I N NOVATI N G WH I LE DR I LLI N G
Combination of extended-reach
drilling, maximum reservoir
contact wells and artificial
islands helps ADNOC access
offshore reserves with land rig
Wellbore tortuosity and instability, hole cleaning
and collision risk among many challenges
ADNOC overcame to drill 32,101-ft MD well
BY STEPHEN WHITFIELD, ASSOCIATE EDITOR
To increase production from shallow-
water reservoirs in the Arabian Sea, the
Abu Dhabi National Oil Company (ADNOC)
has been utilizing a combination of artifi-
cial islands and land rigs to drill extended-
reach drilling/maximum reservoir contact
(ERD/MRC) wells.
Built out of sand dredged from the sea-
bed, these islands can provide a cost-effec-
tive alternative to deploying offshore rigs.
Then, by drilling multiple ERD sidetrack
wells from a single pilot well from that
island, ADNOC can explore the far reaches
of the reservoir in the ocean without need-
ing to install new subsea infrastructure,
said Muhammad Ased Hashmi, Senior
Drilling Engineer at ADNOC Onshore. The
MRC aspect of the wells, which typically
means the well has an aggregate reservoir
contact in excess of 5 km, is intended to
help the operator achieve higher levels of
productivity with each well.
CONDUCTOR INTERMEDIATE CASING
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0 The 32,101-ft MD well had a TD of just 9,127 ft, making it 2 an 000 exceptionally long and
torturous well with a 3.52:1 extended-reach ratio. The well
was drilled this way in
0 order to maximize its aggregate reservoir contact and increase productivity.
20 While this approach to accessing off-
shore reserves has clear benefits, there
are also myriad challenges. For one, drill-
ing ERD wells can be extremely diffi-
cult, as it requires wellbore stability to be
maintained and higher levels of torque
to be managed over longer distances.
Additionally, because ADNOC uses a clus-
ter drilling approach in order to maximize
the well capacity of each island, devising
optimal well locations and trajectories can
be complex due to space limitations. “With
an artificial island, we have a difficult well
scheme from a trajectory point of view,” Mr
Hashmi said. “In one cluster, we can have
several wells being drilled in one area, all
going in different directions and into differ-
ent formations. It’s a planning challenge.”
In this cluster drilling approach, ADNOC
first drills a pilot well, which can serve as
a reference well for acquiring open-hole
data. That data can then be processed to
assess and define nearby opportunities, as
well as determine the number and location
of additional wells to be drilled from the
same pad.
Speaking at the 2023 IADC Drilling
Caspian Conference in Baku, Azerbaijan,
on 8 February, Mr Hashmi discussed his
experience while drilling one such well
offshore Abu Dhabi. As the target reservoir
was shallow, the total vertical depth of
the well was only 9,127 ft even though its
MD reached 32,101 ft. This resulted in a
fairly high extended-reach ratio of 3.52:1,
which is well above the 2:1 ratio that typi-
cally defines an extended-reach well. This
meant that the well would be exceptional-
ly long and torturous, which has implica-
tions on the well completion phase. Other
difficulties anticipated included high
torque, difficulty in hole cleaning, collision
risk and subsurface deviation errors.
The well was drilled in six sections:
■ a 157-ft, 36-in. hole section using surface
casing with an OD (outer diameter) of 30 in.;
a 2,054, 22-in. section with 18 5/8-in.
casing;
a 7,458-ft, 16-in. section with 13 3/8-in.
casing;
a 5,326-ft, 12 1/4-in. section with 9 5/8-in.
casing;
a 3,772-ft, 8 ½-in. section with 7-in. cas-
ing; and
the 6-in. lower completion section,
which was 13,334 ft in length and was
M A R C H/A P R I L 2023 • 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
drilled with a pre-perforated liner and
swellable packers.
Because the well was among the later
wells to be drilled in a cluster of 14 wells,
not to mention in the presence of other
well clusters, congestion in the area was
a big challenge. Actions taken to mitigate
the related risks included utilizing a real-
time gyroscope check-shot survey tool to
check for magnetic interference from adja-
cent wells in close proximity to the cased-
hole sections. “We’ve been drilling these
types of wells for a long time, but after a
while, you don’t have too much space. We
need to take the logging data and check
the boundaries of the reservoir to see what
we can maximize at the boundaries of the
reservoir,” Mr Hashmi said.
