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sediments and the main lithology includes gray matrix-supported conglomerates, sandy
conglomerates and black shales. The mid sub-fan, which is the main part of the nearshore
subaqueous fan and forms the effective reservoir in the study area, is characterized by
braided channels with braided channel microfacies, intra-channel microfacies and leafy
sandbody microfacies. The main lithology of the mid sub-fan includes pebbly sandstones,
conglomerate and block sandstones, with thickness varying between 1 and 55 m. The
marginal sub-fan consists of siltstones, muddy siltstones and mudstone interbedding rocks
(Fig.2). According to well stratigraphic cyclicities and 3D seismic reflection features, the
lower Es4 Formation can be divided further into 5 members, standing for 5 individual
nearshore subaqueous fans with several sub-facies (Fig. 2).
In general, 3D seismic reflection profiles of the nearshore subaqueous fan are characterized
by wedge-shaped, mound-shaped or lenticular-shaped systems, and sub-fans can be further
identified. On the synthetic seismograms record calibration, the root sub-fan is characterized
by weak reflection, non-reflection or chaotic reflection, the mid sub-fan is characterized by
weak to moderate intensity amplitudes, sub-parallel, weak continuous reflection, and the
marginal sub-fan is characterized by continuous medium frequency, moderate to low
intensity amplitudes. The deep lacustrine facies in the sag belt is characterized by either
weak reflection or non- reflection. However, to identify the sub-facies of the nearshore
subaqueous fan using the 3D seismic section is difficult (Fig.3).
Fig. 3. 3D seismic reflection characteristics of the nearshore subaqueous fans along
line B'B (see Line location in Fig.1)
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