microflux - safe drilling operations
DESCRIPTION
Microflux - Safe Drilling OperationsTRANSCRIPT
A L L D R I L L I N G • A L L C O M P L E T I O N S • A L L T H E T I M E
SUBSEA WELL INTERVENTION
Light-duty intervention risers, riserless light
well interventions may be next game-
changers for deepwater production
REGIONAL FOCUS:AUSTRALIA
Industry players Down Under step up
infrastructure, technologies to tap
coal seam, shale gas potential
Dr i l l i ngC O N T R A C T O R
OFFICIAL MAGAZINE OF THE INTERNATIONAL ASSOCIATION OF DRILLING CONTRACTORS
S E P T E M B E R / O C T O B E R 2 0 1 1 W W W. D R I L L I N G C O N T R A C T O R . O R G
Rigs EquipmentDual-BOP systems emerge on deepwater rigs as ultra-mobile rigs carve nichesin land, offshore applications
&
Health, Safety & Environment
Although securing safe working
conditions and creating efficient
operating processes may imply
laborious efforts and cumbersome equip-
ment, Weatherford International’s
approach leverages a fundamental
aspect of all drilling operations – the
mud system. Fluids in and out of the well-
bore provide valuable information about
downhole conditions, which leads to safe
and efficient operations.
Common oilfield technologies, such
as rotating control devices (RCDs),
mass flow meters, automated drilling
chokes and downhole isolation valves,
individually provide incremental safety
and efficiency in downhole operations.
When combined to work conjunctively,
the tools can create a closed mud-return
system that captures and redirects the
free flow of drilling fluids, cuttings and
hydrocarbons from the wellbore annu-
lus. Closing this loop establishes a con-
tained circuit of incompressible drilling
fluid.
When an intelligent control unit (ICU)
is added to the closed-loop configura-
tion, the result is a self-contained system
capable of detecting minute downhole
pressure and volume changes .
The Microflux system helps the mud
system to become a highly sensitive
instrument to implement proactive man-
aged pressure drilling (MPD) strategies .
CLOSING THE LOOP
ON RISKS AND HAZARDS
A kick during drilling and completion
operations poses a major risk to rig per-
sonnel, the environment and the equip-
ment. That risk can be exacerbated by
inadequate downhole data.
With a closed-loop system, kicks and
losses are more readily and accurately
diagnosed. This is a significant advan-
tage given that slow detection or a mis-
diagnosis can jeopardize the safety of
personnel and the viability of drilling
operations. A slow or incorrect response
can also inflict irreparable damage to the
Closed-loop
system provides
real-time, accurate
data for proactive
management of
downhole pressures
BY BRIAN GRAYSON, WEATHERFORD
INTERNATIONAL
Closed-loop drilling systems are
scalable to the task and can help
minimize risk to personnel and the
environment . Additionally, kicks
and losses become more read-
ily and accurately diagnosed in
closed-loop systems.
Safe drilling operationscome full circle
Health, Safety & Environment
environment and cost millions of dollars
in nonproductive time (NPT).
The capability of monitoring, detecting
and quickly reacting to pressure chang-
es in the standpipe and at the surface
enables the downhole pressure profile to
be proactively managed and manipulat-
ed. More control helps the operator and
driller to navigate safely and successfully
through known and unknown hazards.
To ensure the most accurate and expe-
ditious response, more downhole knowl-
edge and control is a must, especially as
drilling reach extends to greater depths,
higher temperatures and pressures, and
more extreme locales.
Early detection of wellbore pressure
fluctuations can have particularly signifi-
cant impacts on deepwater operations,
where it is not uncommon to encounter
high temperatures and high pressures or
formations bearing H2S. In these opera-
tions, drilling windows are typically nar-
rower and more difficult to drill, and the
rig rate constitutes a significant expen-
diture.
Acquiring real-time data at the surface
yields a better understanding of down-
hole pressure and how the formation and
wellbore are responding to the drilling
program. The speed and effectiveness
of pressure management are enhanced
for both conventional mitigation methods
(i.e., mud weight and chemistries and
BOP procedures) and MPD methodologies
made possible by the closed-loop system.
CONTROLLING EQUIPMENT
WITH INSTRUMENTATION
Proactive pressure management via
the fluid system starts with an RCD
placed above the BOP to close the circu-
lating fluid loop. The RCD’s elastomeric
sealing elements and bearing assembly
provide a pressure-tight barrier between
the wellhead and the drill string. This
barrier eliminates open-to-the-atmo-
sphere mud returns to create the closed-
loop system. With the RCD in place,
drilling fluids, cuttings and hydrocarbons
are safely circulated away from the per-
sonnel on the rig floor.
