Petroleum geologic conditions and accumulation history of Middle Devonian, southern Guizhou province

In the Dushan Formation of the Middle Devonian in the southern Guizhou province, the mudstone source rocks of trough-basin facies are widespread with high organic abundance. The average organic carbon content is 3.02%. Most of the kerogens are of type Ⅱ₁, and some are of type Ⅰ, indicating for excellent hydrocarbon generation conditions. In carbonate and sandstone reservoirs, intergranular, intergranular pores and cracks develop well. Cap rocks distribute widely and are preserved well, indicating for strong sealing capacity. Petroleum shows prove that, in both carbonate and sandstone reservoirs in the Middle Devonian, uneven organic matter or asphalt infillings can be found. The homogenization temperatures of fluid inclusions in the Dushan Formation show that the study area has experienced 2 phases of hydrocarbon charging. At the end of Devonian, the southern Guishou province was the uplifting area of the Ziyun Movement, hence was favorable for petroleum charging during the early Carboniferous. Petroleum migrated along cracks to the reef flat limestone reservoirs and the littoral sandstone reservoirs in platforms and platform edges.