Abstract: Architecturally Constrained Spatial Modeling of Permeability within a Fluvial Sandstone Body, Cretaceous Acu Formation, Brazil

Mark D. Barton, Joseph Yeh, Edward S. Angle, Benjamin N. Carrasco, Mauro R. Becker

An outcrop of the Cretaceous Acu Formation was investigated as an analog to a heterogeneous group of reservoirs that have significant potential for reserve growth. In the Potiguar Basin of Brasil, the Acu Formation is a 1000-m-thick clastic unit that accumulated within a series of northeast-trending half-grabens during Cenomanian time as the African and South American continental plates separated. The interval consists of an upward-fining cycle of laterally heterogeneous mudstones, sandstones, and conglomerates deposited by a system of braided to meandering streams during an overall transgressive cycle of sedimentation. Architectural and petrophysical attributes of a sandstone body within this succession were investigated and the information used to construct a geologically realistic odel of permeability.

The outcrop examined exposes a 10-m-thick, 300-m-wide fluvially deposited sandstone body composed of multiple truncating channel storeys. Storeys are 1- to 5-m-thick, 20- to 240-m-wide, and composed of gently dipping beds. A visual comparison of permeability profiles to stratal architecture indicates that (1) permeabilities are reduced one to three orders of magnitude near bed and channel-storey bounding surfaces and (2) beds are characterized by upward-increasing permeability trends. A spatial model of permeability, consistent with the outcrop observations, was constructed using stratal surfaces to define a two-dimensional chronostratigraphic framework of grids (sequences). Permeability was interpolated between measured values using the sequence boundaries to confine the interpolatio . The model will be used as a basis for flow simulation to maximize recovery in the vertically stratified and laterally heterogeneous Acu reservoirs.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela