Abstract A seismic-sedimentologic study was performed to map sediment-dispersal characteristics from the Shahejie-1 to Minghuazhen sequences in Qinan sag, Huanghua depression, China. Guided by third-order sequence-stratigraphic correlations from seismic and wireline-log data, we prepared stratal slices from a three-dimensional seismic volume to reveal high-resolution (10-m levels) sediment dispersal characteristics in a relative geologic-time domain. The strata from the Shahejie-1 to Minghuazhen sequences in Qinan sag can be divided into two second-order sequences and 10 third-order sequences. These sequences underwent a structural evolution history from stable rift faulting, to declining rift faulting, to depression with normal subsidence rate, to depression with accelerated subsidence rate. Many factors related to the structural evolution history controlled the sediment-dispersal characteristics, such as type of basin, dynamic mechanism, faulting activity, subsidence rate, presence of paleohighs, and others. Stratal slices depicted that the depositional evolution of these sequences was from braided-delta front, to delta front, to braided river, and finally to meandering river system.

Abstract The Peng Lai 19-3 (PL 19-3) Oil Field, in the south-central Bohai Bay, People's Republic of China, was discovered in May 1999 with the drilling of the PL 19-3-1 well by Phillips China, Inc., a subsidiary of ConocoPhillips. The PL 19-3-1 intersected a 425-m gross hydrocarbon interval in Miocene-Pliocene sands at a depth of approximately 1000 m. The PL 19-3-2 appraisal well, located 1.6 km south-southwest of the discovery well, intersected a gross hydrocarbon interval of 525 m in the same reservoir interval. Subsequent drilling of an additional five appraisal wells has proved that a large oil accumulation exists. The oil quality ranges from 13° to 23° API, with low pour-point temperatures and low wax content. Gas-to-oil ratios are relatively low and range from 100 to 300 scf/stbo. The oil field is on the northeast extension of a large basinal high and is interpreted as a north-south-trending wrench anticline associated with a major north-south strike-slip fault system (Tan Lu fault). En-echelon northeast-southwest-trending normal faults are intersected by north-south-trending wrench faults that divide and compartmentalize the anticline. Reservoirs are a stacked sequence (600-700 m) of unconsolidated to semiconsolidated postrift fluvial-lacustrine sands of good to excellent quality in the lower portions of the Miocene-Pliocene lower Minghuazhen Formation and the Miocene Guantao Formation. Top seal consists of intraformational mudstones in the lower Minghuazhen. Source rocks are organic-rich lacustrine mudstones in the synrift Oligocene Dongying and Eocene Shahejie Formations located in adjacent subbasins. A significant portion of the oil field is masked seismically by the presence of shallow gas which covers approximately 30% (14 km 2 , or 3460 ac) of the crestal area of the structure. A four-component, on-bottom cable seismic survey was initiated in the spring of 2000 to enhance the seismic imaging of this portion of the anticline.