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Diesel vs. Base Oil for OBM?
04 January 2020
Lectori Salutem,
I would like to consult with the community to explore the advantages and/or disadvantages of using diesel vs. base oil for oil based mud (OBM) systems - I have to admit that I have very little to no experience using diesel based OBM systems and I am not a chemist or mud engineer neither. The obvious differences between using diesel and base oil are cost and possible contaminants in the diesel (assuming the base oil is free of contaminants). The first questions that spring to mind are:
  1. Any HSE concerns? Are these different for using diesel vs. base oil?
  2. What can be done to remove any possible contaminants and is this really necessary?
  3. Has anyone experienced positive or negative results using diesel with the drilling fluid company's chemicals / additives?
  4. Would there be any impact on cementing operations (i.e. bond of the cement) when using diesel vs base oil based systems?
  5. Anything else to consider?
Many thanks in advance.
Harald Benning
5 answer(s)
Senior Wells Advisor
Redstone Drilling
Total Posts: 37
Join Date: 13/09/07
Many thanks for your informative and detailed responses. I assume that with elevated temperatures (140 - 160 deg C) these issues are exacerbated, but perhaps less of an issue on land rigs. Though changing out shaker screens would still not be a pleasant job.

Best regards,
Harald Benning 
Mud Engineer
Total Posts: 4
Join Date: 10/11/16

Previous responses are well founded and I think Ian covered most of them. In a former life I worked for Gearhart Geodata and, on occasions, drill cutting samples were collected from diesel based muds. The fumes were very unpleasant and significant headaches were the norm. In those days ROPs for mud logging units were determined via a kelly bottle linked to a transducer and there was a constant requirement to re-tape the lines to the kelly hose as a result of any diesel mud on the outside of the hose. This is very old school system and no longer in use by mud logging companies. Rig crew were always having to re-tape their lines.

As a mud engineer from 1990 I have not come across any diesel based systems but that is because I have worked exclusively in all the North Sea sectors where regulations have stopped the use of diesel for the oil phase. Mineral oils are the norm and although they still give off fumes with elevated flowline temperatures they are nothing like the fumes experienced in the past from diesel.

If diesel can be avoided then it is best to do so with respect to HSE for the rig and service crews.

Total Posts: 4
Join Date: 10/01/16
Thats a fantastic reply from Ian. I worked with Diesel Based muds at the turn of the century in Aceh and despised their very existence. I know they are still used and potentially the effects could be mitigated by an extensive ventilation/extraction system and PPE but I'm fairly confident that 99% of rigs still using diesel as OBM would not have the proper equipment.
I actually think there is a class action lawsuit waiting somewhere for operators that insist on using diesel for mud considering the dire warnings expressed in the SDS with regards to inhalation of fumes. Those poor guys changing shaker screens are especially hard hit. 
Drilling Mgr
Cairn Energy
Total Posts: 17
Join Date: 15/01/09


One point of note (which may not apply to you but will apply to many readers) is that as part of the OSPAR agreement in Copenhagen in 2000, it was agreed that the use of diesel oil-based drilling fluids is prohibited. This was based on protection of the marine environment in the NE Atlantic but if your company has similar policies as mine then this is followed globally.

(retired) Well Fluids Team leader
SPREAD Associates
Total Posts: 49
Join Date: 14/06/06

Hello Harald,

In the UK sector of the North Sea  we eventually persuaded our internal management to stop using Diesel as a base oil in the early 80s.  Although many people assume this is related to environmental impact of the discharge of whole mud and then contaminated cuttings discharge, the predominate reason for the policy change was related to human HSE issues. In the 70s and 80s there are a number of engineers and logistical staff with severe dermatitis on arms and neck assumed to be from exposure to diesel.When using Diesel mud you are most likely to use Diesel base oil as your solvent for cleaning  etc.   

Most low toxic base oils are manufactured and well defined chemically  while Diesel is just a hydrated cut from the distillation of crude oil. Diesel contains approximately 75% aliphatic hydrocarbons and 25 % aromatic hydrocarbons, naphthalenes and alkyl benzenes. If you look at a gas chromatography trace of Diesel it is very imprecise and " messy " compared to most low toxic  base oils. The flash point of Diesel can be as low as 50 Centigrade  where as low toxic base oils are usually above 80  degree Centigrade

Diesel oil is still classed as "as probably carcinogenic to humans". "Vapour air mixtures may be explosive." For this reason I would never let anyone pump pure Diesel down any well for pressure testing. 
Diesel is irritating to eyes, respiratory system and skin (much worse on hot days and HTHP wells).    
Severe lung injury may occur during breathing in of the liquid ( fumes/mist in shakers area on HTHP wells perhaps). 
Many shaker hands did not come back to the rig due to severe headaches. Need excellent fume extraction system.   
Obviously you can still get dermatitis when using low toxic base oils but should be less of an issue compared to Diesel.   
No difference with your point 3 and 4.
You do need to test your elastomers with the  base oil and /or whole mud you are using.   

To limit dermatitis risk with either oil mud system you need to,keep work clothes away from non work clothes so have separate laundry facilities on the rig for any oil based mud you are using.  

Regards Ian 

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