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SPE DISTINGUISHED LECTURER SERIESis funded principally
through a grant of the
SPE FOUNDATIONThe Society gratefully acknowledges
those companies that support the programby 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.
CEMENTINGPlanning 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 surfaceMMS 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• Isolating production from other fluids
Mud Wt (ppg)
Dep
th (f
eet)
PP FG
Mud Wt (ppg)
Dep
th (f
eet)
PP FG
Production OptimisationOptimising stimulation treatments
Cementing Planning For Success
Drilling Related Problems and Learning
Gas migrationDeep water
Long Term IsolationIsolation breakdownCement bondingMechanical Issues
Integrated Mud and Cement Design
Balancing drilling fluids and cementing requirementsSpacersCement 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
Fully Liquid
Hydration
Set Cement
Early Gelation
Full hydrostatic transmission < 100 lb/100sqft.Migration risk from insufficient slurry density.
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.
SETT
ING
Drilling Related Problems
Effect of gel strength on pressure transmission
Gel Strength to support overbalance = (OBP)*(300)(L/Deff),
whereOBP = overbalance pressure (psi)300 = conversion factor (lb/in.)L = length of the cement column (ft)Deff = effective diameter (in.) = Dc - DOHDc = 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 = 9 lb/100sqft !!!!1000/6
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 3000 ft 3000 ft 6000 ft 6000 ftBHST (oF) Simulated
cementing temperature
(oF)
API Spec 10 cementing
temperature
(oF)
Simulated cementing
temperature
(oF)
API Spec 10 cementing
temperature
(oF)
106 84 87 80 87146 100 128 100 128
Drilling Related Problems
Cement setting at low temperature
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.
020406080
100120140
1 2 3 4 5 6 7 8 9 10 11 12 13
2” cube
Centre of annulus
4” cube
Tem
pera
ture
o F
Time (hours)
Drilling Related Problems
Crossflow in a micro annulus
1
10
100
1000
10000
0 50 100 150 200 250 300 350 400 450 500Microannulus Hydraulic Aperture (microns)
Wat
er F
low
rate
(bpd
)
5,000psi across 65m 10,000psi across 65m 5,000psi across 20 m 5,000psi across 10m 10,000 psi across 10m
AssumptionsWater viscosity 0.3 cPPressure drop only in microannulusMicroannulus all around the liner
Long-Term Isolation
When does cement provide a seal?
Only good primary cement jobs were included in the analysis
Long Term Isolation
Cemented standoff between zones (ft))
No Breakdown Field A Isolation BreakdownNo Breakdown field B
0150 200 300250 3500
2000
50 100
6000
4000
10000
8000
12000
14000
400
Diff
eren
tial p
ress
ure
betw
een
zone
s (p
si)
Cemented standoff between zones (ft))
No Breakdown Field A Isolation BreakdownNo Breakdown field B
0150 200 300250 3500
2000
50 100
6000
4000
10000
8000
12000
14000
400
Diff
eren
tial p
ress
ure
betw
een
zone
s (p
si) High risk zone
Design steps for selecting a slurry
PRO
JEC
TED
IMPA
CT
MANAGEABILITYHigh Low0 Moderate
A
BC
D E
F
G
H I J
A Reservoir isolation B Poor hole conditions for
cementing C Failure to optimise slurry
designD Failure to execute job
according to planE Shallow FlowsF Inadequate Long Term
integrityG Downhole pressure
management during cementing
H Failure to keep the Quality Plan up-dated and alive
I Inadequate short term integrity
J Environmental Impact
Develop an assurance processReview analogous developments
Identify options and risk assessincluding 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?
Long Term Isolation
Cement expansion
0 5 1 0 15
4.54
3.53
2.52
1.51
0.50
Age Days
5% MgO3% MgO
1% MgO
% li
near
expa
nsio
n
Does expansion occur when you need it ?
Long Term Isolation
Internal and external volume changes
Slurry Internal Shrinkage
Bulk Volume Change
16 ppg neat G -4.1% -1.7%14 ppg Pozmix -2.6% 0.5%
1.7 SG Pozmix
1.9 SG Neat Class G
1.9 SG Salt saturated class G
1.7 SG Pozmix
1.9 SG Neat Class G
1.9 SG Salt saturated class G
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
% in
tern
al s
hrin
kage
-4.0
-4.5
0 5 10 15 20 25 30 35 40 45 50hours
Long Term Isolation
Cement mechanical properties
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 indicatessuperior bonds are obtained againstshale's comparedto sandstones.
gamma rayattenuation
Long Term Isolation
Possible explanations for lithology effect
The log is wrong!
