Abstract:

Gaoyou sag is one of the sags with the most abundant oil and gas resources in Subei basin, but the characteristics of geothermal field of this sag have not been researched. According to the temperature data of 16 temperature wells and 53 test wells in Gaoyou sag, the temperature distribution of the main layer groups and the geothermal gradient distribution were analyzed. The result showed that temperature generally increased with depth increasing and also increased from E₂s to K₂t. The slope inhabited the higher temperature than the deep sag. In the same layer the temperature of the deep sag was higher than that of the slope; the temperature of the east part of slope was higher than that of the west. The phenomenon that the higher temperature in the deep sag and lower in the slope showed close relationship between temperature and depth. The buried depth was the main influence factor for the temperature. The geothermal gradient of E₂s-E₂d was between 23 ℃/km and 30.2 ℃/km, and that of E₁f-K₂t was between 28.9 ℃/km and 36.3 ℃/km. The geothermal gradient of E1f-K2t was higher than and that of E₂s-E₂d。The higher geothermal gradient of E₁f-K₂t caused by the high content of low thermal-conductivity mudstones in three sets of hydrocarbon source bed (E₁f4，E₁f2 and K₂t2). The oil and gas reservoirs distributed from E₂s to K₂t in Gaoyou sag. The oil and gas reservoirs overall distributed in the region with the temperature more than 60 ℃, and individual reservoir distributed in the region with the temperature less than 60 ℃. The faults of Hanliu and Zhen 2 were the main pathway leading to oil and gas migration into the upper strata.

Key words: Gaoyou sag, geothermal field, geothermal gradient, oil and gas reservoir