Quantitative Assessments of Petrophysical Properties in Biogenic Dual-Permeability Systems: Facing the Challenge of Highly Bioturbated Heterogeneous Reservoirs
Polo, Camilo A.; Baniak, Greg; Gingras, Murray K.; Pemberton, S. George
In attempting to better understand bioturbation-associated porosity and permeability distributions, the application of statistical methods to predict the bulk properties of bioturbated media is increasingly common. Among the different measures of central tendency are the harmonic, geometric, and arithmetic means, which have numerous applications including characterization of bulk permeability of sedimentary rocks. In bioturbated media; each of these statistical relationships is appropriate for different situations. This study discusses the work-flow for ichnological permeability assessment and the prediction of bulk properties by using the Nise Formation (Norwegian continental shelf) as an example.
A number of factors strongly influence bulk-flow parameters in bioturbated media. In bioturbated reservoirs spot-permeametry studies are carried out in order to characterize and predict bulk permeability. Commonly, minipermeametry data collected using a Pressure-Decay Permeameter are useful in assessing the permeability of matrix and trace fossils. For the Nise Formation, fabric selective minipermeametry testing were carried out on representative plug samples. Five measurements from each point were taken, with the maximum and minimum values for each spot being discarded, and the remaining three values averaged. Bulk assessments of permeability based on core-plug data indicate that, depending on the nature and intensity of bioturbation, the arithmetic or the harmonic mean of matrix versus burrow permeabilities should be applied only in certain circumstances. The arithmetic relationship suggests that flow is largely directed through the flow media via a well-connected burrow network. The harmonic relationship applies to poorly connected burrow systems. In the Nise Formation case, permeability measurements also demonstrate that horizontal permeability (kh) is higher than vertical permeability (kv) and that permeability is anisotropic. Therein, variability between kh and kv is mostly controlled by the intensity of bioturbation (BI). Higher BI increases interconnectivity of a preponderant horizontal burrow-network that reflects the proximal trough distal Cruziana ichnofacies resulting in higher kh values.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013