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  Case Histories Index:    
  1-The Case of the Bad Maturity Data

2-The Case of the Mystery Fluid - It is Oil or is it Diesel?

3-The Case of the Convoluted Data!

4-The Case of the Gas Quandary - Is There Oil Below the Gas
5-The Case of the Cockeyed Kinetics Data

6-The Case of the Vain Valentino - How Much Data Is Really Needed?

7-The Case of the Discontinuous Reservoirs

8-The Case of the API Gravity Enigma - The Charge of the Light Petroleu
9-The Case of the Secret Second System

10-The Case of the Asphalt and the Alligator

11-The Case of the Density Dilemma - Measuring API° Gravities of Heavy Oils and Oil Shows

12-The Case of the Undercharged Prospect - What Does it Take to Make a Profit

The Case of the Bad Maturity Data
Number 1 in a series of illustrative geochemical real case histories.
(copyright 8/98)

The well-worn sign on the door read Rocky Vale, Private Geochemist. Inside, sitting at an old wooden desk amid a clutter of books and papers, peering at geochemical data on a computer screen was the man himself, Mr. Rocky Vale.

Yasmin tabletki antykoncepcyjne
Tabletki bez recepty?

Decades of fast food had rendered him rather stout and years of sun avoidance left his bald head looking like a white-washed cannon ball. Studying geochemical data and gazing into computer screens had taken its toll physically, but mentally Vale was sharper than a splinter on a park bench. The real insiders within the industry knew Vale and his odd assortment of associates were crackerjacks when it came to geochemical problem solving.

As if on cue, the telephone on Vale's desk rang. "Rocky, is that you?" a gruff and somewhat twangy male voice inquired. "Well, if it isn't Arcata Bottoms, our favorite client," exclaimed Vale with a certain wryness to his voice. "How have you been? Is that story about you and the horse they were telling at the geological society meeting true?"

"Well, ahem, some if it," Arcata confessed sheepishly, "but that's not why I'm calling. I have a geochemical problem. It seems one of my new clients had a large number of wells on their concession analyzed with vitrinite reflectance, but a maturity map of the oil source rock developed from that geochemical analysis doesn't fit the distribution of oil occurrences. According to the resulting interpretation large oil fields were often being associated with the 'immature' source rocks. The explanation given was that 'somehow' oil must have been generated "early" from the source rocks in the basin studied. The oils, however, were mature by every geochemical technique available (eg. gc, gc/ms, etc.), and basin geology showed that migration from more mature oil source rocks outside the concession area could not have taken place. As their consultant, they are looking to me for answers. What should I tell them, Rocky?"

"Sounds like something ve hear all too often." replied Rocky thoughtfully as he tilted back in his chair. "Let me call in our lab manager and get him on the speakerphone. You know Dr. Louis Gravel, don't you Arcata?"

Gravel was already entering the room and caught part of the conversation. "Vot do you vant?," impatiently asked the slender, quiet, gray ponytailed, German scientist who had daily experience in dealing with misguided petroleum professionals. He pushed back his disheveled hair and settled himself into a chair.

After making Bottoms repeat his problem, the bespectacled, white coated doctor let out a sigh and began in his very best English, "Too many of our low-cost competitors cut corners and make quick analyses without thinking like scientists. Like you said, it happens all too often. I suppose some one dimensional basin modeling vas attempted on several vells but the reported maturities could not be derived from any reasonable modeling permutation: they vere alvays too low. Is that pretty close to what has been happening, Mr. Bottoms?"

"You're amazing, simply amazing," blurted Bottoms with way too much awe in his voice. "You practically read my mind. How do you do that, and just what the heck is going on down there?"

"I never realized how easy it is to ruin a geochemical analysis without even trying!"

"Oh it's easy," said a sanguine Gravel rolling his blue-green eyes at the ceiling in an exaggerated movement. "Let me explain to you something about vitrinite reflectance, computed oil maturity and how the suppression of vitrinite reflectance can result in a faulty low maturity number.

Vitrinite is an organic matter component derived mostly from lignin and cellulose of vascular plants. It increases in light reflectivity as organic matter in rocks is buried (e.g. lignite, bituminous, and anthacite coals) and this property is used to determine sedimentary rock maturity. Precise vitrinite relectance is measured with a microscope and calibrated to the oil and gas generation and preservation maturity zones. Lipid-Rich Vitrinite is fluorescent vitrinite that contains marine or lacustrine lipids in its structure, usually due to deposition in anoxic or suboxic environments. When the organic matter reaches oil generation maturity, the reflectivity of lipid-rich vitrinite is reduced (suppressed). This can result in anomalously low reflectance measurements which must be corrected to obtain the true maturity.

