Sugiura_subbed.qxp 27/3/09 04:24 Page 78
While-drilling Calliper Images Enhance Rotary-steerable Performance
Figure 3: The Pure Build-up Testing Results – Programmed Figure 4: 2D Calliper Image – Short Push (A), 3D Calliper Image – Short
Offset versus Build Rate with 12.25-inch Hole-size Short Push Push (B) and Calliper Frequency Spectrum – Short Push (C)
Rotary-steerable System
Mechanical calliper image (minimum 5.7 inches, maximum 6.7 inches)
A
8
7
6
5
4
3
6.7 inches
Build rate (º/100ft)
2
1
1,710–1,765ft MD
0
0204060 80 100
Programmed offset (%)
No ledge trimmer With ledge trimmer
ticks every 0.1ft:
rate: approximately 5.7°/100ft in limestone. Furthermore, this bit
Depth (ft):
provided the best balance among steerability, lateral/axial stability,
toolface controllability and borehole quality.
5.7 inches
Gravity toolface (0–359º)
Borehole Oscillation Observed
Obvious borehole oscillation problems were observed in 3D
B
mechanical calliper images and their frequency spectrum plots from
the tapered-gauge bit and the tricone bit running without a ledge
trimmer. In the 3D images (not shown), borehole oscillation problems, 6.8 inches
ledges and erratic borehole surfaces were visually confirmed.
Rotary-steerable Bottomhole Assembly Optimisation 6.3 inches
After the above bit gauge test, the 12.25-inch hole-size push-the-bit
RSS went through design changes to further shorten the distance from
the bit to the steering unit. The objective of this change was to
5.8 inches
optimise the system to work with ‘off-the-shelf’ passive gauge bits for
superior steerability and borehole quality. Also, shortening the
distance is thought to reduce the propensity for borehole spiralling
3D frequency response plot
C
suggested by the test data.
0.15
Bit to
Bit to
Bit to
A few months later, more testing was conducted with the short
0.1
upper stab
pads
trimmer
passive gauge bit shown in Figure 2. In this test, the experimental
Magnitude
‘short’ push-the-bit RSS produced 6.5–7.0°/100ft in limestone. This
0.05
RSS exhibited not only high steerability but also excellent toolface
0
4
controllability, predictable doglegs from 0 to 7.0°/100ft in pure build,
3.5
drop, turn and compound build and turn applications and high-
3
quality borehole. Figure 3 shows the results of the pure build-up 2.5
testing with and without a ledge trimmer. The data reveal that, up to
2
80% offset, the yielded build rates (up to 6.5º/100ft) are linearly
1.5
Depth (ft)
1
proportional to the programmed offset. Also, we confirmed that the
0.5
use of a ledge trimmer did not affect the resultant build rate with this
0
35 40
RSS. The steering consistency of this experimental RSS was excellent.
0 5
10
15 20
25
30
Frequency index (cycles per 25.5ft)
Mechanical Calliper Image maxima are coloured in blue and red, respectively. In this particular
The borehole quality, analysed with the 2D and 3D calliper images, limestone section (drilled to approximately 55ft), the target toolface
was marginally better when running the bit with the ledge trimmer was set to highside (gravity toolface 0°) and the target tool offset was
integrated to the RSS. Figures 4a and 4b show 2D/3D calliper images. set to 75%. The BHA yielded a 6°/100ft build rate while producing
In the 3D image, the right side of the image is highside of the borehole high-quality borehole.
(gravity toolface 0°) and the left side of the image is lowside of the
borehole (gravity toolface 180°). Figure 4c shows their corresponding Frequency Analysis
frequency spectrum plot. In the 3D frequency spectrum plot, The frequency spectrum of the calliper in Figure 4c shows that the
oscillation frequency, measured depth and magnitude are shown on peak of the frequency response is at the distance between the bit and
the x-, y- and z-axes, respectively. The height of the plot in the z-axis pads, but other peaks are located at higher frequencies. These higher-
shows the magnitude of the frequency response. Local minima and frequency components are induced by the different semi-contact
78
EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 1
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