If we have the following 2 different data set:
Date set 1:
Lab-scale Core samples average: 10 milli-Darcy
Field-scale Reservoir average: 100 milli-Darcy
with a relatively small standard deviation
Data set 2:
Lab-scale Core samples average: 10 milli-Darcy
Field-scale Reservoir average: 10 milli-Darcy
with a relatively large standard deviation
How should I delineate whether the reservoir property of interest (permeability) is scale-dependent or NOT?
What is the physical significance of having varying mean values of a reservoir property (k) from the laboratory-scale core samples and from a field-scale reservoir (with a smaller and a larger standard deviation)?
Dear suresh depending on the type of rocks..some time permeability test in lab is smaller then reservoir due to the size of core sample and the limitations of lab apparatus, while feild simulation dont match the lab results ,, other causes is the tight formation and natural fructures.,
Hi Suresh,
This is a problem any time core analysis is compared to actual field data from pressure transient analysis. Core plugs chosen for analysis are 1-D point data, either systematically selected at uniform depth intervals as a time series or preferentially chosen where some interesting feature appears in the core. Either way, their data may vary considerably if sampled at some nearby point in the core. The pressure transient analysis permeability is an average of the entire test interval sampled as a 3-D whole. As such, it will yield a far more accurate reservoir permeability than averaging core plug permeability. Of course, if core plug analysis is all you have, there will always be uncertainty in your reservoir permeability unless you have a truly homogeneous reservoir rock.
Good luck with your project.
Usually, if lab core permeability gives the same results as field scale estimates (Data Set 2), this means that the core represents well the reservoir (absence of major heterogeneity or significant fractures).
Otherwise, if lab core permeability gives results much less than the field scale estimates (Data Set 1), this means that there are important fractures and fracture zones contributing to the overall field permeability, or that the cores represent only a tight part of the reservoir. In this case, it is always advisable to discuss with an expert reservoir geologist to understand the most likely cause of the discrepancy. Fractures and fracture zones (or uncemented, super-permeable sand beds) are typically under-represented in cores, and even less in core plugs!
I would like to mention a third case, where lab core permeability gives results much more than the field scale estimates. This could be a case where the core plug includes a vug (typically in carbonate reservoirs) and the plug does not represent the reservoir as a whole.
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