SEDIMENTARY CHARACTERISTICS AND PETROLEUM GEOLOGICAL SIGNIFICANCE OF NEAR-SOURCE SANDY BRAIDED RIVER DELTA: A CASE STUDY OF THE UPPER THIRD MEMBER OF SHAHERE FORMATION IN LAIZHOU BAY SAG, CHINA

The near source sandy braided river delta sedimentation is an important reservoir in the Upper Third Member of Paleogene Shahejie formation (E2s3(u)) in Laizhou Bay Sag, Bohai Bay Basin. Based on the integrated analyses of core observation, grain size statistics, seismic data and well logging data, combined with the regional research, we found that Laizhou Bay Sag is a faulted basin in the period of the Upper Third Member of Shahejie. The provenance mainly comes from the Kendong uplift 20 kilometers away. The core and grain size show that the reservoir is dominated by sandy sedimentation. The lithology is mainly siltstone, fine sandstone and medium sandstone. The coarse sandstone is relatively few and the conglomerate is undeveloped. Three kinds of subfacies were recognized, including braided river delta plain, braided river delta front and pro-braided river delta, which can be further divided into the following six sedimentary microfacies: upper-river distributary channel, alluvial plain, underwater distributary channel, underwater distributary interchannel, mouth bar and sheet sand. The near source sandy braided river delta is close to the hydrocarbon generating center of the faulted basin and formed a high quality trap combined with the fault system, which is a favorable reservoir for oil and gas accumulation. This provides an important research direction for oil and gas exploration in the sag.