The problem with North Slope lithology is that its very complex, going through at least 4 phases of geohistory as far as I'm aware.
But the GENERAL feel I get for the way in which the thermal maturity history has developed is that the further north one goes towards the Barrow Arch the more immature the hydrocarbons become to a peak of around the Barrow Arch complex where the up-dip into the Arch has resulted in the Brookian/Beaufort sequences contributing to the major Prudhoe Bay reservoirs.
As Lazarus has posted 88E/Bex seem to have been cognisent of the fact via PB's model that the VAPOUR LIQUIDS PHASE was a little further south for the HRZ . As PB states YOU HAVE TO GO A LITTLE DEEPER to get the required pressure/heat to convert the liquids phase into gases.
Ed Duncan was basing his thermal maturity BPSM on the Alsakan Geo's modelling who were targeting the more upper Brookian stratigraphy above the HRZ given Housenecht had ASSUMED the HRZ was too clayey to be considered a possibility for unconventional. At least they saw it as too higher risk in this regard and wernt prepared to throw the dollars at it. However after drilling further north and the Alkaid well poor old Ed suddenly realized it was the Talitha acreage that should have been his target.
This is where PB's open mind to all possibilities comes to the fore as He reasoned that the HRZ could indeed have developed diagenetically in such a way as to retain the permeability/porosity via the silica (glass-particle) volcanics IF they were preserved rather than incorporated by chemical reaction into the shale.
This chemical reaction in actual fact gives the exact type of clays required to make excellent lubricating drill fluids which exist in large amounts across the US because of previous volcanic history.
As far as what these previous Geos assumptions think imo the Ice 1 core says it all.
And this is why the company comment that the SIGNIFICANTLY statement that the core sample has derisked the PB model to a larger degree is probably the most important statement made in the whole annmnt imho , and certainly as regards the unconventional play and why they have moved to the Ice 2H phase of the play.
Just what the SPREAD of the sweetspot is should be able to be determined with the new seismics as they now have Ice 1 data to correlate with seismic reflectance data. My opinion is that we potentially will see a statement made that the HRZ potential is continuous thru most of the acreage which as already been QUALIFYINGLY commented on. And the actual reservoir size that PB is talking of (3Bbbls+) can surely only be accommodated by a wide acreage sweetspotting IF indeed that's what we have.
If one looks at the general cross section in this item:
http://www.geoexpro.com/articles/2013/09/alaska-north-slope-source-rocks-hold-promise
One can see that essentially the North South stratigraphy is one of a large bowl, at least for the Upper Brookian/LCU until you get to the Brooks Range foothills where
the tectonically effected stratigraphy takes over via folding/faulting. This is where the up-dip to the south comes in and we may see these source strata feeding into any potential conventional traps to the south
d.
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