current reserves, page-5

Let me give you a visual example why any number beyond Greg's 1P (cylinder around a drilled well) is hard to calculate for a channel system with suspected stratigraphic closure.

First a normal Eromanga basisn discovery - a sheet sand (meaning the same rock - net pay, porosity is everywhere in the field) closed in a mapped domal structure. Even with one discovery well, simple geometry will come up with a reasonable volume.

Now change two factors. The sand varies from 20m to <5m over the field - seismic gives you a rough idea of the thicks but without further drilling cannot give you a net pay map.

The field has an OWC but the time to depth conversion is so inaccurate that you really dont know how far the field extents. Each time you drill a well the picture changes but so far each new well has expanded the field.

Consider calculating volumes in this situation. 1P numbers will be as solid as the first case but without a reasonable number of appraisal wells the 2P number will have large enough errors bars to make the number useless. Eventually a 2P number can be calculate.

Historically the resultant 2P number is about x2-3 the early 1P number but of course this number cannot be published. It is just a rule of thumb used by geos who have drilled up a lot of strat fields.