Abstract:

The measurement of vitrinite reflectance (R_o) is of great significance to the determination of its maturity and evolution of organic matters. Referring to the studies by D. W. Waples (1980) and combining the practical data from Sichuan and Guizhou,the author thinks that there would be such corresponding relationships between the vitrinite reflectance and the maturity of organic matters:R_o<0.65 prematured dry gas0.65—1.30 matured oil generated1.31—2.20 postmatured wet gas2.2—5.50 supermatured dry gas >5.50 unknown After analysing the vitrinite reflectance data from five coal series in Upper Permian,Lower Carboniferous,Lower Permian,Upper Triassic and Neogene respectively,it is discovered that R₀ for the T_s is 0.4%—1.47%,for P₂ 0.75%—4.08% and for C₁>2%.In Upper Permian,the lateral veriations of vitrinite reflectance are as follows:1. 0.75%≤R_o<1.30%,corresponding to matured zone,mainly distributed in areas of east and west Guizhou;2. 1.30%≤R_o<2.20%,corresponding to postmatured zone,mainly distributed in central Guizhou.3. 2.20%≤R_o<4.10%,corresponding to supermatured zone,mainly located in the north and southwest of Guizhou.In the first two areas mentioned above,there exist oil seepages and soft bitumens but only carbonaceous bitumens in the third area.Results are calculated according to the vitrinite reflectance that the palaeotemperature of the Upper Permian in Guizhou was 90°—215℃,and its ancient geothermal gradient was 19.5°—48.2°C/km. By the analysis of thermal evolution of organic matters in Upper Palaeozoic sediments,one may consider that the Palaeozoic sediments in most areas of Guizhou once were buried at the depth of 5,000—13,000m,that's why the maturity of organic matters.there is very high,and the vitrinite reflectance in some place is even greater than 5.5%. Therefore,oil prospects in Palaeozoic sediments in Guizhou is not perspective,but it is better prospect in gas expioration.