I N NOVATI N G WH I LE DR I LLI N G
The multilayer mapping-while-drilling service doubles the depth of detection range
compared with conventional bed boundary mapping technology. The service
detected coal from 4 m away when drilling in the interburden and simultaneously
mapped the top and the base of the seam .
complexities including faults, fractures
and coal splits are often not characterized
by seismic data, resulting in sidetracks
that are especially challenging in coal.
Wellbore stability also becomes a chal-
lenge when the hole is open a long time
for drilling, logging and multiple trips.
Drillers must use measurements obtained
by crossing the litho-boundary, which
requires reactive steering.
In a geologically complex reservoir
in southwest Queensland, Australia, an
operator faced these and other unique
challenges for developing a CSG reser-
voir. The target formation was at the base
of a mountain, and because of restricted
mountain access, no seismic shooting was
allowed. The operator planned to drill pilot holes
for each dual lateral, but this did not miti-
gate risks linked with faults and structural
uncertainties. The restricted access also
prevented the company from drilling a
vertical intercept well. Instead, the project
required drilling a deviated intercept well
and intercepting the deviated wells from
both horizontal laterals.
The operator had an objective to drill
dual-lateral wells at least 1,000 m within
the seam boundaries, where there existed
a possibility of encountering faults with
unknown throws. The previous conven-
28 tional approach the operator used in the
area consisted of bottomhole assembly
(BHA) components including a motor, a
bed boundary mapping service, and an
integrated measurement-while-drilling
(MWD) platform. However, the conven-
tional reservoir mapping-while-drilling
technology had a limited depth of inves-
tigation of 2–3 m and only mapped one
boundary most of the time. Because the
area lacked existing wells, the technology
limited value for landing and exploring
the area.
To improve the depth of detection, the
operator used a BHA that included the
multilayer mapping-while-drilling ser-
vice, which detected coal from 4 m away
when drilling in the interburden and
simultaneously mapped the top and the
base of the seam. The BHA also included
the ShortPulse integrated MWD platform,
which provided direction and inclination
and gamma ray measurements, and the
PowerDrive Orbit rotary steerable system,
which provided near-bit gamma ray, incli-
nation and azimuth.
As a result, the operator achieved the
objective of drilling a first dual-lateral well
in seam without wellbore stability issues.
The technology enabled the operator to
navigate back to seams despite several
encountered faults. The laterals were 2,200
m long, and the wells landed at 829.5 m
and 988 m in seam. The operator inter-
cepted the deviated well successfully in
one attempt and ran completions without
issues. In the second dual-lateral well, the oper-
ator set the company’s onshore records for
the highest extended-reach drilling (ERD)
ratio and the longest lateral length from
heel to toe. The technology also enabled
the operator to drill the longest lateral in
the Bowen Basin. The multilayer map-
ping-while-drilling service helped gather
information farther out than originally
planned, giving insight for exploring a
complex area where doing so was previ-
ously considered impossible.
By improving detection range and reso-
lution, the service enabled the operator to
efficiently develop the challenging CSG
field. Continuous improvements enabled
the company to drive down the cost per
foot, contributing to significant savings.
Overall, the operator improved footage
drilled per day by 80% and reduced cost
per foot by 31%. As CSG continues to be
a significant part of the Australian gas
industry, the successful operation pres-
ents opportunities for drilling laterals in
seam and improving structure mapping
and geosteering in CSG fields.
Case study: Doubling the
detection range offshore China
An operator drilling two wells in the
Chenghai Block in Bohai Bay, China, faced
challenges where development wells shift
from targeting the center of the sand body
to the end. In two previous wells, because
of large sedimentary changes and sand
body discontinuities, the net-to-gross
(NTG) ratios were lower than expected.
The average thickness of the sand bod-
ies is approximately 8 m. With previous
technology, the depth of investigation was
around 2-3 m, making clear depiction of
the whole sand body difficult. The rapidly
changing reservoir structure made geo-
steering and staying within the sand body
more challenging.
Using the multilayer mapping-while-
drilling service, the operator increased the
depth of investigation to 6 m, doubling the
detection range in the field compared with
previous-generation technology. The tool
mapped the whole sand body, increased
M A R C H/A P R I L 202 2 • D R I L L I N G C O N T R AC T O R
I N NOVATI N G WH I LE DR I LLI N G
reservoir understanding, and enabled
the operator to make informed decisions
for maximizing the NTG ratio for each
well, thus improving the productivity of
the wells. By providing higher-resolution
mapping, the service revealed the internal
layering and quality variation within the
reservoir, optimizing the well path and
production. The PowerDrive Archer high build rate
RSS enabled the operator to effectively
steer the horizontal section of the wells to
handle the abrupt structure changes and
target multiple sand bodies in one well.
The operator used the multilayer map-
ping-while-drilling service in well A to
map the top of the target sand 2.1 m away
and the base of the target sand 5.2 m away
as soon as it came out of the casing shoe.
The service mapped the top and the base
of the sand body throughout the section,
clearly showing the pinchout of the sand
body. The well was drilled for 256 m inside
the sand body, with 50 m/hr average ROP
while achieving 100% NTG.
Well B was drilled in an area lack-
ing control wells, causing uncertainties
about the thickness and dip of the reser-
voir structure. At 2,960-m MD, the service
mapped the abrupt upward dip change of
the base of the current sand body, enabling
the operator to build inclination of the well
path and avoid drilling out of the current
good-quality sand. At 3,030-m MD, the ser-
vice mapped the top of the sand body and
a poor-quality layer at the upper part of the
The multilayer mapping-while-drilling service mapped the top and the base of a
sand body in China, clearly showing the pinchout. The well was drilled for 256 m
inside the sand body, with 50 m/hr average ROP while achieving 100% NTG.
reservoir. The geosteering team dropped
the inclination and avoided drilling into
the poor-quality zone at the top. At 3,123-m
MD, the service inversion showed that the
formation dip changed from 0.5° down-
ward to 8.5° upward. The operator called
for total depth (TD) based on this informa-
tion. For this well, the team achieved a
91.5% NTG ratio, drilling 215 m in sand for
the total horizontal section of 235 m.
Conclusion The ability to double the depth of detec-
tion range compared with previous bed
boundary detection services has helped
operators deliver clearer boundary delin-
eation, enabling more precise real-time
steering and faster turnaround time. By
landing the well more precisely, operators
can avoid drilling out to nonproductive
sand and reduce costs and risks associ-
ated with drilling in complex formations.
Since deployment, the multilayer map-
ping-while-drilling service has drilled and
steered more than 700,000 ft in over 200
runs and 10,000 operating hours. In addi-
tion to Australia and China, it has helped
operators in the United States, South
America and the Middle East place the
well in the best part of the reservoir, lead-
ing to improved production, reduced cost
and risk, and consistent performance. DC
PeriScope Edge,
ShortPulse, PowerDrive
Orbit and PowerDrive Archer are marks of
Schlumberger. The service mapped the abrupt upward dip change of the base of the current sand body, enabling the operator to build
inclination of the well path and avoid drilling out of the current good-quality sand.
D R I L L I N G C O N T R AC T O R • M A R C H/A P R I L 202 2
29