Stumpy, I was concerned that the 9.23 was almost exactly half...

Stumpy, I was concerned that the 9.23 was almost exactly half the 18.6 number that ELK was using, but still believe it is only a coincidence.

The project is tertiary recovery only, the field has already been subject to water flood when the gas cap was blown down in 1977 (refer to presentation Grieve Field CO2 Project: 2011 Status Report July 13, 2011 by Ralph Schulte and Brian Black)

Denbury seem to have always run with lower recoverable reserves than ELK. Even back whent JV was announced in 2011
http://www.asx.com.au/asxpdf/20110509/pdf/41yjt7dzfcm4sf.pdf there is the following note at the bottom of the first page: -

"Denbury is now undertaking further studies to identify the development plan for the Field; these studies are expected to provide new information on the potential oil recovery and production rates from the EOR project; Denbury’s has based its preliminary plans on 12 MMbbls oil recovery, which is consistent with their experience of a 17% recovery of original oil in place in its other operating areas. "

So even back in 2011 Denbury were more conservative than ELK. I have assumed that Denbury are now using information that they have gathered during the repressuring stages and that either Denbury has not provided the work to ELK or ELK has not asked. Denbury haven't certified the Grieve reserves and the numbers are not included in any of their SEC filings that I can find.