SPE DISTINGUISHED LECTURER SERIES
is funded principally
through a grant of the
SPE FOUNDATION
The Society gratefully acknowledges
those companies that support the program
by allowing their professionals
to participate as Lecturers.
And special thanks to The American Institute of Mining, Metallurgical,
and Petroleum Engineers (AIME) for their contribution to the program.
CEMENTING
Planning for success to ensure
isolation for the life of the well
Daryl Kellingray, BP Exploration
Wherever we construct a well, we use cement
Why is cementing important ?
Prevention of flow to surface
z
MMS identified 19 cement related well
control incidents 1992 -2002.
Sustained Casing Pressure
•
25-30% of wells are estimated to
have annular pressure problems,
cementing is one of the primary
route causes.
Why is cement important ?
Mechanical well integrity during drilling
• Isolation of weak formation &
structural support
Reservoir Isolation and Protection
•
FG
D e p th (fe e t)
PP
Mud Wt (ppg)
Production Optimisation
z
Optimising stimulation treatments
Isolating production from other fluids
Cementing Planning For Success
z
Drilling Related Problems and
Learning
z
z
z
Long Term Isolation
z
z
z
z
Gas migration
Deep water
Isolation breakdown
Cement bonding
Mechanical Issues
Integrated Mud and Cement
Design
z
z
z
Balancing drilling fluids and
cementing requirements
Spacers
Cement placement
Classification of annular flows
Annular flow after cementing falls under three general
classifications:
•
Percolation through unset cement
•
Influx via mud channels (poor mud displacement)
•
Flow and/or pressure transmission through set cement (microannuli,
stress cracks, etc.)
In the MMS reporting system nearly all post
cementing flows occurred 3 - 8 hours after the job
Drilling Related Problems
Gel strength terminology
•
Static Gel Strength - rigidity in the matrix which resists forces placed on it
•
Critical Gel Strength - the gel strength which the hydrostatic column
(when accompanied by volume reduction)
•
Zero Gel Time or Delayed Gel Time - time to start of critical gel
strength (approx. 100 lb/100 ft2)
•
Transition Time (nothing to do with thickening time) - time
from zero gel time (usually 100 lb/100sqft) to 500 lb/100 ft2
Drilling Related Problems
Pressure decay
Full hydrostatic transmission < 100 lb/100sqft.
Migration risk from insufficient slurry density.
SETTING
Fully Liquid
Early Gelation
Hydration
Cement static with gels between 100–500 lb/100sqft.
Volume reduction by fluid loss reduces hydrostatic.
High risk of migration, mitigated by <30 min
transition times and compressible cements.
Cement is no longer deformable with rapid
development of strength, pore pressure in cement
dropping. Migration risk if high permeability.
Cement now has high compressive strength
and low permeability.
Set Cement
Drilling Related Problems
Effect of gel strength on pressure transmission
Gel Strength to support overbalance = (OBP)*(300)
(L/Deff),
where
OBP = overbalance pressure (psi)
300 = conversion factor (lb/in.)
L = length of the cement column (ft)
Deff = effective diameter (in.) = Dc - DOH
Dc = diameter of the casing (in.)
DOH = diameter of the open hole (in.)
E.g.
For 26”OH and 20” casing with a 50 psi overbalance 1000 ft beneath
seabed
Gel Strength =
300 * 50
1000/6
= 9 lb/100sqft !!!!
Drilling Related Problems
Prevention of annular flow
•
Quantify the risk (overbalance and cement column
height dependent)
•
Design mud displacement and cement placement
•
Determine rate of static gel strength development
•
Determine fluid loss requirements
Drilling Related Problems
Issues impacting deepwater slurry selection
Common cementing
questions ?
Deepwater
Considerations
Should cement be
tested at seabed
temperatures?
Ignores impact of cement
heat of hydration.
Will WOC always be
extended in deepwater
surface strengths?
Actual strength
requirements are low
(<100psi for pipe support)
Is foam cement the
only option?
API RP 65 favours foam
but not the only solution.
Low fracture gradients
require low density
cements?
