Sub Log-scale Heterogeneity of Fine-grained Sediments – Implications for Effective Permeability and Top Seal Risking
M. Drews, K.D. Kurtev, J. Ma and A.C. Aplin
Event name: 2nd EAGE International Conference on Fault and Top Seals - From Pore to Basin Scale 2009
Session: Top Seal Evaluation and Uncertainties
Publication date: 21 September 2009
Info: Abstract, PDF ( 2.63Mb )
Effective permeability plays an important role in prediction of leakage rates, seal capacity and quality. Current best practice uses conventional log data (15 cm as maximum resolution) to assess effective flow properties in seal sections and, with a maximum resolution of 15 cm, miss out the cm-scale sedimentological variability which is quite common in some mud-rich settings. The aim of this study was to identify and classify a reasonable number of different sedimentological heterogeneities and to investigate their impact on flow properties based on high-resolution data (microresistivity and core images). Four types of fine-grained sediments were defined on a basis of lithological variability and internal structure. Methods from geostatistics, such as the variogram as a descriptor for sedimentary structures derived from microresistivity and core images, were employed to quantify differences on a cm-scale between the four fine-grained sediment types. Furthermore, 2D flow models on a meter scale based on microresistivity and core images were used to determine ranges of effective permeabilities for the different types of fine-grained sediments. Finally, these effective permeabilities were upscaled in 1D and used to compare the differences due to the sampling rate of conventional and high resolution measurements.