An exploration breakthrough in Paleozoic petroleum system of Huanghua Depression in Dagang Oilfield and its significance, North China

Abstract

Abstract In recent years, several wells in the Qibei and Wumaying buried hills of Dagang Oilfield tapped oil in the Carboniferous–Permian and Ordovician strata. This major breakthrough reveals that the deep Paleozoic in the Bohai Bay is a new petroleum system. Through re-evaluating the Paleozoic source rock, reservoir-cap combinations and traps, it is found the oil and gas mainly come from Carboniferous–Permian source rock. The study shows that the Paleozoic strata are well preserved in the central-south Huanghua Depression and developed two kinds of reservoirs, Upper Paleozoic clastic rock and Lower Paleozoic carbonate rock, which form favorable source-reservoir assemblages with Carboniferous–Permian coal measure source rock. The Carboniferous–Permian coal-bearing source rock is rich in organic matters, which are mainly composed of type II2 and III kerogens, and minor II1 kerogen in partial areas. Multi-stage tectonic movements resulted in two stages of hydrocarbon generation of the source rocks. The period from the deposition of Kongdian Formation to now is the second stage of hydrocarbon generation. The matching between large-scale oil and gas charging, favorable reservoir-cap combinations and stable structure determines the enrichment of oil and gas. According to the new comprehensive evaluation of Paleozoic petroleum system, the primary oil and gas resources of the Paleozoic in the Bohai Bay Basin are over 1×1012 m3. The exploration breakthrough in Paleozoic petroleum system, especially Carboniferous–Permian petroleum system in Huanghua Depression is inspirational for oil and gas exploration in similar provinces of Bohai Bay Basin.