Published on Tuesday, November 10 2020
Authors : Dennis Sutton - PetroQual

The following Turning Point blog is provided by Dennis Sutton.  Following a 40-year career with Marathon Petroleum, Dennis is now Principal of the consulting firm, PetroQual and serves as the Executive Director of the Crude Oil Quality Association (COQA).

Obviously, the big story in 2020 in the oil industry is demand destruction and at the recent COQA meetings on October 22, originally planned for Houston, and  held remotely via Zoom, our attendees learned of the changing U.S. refinery landscape, especially in light of COVID.  U.S. crude imports have been on the decline since 2018, and that is expected to continue with several refinery closures, including Marathon Petroleum, Martinez, CA; Marathon Petroleum, Gallup, NM; and PES, Philadelphia.

“I bet you’re wondering how I knew… I heard it through the grapevine”

While topics such as the political landscape and its impact on the petroleum industry, global demand changes, and volatile crude prices are of paramount importance and capture the headlines, aspects of crude oil quality usually take a backseat and are often the subject of rumors and “water cooler talk”- at least when people used to gather around the water cooler or coffee bar.  With social distancing and working remotely, the social grapevine may be even more shredded, and peoples’ knowledge of crude quality issues is often based on incomplete memories of old, one-off events.

At our COQA meetings this year, people discussed a number of crude oil quality related topics that were of concern.  These included:

  •  Organic Chlorides
  •  Hydrogen Sulfide (H2S)
  •  Mercaptans
  •  Oxygenates

Rather than just rely on stories and here say, let’s take a detailed look at each of these crude quality issues.

Organic chlorides

For those who have been in the industry awhile, you’ve heard one or more stories of woe concerning organic chlorides.  Maybe it’s a humorous story (humorous now, although probably not at the time for those involved) of the pipeline station that was told the lab needed to conduct some special crude oil testing.  Unbeknownst to the pipeline personnel, the concern was trace level organic chlorides in the crude.  In their conscientiousness, they cleaned the sample pots particularly well- using a chlorinated solvent, thus totally contaminating the samples and leading to massive confusion.

Or maybe it’s a more diabolical case where hazardous waste containing organic chlorides  from dry cleaning facilities, was being blended into crude oil and transported across state lines, thus involving the FBI, and resulting in significant damage to refinery equipment.

Or, more recently, in 2019, the major crude quality story out of Europe involved organic chloride contamination of Russian Urals crude oil, pipeline stoppage, containment issues, refinery damage, and significant financial consequences.

These are the stories that get passed along, but what is the truth regarding organic chlorides?

First, organic chlorides are not naturally occurring in crude oil.  They are added to the crude, upstream of the refinery,  either by those unaware of this impact,  or intentionally.  They are generally banned due to environmental reasons, but still sometimes find their way into the crude streams.  These compounds, such as chloroform, carbon tetrachloride, and tetrachloroethylene, are often used as cleaning solvents and dewaxers.  As the above example indicated, they are also sometimes (albeit very rarely) blended into crude oil illegally to dispose of known hazardous waste material.  Regardless of their source, they will cause crude unit damage in the refinery, depending on their concentration.  In the case of the Russian crude, levels were detected as high as 300 ppm.  They worked to dilute the contaminated crude to a “usable 6 ppm” organic chlorides, still a high level under normal circumstances.  For comparison, the Capline quality manual states that no crude with >1 ppm organic chlorides is allowed.  While inorganic chlorides, i.e. salts, are separated and go into the water phase in the refinery’s desalter, the organic chlorides remain soluble in the crude, are carried into the main distillation unit, and form hydrochloric acid (HCl), resulting in significant corrosion. 

There are two major practical challenges when dealing with organic chlorides. One, the incidents are very rare, and episodic in nature.  Often, by the time one suspects organic chloride contamination and begins testing, the situation has passed and no evidence is found.  Secondly, trace level (<10 ppm) organic chloride measurements in crude are very challenging.  In many cases, it is not known which compound(s) are present AND it is difficult to avoid interferences from inorganic chloride salts.

An excellent overview presentation from S.A. Lordo is available in the COQA meeting archives.

H2S and Mercaptans

There are many sulfur containing compounds in crude oil.   The sulfur compound of most concern in crude oil is one of  the simplest- hydrogen sulfide, or (chemically) H2S. Hydrogen sulfide is a naturally occurring, highly corrosive and toxic gas that is found dissolved in many (but not all) crude oils.  Because of the toxicity of H2S (levels above ~700 ppm can be lethal), personnel handling crude oils wear monitors (sometimes called “chirpers” because of the sound they make) that indicate the presence of H2S above 10 ppm. 

