristics, porosity, cavity and fracture are determined. We conclude the reservoir is of complex pore-cave-fracture type. 5.The karst reservoir is studied by paleography, leaching time, hydrological regime, lithofaces-paleography, combined with outcrops and drilling data, the karst reservoir model is established.6.Every member and formation are primarily evaluated by petrophysics, drilling accidents and gas show in Dagang oilfield. We conclude that the lower Fengfeng formation and the first member of upper Majiagou formation are of better quality, and the other members are non-reservoir.