�?�?t ε l ρ l v l + �?�?ε l ρ l v l v l = ε l �?�?τ l + ε l ρ l g �?ε l �?p �?β v l �?v sThe minimize in annular return circulation will lead to the movement velocity of drilling fluid inside the annulus to decrease, plus the friction in between it as well as annulus will reduce, Hence the BHP and s