I have attached my file.
I want to build an Oil Field model which:
Production at time t depend on Pressure at time t (Which initial pressure is given)
Pressure at time t+1 is a function of Cumulative production.
Production at time t+1 is a function of P at time t+1.

I have written the model as attached and defined Production and Pressure a variable but when I run the model, I will face Error 149.
Please help me what is the problem?
Thanks RESERVOIR.gms (3.1 KB)

Search for the error 149 in the list (a common mistake).
In short: you defined an equation

ProductionWell .. q_well(t)=e=...

ProductionWell is not defined over t, but your equation is, so Gams complains with error 149 (Uncontrolled set entered as constant).
The equation should be: