4
lateral certainty spot sampling or through gas desorption
and isotherm testing. Permeability data is typically sparse,
and desorption rates and sorption capacity are derived from
laboratory-based tests.
The authors support a change to this methodology
by adopting a risk-based approach that measures a much
greater volume of actual coal seam gas reservoir data and
incorporates a strategy of risk management that propor-
tionally considers the many elements that affect gas out-
burst risk.
The tools now exist to vastly improve our understand-
ing of the gas reservoir properties of a coal seam, where
underground in-seam drill-mounted gas analysis systems
can provide vital geological and gas reservoir data, includ-
ing gas content and make, desorption rate, permeability,
RSI, and Gas Pressure continuously within a borehole. This
provides a database of essential data for the entire length of
an in-seam directionally drilled borehole. Instead of rely-
ing entirely on sporadic and potentially unrepresentative
core-based data, a holistic view of the coal seam gas res-
ervoir ahead of the face is now attainable with the Yabby
GeoSensing System.
Yabby-derived RSI values identify zones of weak coal
that may present an increased outburst risk (see Figure 3).
Another development brought about by the Yabby
GeoSensing System is real-time measurements to deter-
mine dynamic changes in gas flow properties within in-
seam boreholes (see Figure 4 and Figure 5).
Filtering noise from gas surges is the main obstacle for
gathering meaningful gas flow data from in-seam bore-
holes. It is well known that in-seam boreholes produce gas
during drilling. It is less well known that the gas produced
during drilling is a combination of gas that is progressively
released from the formation surrounding the hole, and gas
released by the drilled coal cuttings. By analysis of a con-
tinuous total gas rate signal, the component signals may be
separated and utilised to directly measure gas-related prop-
erties during drilling.
A gas flow rate sensor is installed on the gas outlet of
the Yabby Geosensing System’s water/gas separator. The
capacity of the gas sensor may be tailored as necessary to
accurately observe gas rate and gas rate dynamics.
The signal interpreted by the Yabby Geosensing System
contains multiple layers of information that must be sepa-
rated, including a cumulative gas rate (in litres per second)
which provides the baseline data (as gas from the entire
borehole continues to contribute to the total) and a tran-
sient gas rate which reflects the effect of cutting through
new parts of the strata. Separating the ‘noise’ from the bal-
ance of the signal results in a Formation Gas Production
Figure 3. An example of an RSI log generated from the
Yabby GeoSensing system shows relatively stronger and
weaker parts of the formation. A crush zone (green) related
to a structural disturbance is obvious. Non-coal zones show
up as grey-brown
Figure 4. An example of an underground directionally
drilled borehole and interpretation showing a substantial
fault and higher gas emissions (red) around the structure.
Integration of the model with vertical boreholes (if available)
is part of the process -in this case, two vertical boreholes
have been utilized as data inputs
Figure 5. Outburst event measured downhole. Note sudden
peak gas influx (green) and steadily increasing density of
returning drilling fluid (red) due to structure-related crushed
coal flowing into the borehole
lateral certainty spot sampling or through gas desorption
and isotherm testing. Permeability data is typically sparse,
and desorption rates and sorption capacity are derived from
laboratory-based tests.
The authors support a change to this methodology
by adopting a risk-based approach that measures a much
greater volume of actual coal seam gas reservoir data and
incorporates a strategy of risk management that propor-
tionally considers the many elements that affect gas out-
burst risk.
The tools now exist to vastly improve our understand-
ing of the gas reservoir properties of a coal seam, where
underground in-seam drill-mounted gas analysis systems
can provide vital geological and gas reservoir data, includ-
ing gas content and make, desorption rate, permeability,
RSI, and Gas Pressure continuously within a borehole. This
provides a database of essential data for the entire length of
an in-seam directionally drilled borehole. Instead of rely-
ing entirely on sporadic and potentially unrepresentative
core-based data, a holistic view of the coal seam gas res-
ervoir ahead of the face is now attainable with the Yabby
GeoSensing System.
Yabby-derived RSI values identify zones of weak coal
that may present an increased outburst risk (see Figure 3).
Another development brought about by the Yabby
GeoSensing System is real-time measurements to deter-
mine dynamic changes in gas flow properties within in-
seam boreholes (see Figure 4 and Figure 5).
Filtering noise from gas surges is the main obstacle for
gathering meaningful gas flow data from in-seam bore-
holes. It is well known that in-seam boreholes produce gas
during drilling. It is less well known that the gas produced
during drilling is a combination of gas that is progressively
released from the formation surrounding the hole, and gas
released by the drilled coal cuttings. By analysis of a con-
tinuous total gas rate signal, the component signals may be
separated and utilised to directly measure gas-related prop-
erties during drilling.
A gas flow rate sensor is installed on the gas outlet of
the Yabby Geosensing System’s water/gas separator. The
capacity of the gas sensor may be tailored as necessary to
accurately observe gas rate and gas rate dynamics.
The signal interpreted by the Yabby Geosensing System
contains multiple layers of information that must be sepa-
rated, including a cumulative gas rate (in litres per second)
which provides the baseline data (as gas from the entire
borehole continues to contribute to the total) and a tran-
sient gas rate which reflects the effect of cutting through
new parts of the strata. Separating the ‘noise’ from the bal-
ance of the signal results in a Formation Gas Production
Figure 3. An example of an RSI log generated from the
Yabby GeoSensing system shows relatively stronger and
weaker parts of the formation. A crush zone (green) related
to a structural disturbance is obvious. Non-coal zones show
up as grey-brown
Figure 4. An example of an underground directionally
drilled borehole and interpretation showing a substantial
fault and higher gas emissions (red) around the structure.
Integration of the model with vertical boreholes (if available)
is part of the process -in this case, two vertical boreholes
have been utilized as data inputs
Figure 5. Outburst event measured downhole. Note sudden
peak gas influx (green) and steadily increasing density of
returning drilling fluid (red) due to structure-related crushed
coal flowing into the borehole