Hi there,
i didn't catch the whole thing and i'm a new on this but i'll give you my opinion just in case it might help you out
first of all i believe you wanna do a pressure maintenance in such case you can move to the usual injection patterns procedure and to know whether it gonna help or not you can simulate it by eclipse and if you don't have much data you can go with "petroleum solution; EOR gui software" on the other hand and if you want my suggestion do go with the simulation just put the pattern and inject water to the aquifer (if there is) below the production zone in general and the Q of water can be estimated easily using material balance... Not to make it long on you...you need to open discussion with you co-workers and make up your mind by the use of the existed data you have ...i hope you will solve the problem in no time ...good luck