Minipermeameter gives field data

Downhole Device Idea Applauded

Two engineering societies recently presented major awards to AAPG member Cynthia L. Dinwiddie.

The Small-Drillhole Minipermeameter offers a different way to determine permeability in the field. Users, knowing the injection pressure, can determine the rate at which the gas flows through the rock and apply standard formulae to determine permeability.
Photo courtesy of Cynthia Dinwiddie
The Small-Drillhole Minipermeameter offers a different way to determine permeability in the field. Users, knowing the injection pressure, can determine the rate at which the gas flows through the rock and apply standard formulae to determine permeability. Photo courtesy of Cynthia Dinwiddie

For her paper, "The Small-Drillhole Minipermeameter Probe for In-Situ Permeability Measurement," Dinwiddie received the 2007 Rossiter W. Raymond Memorial Award from the American Institute of Mining, Metallurgical and Petroleum Engineers and the 2007 Alfred Noble Prize from the American Society of Civil Engineers.

Both awards recognize the best papers authored by a person under age 35.

Dinwiddie’s paper documents her work on:

  • Understanding the effect of the measurement instrument on the natural system.
  • Size and shape of and weighting within its averaging volume.
  • General guidelines for its use.

Her paper was published in December 2005 in Reservoir Evaluation & Engineering, a Society of Petroleum Engineers' journal, although Dinwiddie presented an earlier version at the 2001 AAPG Annual Convention in Denver.

"It was unexpected, but it's really nice," she said of the honors.

Dinwiddie was sole author of the paper, which evolved from her doctoral work in Clemson University's Environmental Engineering and Science program.

She and colleagues at Clemson University have a statutory invention registration for the device.

Problem-Solving in Utah

The small-drillhole minipermeameter, according to Dinwiddie, offers a new way to measure permeability in the field.

Previous techniques involve extracting a small cylindrical sample from a drill core, placing it inside a sleeve and injecting nitrogen at one end. Knowing the injection pressure, the user can determine the rate at which the gas flows through the rock and apply standard formulae to determine permeability.

The new idea came while studying a Utah sandstone formation, Dinwiddie said, where the friable rock was not suited to sample extraction.

"We had an outcrop analog for a reservoir system but couldn't extract the cylindrical samples," she said.

The crew noted the ease with which holes were drilled in the rock for securing ladders, and began thinking in a new direction. The idea arose to sample permeability from inside the holes.

"Instead of gas flowing in one-dimension (as in a Hassler sleeve), gas injected by a minipermeameter flows in many directions,” she said.

The small drillhole probe takes the minipermeameter concept and makes it widely applicable for in situ measurements. A torque wheel at the back of the probe seals the device tightly into the hole. Nitrogen is injected through the center of the probe.

In addition to calculating geometrical factors for the new probe, Dinwiddie and her colleagues demonstrated that the energy dissipation rate in the sampled rock volume provides a map of spatial weighting.

Regarding the general concept of spatial weighting functions for measurement instruments, she said it was “an interesting problem to work on," adding that potential applications include fluid, thermal and electrical flow fields.

Out of This World

Dinwiddie, a senior research engineer in the Geosciences and Engineering Division at Southwest Research Institute® (SwRI) in San Antonio, is vice chairperson for the Division of Environmental Geosciences’ program at this year’s AAPG convention in San Antonio.

Her duties are not limited to this planet.

Her work at SwRI includes:

  • Geophysical and geological characterization of terrestrial analogs to Mars.
  • Geomorphologic and hydrologic studies of Martian outflow channels.
  • In situ field measurement and analysis of heterogeneities within volcanic rocks.

She received a NASA grant to study natural analogs to Mars using ground penetrating radar, electrical resistivity imaging and more traditional characterization methods.

Dinwiddie also uses topographic data from channels on the Martian surface to reconstruct information about ancient floods.

She continues to publish recent results from field surveys in which the small-drillhole minipermeameter was used to assess secondary heterogeneities (caused by faulting) in volcanic deposits.

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