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Trend of DKD mud technique
23 February 2018

Dear Colleagues, 

I understand utilization of Dynamic Kill Drilling (DKD) mud technique has become more and more common in deepwater explorations lately because it seems to be very difficult to eliminate a lot of uncertainties in exploration wells, particularly shallow gas risk. 

However, in case that the risk of shallow gas is found to be reasonably low by shallow gas analysis or somehow, is it still common to use conventional seawater gel mud system with some amount of weighted mud even in deepwater exploration wells? Or is DKD mud technique almost the default for deepwater exploration wells? 

Have you had any experience of drilling deepwater exploration wells with conventional / traditional way (seawater gel mud with kill mud) lately?

I'd like to know international industry trend in drilling fluid system for riserless section in deepwater exploration wells.

Regards,

Hide

5 answer(s)
eaosborne
Drilling Engineer
Noble Energy, Inc.
Total Posts: 3
Join Date: 01/12/14
I have only drilled with seawater to a depth that we could control with the additional weight of cuttings in the system then we continue with a pump and dump procedure.  Usually it is 16.4 ppg super salt mud cut back to the estimated required weight on the fly.  The required mud weight is based on the estimated PPFG from the subsurface group based on seismic,hazard surveys and offset information.
HideakiTsukui
Offshore Exploratory Drilling Manager
Japex
Total Posts: 2
Join Date: 21/02/18

Sacha-san,

Peter-san,

Christian-san,

 

Thank you for your replies.

All of them are really helpful to me. I understand DKD mud technique is not the default procedure even for exploration wells and conventional method is still common.

 

Regards,

Hide

grani13
Drilling Ops Manager
SPREADAssociates
Total Posts: 2
Join Date: 14/01/18
Fully agree with the previous comments.

P&D operations are complicated and costly, because they require managing tremendous volumes onshore in the mud plant, logistics and finally the handling on the rig - all in a very constrained time frame that does literally not allow for mistakes. 

Personally I have only used P&D mud as a mitigation to shallow water flows which would (once started) very hard to get control of again.

As for shallow gas: Many company policies do not allow spudding a well in a location that has not been cleared (i.e. negligible risk) of shallow gas hazards. Offshore on a floater it shouldn't be hard to move to another, more favourable spot unless the seismic shows it's full of anomalies. In the latter case it may be required to revert to classic methods like e.g. pilot holes etc for mitigation.
Companyrep
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 361
Join Date: 10/01/05
Hideaki, 

I agree in most with Sacha. 
Further comments to your questions as bellow.


Q) DKD) mud technique has become more and more common in deepwater explorations lately.


PA) Not in my experience. This is used and is no doubt needed is some specific areas where higher risks, sedimentation, lack of data, lack of confidence drive this. 
DKD use more often than not in my experience more so in later stages of dw and UDW wellbores to assist to deepen sections to drive >fracture gradients, stabilise well, deliver better quality, optimise well design drilling times/costs (through being able to adopt) a more slender well design etc.

Q) risk of shallow gas is found to be reasonably low by shallow gas analysis or somehow, is it still common to use conventional seawater gel mud system with some amount of weighted mud even in deepwater exploration wells?

PA) If risk is low, drill with seawater is the standard norm. 
The more silt/sand is experienced then size, frequency quantity and quality of sweeps need to be assessed to assure optimal wellbore quality and avoid (well fracturing or becoming unstable)
e.g. 50bbl sweeps per 45m stand (as typically state by engineers in programs) , through a 100m sand will end up loosing well and getting stuck. Simple maths! 

What one should be doing is? Based on centroid/buoyancy effects of targeted risk horizons? Should gas be present. Dynamic kill calcs are needed to be done by (people it takes more than one discipline to assess this) suitably qualified to assess pump rate and weight needed to kill well in the unlikely event a flow resulted. Note: ROV typically observes gas via sonar at seabed before the driller does (via a reduction in PDW EMW pressure)

Q) Have you had any experience of drilling deepwater exploration wells with conventional / traditional way (seawater gel mud with kill mud) lately?

PA) Last 20wells all drilled using conventional methods. 15 of these in more than 2500m water depth. Gas is more likely prevalent in shallower to mid waters (driven by sedimentation rate etc) see attachment. Note: Experienced a low hazards gas incidents but nothing that created major problems or delays.

I'd like to know international industry trend in drilling fluid system for riserless section in deepwater exploration wells.

PA) Sea water and sweeps and a suitable well engineered plan B. (I use Bill Abel (well control assurance expert) for all dynamic kill modelling, because he is perhaps the only expert I know and trust. Plus he is about 30times cheaper than companies than run fancier software programs but don't understand the practical aspects of the drilling process as well as someone who does.) 

Wishing you success.


Regards,



Sacha
Senior Drilling Engineer
Drilling Consultant
Total Posts: 3
Join Date: 03/12/17
Hide,

As far as I know pump & dump or riserless mud recovery in DW exploration well is not the default procedure. Pilot hole, seawater and Hi-Vis sweep is still more common practice.
Pump and dump is primary used when PP is expected to be abnormally higher than hydrostatic, or eventually when shallow gas and/or shallow water flow risk is high.
I drilled DW exploration wells using only SW and hi-vis sweeps, and some with pump & dump because of the PP (there was a shallow gas risk but main reason for pump & dump was the expected PP).
Kill Mud cut back to required density by mixing on the fly. Kill Mud was used when we had a shallow gas kick (PP was underestimated).
DW riserless gas kick is not as risky for the rig as in shallower water.

I hope it answers your question.

Sacha

Posted by

Hideaki TSUKUI

Offshore Exploratory Drilling Manager

Japex

Total Posts: 2
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