DIAGENESIS EVOLUTION CHARACTERISTICS OF DEEP BURIED GLUTENITE RESERVOIR BED IN THE DONGYING SAG, THE BOHAI BAY BASIN

Diagenesis evolution of deep buried glutenite fans in the Dongying Sag of the Bohai Bay Basin is complicated with multiple influential factors.Reservoir beds are difficult to forecast.Based on microscopic observation of rock thin-sections,intrinsic and extrinsic factors controlling diagenesis evolution are dissected.It has been concluded that,on one hand,there are some advantageous factors influencing reservoir property including sedimentary facies,undercompaction,halite-gypsum pier cement,acidic fluid solution,early stage hydrocarbon infilling,tectonic movement and chlorite film.On the other hand,there are also some disadvantageous factors such as compaction,cementing of carbonate and sulfate,high content of clay minerals,crystallization of high salinity of formation water,and diffuse of dissolved salts.Firstly,middle fan facies,undercompaction,early stage hydrocarbon infilling and chlorite film are favorable for preservation of primary pore space.Secondly,halite-gypsum pier cement and tectonic movement are favorable for fracture development.Thirdly,solution of carbonate rock and feldspar by acidic fluid is the main factor controlling secondary porosity development.All the three elements constitute three-dimensional connected pore-fracture network which is effective to enhance reservoir property in deep buried glutenite.