1. 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.
LIKE TO ACKNOWLEDGE SPE AND THANK YOU FOR THE INVITATION TO TALK TO YOUR GROUP

2. Daryl Kellingray, BP Exploration
CEMENTING Planning for success to ensure isolation for the life of the well
I HAVE WORKED FOR BP FOR 22 YEARS, INITIALLY IN R&D ON WELL CEMENTS BUT IN OPERATION FOR THE LAST 16 YEARS. THIS HAS INVOLVED OPERATIONS IN EUROPE/BAKU/GOM/AFRICA/SOUTH AMERICA / CARIBBEAN. DEEPWATER /ONSHORE / OFFSHORE AND HPHT.
Daryl Kellingray, BP Exploration

3. Wherever we construct a well, we use cement
THE CEMENTING PROCESS IS SIMILAR WHETHER OFFSHORE / DEEPWATER IN THE ARTIC OR THE DESERT. IT REQUIRES CEMENT SIMILAR TO YOU WOULD BUY FOR USE AT HOME BEING PUMPED DOWN THE WELL AND DISPLACED INTO THE ANNULUS TO COVER POTENTIAL FLOW ZONES. CEMENT IS A VERY OLD MATERIAL AND HAS BEEN USED FROM THE EARLIEST WELLS. THERE ARE FEW IF ANY WELLS CONSTRUCTED WHICH DO NOT INVOLVE CEMENT IN ONE WAY OR ANOTHER.

4. Why is cementing important ?
Prevention of flow to surface
MMS identified 19 cement related well control incidents
Sustained Casing Pressure
25-30% of wells are estimated to have annular pressure problems, cementing is one of the primary route causes.
CEMENT PROVIDES PART OF THE PRIMARY ISOLATION IN A WELL.
FAILURE CAN BE SPECTACULAR WITH FLOW EVIDENT WITHIN HOURS OF THEN CEMENT BEING PUMPED AT SURFACE (OR IN THIS EXAMPLE IN THE SEA)
LESS SPECTACULAR BUT WITH POTENTIALLY SIGNIFICANT ECONOMIC AND REPUTATIONAL IMPACTS IS THE FAILURE OF THE ANNULAR SEAL DURING WELL OPERATIONS.
SINCE MOST WELLS HAVE SIMILAR CHALLENGES THE QUALITY OF PLANNING AND ENGINEERING IS CRITICAL TO PREVENTING EITHER OF THESE EVENTS

5. Why is cement important ?
Mechanical well integrity during drilling
Isolation of weak formation &
structural support
Reservoir Isolation and Protection
Isolating production from other fluids
FOR DRILLING CEMENT IS OFTEN VIEWED AS AN EVIL NECESSITY TO ACHIEVE THE PRIMARY WELL OBJECTIVES TO REACH THE TARGET SAFELY. IN THESE CASE ADEQUATE SHOE ISOLATION AND NO IMMEDIATE POST CEMENT FLOWS ARE ALL THAT ARE REQUIRED.
BUT GOOD LONG TERM ISOLATION IS CRITICAL FOR PRODUCTION (PREVENTING X-FLOW OF UNWANTED FLUIDS) AND LONG TERM WELL OPERABILITY AND STIMULATION.
Production Optimisation
Optimising stimulation treatments

6. 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
IN THIS TALK I WILL DESCRIBE LEARNING ASSOCIATED WITH PREVENTING EARLY FLOWS AFTER CEMENTING AND CEMENTING IN DEEPWATER.
THE ISSUES TO CONSIDER WHEN DESIGNING CEMENT FOR LONG TERM ISOLATION.
AND HOW WE NEED TO ENGAGE THE MUD AND CEMENT ENGINEERING DESIGNS TO ENSURE EFFECTIVE CEMENTING TO PROVIDE CEMENT CAPABLE OF PROVIDING LONG TERM ISOLATION.

