Core logging: Optimizing best practice (Part One).

Data derived from diamond drilling cannot be bettered for geological modelling – as long as the log tables are correctly formatted, and the logging phases are correctly scheduled.

Rig-side logging.

Core denatures after extraction and some sections, such as sheared, or altered lithologies, deteriorate more quickly than others. Whilst these intervals are usually small and seemingly insignificant, they can ultimately prove to be the ruination of a project if they are not properly recorded and analyzed. Metaphorically, these transient zones are the “lions in the game park” and, like any predator, they are rare and difficult to spot as they rapidly weather and disappear into the dust of the undergrowth.

It is only by working rig-side that such high risk, red data is captured. Geotechnically, 24/7 rig-side logging is mandatory, to at least profile intact rock strengths along the length of the unspoiled core before any of it degenerates, as well as to record all natural fractures in their pristine state, noting any soft fracture fills and textures especially, since these all have low preservation potential and rarely survive transportation to the core shed.

This 24/7 requirement is particularly true if any advantage is to be gained from triple tube drilling. The whole point of pumping the splits onto an angle iron – so as to carefully lift the top section and reveal the undisturbed contents of the inner tube – is lost if there is no professional present to meticulously go through the sample. Any rubble must be closely examined to determine if the zones are due to natural causes, indicating a predator, or whether they are due to mechanical issues, if the fragments are sharp-edged for example. Then natural fractures have to be distinguished from mechanical breaks, not only to record their descriptors, as noted above, but also to measure their angles if the core is oriented, as well as accurate RQD’s, which index is badly affected as healed joints open with exposure to the elements and core tray movement.

Driller interaction.

Naturally, such a logging regimen is beneficial to both parties. The logger gains an understanding of how the different properties of the rocks intersected affect the drilling process, which observations profit the driller directly. Hence, the opportunities for meaningful continued professional development on the job are priceless, and more so for collating intelligence as to what equipment, consumables, and practices work best for the ground under investigation – a useful resource for subsequent drilling campaigns.

Mechanical fractures, instances of core grinding and rubble zones, can be discussed with the driller to determine if they are due to vibration from a worn drill bit, or a misaligned drill string, or some other factor that may require a mud-mix specialist to improve the clearance of cuttings from the drill face, or to reduce problems caused by swelling lithologies.

Other responsibilities include front-line quality control, to ensure accurate borehole depth measurement, so as to optimize core depth registration – presupposing the driller is released from minimum core recovery penalties, the unintended outcomes of which are discussed in the third post of this series (3_Drill core quality and borehole depth measurement).

Allied to this is the importance of replacing worn core springs or changing from a fluted to a slotted core lifter depending on hard or soft, steatitic lithologies, to minimize slippage when raising the drill string in order to engage the lifter and break the core as close as possible to the bottom-of-hole at the end of every drill run. This is vital to prevent artificial core losses and gains that give rise to overlapping sections, which confuse the uninitiated when depth registering the core using the standard method (1_The depth registration of drill core).

Close supervision must also be given to the borehole surveys (4_Borehole Surveying – money drain, or cash cow). In addition, if the core is oriented, oversight is necessary by measuring the orientation line offset between contiguous runs, to calculate the cumulative offsets and determine whether the orientation tools are working to specification, as outlined in the fifth post (5_Orienting drill core – squandered opportunities). If not, to immediately stop the drilling and either re-calibrate the instruments or swap them out.

Core shed logging.

After the preliminary rig-side logging phase, the core is transported to the core shed to be examined in detail and sampled in a controlled environment. However, even though diamond drilled boreholes and the core produced have been the primary source of information for planning the development of mining and construction projects for more than a century, the formats of the log tables used on many projects are still badly designed, but perhaps of greater concern is the fact that experienced loggers are, and always have been, few and far between.

Thus, by default the bulk of the task is usually assigned to new graduates, few of whom stay long enough to gain the requisite knowledge and become sufficiently skilled to train others to perform competently. This dilemma could be solved if suitable courses were to be incorporated into undergraduate curricula. Curiously though, industry has not promoted or requested such measures at earth science institutions – even though much of the data most geologists and geotechnical engineers are employed to generate, analyze, interpret, and model, are derived from examining costly, cylindrical rock samples in endless lengths of varying diameter – not hand specimens knapped from outcrops.

Could it be that this lack of practical knowledge in firstly understanding the workings of a relatively simple sub-surface sampling technique, and secondly how to gather consistently high-quality data from such a major source of information, be a significant contributor to the latest trend in tertiary education – a rush to defund earth science departments?

