Permeability Distributions in Non-Surface Constrained Biogenic Textural Heterogeneities: A Case Study from the Upper Cretaceous Lysing Formation, Offshore mid-Norway
Polo, Camilo A.; Baniak, Greg; Gingras, Murray K.; Pemberton, S. George
The Coniacian Lysing Formation is distributed across the Norwegian Sea basins and hosts hydrocarbons in the Ellida discovery. Interbedded mudstones and sandstones deposited in an active tectonic setting exhibits an intensely bioturbated reservoir fabric with a complex burial history. Therein, the ichnofossil assemblage is made up of a mix of dominantly deposit-feeding and grazing biogenic sedimentary structures that are representative of the distal Cruziana ichnofacies. X-ray microtomography (Micro-CT), spot- and bulk-permeability measurements and petrographic assessments show that permeability distributions are strongly influenced by the distribution and nature of bioturbation. Spot permeability data taken from core plugs indicates that the burrow permeability can be up to two orders of magnitude greater than the matrix. Thus, it represents a biogenic dual-permeability flow-media. Spatial visualization and thin-section petrography allowed the identification of an intricate, highly connected, mostly horizontal and inclined burrow system. Therein the imposition of coarser grained sediment within burrows in an otherwise low permeability matrix result in selective fluid flow networks.
By comparing horizontal and vertical permeability (Kh and Kv) to bioturbation intensity, it is shown that bioturbation increases isotropy (i.e. Kv approaches Kh). Notably, due to the disruption of sedimentary lamination, homogeneity is also increased. These characteristics are indicative of improved reservoir quality over laminated sandstones and shales.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013