.::FANARCO::.

Your problem is not the EOS, eneither the data. When you try to use a pvt package you first need to calibrate the EOS you chose with experimental data. You say you have a condensate. If you are using PVTI, you need to intdroduce the composition of the fluid in the reservoir (usually this composition...

If the reservoir has produced more than 10% of the OOIP estimated by volumetric data, we can trust the result of material balance.
The difference may be due to averages of porosity, water saturation, thickness, uncertainties in the reservoir area, precense of an aquifer, and so on.