Characteristics and exploration potential of lithologic-stratigraphic hydrocarbon reservoirs in Qikou Sag of Dagang Oilfield

There are various and abundant lithologic-stratigraphic hydrocarbon reservoirs in Dagang prospecting area of Qikou Sag in Huanghua Depression of Bohai Bay Basin. The primary reservoirs in reserves are the updip pinch out reservoir and structural-lithologic composite reservoir. Those non-structural traps rely on matching between palaeostructure background and sedimentary system. According to palaeostructure cosmetics of Qikou Sag in Dagang prospecting area and distribution characteristics of sedimentary system, there are five important domains for petroleum exploration, including CD enclosed slope of palaeohigh, pitching end, and reversal clastic source area of slope break; (2) frequent facies change area; (3) break in gentle slope of palaeohigh; (4) semi-close lacustrine bay area; (5) break in abrupt slope and low-lying offloading areas in depression. According to the exploration principle of macroscopic lithologic-stratigraphic hydrocarbon reservoirs, a special exploration strategy was adopted in Dagang Oilfield. The sedimentary system superposition research method was combined with palaeostructure background. The structural zone was emphasized as the lilhologic change zone, and the exploration of lithologic-stratigraphic hydrocarbon reservoirs was combined with subtle techniques and procedures. Comparing with the structural reservoir, the lithologic-stratigraphic reservoirs in Dagang prospecting area have more abundant types, more wide distribution areas and more reserves, as well as all system tracts and whole pressure fields. So, these reservoirs are the most important exploration targets.