distinguishing wellbore breathing from formation influx

Distinguishing Well Breathing from

Formation Influx

February, 2012

© Copyright, 2012. All Rights Reserved.Geoservices, A Schlumberger Company

Conroe, Texas

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www.geoservices.com

Distinguishing Well Breathing from Formation Influx

presented by

Mark HerkommerGeopressure Technology Center

Geoservices, A Schlumberger CompanyConroe, Texas

February, 2012

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Central Theme – Wellbore Breathing

� Wellbore breathing (ballooning) or Formation Influx are identified during

connections when mud flowback is observed.

� Wellbore Breathing: If the mud weight is too high, when the pumps are switched on pressure applied to the formation can open fractures, which

then take fluid. Shutting the pumps off relieves the downhole pressure allowing the fractures to close and causes the mud to flow back into the wellbore.

� Formation Influx: If the mud weight is too low, when the pumps are switched off the loss of pressure can permit permeable formations to flow into the wellbore.

� An inappropriate response can worsen the problem and lead to lost circulation or a dangerous kick. Early diagnosis is the key.


Formation Influx

February, 2012


Conroe, Texas

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Central Theme – Wellbore Breathing vs. Kick

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Volume of FracturesFracture Volume in Barrels per 10' of

Formation Thickness

radial depth of penetration

fracture

widthinches

length

5 feetarea200 sqft

length10 feetarea

400 sqft

length20 feetarea

800 sqft

length40 feetarea1600 sqft

length

80 feetarea3200 sqft

0.1 0.1 0.2 0.4 0.8 1.6

0.2 0.2 0.4 0.8 1.6 3.2

0.3 0.3 0.6 1.2 2.4 4.7

0.4 0.4 0.8 1.6 3.2 6.3

0.5 0.5 1.0 2.0 4.0 7.9

0.6 0.6 1.2 2.4 4.7 9.5

0.7 0.7 1.4 2.8 5.5 11.1

0.8 0.8 1.6 3.2 6.3 12.7

0.9 0.9 1.8 3.6 7.1 14.2

1.0 1.0 2.0 4.0 7.9 15.8


Formation Influx

February, 2012


Conroe, Texas

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Formation Influx: Detection Methods

�Pit Volume - Small to Severe Losses Detection

�Synchronized Event Display - Fingerprinting

�Pressure While Drilling – ECD Management

�Early Kick Detection - Differential Flow Rates

�Gas and Gas Ratios - Compositional Analysis

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PVT behavior during a connection

Note rounding of Pit Volume Totalizer (PVT) curve as the wellbore returns

and accepts fluid when pumps are turned off and on Legend:Flow Rate (FR)Active Vol.

First

indication of wellbore

breathing


Formation Influx

February, 2012


Conroe, Texas

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Suspected Well Breathing at 4647m

Losses at

4635m: high FR + high RPM

Losses at

4646m: incr. FR + high RPM

Losses at 4646m: high FR + high RPM

PVT Behavior While Drilling and During a

Connection

Legend:

Flow Rate (FR)Active Vol.

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Formation Influx

February, 2012


Conroe, Texas

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Assessment of Normal Flow Back During Connection: Flowback Fingerprinting

Differential

flow shows amount of fluid

returned after the pumps are

stopped

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Well Breathing

Abnormal Flow Back during Connections:

Well Breathing

Normal

Flow Back

Abnormal

Flow Back


Formation Influx

February, 2012


Conroe, Texas

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Well Kicking

Abnormal Flow Back during Connections:

Well Kicking

Normal

Flow Back

Abnormal

Flow Back

4 minutes

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Formation Influx

February, 2012


Conroe, Texas

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Abnormal ECD Response: Well Breathing

� Normal, square shaped ECD during

connection

� With increased ballooning the ECD

adopts a more curved appearance during flow back

� As ballooning worsens, the loss and gain become more rounded

Courtesy Sperry

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Abnormal ECD Response: Well Kicking

� Increasing Connection Gas during each connection

� Increasing active pit levels

during influx and

corresponding ECD response

Courtesy Sperry


Formation Influx

February, 2012


Conroe, Texas

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Abnormal EKD response: Well Breathing

The alarm is green :

nothing to notice.

The flow given by

the flowmeter matches the

theoretical flow out

Abnormally high

return at pump stop.

Warning status.

Losses mitigated with LCM :

Fractures only opening when pump start.

Return volume increasing

with depth: consistent with

fracture enlargement.


