Potential Size of
Yesnaby Sandstone formation consists of over 200m of desert sandstone (dune
bedding clearly shown in the sea stack of the Yesnaby Castle). They are full of
bitumen indicative of being previously full of CRUDE OIL which has rapidly lost
its volatiles on exposure. The
Harra Ebb formation was tilted and eroded before the dune sands were
deposited on the uneven unconformity surface . The sand thus varies in thickness
over the area.
Aeolian and fluvial sands of the
Sandstones . Thickness is zero at the pinchout in the south thickening
to over 200m towards the north. Porosity 13% to 25% and permeability 3mD to 2,000mD - this
quality of reservoir could give high recovery factors.
The upper fluvial sands are barren of
bitumen and commonly have porosity less than15% and permeability less than
2mD (milli-Darcy) so may not have contained liquid hydrocarbons.
Potential Size of Accumulation:
MAP of the reservoir Volume.
With seal on the Borwick/Navershaw
Fault the accumulation would cover a minimum 2,000 acres and contain about
850MMBOIP (204MMBO - million barrels recoverable).
The potential for about 1
billion barrels of oil in place (in an excellent reservoir sand) could make this an attractive target if located at depth
The Yesnaby Dune Sand or equivalent is
not found at Graemsay or Stromness Basement outcrops or in the Warebeth
Borehole therefore is discontinuous in distribution adding an extra risk
factor to the "Exploration Play Concept" - it would be an attractive
Secondary Objective to an
Sandstone Primary Target.