A variety of RCDs have been devel-
oped to work with different pressures,
temperatures and wellhead diameters.
Weatherford recently develop ed the first
marine RCD for riser applications on
floating rigs, which is also the first RCD
to receive API certification. It addresses
deepwater requirements for installation
and maintenance and accounts for heave
compensation in the riser.
Another key element of the closed-loop
system consists of standard pressure
sensors and mass flow meters to acquire
wellbore mass balance information.
These meters measure mass flow past a
fixed point per unit of time. The closed-
loop system denotes minute changes
in bottomhole pressures at the surface
within seconds, while volume variations
of only gallons can be detected almost
immediately.
Adding an annular choke manifold to
this scalable closed-loop system marks
a shift to pressure management using
an MPD approach. The choke enables
manipulation of backpressure, which
provid es dynamic control of the wellbore
pressure and flow.
An ICU completes the equipment circle
for the closed-loop system. This control
unit houses the necessary data to mea-
sur e and analyz e physical properties and
to react to adverse well events. The ICU
uses proprietary algorithms to identify
and relay the slightest downhole change
and allows the engineer to distinguish
between different events, such as bal-
looning, breathing, influxes and losses.
In automated mode, the ICU controls the
MPD chokes to regulate backpressure
as needed. If, for instance, a small influx
is detected, applying backpressure can
minimize the influx to small volumes and
allow the gas to safely circulate out of
the system.
The integration of instrument s and
software enables automation of the sys-
tem and the acquisition of real-time data .
In difficult wellbore environments, this
feature proactively identifies and man-
ages influxes and losses for potentially
faster responses to help retain control.
The result is safer operating conditions.
Additionally, mud weights can be opti-
mized to improve drilling efficiencies and
lower fluid costs.
The accuracy and immediacy of the
data provides a high degree of insight
into what’s happening downhole and
improves the options to respond with
more flexibility than simply weighting the
mud system. On a fixed rig, the closed-
loop system detected kicks at just 0.25
bbl of influx. On a floating drilling unit,
where vessel heave movement introduced
a 25 bbl/min peak-to-peak variation, a
kick was detected at less than 3-bbl
influx.
Because the majority of well control
incidents occur during tripping, a down-
hole isolation valve (DIV) is commonly
employed in closed-loop operations.
The DIV protects against swabbing
while pulling out of the hole and can be
installed as a permanent or retriev-
able component to selectively isolate the
wellbore. The valve is opened or closed
as needed to enable tripping at con-
ventional speeds. Maintaining tripping
speed helps to prevent delays that can
aggravate well control events and cause
excessive NPT.
An MPD system with an intelligent control unit is a self-contained system that
allows engineers to distinguish between ballooning, breathing, and inß uxes and
losses to make more informed drilling decisions.
Health, Safety & Environment
DATA FLOW IN REAL TIME
Avoiding trouble rather than mitigat-
ing causes of NPT and well control issues
is a cost-effective strategy, especially
considering the expenditures associated
with offshore operations.
OFFSHORE EGYPT
HP HT conditions and wellbore bal-
looning in a tight operational window led
some to question the economic viabil-
ity of a field offshore Egypt. Several
attempts to drill offset wells in this field
were unsuccessful as a result of kicks
and losses. Any sign of loss or gain was
treated with caution because the poten-
tial consequences of a gas influx and sub-
sequent expansion at surface could have
resulted in a well control incident. Pore
pressure ranged from approximately 17.6
ppg to 18.4 ppg, and the fracture gradient
ranged from approximately 18.0 ppg to
18.6 ppg.
To continue with the drilling campaign,
the operator revised its approach and
employed a closed-loop system. During
the operator’s first application, the
closed-loop system detected kicks and
losses with a semi-automated choke,
enabling the necessary pressure man-
agement.
The operator’s second application
used the fully automated capabilities of
the system. The MPD approach enabled
the operator to use a statically underbal-
anced mud weight and adjust annular
backpressure at the surface to create a
virtual mud weight. Adding or releasing
annular surface pressure on the closed-
loop system resulted in an almost imme-
diate response in bottomhole pressure.
The 10 5/8 in. x 12 1/
4 in. and 8 1/2 in. hole
sections were successfully drilled to total
depth (TD). In addition to helping reach
the targeted casing points, the closed-
loop system was used to fingerprint well-
bore ballooning and breathing during
connections.
Previously used drilling methods mis-
diagnosed these inciden ts as kicks and
losses. However, the accuracy of the data
obtained with the closed-loop system
enabled the operator to continue the
drilling campaign with a more effective
and safer strategy.