"Vidin the oil vindow," he continued, settling into his lecture room pace, "the reflectance of vitrinite deposited in reducing marine or lacustrine environments is often lower (eg. 0.15-0.55%Ro) compared to vitrinite deposited in more oxic environments. This can be due to: the incorporation of lipids into the vitrinite structure, the formation of vitrinitelike macerals from algae, marine grasses, etc. the impregnation of generated bitumen or incorporation of migrated oil, or several other causes (Mukhopadhyay, P.K. 1994, Vitrinite Reflectance as a Maturity Parameter, Chapter one, p. 7-12, (book) ACS Symposium Series 570)

If lipid reflectance suppression is not recognized, the reported vitrinite reflectance maturities vill be too low and a mature source rock may be identified as immature. Are you vid me so far?".

Porady, jak leczyć

Without waiting for a reply, after all it was Arcata Bottoms on the other end of the line, he continued. "The problem can be recognized in a maturity profile of a vell by anomalously low 'maturities' of oil source rocks that have generated oil compared to the section above and below, but is often overlooked if only the oil source rocks themselves vere analyzed. Fortunately, lipid-rich vitrinite fluoresces and can easily be identified if the time is taken to analyze the samples properly. Unfortunately this isn't alvays done by some low cost geochem shops.

"Lipid-rich, reflectance suppressed vitrinite is very common but is not alvays recognized due to microscopist inexperience or failure to use fluorescence ven doing reflectance work. Several research studies have sought to calibrate suppressed vitrinite reflectance to normal vitrinite reflectance (Mukhopadhyay, 1994)."

"Hey," Bottoms interrupted. I never realized how easy it is to ruin a geochemical analysis without even trying! How come I never heard of any of this before?"

Gravel, and even Vale who was still quietly listening in, could think of at least a dozen reasons, but always professionals, both restrained any impulse to elaborate. "You must have been busy discovering the North Slope," Vale finally butted in with a mock seriousness that Bottoms misinterpreted as high praise.

"Mr. Bottoms," Gravel continued, "tell your client that H.B. Lo of Exxon, based partially on microscopy work done by DGSI, related the degree of reflectance suppression to the hydrogen index of oil source rock and non source rock shales (Lo, H.B.,1993,Organic Geochemistry, Vol. 20, No.6, p. 653657). He found that the degree of suppression is related both to the hydrogen index of the immature source rock and to the maturity. (Click here for the figure 432x301).

"Reflectance suppression increases with oil source rock quality and is greatest at mid oil vindow maturities. DGSI experience has shown this model to be very reliable although some modifications have been made since Dr. Lo's original work was published."
(Lo, H.B., 1998, Abstracts of the 15th Annual Meeting of TSOP, p. 42-43.)

"The lesson here is obvious: If it's worth doing, it's worth doing right."

"Why thank you Dr. Gravel, and you too Rocky." Bottoms was relieved and preening that he had made the right decision to call DGSI. "You guys certainly know how to make an old consultant like me look good in front of my clients. If I listen to you more often, I'll be able to double my rates. What do you suggest I do now?"

Once again, several rather unprofessional equine images appeared in Vale's mind which were quickly suppressed while Gravel's thoughts were already on his next project. Gravel rose and in his odd, stilted kind of walk, left the room, an untied shoelace trailing him into the hallway.

Vale, scratched his shiny domed head, folded his fingers over the hill of his belly and with his eyes closed, slipped into his 'private eye voice. "In a similar horror story of what can happen if reflectance suppression is not recognized, I seem to recall that DGSI was asked to reanalyze some of the wells. The result was soon obvious: the calculated vitrinite reflectance maturities were too low in wells where the oil source rock was in the oil window because they were derived from fluorescing, lipid-rich vitrinite. Corrections were made with the help of DGSI and a new source rock maturity map was prepared which fit the distribution of oil production and oil shows almost perfectly. And best of all, it led to a new discovery that would not have been found if the original source rock maturity map had been relied upon. And Arcata...."


"The lesson here is obvious: If it's worth doing, it's worth doing right. Poor quality data can be worse than no data at all and you (almost always) get what you pay for. Keep this in mind when comparing prices and geochemical laboratories." And with that said, Vale ruminated on the sad state of technical fuzziness that Arcata Bottoms worked in while waiting for the kind hearted, but dimly lit bulb at the other end of the line to respond. Vale knew whatever Bottoms said would surely give Vale's entire team of misfits something to chuckle about on their way home from work.

Just then the intercom buzzed. It was Madam Marvelous, office manager and everyone's favorite confidant. Stiletto heels not withstanding, Marvelous was the glue that kept the office together. In a silken and even tone she breathed, "Call on line 2 regarding diesel oil contamination of hydrocarbon samples. Can you take it?"

Rocky Vale sighed, gruffed out a frazzled yes, bid good-bye to Bottoms and pressed the line 2 button on the phone. "Hello, can I help you?" asked Vale. TO BE CONTINUED in case number two.

Case Histories Index:
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