关键词: 羌塘盆地, 石油地质钻探, 中侏罗统, 岩溶构造, 承压水系统

Abstract: The drilling data from two wells show the characteristics of Gyari, Biqu and Sewa Formations in the Middle Jurassic strata of Qiangtang Basin from top to bottom. There occurre the tidal-flat sandstone, mudstone and gypsolith associations intercalated with limestone in the Gyari Formation. There are the platform carbonate rock associations in Biqu Formation, and delta sandstone and mudstone associations develope in Sewa Formation. The characteristics of the underground gypsolith bear a striking resemblance to those of the outcropped gypsum-salt domes in the Gyari Formation. The higher driving pressure and breakthrough pressure indicate that the underground gypsolith is of excellent sealing capacity. Numerous structural fractures and pressure-solution fissures were observed in the carbonate rocks of Biqu Formation. The structural fractures are mainly filled by calcite, and the pressure-solution fissures are filled by bitumen, iron and mud. Widespread oil and gas indications including fluorescence, oil immersion, oil patches, fluorescent sections, bitumen veins and hydrocarbon fluid inclusions suggest a multistage migration of hydrocarbon. Judged from frequent mud loss and empty drilling, the karsts may be well developed in the carbonate rocks. The kicking phenomena found in different depth of two wells indicate that there exist varying scales confined water systems in both of the wells. The groundwater is assigned to the calcium chloride type and has a wide salinity range from 366 mg/L to 1160 mg/L.

Key words: Qiangtang Basin, petroleum geological drilling, Middle Jurassic, karst structure, confined water system