The Rannoch Formation (lower Brent Group, North Sea) is an important laminated, oil-bearing reservoir in the northern North Sea. Recent work has shown that, at the estimated field frontal advance rates for the Rannoch Formation, capillary effects in laminated sandstones might significantly affect the two-phase (oil and water) flow characteristics. Previous published reservoir simulation models of the Rannoch have not accounted for this. Newly acquired probe permeameter measurements have been used to map the fine scale permeability structure and develop geologically reasonable effective properties. Permeability and capillary pressure data were combined for geologically meaningful groups of laminae to define dynamic pseudo-properties (absolute permeability, relative permeability and capillary pressure) by numerical simulation. A geological model for packages of lamination was then used to combine these lamina groups at a scale of the grid block. The flow performance of this geologically reasonable grid block (containing the laminated structure) is compared with that of 'simple' models based on conventional procedure - i.e. the arithmetic average (in a horizontal direction) or harmonic average (vertical) permeability and rock curves. At this scale, the formation is highly anisotropic using the more detailed model, with quite different flow characteristics in the horizontal and vertical directions. The simple homogeneous models show more isotropic recovery characteristics and give significantly higher recoveries for vertical displacements. From these findings, it is suggested that previous models of the Rannoch Formation should be modified to include the capillary effects associated with lamination. The procedure outlined here is referred to as the 'geopseudo' approach. The approach is widely applicable to laminated reservoirs. © 1993.
|Number of pages||12|
|Journal||Marine and Petroleum Geology|
|Publication status||Published - Aug 1993|
- laminated sandstones
- North Sea
- probe permeametry
- two-phase flow