7. 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 (micro annuli, stress cracks, etc.)
In the MMS reporting system nearly all post
cementing flows occurred hours after the job
ANNULAR FLOW AND SUBSEQUENT ANNULAR INTEGRITY PROBLEMS NORMALLY FALL INTO ONE OF THESE CATEGORIES
I WILL COVER THE SECOND TWO OPTIONS LATER IN THE TALK
THE EARLY FLOW PROBLEMS HIGHLIGHT THE CRITICALITY OF CEMENT PLACEMENT TO PREVENT ANNULAR FLOWS
Drilling Related Problems

8. Pressure decay SETTING 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.
SETTING
ESSENTIALLY AS A FLUID (<100LB/100SQFT) THE CEMENT COLUMN TRANSMITS HYDROSTATIC HOWEVER IN THE EXAMPLE TO COME IN THE CASE OF SHALLOW FLOWS WHERE THERE ARE VERY SMALL OVERBALANCES SMALL GELS CAN BE A PROBLEM.
AS THE CEMENT PASSES THROUGH THE TRANSITION TIME IT MAY PERMIT A FLUID INFLUX, IT IS THE RATE OF THIS TRANSITION WHICH CAN DETERMINE IF THE INFLUX CAN MIGRATE. NORMALLY WE WOULD LOOK FOR A TRANSITION TIME OF LESS THAN 30 MINS TO PREVENT MIGRATION OF AN INFLUX.
ONCE THE CEMENT IS IMMOVABLE (BEFORE HYDRATION KICKS IN) IT MAY HAVE SUFFICIENT PERMEABILITY TO PERMIT WELLBORE FLUIDS TO ENTER THE CEMENT MATRIX, IF THIS OCCURS THIS FLUID COULD MIGRATE AND DAMAGE ISOLATION.
ONCE SIGNIFICANT HYDRATION HAS BEGUN THE CEMENT DEVELOPS VERY LOW PERMEABILITY AND FLUIDS CAN NO LONGER MIGRATE UNLESS CHANNELS HAVE ALREADY FORMED.
Drilling Related Problems

9. 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
THE KEY STEPS TO STOPPING SHALLOW FLOW ARE:
ASSESS THE RISK DETERMINED BY GEOLOGICAL ASSESSMENT AND THE ABILITY OF CEMENT TO CONTROL FLOW
ENGINEER THE CEMENT PLACEMENT, MOST FLOW OCCURRENCES ARE ASSOCIATED WITH POORLY PLACED CEMENT
DETERMINE THE TRANSITION TIME AT THE DEPTH THE FLOW RISK EXISTS, THE GEL STRENGTH DEVELOPMENT WILL DEPEND ON TEMPERATURES.
BASED ON THE ABOVE MAKE A SLURRY SELECTION OF:
FLUID LOSS
COMPRESSIBLE
SHORT TRANSITION TIME
PERMEABILITY MODIFIERS
Drilling Related Problems

10. 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

11. Supporting a cement plug
VISCOUS
REACTIVE PILL
CEMENT
“CATCHER”
INFLATABLE
PACKER
SPACER
CEMENT
MUD
Drilling Related Problem

12. Develop an assurance process
Design steps for selecting a slurry
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
ONCE CEMENT IS ON PLACE THERE IS NOW EVIDENCE THAT ISOLATION CAN BREAK DOWN DURING WELL COMPLETION AND OPERATION.
THE ABOVE STEPS HIGHLIGHT THE STEPS TO FOLLOW IN SELECTING A CEMENT SOLUTION.
UNDERSTAND THE RISK FROM THE SUB SURFACE BY REVIEWING ANALOGOUS OFFSETS
COMPLETE MODELLING OVER THE LIFE OD THE WELL ASSESSING THE EFFECT OF THE CHANGING OPERATING ENVIRONMENT THROUGH THE LIFE OF THE WELL ON THE CEMENT SHEATH E.G.
COMPLETION FLUIDS CHANGES
STIMULATION
DEPLETION
ONCE THE RISK ARE UNDERSTOOD AND QUANTIFIED REVIEW THE TECHNICAL SOLUTIONS AND ASSESS IF THE BENEFITS ARE REAL AND THE ABILITY TO IMPLEMENT EFFECTIVELY (IE CAN PLACEMENT BE DESIGN TO ENSURE FULL ANNULAR COVERAGE ?)
Long Term Isolation

