J55, K55 and N/L80 casing grades are basically the same carbon steel, and are as good (or as bad) at resisiting sewater corrosion as any other carbon steel. The lower strength grades (H40 J55 K55 etc) would be specified over N80 and L80 if stress corrosion cracking is an issue. In many areas, L80 is more readily available than lower grades.
Statoil have done some work that suggests that addition of 1% chrome can improve the resisitance of carbon steel casing to seawater/ oxygen corrosion, so it might be worth getting L80 1%Cr. If oxygen corrosion really is an issue then you may have to go with stainless steel. However, bear in mind that if an ESP goes more than 3 years before breaking it's doing very well indeed, so you'll be recovering the tubing to surface at least every three years (or maybe 6 years if you're using dual ESPs), so one solution is to use stainless steel on the wetted parts of the casing/ liner from the bottom of the well to the ESP and carbon steel from the ESP to surface, and use 1%Cr on the tubing, and inspect the tubing every time you change out the ESP.
