American Oil and Gas Reporter - September 2018 - 56

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Ashley Lees
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56 THE AMERICAN OIL & GAS REPORTER

to extreme levels of vibration (Figure 4).
Once kickoff was established, drilling
continued with minimal vibration. The
DCTD BHA's short length is a significant
advantage for geosteering. The short distance from the bit to the surveying tool,
coupled with real-time continuous surveying, makes steering responsive.
While drilling the hold section, two
significantly productive fractures were intersected. Drilling was stopped, and nitrogen injection began to proceed in an
underbalanced condition. This gave the
operator a simple measure of the productivity of the intersected fractures, demonstrating underbalanced DCTD's "testingwhile-drilling" capability to provide reservoir characterization information.
When compared, the overall modeled
results were found to be within 8 percent
of actual measurements obtained while
drilling. Figure 5 shows examples during
both single-phase/overbalanced (left) and
two-phase/underbalanced (right) DCTD
operations. This should be taken into
consideration when working on wells
with tight drilling windows. The modeled
values can be used to guide fluids selection,
but actual downhole measured values
should be used during operations.
After the basic well test was carried
out, drilling continued through the build
section. However, a marker formation
was observed on the gamma readings
that was much shallower than expected.
This meant the trajectory would drop
significantly below the top of the target
formation. The perceived risk of hitting
a water zone was high, so the operator
decided to reduce the sidetrack's length
rather than drill the full horizontal section.
The final section of the well was drilled
underbalanced with nitrogen at a controlled ROP using samples of cuttings
to determine when the reservoir had
been entered.
The project successfully re-entered
the dry hole and drilled the sidetrack
with DCTD to create a productive oil
well, thereby validating the technology
and the multidisciplinary approach. The
successful field operation offers valuable
lessons that can be used to optimize the
planning of future DCTD wells and maximize the value of re-entering marginal
wells. The lessons learned include:
* The success of DCTD relies on a
multidisciplinary approach and teambased decision making to integrate drilling
with the completion program. This includes geology, 3-D seismic, well trajectory planning, drilling engineering and
completions engineering. Otherwise, the
advantages of DCTD could be lost.
* Creating drilling engineering mod-

els of proposed wells is essential for
planning effective operations and minimizing drilling problems, but there is
always a certain amount of variation between modeled and actual drilling conditions. DCTD parameters must be adjusted based on the data provided by the
BHA during drilling.
* It is important to measure downhole
vibration while drilling, since kicking
off requires low WOB, which causes
large vibration amplitudes. Precautions
must be taken to avoid extreme downhole
vibration.
* Substantial amounts of reservoir
data can be gained while drilling underbalanced on coiled tubing. If these data
are desirable to the operator, it must be
part of a data acquisition plan and suitable
additional equipment must be used.
The project demonstrates some of the
significant advantages high-frequency
data surveying can provide in directional
control and minimizing dogleg severities.
However, additional work is required to
create more suitable error models for use
with high-frequency surveying.
r
PETER HATGELAKAS is chief geologist at Chuck Henry Energy in
Pittsburgh, and owner of Hatgelakas
Consulting. With 42 years of industry
experience, he previously served as
president and chief executive officer
of Intrepid Exploration LLC and as
co-president of Prometheus Exploration
LLC. Hatgelakas holds a B.S. in mineralogy and geochemistry from Worcester Polytechnic Institute, an M.S. in
geology from Boston College and an
M.S. in petroleum engineering from
the University of Pittsburgh.
TONI MISZEWSKI is chief executive
officer and founder of U.K.-based AnTech Ltd. With 35 years of industry experience and 17 patents, he served for
10 years in both field and engineering
positions at Schlumberger before establishing AnTech in 1992. Miszewski
has a degree in mechanical engineering
from Imperial College London.
ADAM MISZEWSKI is global operations manager at AnTech Ltd. Before joining the company in 2015 as
a directional coiled tubing drilling
operations engineer, Miszewski
worked as a drilling engineer at BP
and lead engineer at HalliburtonSperry Drilling Services. He holds a
degree in mechanical engineering
from Imperial College London.

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American Oil and Gas Reporter - September 2018

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