Development Characteristics and Significance of Large Delta of Upper Enping Formation, Baiyun Sag

Zeng Zhiwei; Yang Xianghua; Zhu Hongtao; Xia Chenchen; Niu Xing; Chen Ying; Han Yinxue

doi:10.3799/dqkx.2017.006

Abstract：A large-scale braided delta is developed in the late stage of the Enping Formation in the Baiyun sag,but the sedimen tary process,the internal development stages and the plane distribution of the delta remain unclear.Based on the nine wells which penetrated the third member of the Enping Formation,the detrital zircon U-Pb dating and the 2D and 3D seismic data analyses were carried out in this paper.The sediment supply patterns of the Enping Formation in different depositional periods were determined.During the first-second members of Enping Formation (SQ1-SQ2),sediments derived from the paleo-uplift were mainly composed of Mesozoic igneous rocks and are interpreted to have sourced via relatively short-distance transportation.During the third member of Enping Formation (SQ3),the sediments oriented from South China folded belt (SCFB) which mainly consists of Precambrian-Paleozoic metamorphic rocks.The sediments which are derived from SCFB and transported long-distance pathways through northwest-southeast orientation have deposited in Baiyun sag and the large-scale delta developed subsequently.Meanwhile,the sedimentary characteristics of large-scale delta of the SQ3 within Baiyun sag are described through typical seismic facies and the energy half-time seismic attribute analysis.The delta developed three stages of progradational wedges continuously to the southeast direction and with increasing scale initially,followed by decreasing scale until the rift basin disappeared.The results reveal that the deltaic coal-bearing and terrigenous-marine source rocks are mainly developed in the SQ3 and thus the large-scale delta has an excellent accumulation condition of source-reservoir-cap rock assemblages.And the delta front sand bodies tend to develop the updip pinch-out reservoir which will become an important target for oil and gas exploration in Paleogene of Baiyun deep-water region.