GEO MRI | NMR Roadside Service in the Wild West: NMR signal / noise study @ FLORENCE-COPPER | AZ

Working Realm: Signal/Noise Optimization | Mineral mining | Geotechnics

Toolstring: NMR borehole probe 2.38 inch diameter

Max. Borehole Depth: approx. 1,200 ft

Inner Drill Hole Diameter: 4 in

After the marvelous moments in the ARCHES National Park, and acquiring high-quality NMR data at the UMTRA site in Moab | UT, we continued our journey through the vast landscape from Utah to Arizona. The next NMR-Roadside Service project was waiting for us there: FLORENCE-COPPER | AZ!

On the long transit through steppe-desert landscapes the spectator gets further insights on how hard both the native and settling people must have endured to conquer this piece of land and to make it a home for themselves. However, and as pretty much always in the history of humanity, it is a double-sided forged sword: on the one hand, the indigenous people in this region with their many tribes (here for example the Navajos), and who have been creating a life basis in “their country” for thousands of years. On the other hand: the settlers who practically invaded this new territory within a few short years around the half of the 19th century, and thereby always proclaiming that it was in behalf of "Following God's Voice".

Fig. 1: On the way from Moab | UT to Phoenix | AZ, the journey continues through long plains of the typical steppe and desert landscape, and along the region's adjacent mountains. Wild impressions as in Utah, providing some insight into the harsh life of the former tribal cultures in the region (e.g. the Navajos), but also that of the white settlers who began to subjugate this part of the world since the middle of the 19th century.

Even if the "Pioneers in the Name of God'" supposedly coexisted for a long while with the indigenous population in relative peace, one can assume that conflicts of interest in this region eventually could no longer be resolved in a friendly manner...

Fig. 2: The peace-loving settler pioneers of the region, who arrived from Utah and, according to their own statements, pushed further into the “New Land”, purely carried by the “voice of God”. Initially they faced enormous challenges which nature imposed upon them. Like most settler stories, these are on the one hand very impressive, but on the other hand they have the shortcoming, ultimately through the use of brute force, of appropriating what actually previously “belonged” to others. Like in mining | Gold digger | Mining in Colorado, blacksmithing was also a necessity here in order to conquer the “Promised New Land” agriculturally and in other respects with the appropriate equipment. As you can well imagine, “groundwater supply” was of central importance.

After a long day of driving from Moab|UT to Phoenix|AZ, we were able to start our work the early next morning on the premises of the copper production company FLORENCE-COPPER. For this purpose, the NMR Maestro himself, Vista-Clara Inc. company owner Dr. Dave Walsh, flew in from Seattle to track down the significant noise content previously observed in the NMR signals during logging in designated monitoring wells. Plus, figuring out how to overcome this handicap. Pioneering work in the name of science and technical innovation, indeed...

After a detailed (and very good) introduction to all safety aspects (HSE: Health|Safety|Environment) regarding the company premises and operations, we had liberty to spend the whole day dealing with this NMR signal/noise problem and to work on improving this shortcoming. In this case I was primarily "Observer" rather than "Team Lead" to watch and learn from Dave Walsh how he dealt with this technical problem.

In the first step we initially confirmed that no further improvements could be achieved through additional measures in the experimental setup. This glimmer of hope was immediately checked off within 2-3 test measurements. To deal with the challenge, Dave had to apply his engineering skills and modified the measuring probe right there on site, in a well-cooled and dust-free work room in the factory facility.

Fig. 3: NMR signal noise studies in one of the so-called “monitoring wells” on the FLORENCE-COPPER factory premises were carried out in order to fundamentally improve the previously poor NMR signal recording in the specified boreholes. On the factory site, the precious metal is not extracted from the ground using typical opencast or other mining methods, but rather through a chemical process that involves dissolving the material components and subsequent flushing from the mining depth to the surface. A whole series of geophysical sensors and flushing pumps installed in the well demonstrably generate a large amount of electrical noise, which is superimposed on the actual useful signal of the NMR measuring probe. This was confirmed on this one (1) day of use by our test measurements at various well depths between 100 and 600 ft. Based on this knowledge, a technical solution was subsequently sought and achieved throughout our logging day.

In addition to the technical challenges which we were facing that day (as it was in Utah), the heat beyond 105º F was the chief nemesis, potentially causing "dehydration".

In terms of "negative signal interference", another potential source of that kind for our NMR measurements turned out to be the surrounding weather conditions:Thick and rapidly moving storm clouds appeared in the sky by mid-afternoon on the day of our NMR test operation, enhancing the electrical charge in the atmosphere and thus potentially creating a negative impact on the measurements. Similar to our NMR operations at the Yanacocha mine|Peru, also here at FLORENCE-COPPER were precise precautionary measures and SOPs (Standard Operation Procedures) in place to react immediately in such weather situations.

Fig. 4: Negative NMR signal noise influences from weather events are known and have already been an issue in Peru. As was the case in the Yanacocha mine, there were also precise regulations at the FLORENCE-COPPER premise as to how the safety aspects of the emergency services and the technical installations on site must be ensured in the event of a thunderstorm. In this case, the storm passed us far enough away. Thus, the actual main interference signals in the NMR logging data were ultimately and clearly identified in the form of abundant electrical components in the well systems.

Dave had obviously done a good job, as the “noise”, caused by the other sensors in the well systems, could be blocked out reasonably well after his electrical re-engineering of the NMR probe. During a depth measurement at around 600 ft we suddenly observed almost no “noise” in the data. However, this pertained to this one single data record, and only once. When we re-logged again across this depth interval a few minutes later, the considerable amount of noise had reappeared in the NMR signal. Apparently a flushing pump in another well had switched off briefly and then switched back on automatically, causing the negative Signal-to-Noise-Ratio (SNR) phenomena.

In principle, this "data check" confirmed the negative influence of the electrical components installed in all the surrounding wells on the NMR data quality. Thus, generally speaking: In order to cope with this situation, technical and operational precautions must be taken in order to achieve recording acceptable NMR logging data for this particular location. However, the added value for such a temporary “optimization” for NMR measurements at that site would be considerable:

• In addition to the qualitative | quantitative assessment of fluid-flow properties of the actual earth formation, signs of material fatigue along the concrete injections forming the well walls can be made visible (by detecting flow in the concrete walls where none should take place, e.g., through small cracks).

• Formation | Fluid Permeability studies using NMR logging should certainly also be accompanied by other methods, e.g., high-resolution camera imaging and/or other technologies.

• In concert, such diverse data recordings would provide very good insight and allow conclusions about the type and size of unwarranted “contamination events” from this type of chemical mining operation, which potentially can harm the groundwater aquifer and/or surrounding formation through the copper extraction operations.

In that sense, innovative technologies for both material extraction and monitoring such operations want to go hand and hand to promote a safe and sustainable industrial mining process of that kind.

! Carpe Diem | Drink lots of H2O | Stay healthy !