13. Crossflow in a micro annulus
10000
1000
Water Flowrate (bpd)
100
Assumptions
Water viscosity 0.3 cP
Pressure drop only in microannulus
Microannulus all around the liner 10
ONE OF THE PRIMARY ISSUES IS THE RISK OF MICROANNULUS FORMATION.
THIS PLOT SHOWS THEORETICAL WATER FLOW RATES THROUGH DIFFERENT DIAMETER MICROANNULI
FOR VARYING PRESSURE DIFFERENTIAL ACROSS THE DIFFERENT LENGTH SECTION IT CAN BE SEEN THAT AT A 5000 PSI DIFFERENTIAL ACROSS 20 M THE RATE COULD BE 100 BPD FOR A 100 MICRON MICROANNULUS. THIS MODELLING MAKES NO ALLOWANCE FOR FLOW INCREASING THE DIAMETER OF THE ANNULUS SO THIS COULD BE SEEN AS A MINIMUM.
ESSENTIALLY THIS IS SAYING IF YOU HAD A 20 M SHALE WELL CEMENTED BUT CREATED A 100 MICRON MICROANNULUS DURING COMPLETION A 5000 PSI DIFFERENTIAL COULD RESULT IN 100 BPD OF WATER PRODUCTION. 1 50
100
150
200
250
300
350
400
450
500
Microannulus Hydraulic Aperture (microns)
5,000psi across 65m
10,000psi across 65m
5,000psi across 20 m
5,000psi across 10m
10,000 psi across 10m
Long-Term Isolation

14. When does cement provide a seal?
Only good primary cement jobs were included in the analysis
High risk zone
AS PART OF THE FRONT END DESIGN FOR A HP DEVELOPMENT WE REVIEWED PERFORMANCE IN HP OFFSETS ASSESSING IF A CEMENT SEAL WAS STABLE OVER THE LIFE OF THE WELL. THE GRAPH PLOTS WHERE WE FOUND ISOLATION BREAKDOWN OCCURRED BASED ON THE CEMENT STAND OFF AND DIFFERENTIAL PRESSURE. BREAKTHROUGH WAS IDENTIFIED WHEN FLOW FROM THE HIGHER PRESSURE ZONE WAS DETECTED.
THIS IDENTIFIED THE HIGH RISK WAS ABOVE 6000 PSI DIFFERENTIAL AND LESS THAN 50 FT STAND OFF BETWEEN ZONES THIS LED US TO CONCLUDE THAT IN MOST WELL WHERE WE KNOW WE HAVE GOOD CEMENT IT IS VERY DURABLE. ONE NOT OF CAUTION IS THAT LITTLE DATA EXISTED BELOW 10 FT.
Long Term Isolation

15. Cement expansion 5 1 1 5 Does expansion occur when you need it ?4 . 5
5% MgO 4
3% MgO 3 . 5 3
% linear
expansion 2 . 5
Does expansion occur
when you need it ? 2 1 . 5 1
1% MgO
WITH THE INCREASING CONCERN ABOUT THE STABILITY OF THE SET CEMENT SEAL THERE HAS BEEN INCREASED INTEREST IN EXPANDING CEMENTS PARTICULARLY TO MITIGATE MICROANNULI. CEMENT CAN CERTAINLY BE MADE TO EXPAND HOWEVER STANDARD UNIVERSAL ADOPTION IS NOT APPROPRIATE.
IN VERY WEAK FORMATIONS THERE IS EVEN A FEAR THAT EXPANSION COULD INCREASE THE MICROANNULUS HOWEVER THE BIGGER CONCERN IS THE REACTION OCCURS IN THE FIRST FEW DAYS AFTER SETTING SO IF THE PRESSURE REGIME IS NOT CHANGED IN THE WELL IN THE TIMESCALE THE BENEFIT MAY BE LIMITED OR NON EXISTENT. . 5 5 1 1 5 A g e D a y s
Long Term Isolation