While drilling the surface hole, ADNOC
closely monitored losses vs gains to ensure
the hole was full at all times. If the level of
fluid dropped due to uncontrolled losses,
the drill string would be pulled back to
the conductor casing to avoid loose sand
being dropped on the BHA and leading it
to become stuck.
Because of the presence of multiple
depleted aquifers in the well path, which
could lead to a total loss of fluid, ensur-
ing good hole cleaning would be critical.
Mitigating steps included removing any
surplus cuttings so they wouldn’t increase
the equivalent circulating density (ECD)
on the annulus. Mud weight was also
decreased to further reduce the hydro-
static head on a weak formation.
Interbedded shale formations were
also present, leading to instability issues.
ADNOC alleviated the challenge by
decreasing the angle of the drill bit when
it drilled through the interbedded forma-
tion and then closely monitoring the mud
properties. Further, the shale’s reactiveness
with the water-based mud meant the well
had higher-than-normal torque throughout
the drilling process; this increased the risk
of a stuck BHA. Mr Hashmi said ADNOC
had to closely monitor torque and drag in
real time, as well as conduct several short
wiper trips to prevent the need for exces-
sive back reaming during final POOH (pull
out of hole) operations.
Running casing was difficult, as well.
When casing became stuck in the aquifer
zone, the operator had to pump 100-200 bbl
of freshwater pill, which reduced the hydro-
Last October, ADNOC announced a word record 50,000-ft well, which was also
drilled from one of its artificial islands using a land rig.
static head, cleaned the area across the
casing and freed the pipes to run to bottom.
The use of solid centralizers also helped
with cleaning and lowering the casing.
Finally, because the well was closely
geosteered across thin layers of reservoir
to ensure maximum contact, well tortuos-
ity posed significant obstacles in running
the lower completion to TD, Mr Hashmi
said. ADNOC’s solution was to run 4 ½-in.
tubing to 22,980 ft in the lower comple-
tion section, then utilize swellable packers
with pre-perforated liners for the remain-
der of the section.
The packers, which were installed every
500 feet to total depth, helped mitigate
potential wellbore instability in the section.
The packers swelled on contact with the
drilling fluid and sealed the annulus around
the drill pipe. The small size of the packers
made it suitable for traversing the slim hole
in the lower completion section, enabling
ADNOC to run the section to total depth.
Overall, the successful completion of the
well highlighted the key steps that ADNOC
took to manage the increased operational
challenges associated with drilling ERD
wells in a cluster setup. Mr Hashmi said
the lessons learned from this and other
ERD wells will help the company to con-
tinue exploring the boundaries of its res-
ervoirs. “We have to reach for the edge. We
want to see the boundary of the reservoir.
When we’re planning the drilling, we have
to make sure we have options to diverge
from the main area and explore.”
In October last year, ADNOC announced
it had set a world record for the longest
oil and gas well at 50,000 ft. The well had
also been drilled from an artificial island
using the ERD concept, at its Upper Zakum
Concession. In announcing the achievement,
ADNOC noted that the record ERD well
allowed the operator to tap into an unde-
veloped part of the reservoir, which had
the potential to increase the field’s pro-
duction by 15,000 bbl/day – without the
need to expand or build any new infra-
structure. The artificial island concept has already
resulted in significant cost savings and
environmental benefits, ADNOC said, com-
pared with traditional approaches that
typically require more offshore installa-
tions and infrastructure.
Upper Zakum is the largest producing
field in ADNOC’s portfolio. The company
plans to increase the field capacity to 1
million bbl/day by 2024 through a mega
expansion project valued at AED 110 bil-
lion. The project includes the construc-
tion of four artificial islands in shallow
water: Umm Al Anbar, Aseeifiya, Ettouk
and Al Ghallan. Together, these islands
can accommodate 450 wells and 90 plat-
forms, in addition to drilling rigs, process-
ing facilities and other infrastructure.
ADNOC has said the concept was moti-
vated by goals to reduce its environmen-
tal footprint while delivering additional
energy resources. DC
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