Three-Dimensional Characterization and Cause Analysis of Deepwater Channels and Seabed Pockmarks --A case study in J Research Area, Niger delta

Studies on deepwater channels and seabed pockmarks have been raising more and more attention in recent years. In this study, coherent processing and horizontal slicing　technologies are comprehensively utilized for... [ view full abstract ]

Studies on deepwater channels and seabed pockmarks have been raising more and more attention in recent years. In this study, coherent processing and horizontal slicing　technologies are comprehensively utilized for three-dimensional characterization of deepwater channels and seabed pockmarks based on the seismic data in the Niger delta to explore causes and internal relations of them. Several conclusions have been reached as follows.
(1) It is demonstrated that a large number of deep-water channels developed in different periods from the late Pliocene to early Holocene, which are of lower curvatures and different extending directions, mainly along the NW-SE and NE-SW directions. Large scale sand bodies could be seen along the channels in the RMS chart, which indicate multi-sources and multi-periods of activities of gravity flow.
(2)Studies on typical channels reveal the characteristics as low frequency, high amplitude and strong continuity. Water energy weakens away from the source, while dissected depth shallows and width broadens, which lead to the transformation of incised erosion surface from V-shape to U-shape. Therefore, the source and terrain slopes are significant for the development of channels in this area.
(3)There develop large amounts of pockmarks including isolated and banded ones. Banded pockmarks are superimposed with channels on vertical. In other words, banded pockmarks are generally accompanied with channels in the lower part, which are consistent in the extending direction and thus suggests the causal relationships. It could be roughly concluded that the surrounding gas migrated into the channels and formed overpressure, which was then released, resulting in uplifting and micro cracks and gas escaped. In this situation, overlying unconsolidated sediments were scoured, forming channels. As for isolated pockmarks, they are of considerable area, huge depth, and complex origin. It can be identified that isolated pockmarks are related to channels. In addition, uplifting activity and mudstone erosion can also contribute to them, which could be much more extensive.
Based on above analysis of the development and distribution relationship between channels and pockmarks in Niger delta, internal relationships of them are clarified, which could provide references for the sedimentary system evolution study and reservoir prediction.