Cement shrinkage due to fluid loss or bulk shrinkage
Formation fluids entering cement impacting acoustic properties
Shale squeezing onto the pipe
Mud filter cake
Long Term Isolation
OBM and WBM filter Cakes
OBM @ 280 deg F
24 hour fluid loss = 9.9 ml
“Cake” height = 6/32”
WBM @ 280 deg F
24 hour fluid loss = 40.2 ml
Cake height = 5/32”
Long Term Isolation
Areas of concern
Contamination of fluidsSpacer DesignCement Bonding Cement PlacementExecution / LogisticsAnnular Pressure Build UpCompletion / Productivity
Integrated Mud and Cement Design
Mud Contamination of the cement spacer
Barite Sag due to surfactants impacting oil based fluidsUnpumpable mixtures formed in surface lines or downhole
Spacer compatibility with mineral oil based mud(some values extrapolated as
reading off scale).
Note: Problem notreally evident at 25% mud contamination !
Rot
atio
nal v
isco
met
er 1
00 rp
m re
adin
g
% spacer in mixture
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70 80 90 100
Integrated Mud and Cement Design
Temperature effect on compatibility
0
20
40
60
80
100
120
140
160
180
% Mud / % Spacer
Rot
atio
nal v
isco
met
er, 1
00 R
PM, l
b/10
0ft s
q
70 deg F120 deg F185 deg F
100 / 0 75 / 25 50 / 50 25 / 75 0 / 100
Surfactants are Temperature Dependent,Very Critical in Deep Water
Integrated Mud and Cement Design
Mud contamination of cement
Acceleration of cement due to brine phase in cement (cemented in liner running tools)Retardation by WBM (lignins/HEC/citrates/borates)Impact on strength/acoustic impedance and ability to quantify cement bonding
Mud Contamination Compressive Strength
0
500
1000
1500
2000
2500
3000
3500
0% 10% 20% 30% 40% 50% 60%
Mud Contamination [%]
Com
pres
sive
Str
engt
h [p
si]
SBM
WBM
Integrated Mud and Cement Design
Forces dictating efficient fluid displacement
Pressure ForceDue to rheology hierarchy and increases with increasing flow rate.
Buoyancy ForceFrom the density contrast between fluids, the buoyancy force reduces with increasing hole angle.
Resistance ForceThe 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 POORDISPLACEMENTVERY EFFECTIVE
DISPLACEMENT
POORDISPLACEMENT
Thin muds with goodpipe centralisation and high flow rates
Thicker gelled muds displaced with ineffective
spacers and poor centralisation
Thicker gelled mudsdisplaced with lighter
fluids with poorcentralisation
Variables to Improve Displacement
* Density Difference * Rheology of Pill and Mud * Pipe movement* Flow Rate * Volume / Contact Time
Integrated Mud and Cement Design
Predicted effect of rotation on annular velocity
7” liner in 8.5” holeStand Off = 40%
No Rotation
10 RPM
25 RPM
Axial Velocity(m/s)
2.21.91.61.31.00.70.5
0.350.20.1
0.050.025
0.0
GQS37586_30Integrated Mud and Cement Design
Does pipe rotation help ?
Computer modelling of flow during liner rotation
5 bbl/min1 bbl/min
1.0
0.8
0.6
0.4
0.2
00.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0
RPM
P V / Y P 5 0 / 2 1 , 7 0 % S t a n d o f f
No channelling = 1
Integrated Mud and Cement Design
Extended gel strength development for gel mud
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30
Gel
str
engt
h lb
/100
sqft
hours
Typical timeframe to break
circulation for offshore surface
pipe
Integrated Mud and Cement Design
Conclusions
There is a large industry problem related to the integrity of the cement sheath providing Long Term Isolation.
Cement mechanical properties are important, but are highly dependent on confining forces.
Temperatures in deepwater have a big impact on cementing temperatures and surfactant efficiency in cement spacer.
Mud displacement and subsequent cement placement is the main cause of poor zonal isolation.
END