I'm pretty sure that this strategy not only is risky, it also is not very profitable. The most money you can ever win is the amount of your original bet.
Bet 1: You bet 20, most you can win is 20.
Bet 2: You bet 40, and if you win 40 you have already lost 20 so your net gain is 20.
Bet 3: You bet 80, if you win 80 you have already lost 60 so your net gain is 20.
Bet 4: You bet 160, if you win 160 you have already lost 140 so your net gain is 20.
This pattern will continue forever. And since there is usually a max bet at a table, you would be hard pressed to actually make any kind of profit from this strategy.