Formation Influx

February, 2012


Conroe, Texas

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Abnormal EKD Response: Well Kicking

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Formation Influx

February, 2012


Conroe, Texas

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Underbalanced drilling: Swabbing/Influx

� Formation at higher pressure than static mud column

� During connection, All the gases are exchanged between formation and mud in hole

� No or minor change in gas ratio because the gas is the same composition as the drilled gas

� Time of exchange is limited to Pump Off time : 5-10 min

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Conditions for Well Breathing

� Some mud losses must have occurred, prior the well breathing.

� Losses are due to fractures induced by the ECD (not losses in a permeable formation with lower pressure)

� Hydrostatic pressure (ESD) at TD is below the closing fracture gradient.

� Increasing MW does not stop the PCG, and possibly make them worse.

� Severe or total losses can be expected, if MW is raised above the fracture closing pressure.


Formation Influx

February, 2012


Conroe, Texas

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What Happens During Well Breathing

� At pump off time, fracture closes slowly,

mud flows back to hole

� Multiples fractures at various depth may have been induced or re-opened.

� Mud is charged mostly with light gases

� High gas peak may be expected

� High PCG observed, but with light gases.

Minor increase of the heavier gases C4-C5.

� Time of exchange : during the pumping time, i.e. several hours

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Volume of FracturesFracture Volume in Barrels per 10' of

Formation Thickness

radial depth of penetration

fracture

widthinches

length

5 feetarea200 sqft

length10 feetarea

400 sqft

length20 feetarea

800 sqft

length40 feetarea1600 sqft

length

80 feetarea3200 sqft

0.1 0.1 0.2 0.4 0.8 1.6

0.2 0.2 0.4 0.8 1.6 3.2

0.3 0.3 0.6 1.2 2.4 4.7

0.4 0.4 0.8 1.6 3.2 6.3

0.5 0.5 1.0 2.0 4.0 7.9

0.6 0.6 1.2 2.4 4.7 9.5

0.7 0.7 1.4 2.8 5.5 11.1

0.8 0.8 1.6 3.2 6.3 12.7

0.9 0.9 1.8 3.6 7.1 14.2

1.0 1.0 2.0 4.0 7.9 15.8


Formation Influx

February, 2012


Conroe, Texas

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How Gas Moves From a Formation

Into the Drilling Fluid

� INFLUX: Darcy Flow – Gas flow through a porous media under the influence of a pressure differential between the

formation and the drilling fluid

� WELLBORE BREATHING: Diffusion Flow – Gas flow through

a saturated porous media under the influence of a concentration gradient between the formation and the drilling

fluid

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Gas Peaks Composition: Well Breathing

Evolution toward

lighter composition with same EMW

Evolution toward

lighter composition with same EMW


Formation Influx

February, 2012


Conroe, Texas

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Gas Peak Composition: Well Kicking

No relationship

between compositions before

the kick – even, FG becoming lighter

New (much heavier) composition for the kick

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Gas Ratios – Well Breathing/Ballooning

Pipe Connection Gas

is high and rich in light components

and strong changes

of gas ratios

Gas Ratios

Purple – Balance

Blue – Wetness

543

21

CCC

CCBh

++

+=

54321

5432 100)(

CCCCC

CCCCWh

++++

×+++=

Balance

Wetness


Formation Influx

February, 2012


Conroe, Texas

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Gas Ratios – Well Kicking/Swabbing

Pipe Connection

Gas peaks are sharp and affect all gas

components without

change in gas ratio

Gas Ratios

Purple – Balance

Blue– Wetness

543

21

CCC

CCBh

++

+=

54321

5432100)(

CCCCC

CCCCWh

++++

×+++=

Balance

Wetness

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� When to suspect well breathing

� Section with a very tight MW window � ECD is close to the weakest formation in the open hole section

(weakest point not always at the shoe) � Losses were observed during the section

� Well Breathing Indicators

� Abnormal Flowback, but stabilizing� Pit behavior during medium to severe well breathing� ECD shape has rounded character

� EKD shows losses, followed by an equal gain

� PCG gas composition enriched in lighter components compared to background gas and may not arrive on

time

Well Breathing Identification – Conclusions


Formation Influx

February, 2012


Conroe, Texas

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� When to suspect well influx (kick)

� Section with a very tight MW window � ESD is close highest formation pore pressure in the open hole

section

� Well Influx Indicators

� Abnormal Flowback and NOT stabilizing� Pit behavior shows gain without prior loss� ECD shape has square-ish (normal) character� EKD shows gain without prior losses

� PCG gas composition is similar to background gas and will tend to arrive on time

Well Influx Identification – Conclusions

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distinguishing wellbore breathing from formation influx

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