The May 1, 2000, issue of Oil & Gas Journal carries a feature that begins on page 45 under the headlines "Petrophysical insights contradict Archie's equation" by Lanny Dunham. The article claims in its first paragraph that evidence shows that produced water from hydrocarbon-bearing intervals may have higher resistivity than water in adjacent water-filled reservoir intervals. It goes on to claim in the second paragraph that:
"If true, this would indicate that the Archie equationellipseis invalid."
From this the subtitle of the article is drawn.
The article then goes on for several pages.
I have to observe that from a logical point of view all that is indicated in the first paragraph is that the wrong value for formation water resistivity is used in Archie-based formation evaluations in wells where the postulated condition of variable water holds-not that Archie's equation is invalid. Archie's equation is validated in core laboratories every day.
The article might well point to a real effect that usually goes unrecognized and that, to the extent that it is common or uncommon, might more or less affect the estimation of hydrocarbon pore volumes. However, if Dunham wants to be taken seriously, he should choose his words carefully. His article might have appeared in a refereed journal, but his second paragraph would never have survived peer review. One result of Dunham's gratuitous Archie bashing is that many otherwise interested readers will simply discount his credibility.
If Dunham thinks that Archie's method is crude, many will agree with him. That does not make it invalid.
David Kennedy
Exxon Production Research Co.
Houston