OFFSHORE INDIA
The complex geology in the Asia
Pacific region is prone to tectonic activ-
ity, heavily faulted and folded strata,
lost circulation zones and uncontrolled
mud flows. The conglomerates, igneous
and carbonates prevalent in this region
present many drilling challenges. MPD
is the preferred methodology to mitigate
severe circulation losses associated with
fractured carbonate formations. More
than 100 MPD wells have been drilled
since 2005. Wells that experience kick/
loss and near- or total-loss scenarios are
now being drilled safely and efficiently.
An MPD application offshore India sig-
nificantly reduced time lost to downhole
problems to one day. Mitigation of similar
problems in previous offset wells aver-
aged 10 days. The significant reduction in
troubleshooting was achieved by reduc-
ing kick/loss cycles and other flat time
associated with narrow pore pressure/
fracture gradient. Time was also saved
when more control of the mud weight led
to an increase in ROP.
Fractured carbonate reservoirs off-
shore North Africa are being drilled using
MPD methodologies. In one well, low
bottomhole pressure and H2S gas contrib-
uted to mud losses of 1,400 bbl/hr and a
low ROP. MPD methods eliminated expen-
sive mud losses, prevented sour gas from
reaching the surface and increased the
ROP from 40 ft/day to 220 ft/day (12
meters/day to 67 meters/day) .
ONSHORE SHALE PLAYS
Although the daily rig rate is not as
high and depths are shallower, drilling
objectives for land operations mirror
those set for offshore campaigns – safely
reach the planned depth, within budget,
The Model 7875 below-tension-ring RCD is integrated with a ß oating vessel’s riser system below the surface of the water,
enabling the use of a closed-loop drilling system in deepwater applications.
Health, Safety & Environment
and find enough producible reserves for
adequate return on investment.
The shale gas plays in Northwest
Louisiana and East Texas have seen
wells drilled into formations with low
permeability and high porosity. These
characteristics typically create over-
pressured zones that have obvious drill-
ing concerns. The unconventional gas
target known as the Haynesville shale
requires a horizontal step-out in excess
of 10,000 ft MD. A recent successful drill-
ing strategy employed MPD techniques
to target this Upper Jurassic formation
that contains significant microfracturing.
RCDs without a flow meter or software
have been used as a means to apply back-
pressure on an as-needed basis. Wells
typically employed 16.5-ppg oil-based mud
(OBM) when drilling out the 7-in. casing
shoe and making 6 1/8-in. hole. With the first
deployment of the closed-loop system, the
shoe exited with just 14.8-ppg OBM. The
intent was to hold that mud weight through
the build section and horizontal to TD.
Better downhole visibility and control
in gas-prone sections resulted in several
improvements. By enabling the use of a
lighter mud weight, the rate of penetra-
tion (ROP) increased from about 15 ft/hr
to as high as 60 ft/hr. Improved drilling
rates and less NPT associated with well
control cut drilling time in half. The well
reached TD in 16 days as opposed to the
planned 31 days. This time reduction was
at tributed to an increase in the ROP as a
result of drilling with a lower mud weight
and detection/depletion of microfractures
in a controlled and safe manner.
The Barnett Shale in East Texas also
yields significant gas reserves. MPD has
reliably identified high-pressure kicks,
allowing the wells to be safely shut in. In
one instance, an overbalanced well lost
200 psi when the pumps were stopped.
When flow declined as expected and then
unexpectedly began to increase, the well
shut in.
In the three minutes that transpired
from stopping the pump to shut in, the
well gave a 35-bbl kick. The ability to
immediately see the flow and to expedi-
tiously react by closing the BOP pre-
vented the kick from becoming a major
well control event – an all too frequent
outcome in the area.
BEYOND THE HORIZON
Although drilling objectives are being
pushed further and into more complex
conditions, they are attainable without
putting personnel at risk or jeopardizing
the environment. Continual development
of enabling technologies and processes,
including both the closed-loop system
and MPD methodologies, has put previ-
ously inaccessible reserves within reach.
A sub sea RCD close to commercial-
ization will be installed above the sub-
sea BOP and enable riserless drilling
while enhancing operational safety. A
sub-based continuous flow system in
development will reduce wellbore insta-
bility issues and enhance HSE. More
sophisticated monitoring, analysis and
management software will further extend
the capabilities and applications of the
technology.
Access to more accurate downhole data
and the ability to manage drilling pres-
sures will allow operators to not only see
beyond the horizon but to produce it.
Microflux is a registered trademark of
Weatherford International.