BAKER HUGHES - Drilling Fluids Reference Manual

HYDRAULICS
where:
2 2 1/2
1303.797
J ---------------------A ⎛ ( J 1 ) + ( J 2 ) ⎞
3 = ⎜ – -------------------------------
N – 2 ⎝
t ⎟
1303.797 ⎠
J
1303.797
--------------------- 4
N–
3
A J 1)
2 2 2
⎛ ( + (J 2) + (J 3 ) ⎞ 1/2
= ⎜ – --------------------------------------------------
⎝
t ⎟
1303.797 ⎠
2 2
J
1303.797⎛ ( J
N – 3 --------------------- A 1 ) + ... + J N – 4 ⎞ 1/2
= ⎜
4 t – ------------------------------------------⎟
⎝ 1303.797 ⎠
2 2
J
1303.797⎛ ( J
N – 2 --------------------- A 1 ) + ... + J N – 3 ⎞ 1/2
= ⎜
3 t – ------------------------------------------⎟
⎝ 1303.797 ⎠
2 2
J
1303.797⎛ ( J
N – 1 --------------------- A 1 ) + ... + J N – 2 ⎞ 1/2
= ⎜
2 t – ------------------------------------------⎟
⎝ 1303.797 ⎠
2 2
J
1303.797⎛ ( J
N --------------------- A 1 ) + ...+ J N – 1 ⎞ 1 ⁄ 2
= ⎜
1 t – ---------------------------------------- ⎟
⎝ 1303.797 ⎠
N = the number of jets desired
J 1 , J 2 , etc. = the jet size in 32nds of an in., which must be rounded to the nearest whole
number (i.e., 11, 12, etc.).
ADVANTAGE SM Engineering programs contain the necessary tools to recommend bit nozzle sizes.
SWAB AND SURGE
Tripping into or out of a wellbore involves movement of the drillstring within a non-circulating
fluid colum n. Many blowouts have occurred when tripping out of the hole, while lost-returns
problems are often associated with trips back into the hole. The common factor in both cases is the
movement of the drillstring and its effect on hydrostatic pressure, typically at the last casing seat
and at total measured depth. Swab and surge pressures are caused by the combined effects of
viscous drag of the drilling fluid on the drillstring and annular velocity due to displacement of the
drilling fluid by the drillstring.
The key variables influencing swab and surge pressures are:
• Wellbore geometry – Such factors as gauge hole, cuttings beds and washouts can have a
very strong effect on the wellbore geometry.
• Fractures pressures, pore pressures and depleted zones – These determine how high/low
pressure surges a wellbore will safely tolerate.
• Drilling fluid density and rheological properties – Gel strengths are considered in
calculations and directly impact the pressure necessary to initiate fluid flow.
• Tripping speed – This is the most easily controlled variable and is the one that is used by
ADVANTAGE SM Engineering to limit swab and surge
pressures.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 9-20