The Exploration Directive
CAGC
Column:
The
Exploration Directive
DOUG
IVERSON
CANADIAN ASSOCIATION OF GEOPHYSICAL
CONTRACTORS
CAGC
represents the business interests of the seismic industry within Canada –
cagc.ca
The CAGC article,
June 28, 2022, discussed the changes to 13 sections of The Exploration
Directive, associated with the geophysical Exploration Regulations. Many of the
changes were administrative in nature but several changes were operational.
Most of this article will discuss the significant operational change.
At the annual
Regulator/Industry September meeting, the Alberta Energy Regulator (AER) and
Alberta Environment and Parks (AEP) gave a joint presentation. The AER/AEP
presentation included a very good brief summary of all the changes adopted
within The Exploration Directive.
That presentation
can be found on the cagc.ca website or with this link: https://cagc.ca/index.php?DL=dViIxR
Slides 4 to 16 of
their presentation highlighted the changes to the various Sections of The
Exploration Directive. The slides are a good reference guide to determine which
changes could impact you.
As mentioned
earlier, many of these changes were administrative with Section 15 being the
major technical and operational transformation. Section 15 deals with the
Distance Requirements for energy source proximity to specified structures. This
update is significant as it may improve shallow subsurface imaging.
The Exploration
Directive can be found here: https://open.alberta.ca/dataset/cc5d9ee6-faab- 4ada-b399-1d5beeddad9c/resource/ddbd8c08-d379-434b-a103-b14c40b950dc/download/aep- exploration-directive-2022-04.pdf
The following
is a 50,000-foot view of the main things you should know about Section 15 and,
at times, will drop to a 50-foot level to ensure you maintain regulatory
compliance. The first four items listed below could easily become
non-compliance issues if you simply repeat a 4D, as recorded previously.
1.
Previously, low-pressure pipelines had a minimum
offset distance of 3 m for explosive sources that were 20 kg or less. Now there
is a Scaled Distance requirement for low- pressure pipelines which requires
greater offsets than used before. That means, if you are
2. Dams
within The Exploration Directive have a new definition. This new definition now
includes many more dams across the province and also includes tailings ponds.
There is no reduced setback allowed at this time and the minimum distance is
200 m for an explosive charge and 50 m for a lower fundamental force vibrator.
Dams are structures that provide live storage capacities of 30,000 cubic metres or more and are 2.5 metres or more in height; or, are structures that are classified as being a significant, high, very high or extreme consequence in the Dam and Canal Safety Directive under the Water Ministerial Regulation; or, are structures that exist for the purpose of storing flowable tailings.
3. If you add new dynamite locations to an existing geophysical program, you will very likely require a program tag to mark the location. These were previously called permit tags.
4. The “Setback distance with consent of the owner” within the Tables means written consent and must be produced to the regulator on request. You may also need a strategy to acquire consent from the owners of structures. The CAGC had an example permit form that was used previously for written consent. You will need to develop a newer document for consent.
5. The usual protocol, if you load a seismic charge into a seismic shot hole is to check the integrity of the detonator. If the detonator fails (very rare) the driller then places a second charge on top of the first charge. The intent is to sympathetically detonate the first charge. While this is the best practice to manage a potential misfired charge, you could be in non- compliance by virtue of charge size and distance to a structure. In a situation like this you may wish to measure the Peak Particle Velocity (PPV) close to the structure.
6.
Now you can get closer to company-owned
structures, such as water wells, piezometers, observation wells, and buildings
with consent. These structures are listed in column C and include structures
owned by other companies. Ensure your
internal company departments, responsible for said structures, are aware you
may be using energy sources closer than previously.
7. While
you could approach a structure with continually smaller charges, simplicity is
much easier to manage. Let’s say 11 m is the nearest offset you would like from
a company- owned structure. If you were mainly using 2 kg, then consider using
2 kg charge to as near as 64 m (with consent) and then everything closer
becomes either 0.250 or 0.125 kg (just pick one). Ensure you have robust
administrative and field controls to manage this. Introducing greater
complexity using numerous charge/distance options could allow things to go awry
very quickly.
