Measurement and Geologic Application of HomogenizationTemperature and Salinity of Inclusions in Aut6igenic Quartz of Sandstone

The measurement results of homogenization temperature and salinity of gas-liquid inclusions inauthigenic quartz of deep sectional sandstone in eastern Songliao Basin are presented, and the mechanism ofthe authiqenic quartz forming, the application of the mentioned results are discussed in this paper. Authigenic quartz is one of the main diagenitic minerals in sandstone, the homogenization temperatureand salinity of gas-liquid inclusions in which may approximatly stand for the diagenitic temperature andsalinity of pore fluid. The index of secondary growth, which is one of the main forms of authigenic quartzforming, reaches to 4-6 in Songliao Basin. It is shown by electronic probe that the enlarged quartz werefromed in different stages and controlled by buried diagenese. The inclusions in the secondary enlargedquartz may represent partially the changing of temperature (76℃-173 ℃)and salinity (0-4 g/100m1) o'f po;e-uid during the forming of the secondary enlarged quartz. The normal relation between homogenizationtemperature (135=150'C ) and salinity has been set up according to Well Chao N0.2. Temperature(℃)=128.85+5.04 x Salinity, with the coofficient of 0..5932. Based on the comparition of homogenization temperature in different depth of several wells, thepalaeothermal gradient of eastern Songliao Basin can be estimated as 4.66"C/100m which is a little higherthan the average thermal gradient 4.2'}/100m of present, this kind of differences may be caused by the dif-ference between palaeo-burial depth and the modern depth. The relative risen height of Chaoyanggou area iscalculated as about 400-SOOm when compared with Sanzhao aera. The functional relation between depth and palaeotemperature in Sanzhao area can be deduced accordineto the data of palaeothermal qradiend and the present thermal gradient: H_b=21.46T_b-137 it can be calculated based on this formula that: The large amount of authigenic quartz formed in 1494.0m(T_b= 76℃);the threshold of oil generation is at I150.Om(T_b60℃);the initial hydrocarbon expelling atdepth of 1365.2-1794.4m (T_b=70-90℃)and the limit depth of petroleum exploration is 2459.7m (T_b=121℃) Salinity of inclusions, carbon and oxygen isotopic compositions of calcite cement in sandstone indicatethat the sedimentary environment was most likely be large fresh-brackish lacustriae rather than marine dur-ing the Early Cretaceous Epoch. The authors are sure that the data of homogenization temperature is quantitatively believable and thatof salinity is semi-quantitative.