If you pump water into a hole in the ground, how do you make it only go west and not east? It will flow along the pressure gradient. So with Harmaliyah in at least minimal contact at the aquifer level, water will flow so as to equalize the pressure between the injector bottomhole and the Harmaliyah wells. Even with the wells flowing, they probably wouldn't notice the effect at the Ghawar injectors.

"they probably wouldn't notice the effect at the Ghawar injectors."

well, they probably didn't notice, but the model they ended up with (the history match)was not really representative of the actual reservoir. injection of xe9 barrels of water should have produced y pressure response in ghawar, if they had all the parameters correct. as i have pointed out on previous threads, a reservoir model doesnt give a unique solution. and that is why they need to be taken with a grain of sand.