What impact does core logging have on the future of Earth sciences?

The seriousness of the situation is plainly evident in the following statements, quoted from the editorial of Nature Reviews, Earth & Environment volume 2, published this month, September 2021, under the headline Geoscience on the chopping block. https://doi.org/10.1038/S43017-021-00216-1 viz:

• “Universities are ruthlessly cutting geoscience departments, funds and staff, bringing a terrible blow to Earth science research worldwide.”
• “Academics found themselves stranded, postgraduates were left without supervisors, and undergraduates faced transfers to other institutions.”
• “Culling Earth science talent pools, rather than increasing and nurturing them, is incredibly impetuous and will have long-term negative consequences — without geoscientists there will be no sustainable future.”
• “There are many inaccurate perceptions that geology graduates’ only career options are in the oil industry.”

Are these exaggerated claims, or is this a real threat? Alarmingly it would appear so, otherwise how can the closure of centres of excellence, some of which are listed in the editorial, that have built up enviable reputations for top-flight research supported by well-equipped laboratories, be explained? Surely the very elect intelligentsia of the world in the exalted halls of academia cannot be so confused as to suppose that these institutions, along with their collaborative international ecosystem of smaller departments, have completed their mission?

Do we now know enough about the makings of our planet that the tempo of pure research can be dumbed down to this extent? Or is the decision purely a numbers game: Low student enrolments, equals low interest, equals reduced budget allocations, equals cut-backs until closure is inevitable? Earth sciences are used to such demand cycles, driven largely by mineral economics, but, in the main, industry has not reduced support for these programs over the tough times, so as to be sure that they will continue to be well served with high performers when fortunes turn around.

What is happening now? Was industry caught off-guard by the indecent haste of these ruthless measures? Could the idiocy that the only employers of geologists are in the ill-fated oil industry, which it is now politically incorrect to sustain, be an argument that carries weight in these decisions? Have the geosciences a diminished role to play in developing alternative energy resources? Why were the professors, tasked with defending the very survival of their departments in the various faculty and university senate debates, not able to convince their colleagues that, if anything, their discipline should be boosted and strengthened as it alone holds the keys to ameliorating the excesses of the Anthropocene epoch, while still enriching civilization?

How can the members of our profession assist and instigate an urgent turnaround? That is a huge topic, but to return to the lowly core shed and our original query as to whether logging prowess may also be partly responsible. Because, if this is not the case, why are the engineering faculties that train our customers – the mining and civil engineers, and metallurgists – not equally affronted by the degeneration of the geosciences, and the consequent inability of the smaller graduate pool to service their industry properly?

Is it because we tend to shrug off the sometimes gross inaccuracies that are exposed in our subsurface models as dirt is extracted from the mine, by saying that ours is not an exact science? Could the expectation used to lure investors, that semi-robotic solutions using artificial intelligence, machine learning, cloud computing, hyperspectral scanning, and big data manipulation, will be far more effective and reliable than ‘eyes-on-core’, be true? Ergo geologists, at this level at least, are all but dispensable?

Such a sentiment was succinctly expressed in a recent post, ?https://www.dhirubhai.net/posts/michelle-tappert_hyperspectral-hyperspectralimaging-innovation-activity-6833766273952944128-agt0 , viz: “After running this company for five years, I can honestly say two things: (1) Logging drill core visually is very difficult because humans are subjective observers that are easily distracted, and (2) with the aid of technology, geology is now starting to push itself [into] a new age of objectivity and accountability, which is long overdue.”

Has it really come to this? Is it to be believed that semi-robotic interventions are capable of taking over? Are the stranded academics and supervisorless postgraduates to be ostracised and left to mutter incoherently to each other in bar corners? Is the commercially astute assertion that loggers are easily distracted and subjective observers, requiring more accountability, justified? Are we not dedicated professionals that desire the technological advances of the ‘new age’ to be seen for what they are – just as valuable aids for our work as the invention of the polarizing microscope, downhole geophysics, Landsat multispectral imagery, etc., etc.?

On 23rd September Landsat 9 will be launched, almost 50 years after Virginia Norwood designed and developed the multispectral scanner which was carried by the first satellite. Meet the Landsat pioneer who fought to revolutionize Earth observation | Science | AAAS . This instrument played a major role in ensuring the Landsat program, a joint effort by NASA and the U.S. Geological Survey, and the Landsat database became the gold standard in Earth imaging. There was no suggestion then that the technology would reduce ‘boots-on-rocks’, but rather it was rightfully seen as the indispensable aid it has become for ground-truthing and more detailed mapping.