渤海湾盆地埕北凹陷古近系沉积体系及砂体成因类型OA北大核心CSTPCD

Chengbei sag is a half graben basin in the Bohai Bay Basin.Its exploration potential is limited by the understanding of the genetic type of sand bodies and the distribution of reservoirs.This pa-per has analyzed the sedimentary characteristics,sand body genetic types and reservoir distribution pat-terns of the Paleogene in the Chengbei sag,using the drilling cores,log curves,and 3D seismic reflec-tion data.The Paleogene in this sag has been developed with fan delta,braided river delta,sub-lacustrine fan sedimentary facies.The fan delta is developed in the steep slope zone on the northeast side of the sag,with lithology dominated by massive gravelly coarse-grained sandstones.The seismic reflections show len-ticular and wedge progradation and retrogradation morphologies and chaotic and the logging facies mainly show low-amplitude jag-shaped,jagged box-shaped,and bell-shaped.The braided river delta is deve-loped in the gentle slope zone on the southwest side of the sag,with lithology mainly consisting of cross-bedded sandstones.The seismic reflection shows S-shaped progradation and imbricated progradation pat-terns.The logging facies mainly show box-shaped,bell-shaped and funnel-shaped patterns.The sub-lacus-trine fan is controlled by gravity flow and developed in the deep lacustrine area of the sag center.The seis-mic reflection is featured by worm-like progradation.The lacustrine shoal-bars are developed at the edge or central uplift of lakes,controlled by wave action,and are characterized by sheet-like sandy deposits sur-rounded by mudstone.The seismic reflection is featured by lens-shaped reflection,and the logging facies mainly show finger-shaped and funnel-shaped.Vertically,the Member 3 of the Shahejie Formation is mainly composed of braided river delta,fan delta,and lacustrine sedimentary facies.The Members 1 and 2 of Shahejie Formation are mainly composed of braided river delta,fan delta and lacustrine sedimentary facies.The Member 3 of Dongying Formation is mainly composed of braided river delta and fan delta sedi-mentary facies,while the Member 2 of Dongying Formation is mainly composed of braided river delta sedi-mentary facies,with the scale of fan delta development being small.The generation and development of Paleogene sand bodies in the Chengbei sag are mainly influenced by tectonic activity,sediment supply,palaeo-microgeomorphologies,and lake level changes.The predominant genetic types of these sand bodies include fan delta sand bodies,braided river delta sand bodies,sub-lacustrine fan sand bodies,and la-custrine shoal-bar sand bodies.