Groundwater Charcateristics Of Paleogene And Its Relationship With Oil And Gas In Jinhu Depression

Jinhu depression is a secondary depression which is located in the west of Dongtai depression in the Subei basin. It is also one of the main exploration plays in Jiangsu oilfield. The paleogene sequences in the Jinhu depression are well developed and distributed steadily, including Funing Formation, Dainan Formation and Sanduo Formation. According to the hydrochemistry data of formation water and its isotopic vaule, the statistics of formation water hydrochemistry and related combination parameter of many main reservoirs in Jinhu depression paleogene are analysed,based on above research, this paper has analyzed the vertical and horizontal distribution and variationregulation of formation water geochemistry characteristics, in different zone and different strata According to the pressure feature and oil-gas density in different well and different strata in Jinhu depression of Subei basin, fluid potential is used to analyze the hydrodynamic characteristics and divide the hydrodynamic units of the petroliferous sedimentary basin. The fluid pressure field and its distribution law in Jinhu depression are well investigated. The research of groundwater hydrochemical-hydrodynamic and the relationship between paleogene hydrogeology characteristics and hydrocarbon migration-accumulation can offer the necessary theory support for oil and gas exploration. The results in the research as follows:(1) Influenced by meteoric water strongly, the salinity of formation water is low. The variation of sanlinity of formation water is small, which shows that the connectivity of Strata is relatively superior.The fluid on the central-north part of Jinhu depression is dominated by lateral migration and the migration distance is relatively long,so the concentration degree of formation water is low. Because of the antithetic faults, the migration distance of formation water in Anle of southern west slope and chajian slope is short. And the vertical migration is stronger than horizontal migration. Therefore, the concentration degree of formation water is high and the salinity is high. Because of the freash water squeezed from mudstone, the salinity is low in Sanchahe subsag, Longgang subsag, Chajian subsag, Sishui subsag and so on. Bianminyang zone is a intra-sag uplift between Longgang subsag and Sishui subsag. Due to two sides centrifugal flow develop in the Bianminyang zone, it is a interaquifer flow weepage zone and the salinity of formation water is hishest in the Jinhu depression.Maybe affected by the meteoric water connected by fault, some parts develop low salinity formation water.(2) According to the result of deuterium and oxygen isotope testing of formation water, Funing Formation, especially the shallow strata, is influenced by meteoric water apparently.(3) There are two reasons to explain the oil density is high in the east of Bianminyang. Firstly, the oil is mixed with low-maturity crude oil; Secondly, in this area, fault developed, fault block cracked and meteoric water connected by fault led to the oil degraded.(4) The Sanhe subsag, Longgang subsag, Chajian subsag and Fanshui subsag is high liquid potential zone, and Bianminyang uplift, west slope and Chajian slope is low liquid potential area, which is the fluid migration oriented region and are in favor of hydrocarbon accumulation.(5) The favorable areas for oil and gas exploration are north part of the west slope, southwest part of Anle oil field, central-north part of Chajian slope and the north footwall of Tongcheng fault. Fanshui subsag is the relatively favorable area for oil and gas exploration.