In deep water the
seawater column reduces
cementing ECD’s and can
permit use of 1.92 SG
slurries
Drilling Related Problems
Cementing temperatures in deepwater wells
Computer simulated cement circulating temperatures v API
circulating temperatures for a deepwater 13 3/8” casing string
9000 ft below seabed.
Water depth
BHST (oF)
3000 ft
3000 ft
6000 ft
6000 ft
Simulated
cementing
temperature
API Spec 10
cementing
temperature
Simulated
cementing
temperature
API Spec 10
cementing
temperature
(oF)
(oF)
(oF)
(oF)
106
84
87
80
87
146
100
128
100
128
Drilling Related Problems
Cement setting at low temperature
Temperature oF
Are industry compressive strength tests representative when cementing
surface strings in deep water ?
Large scale experiment in temperature controlled room at 43oF using
simple 16 ppg class G cement.
140
120
100
80
60
40
20
0
Centre of annulus
4” cube
2” cube
1 2 3 4 5 6 7 8 9 10 11 12 13
Time (hours)
Drilling Related Problems
Crossflow in a micro annulus
Water Flowrate (bpd)
10000
1000
100
Assumptions
Water viscosity 0.3 cP
Pressure drop only in microannulus
Microannulus all around the liner
10
1
0
50
100
150
200
250
300
350
400
Microannulus Hydraulic Aperture (microns)
5,000psi across 65m
5,000psi across 10m
10,000psi across 65m
10,000 psi across 10m
450
500
5,000psi across 20 m
Long-Term Isolation
When does cement provide a seal?
Only good primary cement jobs were included in the analysis
Differential pressure between zones (psi)
14000
High risk zone
12000
10000
8000
6000
4000
2000
0
0
50
100
150
200
250
300
350
400
Cemented standoff between zones (ft))
No Breakdown Field A
No Breakdown field B
Isolation Breakdown
Long Term Isolation
Design steps for selecting a slurry
Develop an assurance process
z
Review analogous developments
z
z
z
z
Identify options and risk assess
including assessment of flow potential
Determine mechanical loadings and
complete modelling
Can robust pumpable slurries be
designed which can be effectively
placed?
Are the benefits real ? Warranting
cost and complexity?
PROJECTED IMPACT
A
C
0
B
F
E
A Reservoir isolation
B Poor hole conditions for
cementing
C Failure to optimise slurry
design
D Failure to execute job
according to plan
E Shallow Flows
F Inadequate Long Term
integrity
G Downhole pressure
management
during cementing
H Failure to keep the Quality
Plan up-dated and
alive
I Inadequate short term
integrity
J Environmental Impact
D
G
H
I
J
High
Moderate Low
MANAGEABILITY
Long Term Isolation
Cement expansion
4.5
5% MgO
4
3% MgO
% linear
expansion
3.5
3
2.5
Does expansion occur
when you need it ?
2
1.5
1
1% MgO
0.5
0
0
10
5
15
Age Days
Long Term Isolation
Internal and external volume changes
0.0
-0.5
% internal shrinkage
-1.0
1.9 SG Salt saturated class G
-1.5
-2.0
1.7 SG Pozmix
-2.5
1.9 SG Neat Class G
-3.0
Slurry
-3.5
-4.0
16 ppg neat G
14 ppg Pozmix
-4.5
0
5
10 15
20
25
30
35
40
45
Internal
Shrinkage
-4.1%
-2.6%
Bulk
Volume
Change
-1.7%
0.5%
50
hours
Long Term Isolation
Cement mechanical properties
z
z
To impact the mechanical resistance novel cements must decouple
stiffness (Young's modulus) from tensile strength.
Determination of mechanical properties under triaxial conditions is critical
for modelling.
