Seismic Geomorphology and Stratigraphy of Coalescing Slope Apron in Taibei Depression, East China Sea

Guo, Rui; Liu, Chuncheng; Liang, Jianshe; Zhao, Zhigang; Wang, Cunwu

Coalescing slope aprons are fan shaped depositional wedges fed from a continuous source with multiple feeders. A group of Paleocene linear-sourced slope aprons propagated from the northwestern margin to the Taibei depression, East China Sea. Six lobes were covered by two 3-D seismic volumes of 1063 km2. The reservoir geometry of gas bearing sand at the top of the lobe is exceptionally clear with the hidden of the synsedimentary prodelta shale and overlying condensed section in the 3-D visualization environment.

Six lobes share the similar scale, geometry, and have been relatively confined by the fault controlled ramp. The fan size is 30-120 square km2 compared with the 500-1500 square km2 of the present configuration along the California borderland. The fan body has concave upward top-surface in profiles along the drainage direction; and convex upward top-surface and Lateral pinch-out geometry with bi-directional downlap in axial seismic profiles. The maximum erosion depth in the root of the depositional lobe is about 160m, which developed near the fault of the Cretaceous basement.

The absence of a large river-submarine canyon system backward in 2-D seismic lines was evidenced by the no observation of continuously active meandered channel and natural levee in the fan system. The cored sections include reservoir quality massive sands with sharp upper contacts, slumped sands and debris flow sands; and muds, laminated muds. Vertical stacking of facies forms a succession of not well-defined coarsening-upward cycle with rare normal grading and predominantly mud-rich in the base.

The gas bearing sands penetrated in the well 1 and well 2, but do not extend (up the depositional dip) all the way to sheet sands of the well 3 of the same lobe, indicating the sand body die out about half way between. The noncommercial well drilled out of the structural trap reveals the sealing risk of the lobe system as the lithologic trap.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013