As long as you are following the oil change interval outlined in your owner manual, then there should be no sludge in the engine. Most modern oils are pretty heavy on the detergents even with conventional oil. The only way you are going to have sludge is if your pushing your oil change intervals to the limits.
Now, I am not a synthetic expert by any means. I have grown up in a mechanic family though. Some engines simply don't like synthetic oil for some reason. My brother in-law, a mechanic, said some of the late 90's Ford Explorers hated synthetic oil for some reason. He said they would ping and skip, especially going up hills. Switch it back to conventional, no problems
Long story short, this shouldn't be a problem with your car or any newer cars.