Production Forecast from Log WOR vs Np Graph.

[Chee Koh Peh]

Guys,

A tricky one.....I have a field exhibiting strong waterdrive producing at 96% watercut

The log WOR vs Np is a straight line as would be expected under harmonic decline (Under harmonic decline the Log WOR vs Np tends towards a staight line inferring the field production decline is harmonic in the same way a Log Oil Rate vs Np is straight line under harmonic decline). This assumes of course a fixed total liquid rate in the field.

So the Log WOR vs Np plot can be extrapolated to give me a field EUR at WOR cut off 50 etc....

Now here's the challenge I need to convert this to a time based forecast that is rate vs time. The only way I can see to do this is the following (and yes it's complicated):

1. Knowns, the decline is harmonic therefore b=1 and I know inital rate Qi, unknown inital decline Di.

2. I therefore would have to "guess" a initial oil decline Di for the field, and then calculate Np and WOR (from the Oil rate vs time graph) at say 1 month timesteps using Arps decline equations and then compare those Np and WOR as calculated from the Log WOR vs Np.

3. I would keep adjusting Di until the Np and WOR calculated from both the Oil rate vs time plot and the Log WOR vs Np were the same i.e. I have a match.

Okay does anyone know an easier way to do this or whether OFM or equivalent can be manipulated to do this?

Thanks

Rgrds

Chee Koh Peh...