It would depend on the reservoir. You have to look at how much of the oil will be left in the formation without secondary lift and also how much oil has already been removed. Once you pass a certain point it would not pay for itself as you would get too much water back for the amount of oil. It would be something to look at though. I don't know about on land but it cost a lot of money offshore. I guess if we have some wells close by that are making way too much water we could use them but the pumps and the tanks and the lines can get very costly. Not to mention we would have to drill an injection well. Someone smarter than me will have to make those decisions. There is also CO2 flooding.