Production Forecast from Log WOR vs Np Graph.

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...

Dear Chee Koh Peh, you can do that in OFM, but it is not easy and you are required to know a little about the syntax used by OFM functions. I do this by defining 2 user functions:
1. The first needs to calculate the total liquid production for the future. That is, you can maintain the last data fixed forward, or you can use an equation, for example in order to increase the liquid production a certain amount per year, as seen in many fields.
2. The second variable calculates the future oil prodution using the future liquid production (from variable #1) and the extrapolated Log WOR vs Np trend built-in in OFM.
I'll look for the variables definitions and I'll post them here. If I have time maybe I can do a little tutorial. I used to this in OFM version 2005, in fact I prepared the whole 2009 prodution budget in my company with this technique, and it worked, but sometimes it was very unstable and the system crashed constantly. At the end the next year I ended up doing it in Excel, but maybe the newer versions of OFM are more stable, I don't know.
Regards.

Dear Newbie ,
Thank you so much for your explaining could you please uploade any excel sheet regarding the oil production forecast.
Thank you in advance

Dear Newbie,

Thanks, for the reply. I was able to generate the Log WOR vs Np in OFM but like you said I takes some trick OFM Syntax. In the end I gave up and used Excel, but I used Watercut vs Np and it worked.

What I did here was generate a forward Np forecast extrapolating the watercut trend (just used slope and intecept funtions) to determine the linear Watercut extrapolation.

I then fixed the total fluids liquid rate and then selected an oil exponential decline rate and summed up the production month by month (Np) and since I new the Np vs Watercut relationship I could calculate the watercut profile at each monthly production. I then overlayed that watercut profile from the monthly production against the Np vs Watercut extrapolation and simply adjusted the oil decline rate until I had an overlay.

The key here is to fix the total liquids rate, then if you have linear extrapolation on the Watercut vs Np curve then the oil decline must be exponential.

It would great if you could post an OFM tutorial and I'll see if your method works in OFM 2009 and let you know.

Thanks

Rgrds
Chee Koh Peh