Legions of aspiring geologists have enjoyed (endured?) the challenge of summer field camps where they spend their days traipsing across rugged terrain – often in the Rocky Mountains – to map the territory.
Until fairly recently, any thought of someday trading alidades and plane tables for fixed wing aircraft to use remote sensing technology to handle mapping chores would have been only a fantasy.
But we’ve come a long way, baby.
Airborne LiDAR (Light Detection and Ranging) remote sensing technology is much in vogue in the industry today, largely because it continues to make integral contributions to the exploration game.
High-flying technology is an apt description given that LiDAR measures surface elevation via a laser scanner mounted on a fixed wing aircraft or helicopter.
It’s particularly useful to provide an accurate high-resolution representation of the earth’s surface in areas having steep terrain and coniferous canopy – so long as the light can penetrate.
“LiDAR mapping technology enables rapid collection and processing of datasets used to develop an accurate and detailed digital terrain model within three inches of elevation,” said Jerry Boyd, project manager at Merrick & Company in Aurora, Colo.
He summarized some of the applications:
- Support well pad site selection.
- Improve drilling permit application approval.
- Hyperspectral imagery can be used to perform oil seep anomalous zone detection.
“We map the entire area and the client gives us criteria, such as pad requirements they want to achieve, like distance to navigable roads, maximum acceptable slope, proximity to a water source for permitting requirements,” Boyd said. “We run an analysis on the surface model after we process it and do initial probable pad identification for them – this lets them better focus on these areas to do field investigations to decide which ones to use.
“For the drilling permit and approval process, they have this very accurate information and analysis they can show to the BLM,” Boyd said.
“This validates why they want a permit at this specific location, based on these parameters.”
Step by Step
Hyperspectral imagery is the arm of this technology that really gets into the intricacies of the land and the vegetation.
A regular color image has three bands of light – red, green and blue. Each band has 0-255 values of saturations of that color.
Hyperspectral imagery covers a much wider range of the light spectrum.
“The two main light spectrum ranges we use are visual near infrared (VNIR) and short wave infrared (SWIR),” Boyd said. “In the range of these, we have 359 bands of light we can analyze, and each of these bands has 255 values.
“You could see two different kinds of trees that appear to be the same when looking with the naked eye,” he said. “Using hyperspectral imagery, we can track things down to the individual species of vegetation, as each vegetation type has its own specific signature across this band of information.
“Besides looking directly for hydrocarbons, we can detect distressed vegetation,” Boyd emphasized. “Where oil is seeping to the surface, the vegetation is growing in an environment that’s not normal soil composition; this is referred to as a geo-botanical halo that basically indicates there’s distressed vegetation in this area.”
The technology also can be used to detect specific minerals in the soil and to identify mineral alterations that are a direct result of hydrocarbons in the soil. These mineral alterations differ depending on the predominant soil composition.
“When we run the analysis on hyperspectral imagery, we’re trying to find coincident occurrence of multiples of these conditions to give us the highest probability there’s oil seepage in the area,” Boyd said. “We’re rank ordering all these anomalies we’re finding and coming up with a statistical analysis of the probability there’s oil in the vicinity.
“Then we or the oil company go to the field with a (portable) spectrometer and go to the high probability sites to collect spectral signatures in a much more macro environment,” Boyd added. “We do soil or liquid sampling and have lab analysis done to confirm the presence of hydrocarbons.
“When you’re looking at big tracts of land, hyperspectral is a much lower cost alternative to more costly exploration processes,” he noted.
A Costly Choice
LiDAR application has become almost routine for seismic data contractors in rugged areas like the Rockies.
For example, when implementing a data acquisition program using dynamite as the source, it’s common to move the dynamite onto the location via a buggy or truck. However, this may be impossible without specific data for the rugged terrain – and a helicopter may be required to drop in and then retrieve a heliportable rig, which can eat up a bundle of greenbacks.
Using LiDAR-derived data the contractor can adjust the target points for drilling the shot holes such that they become accessible via drill buggy or vibrator, which is considerably less costly than the alternative.