Sedimentary architecture of the deep-water turbidite system in A oil field, Nigeria Delta, West Africa

doi:10.13745/j.esf.sf.2022.10.10

Abstract

Abstract:

The deep-water turbidite system in A oil field, Nigeria, West Africa is extensively studied by seismic sedimentology method, combined with abundant core, outcrop, drilling and well-log data. Based on the obtained high-resolution stratigraphic sequence, deep-water fan types and channel depositional stages, the turbidite channel system is divided into three hierarchical stages—turbidite complex, multichannel complex (AU1-3) and single channel, and AU1 of reservoir A, Agbada group is divided into four single channels. The sedimentary evolution of the turbidity current channels is illustrated in detail. Constrained by ancient valley geography, the channel is mainly formed by vertical accretion, where it narrows upward, with thick sandstone with thin mud interlayers developing at the bottom and mud content increasing upward, as indicated by the bell/block-shaped GR well-log curves, and consistent with a strong-amplitude wavy reflection on the seismic profile. The general succession is lump-debris flow followed by multichannel and channel-levee complexes. Influenced by valley geography, the turbidite channel system mainly consists of restricted and semi-restricted channels. The ancient river valley, 5000-7000 m long, contains 3 stages of turbidite channels, and each stage (i.e., a single channel belt) is composed of 2-4 sub-stages of channel bodies. The multi-stage channels extend laterally and longitudinally to form a giant, thick sand body with a ternary structure: at the bottom is poorly sorted debris flow with relatively high clay content and low permeability; the middle part is low-sinuosity multichannel complex with low sand/land ratio and high permeability; and the top part is high-sinuosity single channels with low sand/land ratio and low permeability. This sedimentary model is supported by the time-lapse seismic data which show that water flooding are within the turbidite channel system. According to the fine staging of deep-water turbidity current channels and related time-lapse seismic features, residual-oil reservoirs are identified and a oil producing well is designed to provide a solid foundation for future research on the deep-water sedimentary system in the oil field.

Key words: hierarchies, sedimentary model, time lapse seismic, deep water tuibidite channel system, Nigeria

CLC Number:

P618.13

CHEN Fei, FAN Hongjun, FAN Ting’en, ZHANG Huilai, ZHAO Weiping, JING Yongquan. Sedimentary architecture of the deep-water turbidite system in A oil field, Nigeria Delta, West Africa[J]. Earth Science Frontiers, 2023, 30(4): 209-217.

Figures/Tables 9

Fig.1 Location, structural map and lithologic unit of the study area

Fig.2 Gravity sedimentation characteristics in well K-2

Table 1 Hierarchical architectural divisions of the turbidite channel system and corresponding fluvial systems and relevant sedimentological data

深水浊积水道	典型厚度/m	沉积相	与油组对比	Vail层序地层分级	河流体系
复合浊积体	10~50	古河谷充填体叠置河流沉积体	砂层组	准层序	复合河道带
复合水道	5~20	水道复合体	单砂层/小层	层组	单一河道带
单一水道	3~10	砂质水道/泥质水道组合			复合点坝

Fig.3 Stratigraphic boundary determination in the deep-water turbidite channel system

Fig.4 Vertical seismic reflection profile of AU1 isochronous stratigraphic framework

Fig.5 Planar distribution of AUI sedimentary facies in the early (left panel) and late (right panel) depositional stages

Fig.6 Paleogeomorphic characteristics of AU1 before deposition

Fig.7 Depositional model of the deep-water turbidite channel system

Fig.8 Time-lapse seismic image of AU1 showing 2D water flooding features (in blue)

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