Depositional filling model of the Eocene Wenchang Formation in rift stage of L sag, Pearl River Mouth Basin
Jia Langbo1, Ji Youliang1, Zhong Dakang1, Yan Ruitao2, Liu Junlong1, Mi Lijun3, Yi Zhen3, Yu Jiasong1, Zhang Pengcheng4
1 College of Geosciences,China University of Petroleum(Beijing),Beijing 102249; 2 Xi'an Shiyou University, Xi'an 710065, Shaanxi; 3 Shenzhen Branch of CNOOC,Guangzhou 510420,Guangdong; 4 Sinopec Eastern China Branch, Nanjing 210011, Jiangsu;
Abstract：The exploration of the Eocene Wenchang Formation in L sag,Pearl River Mouth Basin,is in the initial-exploration stage. Due to limited drilling data and their uneven distribution,the conventional multiple-data research methods of sedimentary facies is restricted in this area,resulting in the lack of systematic analysis on sequence stratigraphy and depositional system. Based on cores,well logs and seismic data,the integrated seismic facies analysis was carried out in this area. The integration of well and seismic data was applied to predict the distribution of the Paleogene rift sedimentary system,and the sedimentary model of the Wenchang Formation in rift period has been established. The results show that the Wenchang Formation developed three 3rd-order sequences,consisting of 8 system tracts. According to the differences between externel form and internel reflection characteristics in the sequence system tracts,five seismic facies types were identified in the study area,which are filling type,mat type,wedge type,massive type and hummocky type. Seismic facies were converted to sedimentary facies based on the combined analysis of core facies,well-log facies and seismic facies. Braided-river delta,fan delta and lacustrine facies were identified. The study area developed the model of small basin with small lake in the initial syn-rift stage,when several small isolated sags were mostly filled with near-source fan delta clastic deposits. Model of large basin and shallow lake was developed in the early rift-climax stage,when the sags became connected with each other,filled with braided river delta originated from the southwest. Large basin with deep lake model was formed when the tectonic stage entered middle-late rift-climax,therefore deep lake mudstone was widespread. The model of large basin and shallow lake in the late syn-rift stage was developed,when the accommodation was gradually filled by a large-scale braided-river delta originated from the northeast along the long axis of L sag.
Jia Langbo,Ji Youliang,Zhong Dakang et al. Depositional filling model of the Eocene Wenchang Formation in rift stage of L sag, Pearl River Mouth Basin[J]. JOPC, 2017, 19(3): 525-540.
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