Hydrothermal Effect Of Sinian Dengying Formation And Its Effect On Reservoirs In High - Staircase - Mody Area,

This thesis is an intense research of dolomitic hydrothermal process in Dengying Formation (Sinian) belonging to Gaoshiti-Moxi area, which is mainly guided by Stratigraphy, Petrology, Mineralogy, Geochemistry, Reservoir Geology and the latest domestic and international research and based on the drilling data, logging data and seismic data. It provides the evidence for hydrothermal dolomite from the petrologic and geochemical characteristics and analyzes the hydrothermal formation condition and mode. And it also states that hydrothermal process transforms the reservoir space and how hydrothermal dolomite evolves.The research of hydrothermal petrology indicate that there are sphalerite and galena generated from Mississippi Valley-type deposits hosted in hydrothermal dolomite in study area. There are also hydrothermally paragenetic mineral, such as saddle dolomite, feldspar, fluorite, quartz, pyrite and calcite. All of them are existed in hydrothermal dolomite as filling or replacing material in fractures and vugs. And it is widely believed that saddle dolomite is the indicator of hydrothermal process.The research of hydrothermal geochemistry indicate that the value of818O isotope in hydrothermal dolomite is less than that in early dolomite and sea water, because temperature effect force the heavier18O into fluid while lighter16O into dolomite. It also shows that87Sr/86Sr ratio is slightly higher, because radioactive strontium, which came from siliceous elastics or irreducible water from magmatism and metamorphism, enters into hydrothermal dolomite in buried condition. The microelement is also slightly higher since the low valent Mn and Fe in hydrothermal fluid could enter into dolomitic lattice in reducing environment of hydrothermal dolomitization process. The rare earth element indicate positive anomaly of Ce and Eu effected by hydrothermal fluid, which is opposite with the rare earth element of sea water.Combined with tentonic characteristics, evolution history and stratigraphic characteristics in study area, it analyzes the formation condition of hydrothermal process. The process include tension tectonics by Xingkai Taphrogeny, hydrothermal reservoir underlined clastic strata and the upper cover or seal formation. And it establishes mode pattern of hydrothermal process.Furthermore, it states the reservoir characteristics transformed by hydrothermal process in details, which includes intercrystalline pore and vugular space, brecciated space, hydrothermal corrosion vugs and fractures. It also analyzes the mainly diagenesis in study area, which means the positive diagenesis include recrystallization and neomorphism, karstification and hydrothermal corrosion. At last, it discusses the process of reservoir formation and evolution and established the evolution model of reservoir pore in Dengying Formation.