marquis/block21/6b details

If like me,you are new to EXR,here are some details of block 21/6b where Marquis will be drilled.
If you want the pictures as well,go to asx announcement 12-05-05,beginning page 30

Block 21/6b is located on the north-west margin of the Central Graben at the foot of the early
Tertiary depositional slope between the shelf complex to the north and the basin floor to the south
(see Figure 3). Block 21/6b was a 21st Round award in 2003 and is, therefore, in a more advanced
technical position than the 22nd Round blocks. Since the award, a 3D seismic grid has been
purchased and interpreted across the block and has resulted in a well-defined Forties sand prospect
with mapped four-way dip closed prospect of medium risk (Figure 4). Seismic data have been
reviewed across the prospect and clear depositional mounding is observed in the dip direction and
demonstrates a west-east trending channel system (Figure 5).
This prospect is one of the best defined and lowest risk in Elixir’s portfolio and has significant
resource potential. At a depth of 1650m, it will be relatively inexpensive to explore and operations
are expected to commence in 2005. Seismic expression of the prospect indicates that the channel is
fairly localised with an erosive base. This is indicated by variable Forties sand thickness in nearby
wells. Well 21/6-3 (300m to the north of the prospect) had 29m of Forties sand, whereas 21/6-4
(2km to the south) had little or no Forties or Cromarty sand. Yet, well 21/7-3, located along the strike
of the channel to the east, contained 121m of Forties sand. A critical risk is dip closure in an up-dip
and strike direction to the west, and this aspect was examined on seismic lines provided. Dip
closure has been mapped to the west and westerly dip of beds is interpreted on the seismic data.
However, this remains a critical risk factor of the prospect. In addition, there are risks on top seal as
the prospect is cut by two NNE-SSW trending faults (see in Figure 4), which could have breached
the top seal, and also the overlying Cromarty sand channel may have eroded the Forties channel
top seal of Dornoch shale (Figure 5).
However, reservoir presence and hydrocarbon charge into the prospect have lower risks. Well 21/6-
2, located to the north-west (see Figure 4), flowed 18 degree API oil from the Dornoch sands, which
are the shelfal equivalent of the Forties sands. This proves that oil has migrated into the Palaeocene
sand complex. There is no obvious seismic amplitude anomaly associated with the prospect, which
would be expected if the hydrocarbons were a relatively high API gravity (in the 32-45 range).
However, the shallowness of the prospect (1650m) allows that 20 degree API oil gravity could be
expected. This same gravity oil occurs at the Captain field in block 13/22a and no seismic amplitude
anomaly is present. Therefore, the absence of such an anomaly does not mean the absence of
hydrocarbons. The Palaeocene prospect in block 21/6b represents a medium risk and shallow target
with significant reserves potential.