�?�?t ρ l k + �?�?x i ρ l k v l = �?�?x j μ + μ t σ k �?k �?x j + G k �?ρ l ε �?Y M The lower in annular return circulation will cause the movement velocity of drilling fluid inside the annulus to minimize, along with the friction in between it along with the annulus will decrease, Therefore the BHP and standpipe t