Study of sedimentary characteristic in Denglouku formation, southern Songliao basin, Northeast China

Abstract

Based on geological and geophysical data (e.g., core observation, well-logging curves, logging, analysis assay, and seismic data), the sedimentary facies, characteristics and distributions of the Lower Cretaceous Denglouku formation in the southeast uplift region of southern Songliao Basin are analyzed. The study shows that four types of sandbodies developed in Denglouku formation: alluvial fan, fan delta, braided river and braided river delta. In the early stage of the transition period named D1 period, the deposition is significantly controlled by the fault depression, resulting in rapid unloading of the sediments. Five large-scale divided fault-depressions and two small fault depressions have been developed. The ancient uplift at the periphery of the fault depression refers to the main development area of alluvial fan depositional system, Fan delta deposits are distributed around the fault depression, and the fan delta front extends into the lake. During D2 (the end of the transition period), several geological processes exist: (1) the alluvial fan, fan delta, braided river, braided river delta and lake sediments developed; (2) the unified sediment unloading area is formed. Taking the community of the floodplain and shore-shallow lake contact zone as a boundary, the western part of the boundary mainly developed alluvial fan and braided river sedimentary system from the provenance highland in the western and northern, the east part mainly developed lacustrine facies massively. With the debris sediments of provenance highland injected into the lake basin successively, it constituted retrograde fan deltas in different scales. Among them, the fan delta front and braided delta front subfacies are the main enrichment reservoirs for oil and gas, which is the favorable facies of oil and gas exploration in the Denglouku formation in the future.