Accumulation condition and exploration areas of natural gas in the northeast of Qikou Sag

Qikou Sag is one of the richest sag in Bohai Bay basin. Two gas-bearing formations include Carboniferous-Permian and Sha-hejie formation of Paleogene. The northeast of Qikou Sag is near the main depression, so it has the conditions that large natural gas field formed. Also the northeast was affected by several provenance in Paleogene, reservoir-seal assemblage is very developed. Over-pressure of the Shahejie formation in the sag protected the property. All the conditions makes the northeast area the most favorable area to prospect natural gas. Based on tectonic, sediment and petroleum migration characteristics, it is believed the structural traps, strati-graphic traps near the west pitching end of Shaleitian uplift and lithologic traps in the deep of the sag are important exploration area of natural gas.