American Oil and Gas Reporter - April 2016 - 62

SpecialReport: Drilling Technology
As a result of the study, the success
rate of one-run wells increased from 25
to 85 percent over seven months. Achieving this success involved analyzing vertical
parameters (specifically through the highly
abrasive Wilcox Sandstone formation),
geographic location (correlated with
Wilcox thickness), motor bend, BHA
components, well trajectory, bit selection,
and overall well length. Improving the
efficiency of drilling Eagle Ford wells in
one run proved to depend most on optimizing vertical parameters, Wilcox thickness, and overall well length.
The method used in the Eagle Ford
project should be considered seriously
for any wells with geologic formations
and temperature ranges that can tolerate
the necessary variations in mud parameters
throughout the vertical, curve and lateral
sections. One-run wells can prove profitable by sacrificing single-section rates
of penetration to gain overall well ROP.
For example, a slight reduction of the
drilling parameters in the vertical section
may reduce the vertical ROP, but will
maintain the BHA integrity for the curve
and lateral sections, which will result in
an increased ROP over the length of the
well.
Significant reductions in rig time and
the amount of equipment used in onerun applications result in overall increased
economic efficiency-specifically time
and cost savings associated with eliminating a trip to pick up a second BHA-

and create a simpler operation that provides
a safer work environment for rig personnel.
Initial Results
The first one-run attempts were encouraged by third-party successes in other
parts of the Eagle Ford play. Although
the acreage owned by BHP Billiton was
known to vary geologically from the
areas in which the technique had been
applied successfully, parallels in well design and basic geologic trends led to
testing the idea.
The initial attempts were promising,
which was attributed largely to motor
and bit changes in the BHA. The time
and money saved by eliminating a trip
and additional BHA run led to applying
the changes on other rigs. However, the
results were not duplicated. Bits from
unsuccessful attempts experienced noticeably different dull conditions than
those observed on bits from successful
one-run efforts.
Minor variations in motor and bit selection revealed useful insights. A fixed
motor with a 2.0-degree bend drilled the
vertical section efficiently and produced
consistent results in building the curve.
Motors with lesser bends (adjustable 1.83
or fixed 1.75 degrees) did not yield the
required doglegs in the curve (motors
with a greater bends were not tested because of rpm limitations).
One-run bit testing involved variations

FIGURE 1
Initial Comparison of Parameters Run Through Wilcox and Bit Damage
On One-Run Attempts Unable to Achieve Curve Build Rates

of steel and matrix fixed-cutter PDC bits
from multiple providers. In traditional
two-BHA drilling operations, the bit of
choice for the vertical section is a fiveblade matrix option with a cone angle
and dual-row, 16-millimeter cutters. The
preferred design for the curve and lateral
section is a six-blade steel body bit with
11-mm cutters and an extremely flat profile. Both of these bits were tried initially
in one-run applications, but neither yielded
successful results.
In selecting a new bit design, fiveand six-blade options with 11-16 mm
cutters and a variety of profile shapes
were considered. The most successful
designs showed no preference in body
material, contained either five or six
blades, 13-16 mm cutters, and relatively
flat profiles. Cutter and blade-count aggressiveness enable efficient drilling in
the vertical and lateral sections, whereas
a flatter profile theoretically helps maintain
the tool face for directional drilling.
After bit options were narrowed, the
exact preference was determined by directional drilling capability. Generally
speaking, each one-run bit is considered
to be more of a vertical or lateral bit that
is directionally competent enough to drill
the curve on a 2.0-degree motor.
Most one-run BHAs drilled the vertical
and lateral sections faster than average,
while drilling slower than average in the
curve. These findings led to investigating
drilling parameters for the Wilcox, and
more specifically, the Lower Wilcox,
which is composed of marine shale and
fluvial/deltaic sands.
In two-run designs, the motors and
bits used in vertical BHAs are aggressive
enough to drill the coarse Wilcox, but do
not necessarily contain the design elements
necessary for building an efficient curve.
On the other hand, the BHAs used in the
curve and lateral sections are designed
for precision, and would be more likely
to sustain significant damage in an abrasive
formation.
Optimized BHA Design
Optimizing a one-run BHA design
(especially with respect to selecting a
bit) involved determining a balance between necessary aggressiveness and the
ability to adequately control drilling in
the curve and lateral sections. The Wilcox
presented an obvious challenge while
drilling with a less aggressive BHA. The
study determined that the most effectively
drilled one-run wells compensated for

62 THE AMERICAN OIL & GAS REPORTER

American Oil and Gas Reporter - April 2016

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