HEF’s stratigraphic analysis and interpretation service offers a high quality, cost effective and prompt approach to detailed and reliable lithofacies interpretations. These interpretations, comparable to core analysis, result from combining detailed image log interpretations with advanced petrophysics. Image logs can also be used to provide a reliable measurement for borehole-scale sand, mud and breccia compositions and geometries.
Derived from hundreds of Canadian Oilsands core and image log comparisons, our stratigraphic analysis has become an integral part of our client’s production well planning and in anticipating production well performance and geology. This analysis, conducted in vertical or horizontal wells which were drilled using conductive or non-conductive mud includes:
• Lithofacies interpretation of composition and depositional texture
• Bioturbation index
• High resolution image-derived shale volume
• Bedform identification of various types of cross-beddings and truncations
• Identification of slumps and other syn-sedimentary deformation structures
• Caprock integrity evaluation
• Permeability and bitumen saturation
Stratigraphic Bedform Classification
HEF identifies scour and erosional surfaces, lateral accretion, unconformities, flow cross bedding, and convoluted bedding in our stratigraphic analysis. These bedforms are used to interpret the depositional environment, allowing you to predict the areas of maximum permeability.
View Dip Type glossary here.
Lithofacies and High-Resolution Vsh Interpretation (Oilsands)
In oilsands and other heterogeneous reservoirs, it is of particular interest to have a continuous log of the nature of the bedding (layered, cross-bedded, interbedded or brecciated) in order to estimate and model steam chamber growth for in-situ steam assisted gravity drainage (SAGD) production. We use log-derived high-resolution shale volume (Vsh) and the image bedding texture as the lithology constraints on our facies interpretation.
In horizontal wells, LWD image logs can be used to differentiate between potential permeability barriers like strong, muddy IHS bedding, brecciated zones and horizontal mud layering, either on the high or low side of the wellbore. The challenge is that without image data (and only a single point gamma ray and resistivity measurements), the aforementioned three reservoir facies can be indistinguishable, while contiguous mud layering can be detrimental to steam chamber growth and production.
Lithology plot - Our lithology plot shows the lithofacies and their boundaries, as well as a high-resolution Vshale down to the centimetre-scale. These are used to calculate the net pay, shown in the last column. Click image to enlarge
Using openhole resistivity data and borehole image log data, a high resolution resistivity can be calculated. This can then be used to calculate water saturation and permeability to a sample rate of 0.2cm.
The VSH can be used to calculate mud layers. The strength and continuity of the mud layers can be predicted by calculating thickness, mud content, continuity across the borehole, bioturbation and lithology. The mud layers are used to calculate effective vertical permeability, and steam chamber barriers can be accurately predicted.
Permeability and stratigraphic interpretation plot - In fields with a large amount of core permeability data, it is possible to develop useful models that take borehole image and other openhole data and use those inputs to predict permeability in three directions (Kv, Khmin, Khmax) Click image to enlarge
HEF has encouraged us to take a much deeper look at the image log data for our McMurray Oil Sands wells. Helping us to see beyond the tadpoles, and to consider what the images tell us about depositional texture, lithology, calculating Vshale and even permeability directions.
-Ian Perry, Geologist, Meg Energy Corp.