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Oilfield Technology
August
2015
causes both increased bit wear and damage to themudmotor from
stalling/spudding events. The result is reduced bit life and an increased
number of trips, which ultimately impacts the overall efficiency of the
well. Due to the increasing length of the lateral sections, the drill pipe
tends to rest on the low side of the wellbore, causing frictional drag and
impairing the ability of drilling fluids to provide effective hole cleaning,
both of which further slow the progress and efficiency of the well. All of
these issues combined add up to reduced bit and tool life, lower average
ROP and ultimately lower profitability.
While extended reachwells offer huge benefits for the operator, such
asmaximisingwell productivity and reduced environmental impact from
a singular pad-type drilling site, the extreme lateral distances amplify the
hurdles the driller faces. Drilling increasingly longer laterals poses intrinsic
complications that result in reducedROP and overall cost-effectiveness of
thewell. Perhaps the greatest culprit is friction along the drill stringwhen
attempting directional corrections, which leads to stick/slip, buckling,
lock-up, poor tool face control, lower differential pressure, motor stalling,
high tortuosity, ECD fluctuations andmore. Aswellbore friction builds,
forwardmotion of the drill string suffers, cuttings settle in the bottomof
thewellbore, further increasing friction, which creates a vicious cycle of
frictional drag and sluggish hole cleaning.
Two types of downhole tools are generally employed to address
friction along the drill string: axial oscillation tools (AOTs) and lateral
vibration tools (LVTs). AOTs typically employ a valve driven by themud
flow to generate pressure pulses. These pressure pulses are converted
to axial oscillatingmotions by a shock tool that is run above or as part
of the AOT. Themotion travels up and down the drill string to reduce
friction between the drill string and wellbore. While axial vibrations can
help reduce frictional drag
1
, they have little or no effect on hole cleaning,
and the jarring impact can causemore harm than good by damaging the
MWD, interfering with signal transmission and drill bit wear or breakage.
LVTs typically utilise a rotor and stator to drive an eccentric mass.
The resulting action creates lateral vibration (perpendicular to the long
axis of the tool) between the tool and the borehole to reduce friction in
the BHA and along the drill string. The rockingmotion created by LVTs
induces enough energy in the BHA to reduce friction for more efficient
sliding and rotating in the curve and lateral.
The inherent advantages of LVTs over AOTs have been further
enhanced with the introduction of Logan International’s Xciter™
extended reach LVT. The tool utilises positive displacement motor (PDM)
power to rotatemasses of varying sizes, to excite the drill string with
lateral vibrations. Themotion introduced into the stagnant wellbore
reduces or eliminates stick/slip, increases ROP, enhances tool face
control and extends drill bit life.
The Xciter tool is typically run one stand (or three singles) above
the top Monel. The extended reach LVT is positioned close to the
BHA, directly above the MWD, and is effective in all directional drilling
applications (S wells, curve sections and lateral sections). As the driller
reaches the bottom, the tool will use the bit as an anchor, and the
vibrations resonate back up the drill string, allowing the BHA tomore
efficiently do its job. Because the tool creates a side-to-sidemotion
instead of an axial up-and-down hammeringmotion, it is safe for MWD,
LWD and EM, and does not cause signal interference.
The extended reach LVT is added to the drill string when the driller
begins the curve to further enhance slide and rotary drilling performance
under themost challenging wellbore conditions. Running the tool in the
build section helps producemore consistent curves andmaintains build
angles for smoother intermediate casing runs andmore efficient lateral
drilling.
Proximity to the BHA enables direct impact and benefit to the sliding
process as directional drillers are affordedmore control over tool faces,
differential pressure and weight on bit. This enhanced control allows
drillers to orient much faster after surveys and holdmore accurate and
consistent tool faces while sliding to producemore efficient slides.
As lateral vibrations inducemovement in the drill string, the rocking
motion helps to stir up cuttings that have settled on the low side of
the wellbore, and stimulates slow-movingmud. Getting the stagnant
cuttings integrated into the increasedmud flow in turn promotes more
efficient hole cleaning, which enables the drill pipe tomove through the
lateral with greater ease and efficiency. As the tool stimulates activity in
the wellbore, drillers can expect minimal pressure drop, typically around
150 psi.
Casestudy: thePowderRiverBasin
The Powder River Basin, a region that spans 43 000 squaremiles
primarily in northeast Wyoming and southeast Montana, is well known
for its abundant supply of coal, which is its largest natural resource.
However, the Basin is also a substantial source of oil and natural gas,
with ties to the industry as far back as 1889. The Powder River Basin
experienced a lull in oil and gas production during the first decade of the
2000s, reaching a low of 38 000 bpd. Experts attribute the slump to the
previously uncharted territory of shale. Producers had tapped as much
of the region as possible and stalled out because of the inaccessibility of
resources deep within the shale plays. All that began to change in 2009.
The development of directional drilling applications has made
tapping these resources a reality and is largely responsible for the
resurgence the region has experienced. According to the US EIA,
production has jumped from38 000 bpd to 78 000 bpd andmore than
590 wells have been drilled since 2009. Increased production occurred in
all six shale plays in the Basin, including the Shannon, the Sussex and the
Frontier formations, which rose from8900 to 17 000 bpd. Nonetheless,
the overall regional growth is heavily concentrated in the Turner,
the Parkman and the Niobrara-Codell formations, which collectively
increased from4700 bpd tomore than 36 000 bpd in early 2014.
The Xciter vibration tool has over 200 runs in this basin. A case study
was performed on 25 wells fromone operator in both the Parkman and
Turner formations. These complex horizontal wells are approximately
7000 ft and nearly 10 000 ft below the surface, respectively. Overall,
(including curve and lateral sections), the tool delivered significant
Figure 1.
Overall rate of penetration. The Xciter delivered improvement
in overall ROPof 10.5 ft/hr (all wells, curve and lateral sections).
Figure 2.
Overall rate of penetration. Xciter performance gains in curve
sections and lateral sections of 3.6 ft/hr and 9.3 ft/hr.
