Formation Evaluation Education & Training
Formation Evaluation Education & Training
Much that is taught in modern petrophysical education is based upon the mis-education of the educators. Consequently, much that students believe regarding Archie's model and its provenance is not true. This video will open Archie's original paper to examine and discuss what Archie really did say!
Based upon David Herrick's three principles of conductivity in Archie rocks, a model of conductivity in rocks that subsumes all of the original Geometrical Factor Theory, Kennedy's Pseudo-Percolation Threshold Theory, Archie's model, and can be used with the Waxman-Smits and Dual Water models.
The crossplot of density against neutron porosity is bounded by lines connecting the neutron-density coordinates of brine, mineral matrix, and clay, forming a triangle. Is the proper scaling of the triangle's interior a ternary grid of iso-porosity, iso-clay volume, and iso-matrix volume, or is it a grid connecting the brine point to points along the matrix-clay line?
Induction logging instruments are often used in high-resistivity formations where laterologs would be preferred but cannot be used due to the drilling fluid being oil based mud. Induction log responses are frequently seen to be constant at high resistivity values such as 2000 ohm-meters. Why do induction instruments respond in the way?
In 1953 J.J Arps published his method for deriving an approximation for a brine's resistivity at any temperature given its resistivity at any other temperature. This now ubiquitous formula is developed from 81 published data values by transformations recorded in 5 tables and four pages of text. In this video I show how to develop the same formula using beginning with a simple observation and derived in four simple equations.
In 1969, '70, and '71 three researchers published four similar, but distinct, graphical functions for estimating clay and shale volume from gamma ray intensity. These functions share the property that an incremental increase in radioactivity of rocks diminishes as clay or shale volume increases. There has been no physical model to account for these observations. A model that invokes zircon to account for this observation is proposed and explained..
How "thin" is a "thin bed"? It depends upon the logging instrument used to log the bed.
The popular Waxman-Smits model for evaluation of shaly sands is based upon an unjustifiable assumption at the outset of its development. Does this impact the results obtained when using it? Undoubtedly, it must. Formation evaluators should be aware of this potential pitfall when using this model.
Many log interpretation models are based upon two paths for current flow through the pore space of the rock. To a first approximation the paths are in "electrical" parallel. What does this mean? What does it imply for interpretations.
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