SOURCE ROCKS IN HUAGANG FORMATION OF H AREA, EAST CHINA SEA SHELF BASIN

With the discovery of oil and gas in the H area of East China Sea Basin, source rocks in the Huagang Formation have raised great attention from geologists. This paper is specially devoted to the source rocks with the newly acquired data of pyrolysis, carbon stable isotope, vitrinite reflectance and kerogen composition. The characteristics of carbon isotopic composition and CV value of saturated hydrocarbon and aromatics suggest that both marine and continental organic matters coexist in the mudstone source rock of Huagang Formation. The vitrinite reflectance varies from 0.76% to 1.11%, and the maximum pyrolysis temperature changes between 440 ℃ and 465 ℃, suggesting that the source rocks remain in a stage of hydrocarbon generation. The kerogen type index of mudstone source rock is less than 0, the pyrolysis hydrogen index is less than 150 mg/g, and the source rocks of the Huagang Formation are characterized by the kerogen of type Ⅲ. The TOC of mudstone source rock is mostly less than 0.5%, the pyrolysis potential of S₁+S₂ is less than 1mg/g, and the chloroform asphalt “A” is mostly less than 0.05%, so the mudstone source rocks are poor in quality. Analysis of coal samples from source rock of Huagang Formation show that the values of S₁+S₂, chloroform asphalt “A” and hydrogen index HI are mostly >100 mg/g, >1.5%, and >275 mg/g respectively, indicating a high quality coal-bearing source rock. In a word, the coal-bearing source rocks are better than mudstone source rocks in quality, and the abundance of continental organic matter is higher than that of marine organic matter.