For those that cannot viksualise the 2 drills RKH will do in early 2011 one can look at the pic below. (and please, this is just very rough in order to illustrate and its not to scale)
The original Sea Lion discovery drill is in the red circle. As you can appreciate this is not in the centre of the structure and this is why present estimates are just P50 of 170 million recoverable barrels, as the CPR only includes the area within the red circle.
The Southern lobe is big and the northern lobe is a bit smaller than the southern one.
So, the first drill ( 1 x ) will be a test of the Northern Lobe and by association will, if it hits oil, make the P10 figure become near to the new P50 (all of the green shaded area) in excess of 1 billion barrels recoverable potential. It will derisk the blue circle area considerably and some of that, after flow test, can be added to P90 figures.
The second drill ( 2 x ) will be a test of a more central location of the Southern Lobe, and hopefully being more central they will encounter thicker net pay. Success here will allow the present discovery area of the red circle to be extended to be the size of the yellow circle, again which will boost up the P90 and P50 figures.
Further appraisal wells will be to test and prove up the area's not in the circles at the moment, so in between the north/south lobes and possibly one to the West.
Hopefully that allows a bit of a better understanding as to why the first drill is classed as "exploration" and has a massive upside effect, but no effect on the present defined small Sea Lion discovery area. Also, one can understand why the second appraisal well will have a significant effect on the P90 size and the P50 size.
One should also note that the data so far is based on 2 stacked fans however, there is a very real chance Sea Lion is up to 7 stacked fans and they have not found the oil/water contact point meaning that there might be a lot more oil there than presently envisaged in the P10 recoverable size estimates.
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