�?�?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 s The reduce in annular return circulation will induce the move pace of drilling fluid within the annulus to lessen, and the friction among it and the annulus will lower, Therefore the BHP and standpipe tension will lower lin