Long Term Isolation
Bond variability across sands and shale
Commonly, cement
evaluation indicates
superior bonds are
obtained against
shale's compared
to sandstones.
gamma ray
attenuation
Long Term Isolation
Possible explanations for lithology effect
z
The log is wrong!
z
Cement shrinkage due to fluid loss or bulk shrinkage
z
Formation fluids entering cement impacting acoustic
properties
z
Shale squeezing onto the pipe
z
Mud filter cake
Long Term Isolation
OBM and WBM filter Cakes
OBM @ 280 deg F
WBM @ 280 deg F
24 hour fluid loss
= 40.2 ml
24 hour fluid loss
= 9.9 ml
Cake height
= 5/32”
“Cake” height
= 6/32”
Long Term Isolation
Areas of concern
z
z
z
z
z
z
z
Contamination of fluids
Spacer Design
Cement Bonding
Cement Placement
Execution / Logistics
Annular Pressure Build Up
Completion / Productivity
Integrated Mud and Cement Design
Mud Contamination of the cement spacer
z
Rotational viscometer 100 rpm reading
z
Barite Sag due to surfactants impacting oil based fluids
Unpumpable mixtures formed in surface lines or downhole
1000
900
Spacer compatibility
with mineral oil
based mud
800
700
(some values extrapolated as
reading off scale).
600
500
Note: Problem not
really evident at
25% mud
contamination !
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
100
% spacer in mixture
Integrated Mud and Cement Design
Rotational viscometer, 100 RPM, lb/100ft sq
Temperature effect on compatibility
180
70 deg F
120 deg F
185 deg F
160
140
120
100
80
60
40
20
0
100 / 0
75 / 25
50 / 50
25 / 75
0 / 100
% Mud / % Spacer
Surfactants are Temperature Dependent,
Very Critical in Deep Water
Integrated Mud and Cement Design
Mud contamination of cement
z
Mud Contamination Compressive Strength
3500
3000
Compressive Strength [psi]
Acceleration of cement due to
brine phase in cement
(cemented in liner running
tools)
z Retardation by WBM
(lignins/HEC/citrates/
borates)
z Impact on strength/acoustic
impedance and ability to
quantify cement bonding
2500
2000
1500
1000
WBM
500
SBM
0
0%
10%
20%
30%
40%
50%
60%
Mud Contamination [%]
Integrated Mud and Cement Design
Forces dictating efficient fluid displacement
z
Pressure Force
z
z
Buoyancy Force
z
z
Due to rheology hierarchy and increases with increasing flow rate.
From the density contrast between fluids, the buoyancy force
reduces with increasing hole angle.
Resistance Force
z
The resistance to movement of the gelled mud in the annulus,
increases as mud rheology increases and casing centralisation
decreases.
Simplistically for mud removal
Pressure + Buoyancy > 1
Resistance
Integrated Mud and Cement Design
Displacement variables
VERY POOR
DISPLACEMENT
VERY EFFECTIVE
DISPLACEMENT
POOR
DISPLACEMENT
Thin muds with good
pipe centralisation
and high flow rates
Thicker gelled muds
displaced with lighter
fluids with poor
centralisation
Thicker gelled muds
displaced with ineffective
spacers and poor
centralisation
Variables to Improve Displacement
* Density Difference
* Flow Rate
* Rheology of Pill and Mud
* Volume / Contact Time
* Pipe movement
Integrated Mud and Cement Design
Predicted effect of rotation on annular velocity
Axial Velocity
(m/s)
7” liner in 8.5” hole
Stand Off = 40%
10 RPM
No Rotation
25 RPM
2.2
1.9
1.6
1.3
1.0
0.7
0.5
0.35
0.2
0.1
0.05
0.025
0.0
Integrated Mud and Cement Design
GQS37586_30
Does pipe rotation help ?
Computer modelling of flow during liner rotation
P V /Y P 5 0/2 1 , 7 0 % S ta n d o ff
1.0
No channelling = 1
0.8
0.6
0.4
5 bbl/min
1 bbl/min
0.2
0
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5 25.0
RPM
Integrated Mud and Cement Design
Extended gel strength development for gel mud
140
120
Gel strength lb/100sqft
100
80
Typical timeframe
to break
circulation for
offshore surface
pipe
60
40
20
0
0
5
10
15
20
25
30
hours
Integrated Mud and Cement Design
Conclusions
z
There is a large industry problem related to the integrity
of the cement sheath providing Long Term Isolation.
z
Cement mechanical properties are important, but are
highly dependent on confining forces.
z
Temperatures in deepwater have a big impact on
cementing temperatures and surfactant efficiency in
cement spacer.
z
Mud displacement and subsequent cement placement is
the main cause of poor zonal isolation.
END