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Hydrochemistry field origin and its coupling relationship with overpressure system, Dongying depression
WANG Bing-jie1,HE Sheng1,WANG Jing2
(1.Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074,China;2. School of Environmental Studies,China University of Geosciences, Wuhan 430074,China)
Abstract:
According to the measured pressure of formation,hydroohemistry data from more than 2 000 wells in oilfield, and the paleao-pressure from 149 fluid inclusion thermodynamics modeling in Dongying depression, the mass balance relation of cation and anion was calculated to study the water-rock interaction. Based on these, the generation process of the formation water and its relation to the pressure evolution and oil preservation conditions were analyzed. The results show that in the vertical, the formation water salinity is lower than 100 g/L in the normal pressure system (from Es2 to Qp) with the depth above 2. 2 km, and the formation water belongs to salt water. The formation water salinity is higher than 100 g/L and the highest value is 336 g/L in the overpressure system ( Ea4 and Es,) wilh the depth under 2.2 km, and the formation water belongs to saline. In the plane, the. formation water salinity in the east of Dongying depression is higher than that in the west, and the saJinily in the north is higher than that in the south. The high salinity formation water in Es2 and Es5 distributes along the fault zones of depression center. The formation water salinity in Es4 reduces from the center of north depression to the outside, exhibiting zonal distribution. For the coupling relation between hydrochemical field and overpressure system, water-rock interaction in overpressure fluid compartment has a signification impact on forming high salinity CaCl2 formation water in the center depression. The forming of high salinity formation water was influenced by the salt dissolution of evaporite forma-tion in Es4. The density from different member and area is different. The depression edge normal pressure zone is an open hydro-geological system. The formation water salinity is reduced by inflltration of surface water. The oil light components are lost and oil density increases. The oil preservation conditions of the zone are poor, but the top and inside of overpressure system in the center of depression is a closed hydro-geological system. Most of oil density is lower than 0.9 g/cm3,and the oil and gas preservation conditions are good.
Key words:  Dongying depression  overpressure system  salinity characteristics  ions characteristics  water-rock interaction  oil distribution and preservation