Improved modeling an ultimate beneficiary

Research Getting Unconventional Boost

American Association of Petroleum Geologists (AAPG)
Ken Peters
Ken Peters

Geoscience research is undergoing a renaissance, driven by favorable crude oil prices and the development of unconventional resources.

Research in geochemistry, especially, now rivals the recent period of significant advances in geophysics – today’s geochemists help define shale gas plays, analyze hydrocarbon sourcing and make important contributions to basin and reservoir analysis.

The effort to develop new types of oil production and facilitate improved oil recovery also has produced geoscience research relevant to conventional oil, heavy crude, shale oil and tar sands.

Reflecting the broad range of current work, recent AAPG Hedberg Research Conferences have examined “Applications of Reservoir Fluid Geochemistry,” “Geological Carbon Sequestration” and “Basin and Petroleum System Modeling.”

Upcoming Hedbergs will focus on assessment of shale resource plays, evaluation of carbonate reservoirs and enhanced geothermal systems.

Ken Peters, scientific adviser for Schlumberger Information Solutions in Mill Valley, Calif., serves as a chair of AAPG’s Research Committee.

“There’s a revolution going on in geology that has revitalized the exploration and development of petroleum resources,” he said, relating the recent upsurge in research to the development of shale gas and other unconventional resources.

“Just a few years ago in the United States we were talking about importing gas,” he noted. “Unconventional resources have the potential to drastically alter the global energy picture.”

Spotlight On …

Peters identified several current areas of interest in research:

Diamondoids and the extent of secondary oil cracking.

“Everybody is scrambling right now to do geochemical analyses,” Peters said. “One thing that has captured the attention of a lot of people in the industry is the diamondoids.”

“Diamondoids,” also called nanodiamonds, refers to variants of adamantane, the smallest molecular structure recognizable as a diamond. Put simply, diamondoids are three-dimensionally fused, carbon cage molecules having the structure of a diamond crystal lattice.

“Adamantane is the smallest pseudo-homolog in the series,” Peters said. “It’s got 10 carbon atoms and 16 hydrogen atoms, and it looks like a little ball.”

Diamondoids occur naturally in petroleum, and they have become an important indicator of oil maturity while helping to identify deeper crude sources, according to Peters. They also offer the potential to directly measure the extent of oil-to-gas cracking, which could greatly enhance our ability to identify and develop the most prolific zones in gas shales.

When younger crude is mixed with deeper, more mature oil, the deeper crude can be difficult to identify. Geochemists use diamondoids to gauge cracking and spot the likelihood of deeper sourcing.

“Usually, the deep source is so mature that there are no biomarkers – they’re gone. They’ve all been cracked,” Peters said. “Once you start cracking these things into gas, the diamondoids start piling up.”

Peters said geochemical analysis using diamondoids is a way to determine ultra-deep sourcing in oils.

“All the majors are doing piston core analysis all over the world,” he noted. “Diamondoids tell them how mature the oils are and if there’s a deeper source.

“That turns out to be critical in places like Saudi Arabia, where they have that deep Silurian source,” he added. “It’s also critical for offshore Brazil.”

Silica diagenesis and stratigraphic traps.

Studies in silica diagenesis deal partly with reduction in porosity as diatomite or opal-A transitions to opal-CT and then quartz.

“The funny thing is the opal-CT has low porosity but pretty good permeability. It’s a diagenetic trap. And in a diagenetic trap you can trap hydrocarbons on a monocline,” Peters observed.

“The question is similar to that in gas shalesn – where, for example, in a tight source rock can you expect to produce oil?”

Peters draws on his past experience in industry, government and academia. He now serves as a consulting professor for Stanford University’s Basin and Petroleum System Modeling Group, where students are working on various topics, including silica diagenesis research.

“We’re going to be adding this into a module in our basin-modeling program,” he said. “The kinetics can be used to assess depth better than just guessing. These rocks are all over the Pacific Rim – the Japanese are very interested.”

Carbon isotope rollover in gas shales.

Isotope rollover is an emerging research area of special interest in shale gas production. Rollover seems to occur at a vitrinite reflectance of about 1.5 percent Ro, said Kevin Ferworn, vice president at GeoMark Research in Houston.

The isotope rollover effect has been identified in the Barnett, Fayetteville, Haynesville, Woodford and Appalachian shale plays, as well as in the Horn River Basin in Canada.

“Ethane and propane and CO2, which normally get isotopically heavier (enriched in 13C) with increasing maturity, all get lighter (enriched in 12C) at about this 1.5 percent Ro point,” Ferworn noted.

“Also, the wetness of the gas drops along with it,” he said. “Sometimes this happens within 10 feet as you go through a formation.”

Conversely, the pressure gradient increases. Geochemists can use isotope rollover to identify the most promising – that is, the most gas-productive – areas in a shale gas play.

From a scientific viewpoint, one interesting thing about the reversal in the isotope trend line is that it shouldn’t happen, and no one seems to be sure why it does.

Ferworn said an early theory posited the rollover resulted from cracking as gas stayed inside the shales at high temperature and pressure, but the type of 12C-13C bond-breaking seen did not support that idea.

A more recent theory holds the rollover effect may be a natural steam reforming reaction, where hydrocarbons in the presence of water and a ferrous catalyst at 180-200 degrees C undergo a Fischer-Tropsch-like conversion.

“We’re still at the theoretical stage,” Ferworn said. “The main target for operators is that they get lucky enough to be in a rollover area.

“Whatever the mechanism is that causes this change in isotopes and decrease in wetness, it’s something to do with bigger molecules being replaced by more, smaller molecules,” he added.

Peters described the isotope rollover as “a little strange,” but it seems to work.

“It’s fascinating,” he said. “To me, it warrants a lot more study. I have some ideas but they’re based more on thinking than on experiments.”

‘The Frontier for Research’

Much of the current research in geoscience directly addresses challenges faced by the industry, producing work that is more practical than purely theoretical.

“A lot of this is flat-out exciting. The funny thing is, a lot of people in academia are not yet aware of this current revolution in geology,” Peters said.

Interest in unconventional resources and the higher oil prices have contributed to the recent upsurge in research – but sustained support for long-range research programs can be difficult to secure.

“Industry has always had this problem,” he said. “When the industry’s doing well, all these universities pop up with things that can be tied back to industry funding. Then when things turn down, most of these projects disappear.”

When the oil industry won’t commit to long-term research funding, it loses the benefits from research programs that produce their best results over a 10-year period or longer, he noted.

Today’s geoscience research is contributing to a better understanding of petroleum systems – basin and petroleum system modeling (BPSM) traces the evolution of sedimentary basins as they fill with sediments that may generate large hydrocarbon accumulations.

Using comprehensive modeling software, BPSM combines geological, geochemical, geophysical, hydrodynamic and thermodynamic data. It draws on dynamic processes that include deposition, faulting, burial, kerogen maturation and multiphase fluid flow.

“In my view, basin and petroleum system modeling is the Grand Central Station of the science right now. All the other research is feeding into it,” Peters observed.

“It’s the frontier for research,” he said, “and 20 years ago people said, ‘You can’t do it.’ We’re doing it now.”

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