Prospect Risking - Scheme 29 |
  
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Prospect Risking - Scheme 29 |
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In this scheme, Overall Prospect Chance is divided into Play Chance, Prospect Specific Chance and amplitude modifier. The amplitude modifier is based on a Bayesian assessment of the probability that a DHI is true compared to the probability that it is false. It can increase or decrease the GPOS.
Play Chance is divided into three categories: Reservoir, Seal and Source (or Regional Reservoir, Regional Seal and Regional Source).
Prospect Chance is divided into four categories: Reservoir, Trap, Charge and Retention. This follows the NPD scheme.
Each category has one of more subcategories. You are required to assign a chance to each element.
This is a multiplicative scheme, so all chances in all categories are multiplied together to get the final GPOS. For example, Reservoir Chance has 2 elements: 'presence' and 'producibility'. If you assign 'presence' a chance of 80% and 'producibility' a chance of 90% then the Reservoir Chance is 72%.
There is also an amplitude modifier, based on the method of Rob Simm and Mike Bacon as given in their seminal work "Seismic Ampltude - An Interpreter's handbook.
P(hc | dhi) = P(dhi | hc) . P(hc) / { P(dhi | hc) + P(dhi | nohc). P(nohc) }
where: P(hc | dhi) is the probability of hydrocarbon with the observed DHI = final GPOS
P(dhi | hc) is the probability of the DHI happening if there really is hydrocrbon
P(hc) is the probability of hydrocarbon ignoring the DHI = play x prospect specific chance
P(dhi | nohc) is the probability of the DHI happening when there is no hydrocarbon
P(nohc) = 1 - P(hc)
You have to enter the prior probabilities P(dhi | hc) and P(dhi | nohc)
R is the ratio P(dhi | hc) / P(dhi | nohc).
In consolidations you can "share" the amplitude modifier. This is done by "sharing" the ratio GPOS(final) / GPOS (pre-dhi)
The overall Prospect Chance is the multiplication of the Play Chance and Prospect Specific Chance, as modified by the amplitude prospect probabilities
Overall Prospect Chance = P100 = P(play) x P(prospect specific) * amplitude modification (equation as above)
P(play) = P(regional reservoir) x P(regional seal) x P(regional source)
P(prospect specific) = P(reservoir) x P(trap) x P(charge) x P(retention)
Click the 
button for further guidance on each entry. Comments may be entered in the boxes on the right. There's a drop arrow at the top right of each box. Click this to view/enter the full commentary.
The [Plot] button bottom right will show this plot:
The options in the left panel are self-explanatory.
Q and A
This is questionnaire scheme which arrives at a chance of success based solely on consideration of the DHI. It was devised by Mike Bacon, and produces a chance for comparison (use the [Comparison] button) with the GPOS and amplitude modified GPOS.