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