Thanks DAH7542 for your in-depth reply. Some of the things you suggested to look at had been implemented i.e stability of the model, rates in reservoir volumes, making sure pressure is at datum during comparison. Right now all what I am doing is having big pore vol on the edge of the reservoir(changed by MULTPV). The analytical aquifer that I started initially was abandoned due to run time issue. But I will go back to it again based on your suggestion. Thanks for your time and effort to respond. Many thanks again and will update you shortly.

Aries