MANAGED PRESSURE DRILLING
Click here to see more graphics from this article.

Figure 1 (left): A new dilution-based dual-gradient technology allows for well designs with fewer casing strings compared with
a conventional single-gradient well, as illustrated in this simulation of an ultra-deepwater gas well in the US Gulf of Mexico.

This is primarily because of the more favorable mud density gradient profile (red dotted line) of dual gradient compared with
single gradient. Figure 2 (right): For the well shown in Figure 1, reducing the number of casing strings also reduces the pre-
dicted days needed for drilling, from 140 for a single-gradient well design to 80 with a dual-gradient design.

tions, usually a significant drilling limiter,
can be mitigated with a stiffer drillstring.

Rate of penetration is expected to benefit
from these measures. The larger production
hole size is particularly important when
pursuing geothermal targets, which typi-
cally require larger diameters for produc-
tion fluids than oil and gas wells for eco-
nomic heat and power production.

Application in geothermal
well construction
New geothermal technologies vary in
focus and areas of advancement. Surface
technology is generally coupled to a spe-
cific subsurface design or targeted heat
source. There are also a smaller num-
ber of other technologies focused on heat
transfer innovations and new wellbore
construction methods that deviate from
current oil and gas drilling practices. Few
of these technologies, however, are at an
elevated technology readiness level (TRL),
and even fewer are operationally ready for
implementation. 34
UltraDeep’s dilution DGD package is at a
high TRL and can be deployed with exist-
ing land-based drilling rig operations. The
integration with standard drilling tech-
nologies provide access to deep (15,000-
25,000-ft TVD) and ultra-deep (25,000-
35,000-ft TVD) well construction opportu-
nities. The ability to drill these geothermal
wells to these depths with large bore is
critical to implementing the Geothermal
Anywhere concept while drilling through
geopressured sedimentary rock in pursuit
of deep targets.

The large-bore well design at depth pro-
vides several benefits, including reduced
well construction time and costs, as well
as a reduced carbon footprint from rig
operations, casing and cementing time.

The larger bore at TD is the required con-
duit needed to scale heat and energy trans-
fer. Additionally, the well integrity and
zonal isolation improvements enabled by
DGD are essential for long operational life,
as well as the ability to implement new
technologies restricted to large-bore wells.

Accessing ultra-deep gas
reserves Sizable deep and ultra-deep gas reserves
exceeding 100 Tcfe are present along the
US Gulf Coast. From 2000 to 2010, sev-
eral attempts to access these reserves
were undertaken with various projects,
such as Davy Jones, Blackbeard, Joseph,
Highlander and Lineham Creek.

Except for the Highlander project, the
technical and economical limits of con-
ventional drilling methods of the time
were reached on most of these wells, and
the projects ended prior to completion.

This was primarily due to drilling prob-
lems associated with well control, induced
lost circulation and wellbore instability.

However, by using dual-gradient drilling
technology, in combination with conven-
tional MPD technology, the industry can
eliminate most, if not all, of this nonpro-
ductive time.

“Dilution-based dual-gradient drilling”
continued on page 36
JAN UARY/FEB RUARY 2023 • D R I LLI N G CO N T R ACTO R