I N NOVATIVE DR I LLI N G TECH N IQU E S
Figure 2 (left): CML has potential to help the industry achieve dual-gradient drilling so that offshore wells can be drilled like
land wells. Figure 3 (right): By reducing well costs and increasing recoverable reserves, CML can allow operators to add more
wells to a drilling program while maximizing project ROI.
surface footprint and ecological impact.
Moreover, CML results in less fluid and
mud losses, minimizing the environmen-
tal impact of creating them. Additionally,
the reduced need for re-drilling due to
wellbore instability, as well as rig time
savings, decrease the carbon footprint.
Dual gradient
Dual-gradient drilling (DGD) represents
the pinnacle of managing pressure down-
hole, which the industry has yet to achieve.
As stated by one offshore operator: “It will
enable us to drill offshore like we drill
land wells.” As analysis and application
continue on CML, it reveals that DGD may
not be as far away as previously thought.
Traditionally, DGD utilizes a lighter mud
weight, typically seawater, in the riser on
top of the applicable drilling mud below the
mud line. With CML, the lighter mud weight
is air on top of the controlled mud height.
For example, in a typical deepwater well in
the GOM, using a 12.5-ppg mud weight, the
seawater depth and 12.5-ppg mud weight
produce the same annular pressure profile,
with CML lowering the mud height 2,500 ft
(762 m). No device is needed near the mud
line as previously thought to achieve DGD.
To maintain a tight drilling window,
standard DGD practices would fall short,
whereas a CML system performs constant
BHP-enabling MPD while never changing
the mud weight.
Shifting financial model
The combined outcome of these ben-
efits can transform development project
economics for operators adopting CML
technology. Well architecture simplifi-
» Shell Senior VP of Wells: CML system shows promise in US Gulf
of Mexico
Watch DC’s
one-on-one conversation with
Michael Collins.
bit.ly/45g78xG 32
cation and drilling operational improve-
ments reduce well cost, and completion
results increase recoverable reserves. As
shown in Figure 3, that combination of
reduced well costs and increased recover-
able reserves in wells 1-4 changed well
economics and allowed additional wells
(5-7) to pass the hurdle rate.
Several offshore operators have stated
that they now require their drilling teams
to justify not using MPD, signifying that
MPD has proven to result in lower overall
costs and faster well completions due to
less nonproductive time from pressure-
related incidents. MPD is a proven offshore
technology for SBP and now for CML.
While CML holds immense promise, it has
similar challenges to SBP. Implementing
these advanced techniques requires spe-
cialized equipment, well-trained person-
nel and significant upfront investments.
However, as the oil and gas industry
seeks to strike a balance between energy
demands and environmental sustain-
ability, the future of CML appears bright.
Ongoing R&D efforts will lead to further
optimizations and cost reductions, mak-
ing CML a standard offshore practice. As
one operator customer shared, “SBP is
the right technology for exploration drill-
ing as we are dealing with high levels of
uncertainty. CML is the right technology
for development drilling as we should be
able to plan the pressures we need to
achieve best-in-class drilling, cementing
and completions.” DC
SEPTEMBER/OCTOBER 2023 • DRILLING CONTRACTOR