Wellbore quality characterization for securing successful ...
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SPE DISTINGUISHED LECTURER SERIES is funded principally through a grant of the SPE FOUNDATION The Society gratefully acknow ledges those companies that support the program by allow ing their professionals to participate as Lecturers. And special thanks to The American Institute of Mining, Metallurgical, and PetroleumEngineers (AIME) for their contribution to the program.
Transcript of Wellbore quality characterization for securing successful ...
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 surface 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 ?
Production Optimisation Optimising stimulation treatments
Mud Wt (ppg)
Dept
h (fe
et)
PP FG
Mud Wt (ppg)
Dept
h (fe
et)
PP FG
Mechanical well integrity during drilling• Isolation of weak formation &
structural support
Reservoir Isolation and Protection• Isolating production from other fluids
Cementing Planning For Success
Drilling Related Problems and Learning Gas migration Cement Plugs
Long Term Isolation Isolation breakdown Cement bonding Mechanical Issues
Integrated Mud and Cement Design Balancing drilling fluids and
cementing requirements Spacers Cement placement
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 (micro annuli, stress cracks, etc.)
In the MMS reporting system nearly all post cementing flows occurred 3 - 8 hours after the job
Classification of annular flows
Drilling Related Problems
Pressure decay
Drilling Related Problems
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.
SE
TT
ING
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 at relevant temperature
• Determine if potential for fluid loss exists which can impact loss of hydrostatic and gel strength
Drilling Related Problems
Cement plug primary rules
• Use a mechanical base or viscous reactive pill (VRP) to prevent slippage.
• Rotate cement stinger during placement to aid placement
• The top of plug will be contaminated (>10% of length)
• Optimise mud and spacer properties
• Ensure accurate displacement volumes.
Drilling Related Problem
Supporting a cement plug
MUD
CEMENT
SPACER
VISCOUS REACTIVE PILL
CEMENT “CATCHER”
INFLATABLE PACKER
Drilling Related Problem
Develop an assurance process Review analogous developments
Identify options and risk assess including assessment of flow potential
Determine mechanical loadings and complete modelling
Identify options that really reduce risks
Assure system complexity does not impact reliable execution
Design steps for selecting a slurry
Long Term Isolation
Crossflow in a micro annulus
Long-Term Isolation
1
10
100
1000
10000
0 50 100 150 200 250 300 350 400 450 500Microannulus Hydraulic Aperture (microns)
Wat
er F
low
rate
(b
pd
)
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
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
Cement expansion
0 5 1 0 15
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Age Days
5% MgO
3% MgO
1% MgO
% li
nea
rex
pan
sio
n
Does expansion occur when you need it ?
Long Term Isolation
Cement mechanical properties
Long Term Isolation
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.
Commonly, cement evaluation indicatessuperior bonds are obtained againstshale's comparedto sandstones.
Bond variability across sands and shale
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
Areas of concern
Contamination of fluids
Spacer Design
Cement Bonding
Cement Placement
Annular Pressure Build Up
Integrated Mud and Cement Design
Mud Contamination of the cement spacer
Spacer compatibility with mineral oil based mud (some values extrapolated as
reading off scale).
Note: Problem notreally evident at 25% mud contamination !
Ro
tati
on
al v
isco
met
er 1
00 r
pm
rea
din
g
% spacer in mixture
Integrated Mud and Cement Design
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70 80 90 100
0
20
40
60
80
100
120
140
160
180
% Mud / % Spacer
Ro
tati
on
al v
isco
met
er,
100
RP
M,
lb/1
00ft
sq
20 deg C52 deg C85 deg C
100 / 0 75 / 25 50 / 50 25 / 75 0 / 100
Surfactants are Temperature Dependent,Very Critical in Deep Water
Temperature effect on compatibility
Integrated Mud and Cement Design
Mud contamination of cement
Acceleration by brines
Retardation by WBM (lignins/HEC/citrates/borates)
Impact on strength/acoustic impedance
Mud Contamination Compressive Strength
0
500
1000
1500
2000
2500
3000
3500
0% 10% 20% 30% 40% 50% 60%
Mud Contamination [%]
Co
mp
res
siv
e S
tre
ng
th [
ps
i]
SBM
WBM
Integrated Mud and Cement Design
Forces dictating efficient fluid displacement
Pressure Force Due to rheology hierarchy and increases with increasing flow rate.
Buoyancy Force From the density contrast between fluids, the buoyancy force
reduces with increasing hole angle.
Resistance Force 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 EFFECTIVEDISPLACEMENT
POORDISPLACEMENT
VERY POORDISPLACEMENT
Thin muds with goodpipe centralisation and high flow rates Thicker gelled muds
displaced with lighter fluids with poorcentralisation
Thicker gelled muds displaced with ineffective
spacers and poor centralisation
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
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.
Failed cement plugs are the most common cementing problem, design and engineering needs to use same process as a primary job
Mud displacement and subsequent cement placement is the main cause of poor zonal isolation.
END
