BALLOONING PRESENTATION.pdf

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Ballooning
Ballooning
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Ballooning refers to well bore behaviour where a volume of mud is
lost when circulation is started but some or all of it flows back
when circulation stops
Ballooning occurs when the Equivalent Circulating Density >
Fracture closure stress and > the mud density
It is due to fracture extension and contraction
The fracture opens when the ECD exceeds the FCS during
circulation
The fracture pressure closes during shutdown because the FCS
exceeds hydrostatic head and mud is squeezed back into the well
bore.
Ballooning is not due to elastic stretching of the well bore .Well
bore expansion due to ECD is typically on the order of a few bbls
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Ballooning from PWD data
13.0
12.8
12.6
Leak off test 12.4 FCS
12.4
12.2
12.0
0
200 400
600
800
1000
• The fracture initiates
at the same pressure
after each connection
as the pump rate and
ECD are being
increased
Time in seconds
SPE /IADC 67742
Diagnosis from MWD data
Fluid in the fracture causes a shift in the resistively curve . The magnitude of the
Shift depends on the width of the fracture and relative resistively of the fluid.
The plots below shows the effect of OBM on the resistively in shale
10
GR
res
GR
gr
GR
0
120
1OO
1
5150 5175
5200
5225
0
6740
6750
6760
6770
6780
Ballooning vs Lost returns
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The tendency for ballooning to occur rather than a continuous lost returns is
related to many issues:
ECD is only slightly above minimum stress. As the fracture lengthens the
pressure drop down the fracture reduces the pressure at the tip to below
minimum stress. Growth then stops
Usually occurs in viscous mud which has a greater pressure drop
More common in NAF mud. Low leak off of carrier fluid keeps mud solids
from eventually blocking fracture
More common in low permeability or shales due to low leak off
May occur in permeable zones if permeability is damaged sufficiently by
continued expose to lost returns to prevent leak off.
Larger ballooning volumes are observed in soft formations due to storage
capacity of wider fractures
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