Trip and Riser Margin – Audit

NOTICE: Our Mathcad database got attacked and infected with a virus. Unfortunately, we've had to shut it down until further notice.

You can safely browse the pages, as the Mathcad server was separate to this main website, and was only accessible here. (We used something called an iFrame, which is like a window into a different website).

UPDATE 28th of January 2020: the virus happened just over a week ago. We've temporarily cut and pasted the text parts of the Mathcad pages rather than having blank pages there.

UPDATE 3rd of February 2020: We've been unable to recover the Mathcad worksheets and offer them in a format that provided total security to users. They were published a decade ago, and our IT people say that they would need a complete re-creation with the latest code and security fixes.

APPEAL: These 44 pages were created, and offered as a free resource for over a decade. We know from our website analytics that more than 1000 users visited each month. If only half of these regular visitors donated $20, we would have enough to create an even better solution. As you know, time is money, have these Mathcad pages saved you $20 in time over the years? We expect that they have, not to mention the learning opportunities provided to new engineers entering the industry.

Please, donate at least $20 as a one-off payment, to bring back the drillers Mathcad back as an always free to use resource!

YES! I've gotten value from the drillers Mathcad in the past, and a $20 is a very affordable way of saying thanks. I also want to preserve this tool for future engineers.

NO! I can't or won't donate to the restoration fund. I'm happy to spend a few minutes to offer a testimonial to help encourage the effort. These worksheets do have value. Offer Feedback.

Trip & Riser margin, version 4, issued 29 March 2013. AUDIT 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





Enter the hole diameter. L_dh =





Enter the drillstring OD. L_Ddp =





Enter the mud yield point. Pσyfluid =




psi/ftSG or kg/lppglb/ft3ppbkPa/m

Mudweight to balance formation pressure. ρemwfm =

(Optional input for riser margin)




psi/ftSG or kg/lppglb/ft3ppbkPa/m

Enter the local seawater density. ρsw =





Enter the water depth. L_Vwd =





Enter the flowline height above sea level. L_Vfl =





Enter the well TVD. L_Vtd =


Click here when any values are modified to update the result.


Calculate the trip margin to avoid swabbing under normal trip conditions.

and in ppg;

Calculate the mud density gradient to include trip margin.

and in ppg;

Assume that the mud in use actually just balances formation pressure. Calculate the riser margin, then the mud can be weighted up to account for both riser and trip margin (ie what is the minimum mudweight that will satisfy both issues?).

Calculate the pressure lost if the riser disconnects; this is the difference between mud and seawater hydrostatic pressure at the seabed.

Calculate the riser margin to account for riser disconnect. This is the amount to increase the mud density to give the required extra hydrostatic pressure in the mud column from seabed to TD (which in this case is   ).

and in ppg;

Calculate the mud density gradient to include riser margin.

and in ppg;


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)

Malcare WordPress Security