From an analytical standpoint, two characteristics make H2S detection very challenging:

  1. H2S is very Volatile! When analyzing for a gaseous component is a liquid, obtaining representative samples is very difficult.
  2. Because of the volatile nature of the H2S, some measurements are made on the vapor space above the liquid crude oil and some measurements are conducted on the liquid.  These results will often vary by a factor of 100!  Thus, it is not unusual to hear through the grapevine of someone talking about H2S levels of 2000 ppm, and someone else mentioning the level was only 20 ppm- for the same sample.  It is imperative to know whether the values refer to a vapor sample or a liquid sample.

There is much, excellent information available on H2S in crude oil, including two recent panel discussions from 2019 COQA meetings.  Please check these out for more detailed information.

One can think of H2S and mercaptans as “cousins”, because chemically, they are quite similar.  While H2S is one compound, mercaptans (also called thiols) refers to a group of sulfur containing compounds with the general formula R-S-H, where R is a hydrocarbon group.   Like  H2S, mercaptans are naturally occurring in the crude oil.  They too have undesirable odors.   Though there are routine processes in the refinery to remove the mercaptans, the odor considerations can lead to some buyers having a reluctance to purchase mercaptan containing crude oils, or desiring to have a specification in place to limit their content.  In 2020, there have been reports of light, tight oil from the Permian Basin occasionally having elevated levels of mercaptans.  Though unconfirmed, this may be the result of sour condensate being blended into the crude.


The term “Oxygenates” refers to a class of compounds containing oxygen.  While there are some naturally occurring oxygenated compounds in crude oil, such as organic acids, the compounds generally called “oxygenates” refer to things such as methanol, ethanol, and MTBE. These are not naturally occurring in crude oil. Thus, they are introduced into the crude through the handling or transportation of the crude oil from production point to receipt point.  For example, methanol is used for hydrate inhibition in producing wells in the Gulf of Mexico.  This practice is used when production disruptions are expected, such as when hurricanes are threatening facilities, as frequently occurred in 2020.  At the refinery, these light, water soluble oxygenates will partition into the water phase in the waste water treatment plant, potentially causing damage to the microorganisms.  Like many crude quality issues, communication between producers (who use the oxygenates) and the refiners (who must handle them) is imperative!

In 2019, it was reported that South Korean refiners had rejected two cargoes of US crude due to unacceptably high levels of oxygenates. The crude in question was Eagle Ford, a light, tight oil  produced in Texas and moved to the Texas coast for loading on ships. Though details are not totally known,  one can speculate that the oxygenate in question may have been ethanol, a common blending component in gasoline. Somewhere in the supply network, contamination may have occurred. 

Again, like organic chlorides, contamination from oxygenates is very rare, but leaves a lasting memory in people’s minds.  Also, the episodic nature makes detection, and determination of source very challenging. 


If you or your colleagues would like to learn more about these important, but often misunderstood, crude quality issues, our  Crude Oil Quality Association (COQA) meetings are open to all, and we would welcome your attendance at our next meeting in early 2021 that will again be held remotely.  One major advantage of the remote meetings is that people worldwide, who might not normally be able to attend in person, can participate from the convenience of their home or office!

We would like to thank Dennis for today’s blog and support the work COQA is doing in coordinating efforts in the crude oil quality arena.  In the course of our business, Turner, Mason & Company has been involved in a variety of studies and engagements where crude quality issues have been of primary or secondary interest.  These issues are only becoming more vital to refiners as new fields are discovered, changes take place in existing fields, “above ground” factors impact both volumes and qualities of produced crude and product specifications become ever more stringent and wide ranging.  We have and continue to assist all segments of the oil industry in responding to these and other developments which impact petroleum markets and also provide in-depth analysis of the impacts in our subscription products, including our Crude and Refined Products Outlook and Worldwide Refinery Construction Outlook.  For more information about these products or how we can assist in any specific consulting engagements, please visit our website: and send us a note under ‘Contact’ or give us a call at 214-754-0898. 


Leave a Reply

Copyright © 2021 Turner. All Rights Reserved.
  • Sign up

Your email address will be your User Name

Password Strength Very Weak
Lost your password? Please enter your username or email address. You will receive a link to create a new password via email.
We do not share your personal details with anyone.