Ocean-bottom seismic systems are emerging as superior information-acquisition methods in seismic monitoring of petroleum reservoirs beneath ocean beds. These systems use a large network of sensor nodes that are laid on the ocean floor to collectively gather and transmit seismic information. In particular, underwater wireless sensor networks are gaining prominence in continuous seismic monitoring of undersea oilfields. They are autonomous and use wireless acoustic transmission for transferring data. However, the deployment period of such networks extends well beyond the battery lifetimes of the nodes. Hence, to ensure continuous monitoring from all node locations, it is required to replace the energy-depleted nodes on the ocean floor. Replacing these nodes at remote undersea locations is very expensive, and hence, the total node replacement cost in large seismic node networks is extremely high. In this paper, we develop effective joint policies involving routing and node replacement decisions to minimize the replacement costs per unit time. Our routing approach is simple and suitable for this application, and it strives for energy efficiency at all times. We propose a few node-replacement policies and compare their performances when they are combined with our proposed routings.