An alternative, seismic-assisted method of fluvial architectural-element analysis in the subsurface: Neogene, Shaleitian area, Bohai Bay Basin, China

Abstract We develop an alternative fluvial architectural-element analysis using limited core and wireline logs in sparse wells with the assistance of stacked and migrated 3D seismic data. To pursue high resolution, we implement a novel workflow that integrates seismic lithology, seismic geomorphology and core- and wireline-log-based sedimentology. Seismic lithology is performed using 90° phase wavelet and frequency fusion; lithofacies are classified by combining seismically derived lithology (shaliness) and core and wireline-log description of lithology, grain size, and sedimentary structures; seismic geomorphology is conducted on seismic stratal slices. A feasibility analysis concludes that macroform and large mesoform fluvial elements (4–50 m thick) can be revealed using 10–100 Hz bandwidth, 50 Hz dominant frequency, 3D seismic data. The workflow is applied to the study of the Neogene fluvial sediments in the Shaleitian area, Bohai Bay Basin, China. Nine fluvial architectural elements are recognized, including fluvial valley, floodplain, sand-filled and mud-filled channels, sand fan, lateral-accretion complex, sandbar, chute channel, incremental lateral accretion, and overbank. These elements were then assembled for various depositional styles in the meanderplain and braidplain. Interpretation of the fluvial architectural-element maps reveals (1) braidplains and meanderplains characterized by distinctive elements, (2) sand-filled and mud-filled channels that coexisted in the same system, (3) recurrent transitions between different channel types, and (4) thick braided fluvial sediments preserved in a large basin. This workflow provides new strategies to improve mineral exploration, development, and reservoir modeling in the Bohai Bay Basin as well as scantly drilled basins elsewhere.