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.