OFFSHORE TECHNOLOGIES & MARKETS
Case study: Chevron deploys
below-tension-ring MPD to drill
highly depleted reservoir in GOM
potential benefits include quicker leak-
off detection and reaction to losses, safer
determination of drilling parameter and
mud weight adjustments, greater control
of pressure to prevent borehole instability,
and more efficient cementing of produc-
tion liner.

Strategy helped to reduce risk for fluid loss
and decreased mud weight requirements
Choosing the right
equipment BY JESSICA WHITESIDE, CONTRIBUTOR
Complex deepwater drilling environments
can become even more challenging as res-
ervoirs mature. Pressure concerns tied to
high levels of depletion increase the poten-
tial for fractures, downhole fluid loss and
well control hazards. To reduce these risks
and associated remediation costs, Chevron
has found success deploying drillships
outfitted with customized surface-back-
pressure managed pressure drilling (MPD)
systems in mature reservoirs in the deep-
water Gulf of Mexico.

At the 2022 IADC/SPE International
Drilling Conference in Galveston, Texas,
on 9 March, Ken Vaczi, Deepwater Drilling
Engineer for Chevron, described the com-
pany’s experience with its first two deep-
water BTR MPD systems in the Gulf of
Mexico during a four-well campaign. The
company has since expanded its use of
the technology to other operations in the
region. BTR (below tension ring) refers to a sur-
face-backpressure MPD system in which
the rotating control device (RCD), used to
control pressure during drilling, is placed
near the surface in the riser but below the
telescopic joint.

By maintaining near-constant bottom-
hole (or other target location) pressure,
this MPD approach helps the operator to
navigate narrow drilling margins. Other
Ken Vaczi, Deepwater Drilling Engineer for Chevron, described the company’s
experience with two deepwater BTR MPD systems in the Gulf of Mexico. He was
speaking at the 2022 IADC/SPE International Drilling Conference in March.

Chevron decided to apply BTR MPD to
the four-well campaign after experienc-
ing major downhole fluid losses during an
earlier conventional drilling operation in
highly depleted Gulf of Mexico reservoirs.

Modeling predicted that the new cam-
paign could face similar conditions, which
could trigger downhole losses and make it
difficult to reach planned total depth and
achieve other well objectives.

Through MPD, the team hoped to miti-
gate the potential for thermally induced
fractures and differential depletion, with
some sands in virgin condition and others
with high depletion levels up to 8,000 psi –
the highest level of depletion that Chevron
has drilled in the Gulf of Mexico to date,
Mr Vaczi said.

Smaller flow meters tend to be standard
on MPD packages, which concerned the
project team in light of the erosional veloc-
ity of the mud expected to flow through
the meter, especially in combination with
some of the lost-circulation material they
anticipated using for the project.

“To fix the problem, we elected to do a
two-size implementation,” Mr Vaczi said.

“The larger flow meter could be used for
the larger hole sections and the smaller
flow meter could be used in the smaller
hole sections where the flow rates were
less.” They also included a dual junk catcher
to prevent large debris from plugging the
automatic chokes and disrupting the abil-
ity of the MPD system to automatically
manage surface backpressure. When one
catcher was plugged, they could switch
to the redundant catcher on the fly with
minimal impact to operations.

While Chevron had used other forms
of surface-backpressure MPD around the
world, the four-well campaign marked its
first use of the BTR MPD variant on deep-
water floating rigs in the Gulf of Mexico.

The company worked with MPD equip-
D R I L L I N G C O N T R AC T O R • M AY/J U N E 202 2
35