|
New technologies for Alaska geology
Automated scanning system analyzes and logs fine-scale rock properties of the Nanushuk — merged with wire logs, published data Steve Sutherlin for Petroleum News
“The future is now” was the unspoken theme at a May 31 technical breakout session in Anchorage at the state Geologic Materials Center focused on the potential for new investigative technologies and machine learning systems to better assist geologists and resource companies to meet the challenges of interpreting Alaska geology.
Dr. Ramil Ahmadov, principal scientist, New England Research Inc., spoke on the use of his company’s automated scanning system - AutoScan - to analyze fine-scale rock properties and automatically log rock properties in the Nanushuk formation of the North Slope.
“Using a fast, nondestructive and relatively cheap and not real labor intensive system, we can acquire a lot of data and that data could be mined or as we call it, massaged, and some useful things might come out of it that we can then use in propagating a system that actually mimics the reservoir conditions,” Ahmadov said.
AutoScan is an integrated system for scanning slabbed core, whole core, or core plugs for gas permeability, resistivity, ultrasonic compressional and shear-wave velocities, composition, mechanical strength, and elastic stiffness, according to NER.
Ahmadov and his co-author Gregory N. Boitnott scanned a 40-foot slabbed core section from the 760-foot level to the 797.9-foot level of the Umiat 18 well, in preparation of their report, “Non-Destructive Automated Scanning of Fine-Scale Geological, Petrophysical and Geomechanical Rock Properties of Nanushuk Formation.”
“AutoScan, the name misrepresents the actual outcomes because usually when people think or hear scan, they think about CT scanning or some other scanning where you are actually not measuring the direct rock properties,” Ahmadov said, adding that 90% of the device’s outcomes or measurements are actual physical property measurements.
“It works with all sorts of core from regular or irregular shaped core sidewall rotary slots, lap core, whole core, even sometimes cuttings if they’re competent enough, and what the system provides is a number of different physical property measurements down to millimeter scale,” he said.
AutoScan shines in a trio of functions, Ahmadov said: rock typing; an ability to optimize the quartile integrations and upscaling to merge the data with wireline logs; and thirdly, the data can be incorporated into the petrophysical model directly from the device - there is no post-processing.
“If you’re a geologist you’re primarily interested in mineralogy, if you’re on the reservoir engineering side, or the petrophysics side, you’re interested in the acoustic, electrical and hydraulic properties, and those in geomechanics are interested acoustic and mechanical properties,” Ahmadov said.
Nanushuk AutoScan The section of Nanushuk core that was used - primarily composed of sandstones and shales - “was analyzed and measured at 5-millimeter-scale to quantify heterogeneity in sonic velocities, FTIR, permeability, and mechanical properties (Young’s modulus),” according to the report abstract. “The measurements were then compared and complemented to/with more conventionally derived triple-combo of gamma ray, density, and resistivity (wireline logging) measurements.”
After obtaining FTIR (Fourier-transform infrared spectroscopy), velocity data, and permeability, the FTIR is subdivided into four categories indicating clay, carbonates, silicates, and oil signature - which is basically staining of the material, Ahmadov said. As to velocity, Vp and Vs are obtained to use the two in combination as a Vp/Vs ratio (ratio of compressional wave velocity to shear wave velocity).
“We round these measurements at around 5-millimeter resolution so we’ve got about 2400 measurements of each of these different properties on a 40-foot interval,” he said.
Finally the data from the auto scan is analyzed and merged with the published data and the wireline logs from the Umiat 18 well - “which had that triple combo data.”
Using the color-coded display of the core interval from the combined data, Ahmadov was able to show a transition between the shale dominated to somewhat cleaner sands.
In a display color coded by resistivity versus the same quadrant color-coded by porosity, Ahmadov could differentiate not only the shales from the sandstones, but also look at the variation of the sandstone quality within that interval.
“From the other perspective again very straightforward petrophysical plots here, gamma ray versus resistivity color coded by density again, we have the differential between sandstones and shales,” he said. “Now we try to bring data from the AutoScan onto this particular interval; we’re looking at the oil indicator so anything here above five would indicate strong staining of the core - it can differentiate your reservoirs from your non-reservoirs and this is color coded by the clay.”
Later in the presentation, Ahmadov isolated a 9-foot core interval.
“If you were to draw conclusions from the wireline logs, in that 9-foot interval you would be confined to about 18 measurements and how much value you can add from 18 measurements from wireline and log data is questionable,” he said.
“The corresponding AutoScan data has hundreds of different points,” he said. “The message here is that just within that 9-foot interval, if you were to use the AutoScan data you can differentiate in terms of the lithology as a function of the permeability for all that data and you’ll figure out that there are more than two orders of variation over a 9-foot interval and almost a 50 times variation in elastic properties over the same interval.”
| 