English Edition (6 MB pdf) - Saudi Aramco

Despite these improved techniques, weight transfer in
CTDD projects continues to be problematic. Unlike
conventional rotary drilling, in CTDD the coil cannot be
rotated, and therefore the drilling can only be done in sliding
mode. Consequently, when operating in the horizontal or
tangent section of the well, the CT undergoes constant
orientation and tool face (TF) correction to stay close to the
vertical section of the desired well path. TF changes lead to a
tortuous wellbore, which increases drag and reduces weight
transfer to the bit. By reducing the tortuous wellbore profile,
friction losses can be reduced, which in turn improves weight
transfer to the bit to allow drilling of longer laterals.
Elimination of TF changes altogether, while still allowing
operators to geosteer and navigate in the reservoir as needed,
is required to overcome this limitation. The theory behind
good weight transfer to the bit comes directly from
conventional rotary drilling systems; the lateral lengths drilled
will be longer if wellbore sections can be drilled without
curvature.
A RSM BHA that uses pads to push against the formation
rock to maintain the wellbore in the desired well path —
rather than orienting a bent motor to stay close to the desired
vertical section — is proven technology 4 that has been
recognized as an excellent means to reduce friction losses due
to TF changes. The challenge was to design such a BHA and
miniaturize it to the 3”size frequently used in CTDD
worldwide. Additional necessities include real-time
communication with the tool and the functional capability to
navigate and geosteer as desired in the pay zone or fault
blocks. The existing e-Line based system was the ideal choice
for the implementation of rib steered technology without
sacrificing its other valuable features, such as fast data
transfer rates and control of direction as necessary 1 .
The current rib steered tool design has a reduced length,
compared with a conventional oriented bent motor coil drilling
assembly, which places the measured while drilling (MWD)
sensors closer to the bit, and it also has an integral near bit
inclination (NBI) sensor to assist in geosteering. Availability of
this technology in 3” and 2 3 ⁄8” sizes further improves extended
reach drilling (ERD) applications using slim hole CT reentry.
Rib Steered Technology Introduction for CTDD in North
America
The idea of using rib steered technology to successfully
geosteer the well in thin pay zones while improving
borehole quality and extending lateral reach appealed to
CTDD operators in North America. Subsequent field tests
of the RSM were carried out to evaluate its functionality
and integration with existing e-Line based CTDD BHAs.
Since its first deployment in 2007, the RSM has been
successfully used to drill seven wells on the Alaskan North
Slope and three wells in the Texas Panhandle as part of the
field tests in North America.
RSM Case History – North Slope of Alaska
The Prudhoe Bay field is the largest oil field on Alaska’s
North Slope. The highlighted well is located in the northern
part of the field. The majority of Prudhoe Bay’s wells were
drilled in the 1980s and the field is now depleted. With few
faults the producing reservoir is, for the most part,
homogeneous, making it ideally suited for field testing the
prototype RSM tool.
The original well was drilled vertically to 2,500 ft and then
gradually built an angle to 50° at 13,000 ft measured depth
(MD). The planned reentry involved kicking off at 12,600 ft
and drilling a 2,400 ft lateral section to total depth (TD) at
15,000 ft. A conventional CT drilling assembly was used in
the build section to drill a 20°/100 ft curve. To maximize the
lateral extension it was critical to reduce wellbore tortuosity
and therefore minimize hole coil drag. The RSM was used to
successfully drill the first lateral, maintaining a straight line
trajectory in the pay zone as per its objective. The average
DLS was reduced to 2°/100 ft, resulting in a less tortuous
lateral section and reduced hole drag. Originally planned for
19 days, the lateral section was drilled in six days, allowing
for a second sidetrack to be drilled from the first lateral. Both
laterals were drilled in one run. The first lateral leg was 2,049
ft and the second leg was 1,417 ft in length, representing the
longest combined lateral footage drilled with the rib steered
assembly at the time. The success of the rib steered technology
in improving drilling performance and extending lateral reach
opened new reentry well candidates on the North Slope of
Alaska with targets that could not be reached otherwise.
RSM Case History – Texas Panhandle
A UBCTD reentry campaign was executed to improve
production from the tight gas reservoir and rejuvenate the
existing basin. The existing vertical motherbores had a 5½”
completion in place making slim hole reentry the ideal
solution to perform a casing exit and construct a wellbore in
the target. A high DLS of 25°/100 ft from the vertical
motherbore was required to minimize shale exposure prior to
target sand intersection. The build section was drilled using
conventional drilling from the window exit in the existing
5½” completion and isolated with a 4½” liner. The target pay
zone was drilled underbalanced to prevent fluid losses as well
as formation damage. CT drilling was viewed as the enabling
technique due to its benefit of allowing pressure deployment
and ease of operation with compressible fluids. An RSM tool
was introduced to the project in the Fall of 2008 and was
successfully tested on three wells.
The first well was drilled in two days (1,562 ft lateral)
compared with nearly four days as originally planned. Due
to the success of the first test, the rib steered assembly was
used to drill two more wells with lateral departures of 1,510
ft and 1,817 ft, respectively. Rate of penetration (ROP)
improve ment averaged 130 ft/hr, compared with 50 ft/hour
12 SUMMER 2010 SAUDI ARAMCO JOURNAL OF TECHNOLOGY