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Trip and Riser Margin - Work
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Trip & Riser margin, version 4, issued 29 March 2013. WORK version.
The current release of this worksheet exists in 2 versions. They are identical apart from the way they are formatted. The Work version shows inputs and outputs, hiding intermediate calcs. Audit version displays the intermediate calculations.
This worksheet calculates a minimum additional mud density over what is needed to balance formation pressures, to give a safe trip margin. For subsea wells, this is NOT added to the riser margin – the greater of trip or riser margin should be used.
User input
8.5 |
inmm |
Enter the hole diameter. L_dh =
5 |
inmm |
Enter the drillstring OD. L_Ddp =
13 |
lbf/100ft2Pa |
Enter the mud yield point. Pσyfluid =
1.354 |
psi/ftSG or kg/lppglb/ft3ppbkPa/m |
Mudweight to balance formation pressure. ρemwfm =
(Optional input for riser margin)
8.5 |
psi/ftSG or kg/lppglb/ft3ppbkPa/m |
Enter the local seawater density. ρsw =
2300 |
ftm |
Enter the water depth. L_Vwd =
25 |
ftm |
Enter the flowline height above sea level. L_Vfl =
5000 |
ftm |
Enter the well TVD. L_Vtd =
Click here when any values are modified to update the result.
Results
Mud density including trip margin
Mud density including riser margin
Note; in deep water, often the difference between pore and fracture pressure is too small to be able to carry the mudweight with full riser margin. In this case, emergency disconnect procedures are critical and must ensure that the BOP is closed (and if necessary the pipe sheared) before riser release.
Worksheet references
Original trip margin formulae (imperial units) from Shell (1979).
Version 1 of this worksheet was issued on 27 June 2008 by Steve Devereux.
Version 2 added riser margin and calculated resulting mud gradient and weight.
Version 3 accounted for sea level to flowline height and added ppg equivalents.
Version 4 added Specific Gravity to the results (kg/l)