8. Your
geographic location and near-surface ground conditions could be very different
from all of the areas previously tested in the province. There is an
expectation, within Section 15, you maintain vibration levels below certain
thresholds. If you are working in an area with unusual material (a very compact
near surface material like a drill pad), you could have vibration levels above
expected values.
9. You
can get even closer to these specified structures (excluding dams) with an
approved request from the regulator. The main intent of including smaller
charges to the Table was to provide a safe Table of Distances for specified
structures that could be used without having to adopt PPV monitoring on all
programs. You will likely have to include PPV monitoring in any proposal to get
closer than the current specified Distance Requirements.
10. While
it may be safe to get significantly closer with sources to some of these
structures it was decided that: a)
the Distance Requirements should follow the previously accepted Scaled Distance
formulas, b) getting closer than 5 and 8 m from structures with mobile
equipment becomes another risk (vehicle hits the structure), and finally c) the
predicted vibration trend as you decrease the offset distance below 6 m may
have a greater PPV response than predicted.
Here are some other important aspects to consider:
1. An
operator may be in regulatory compliance with a closer offset but will remain
liable if there is damage to a structure. The onus may be on the operator to
defend themselves and prove the damage was not caused by their energy source,
as this will likely become a strict liability case. PPV monitoring and a
pre-inspection is the best defence for an issues like these.
2. Some
structures are more susceptible to shear forces than vertical forces. Think
about standing on a small wooden platform. The platform is hit from below,
upwards. You would probably remain fairly stable. If that platform were hit
from the side (think pulling a rug out from underneath you) you may perhaps
topple. The natural frequency of most residential structures ranges from 4 to
12 Hz. When seismic frequencies are in this range the structure may shake more
vigorously. Above 20 Hz, very little seismic energy transfers to the structure.
An old wooden shed near collapse could perhaps be toppled easily by excessive vibrations.
3. If
you introduce large shear wave vibrators or spend a great deal of time sweeping
between 2 and 18 Hz you could generate constructive wave interference. In most
cases, vibrators do not transmit much low-frequency energy into the ground as
the hydraulics simply cannot deliver [a 62,000 lb vibe generates 6700 lbs at 2
Hz, and 31,000 lbs at 5 Hz]. As technology evolves and more low-frequency force
may be achievable, consider PPV monitoring and adjust the setback distances accordingly.
4. As
dynamite use evolves, one may have to consider: fly rock, air blast, and shear
wave energy. Our dynamite sources are generally confined (stemmed hole), have
been in the ground a while (sluffing of material and frozen in), and the blast
noise is attenuated by the depth. If one was to use, very shallow charges or
larger charges, detonated immediately after drilling, and the holes were
plugged with rocky material you could generate fly rock. Shallow holes, Poulter
blasting, or very large charge sizes can be louder and unpleasant. Very large
air blasts from quarry blasting can damage windows (rarely a geophysical issue)
so be aware. Additionally, if you were to use detonating cord in shallow
trenches, as your energy source, you could perhaps generate more shear waves
than an a similar weight of explosive charge at depth.
Previously when
conducting geophysical operations there were several junctures where
individuals could potentially discover a non-compliance issue and prevent
detonation or triggering of the source energy. An example could be a HP
pipeline missed by the survey crew. This could perhaps be noticed by other
individuals on the program observing pipeline markers, trench, uplift, well
heads, … where the drill location was marked. With all source points the
following people could potentially catch an error: program designer, QC
reviewer, chainer, surveyor, driller, another senior person on program, the
seismic blaster or helper, and finally the recording observer. You may still
have a problem if you drilled and loaded the charge, but the checks and
balances could prevent initiation of the charge. Again, in cases like this it
would be recommended to share the information and PPV monitor the event.
Clearly, if you
plan on introducing different charge sizes within your program, ensure robust
protocols are adopted to ensure compliance. Simplicity is the key to success.
Further
information can be obtained by contacting the Canadian Association of
Geophysical Contractors or the Alberta Energy Regulator at info@aer.ca.
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