Hierarchy of Deep-Water Architectural Elements with Reference to Seismic Resolution: Implications for Reservoir Prediction and Modeling

Prather, B.E., F.B. Keller, and M.A. Chapin, Shell Deepwater, Houston, Texas

Abstract

Seismic acquisition and processing imposes a spatial filter on the resolution of stratigraphy. In deep water settings, we recognize four orders of seismic and several orders of subseismic stratigraphy. Submarine sandstones are usually resolvable on conventional 6-60 Hz seismic data as amalgams of seismic loops or wavelets (4^th-order seismic).

Upon closer inspection, units within many of these sandstone bodies display a complex internal architecture related to the influence of depositional topography and various small-scale erosional processes. Internal (1^st-order subseismic) reservoir architecture is locally manifest on seismic data as changes in waveform morphology. Internal reservoir architecture forms from episodes of starvation, bypass, and/or erosion locally producing surfaces that pass from the tops to the bases of reservoir units. These surfaces control bed-length and connectivity within the reservoir. Outcrop and near-seafloor data sets show us that these surfaces are too large to be easily detected with wireline tools and too small to be confidently mapped at reservoir depths on conventional seismic.

In the outcrop, first-order subseismic features occur within sand bodies deposited over periods of hundreds(?) of thousands of years. Because of higher rates of subsidence and sediment influx, many of the reservoirs we currently produce from, and explore for, are at the same spatial scale as those in the outcrop but have been deposited over only tens of thousands of years. Questions that arise include what is the level of potential temporal disconnect, and what are the implications for applying outcrop-based measurements in the of construction subsurface models.