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Cryo: cutting edge cuttings analysis
The measurement of volatiles from drill cuttings — the under-utilized byproduct of drilling; cuttings free, but not worthless Steve Sutherlin Petroleum News
A cutting-edge technology to analyze volatiles from drill cuttings via a cryo trap mass spectrometer can provide significant cost savings compared to conventional methods of petroleum system analysis, according to Mike Smith, President of Advanced Hydrocarbon Stratigraphy Inc.
“It’s a pretty inexpensive operation because you’re just using the natural byproducts from the well,” Smith said in a presentation to a May 31 technical breakout session at the state Geologic Materials Center in Anchorage. The session focused on the potential for new investigative technologies and machine learning systems to better assist geoscientists and resource companies to meet the challenges of interpreting Alaska geology.
The proprietary volatiles analysis service invented by AHS is distributed by Baker Hughes.
“This machine is aimed at present day volatiles that are in rocks, not the ancient volatiles,” Smith said.
The process yields two types of deliverables, operational recommendations and acreage and basin assessment, he said.
“VAS delivers the occurrence and composition of oil and gas in the cuttings, as well as mechanical strength, permeability, oil saturated water, proximity to pay and location of potential pay zones and faults,” Smith said. “This approach allows for rapid cost-effective data integration across well generations for understanding bypassed pay, optimizing landing zones, and petroleum system assessments.”
The analysis has two main focuses, Smith said.
The first is pay identification and evaluation, he said, adding, “Where is it, what is it, and how much is there?”
The second is reservoir properties, he said. “How is it going to produce, and will it produce?”
Gently, please Smith said the rocks from the well site require very gentle handling, particularly in light of modern polycrystalline diamond compact drill bit technology.
“We had a big change in the ’90s when we introduced PDC bits on a wide scale: the cuttings became very small and difficult to analyze for volatilizes,” he said. “We’re very gentle when we catch the cuttings; we don’t want to get them on the shaker table; we take a kitchen strainer where the flow line pours into the possum belly.”
There are two kinds of cutting analysis, one where samples are sealed at the well, and one where samples are washed and dried before shipping to the lab. Smith said, adding, “They tell somewhat different information.”
“The seal-at-the-well ones (with) water based mud, we rinse them off and they’re sealed in a little brass tube, and we put them in as they’re coming to the surface.
“If it’s oil based mud - you know those little tea balls when you make tea, you have the leaves of tea and you kind of bob it up and down - we fill those with cuttings, take a hose to it and wash the oil based mud off of it,” he said. “We never use solvents; we don’t use detergents; we don’t use diesel; we just use water from the hose to get rid of the oil.”
Cryo time The captured cuttings are fed into a cryo trap mass spectrometer invented and built at AHS, Smith said.
The measurement of volatiles from drill cuttings relies on an extraction and analysis technology that utilizes all of the volatilizes in the cuttings sample, he said.
“Volatilizes from samples are frozen onto liquid nitrogen traps and analyzed by allowing the frozen volatiles to sublimate and enter the mass spectrum spectrometer, according to their sublimation points under high vacuum,” he said. “With the cryo trap mass spectrometer, if it freezes it’s gonna get analyzed - so you see everything; you see the hydrocarbons; you see the organic acids; the inorganic acids.”
Helium and methane are analyzed prior to beginning to warm the cryo trap as they aren’t frozen.
“Some things don’t freeze: the helium and the methane are two biggies; we catch them in a little valve and then we burst them into a pipe by themselves.
“It’s kind of like the butcher and the pig, ‘everything but the squeal;’ we even want to catch the squeal.”
Volatiles are extracted from each individual sample at two distinct pressures. This provides a measure of compound separation and quantification like that obtained in gas chromatography-mass spectrometry systems - however unlike GCMS this unique CTMS system is non-selective. All volatile compounds that can be extracted and frozen are analyzed.
“It’s non-selective.” Smith said. “Do I want to do core compounds, do I want to do noncore compounds … acids, non-acids?”
Multiple millibars “Our samples go into a little brass tube, a quarter inch in diameter, we come in with a piston and we squeeze them - we always squeeze with the same amount of pressure, we always put in the same amount of rock,” Smith said. “The soft rocks are very thin and the hard rocks are very thick, so we just measure that with a micrometer and plot it, and then we have permeability from cuttings.
“So how do you get permeability from cuttings? This machine was designed to do that,” he said. “We analyze each sample under two different pressures, the washed and dried samples we analyze at 20 millibars, we do a chemical analysis of that.
“Same exact piece of rock, same sample, we pull out another extract at 2 millibars - so first a 50th of an atmosphere then a 500th of an atmosphere; we analyze that and then we compare those and that’s what lets us do permeability.”
High is low At the beginning developers at the company thought the higher pressure - 20 millibars - would yield more oil and gas from high permeability rocks.
“It turns out to be just the opposite,” Smith said. “The real high permeability rocks don’t give anything at 20 millibars and they give a lot at 2 millibars.
“Between the drilling and coming up two miles in the mud, and washing, and drying, and everything else, your good reservoir rock - you lose your oil and gas from those.”
“Old timers like me will talk about seeing a core: ‘if it doesn’t bleed oil till it gets to the surface, it’s probably too tight to produce.’
“It’s the same thing with cuttings, if you have sub-millimeter cuttings and they’re still loaded with oil and gas, they’re probably not going to produce much of anything,” Smith said.
“Then we have stuff that tells us about the nature of the oil,” he said, adding, “The benzene/xylene ratio is very important for mapping oil migration pathways.”
AHS delivers two kind of logs, a property log and an oil and gas component log.
“We use about 400 microliters of rock, so that’s a little bit less than a tenth of a teaspoon,” Smith said. “We like to get a teaspoon if we can; we can go down to 200 microliters if we have to.”
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