16. Cement mechanical properties
ONE OF THE MAIN AREAS OF RECENT RESEARCH IN CEMENT HAS FOCUSSED ON THE MECHANICAL PROPERTIES OF THE SET CEMENT. CEMENTS CAN BE DESIGNED WITH A RANGE OF YOUNG'S MODULI ESSENTIALLY CEMENTS CAN BE MADE MORE OR LESS FLEXIBLE THAN NEAT 16 PPG G/H
HOWEVER LIKE ROCKS THEIR MECHANICAL PROPERTIES ARE DETERMINED BY THE CONFINING STRESSES AROUND THE CEMENT. THIS SET OF RESULTS SHOWS THAT FOR A SIMPLE 16 PPG SYSTEM INCREASING THE CONFINING STRESS FROM 100 –TO 7500 PSI HAS A DRAMATIC IMPACT ON THE FAILURE (THE LOAD AND RECOVERY. ESSENTIALLY AT HIGH PRESSURE CEMENTS ACT IN A MORE PLASTIC WAY WHEREAS THEY ARE BRITTLE IN UNCONFINED CONDITIONS (BLUE LINE)
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

17. Bond variability across sands and shale
Commonly, cement evaluation indicates
superior bonds are obtained against
shale's compared
to sandstones.
HAVING SUCCESSFULLY COMPLETED THE CEMENT OPERATION OFTEN WE WANT TO DETERMINE THE INSITU CEMENT QUALITY. THIS HAS BEEN NOTORIOUSLY DIFFICULT AND CEMENT “CONFUSION” LOGS IS THE USUAL DESCRIPTION.
A COMMON OBSERVATION IS THE FACT THAT BOND QUALITY SEEMS TO REFLECT FORMATION CHARACTERISTICS.
THAT IS GOOD CEMENT BOND ACROSS SHALES COMPARED TO A SANDSTONE.
gamma ray
attenuation
Long Term Isolation

18. 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
AFTER MANY YEARS OF IGNORING THESE LOGS (CEMENT “CONFUSION” LOGS BECAME A COMMON EXPLANATION) WE ARE MORE INCLINED TO BELIEVE THAT THE LOGS ARE REALLY INDICTING A DIFFERENCE IN THE CEMENT.
THE EXPLANATION IS STILL BEING INVESTIGATED
Long Term Isolation

19. Areas of concern Contamination of fluids Spacer Design Cement Bonding
Cement Placement
Annular Pressure Build Up
ONE OF THE PRIMARY FAILINGS IN CEMETING DESIGN AND EXECUTION IS THE LACK OF ENGINEERING ALIGNMENT BETWEEN THE DRILLING FLUIDS AND CEMENT PROGRAMMES.
MUD CAN
CONTAMINATE SPACER AND CEMENT
IMPACT BONDING
BE DIFFICULT TO DISPLACE
COMPROMISE PIT LOGISTICS
END AS TRAPPED VOLUME LEADING TO ANNULAR PRESSURE BUILD UP
IMPACT WELL INTERVENTION ACTIVITY
OFTEN THE OPTIMUM DRILLING FLUID IS NOT OPTIMUM FOR CEMENTING.
Integrated Mud and Cement Design

20. Mud Contamination of the cement spacer
Spacer compatibility
with mineral oil
based mud
(some values extrapolated as reading off scale).
Note: Problem not
really evident at
25% mud
contamination !
Rotational viscometer 100 rpm reading
ONE OF THE FIST CONCERNS IS TO ENSURE MUD AND SPACER COMPATIBILITY
POOR COMPATIBILITY WILL RESULT IN CEMENT CHANNELLING AND POOR ZONAL ISOLATION
THIS EXAMPLE HIGHLIGHTS THAT THE COMMON RATIOS OF COMPATIBILITY TESTING ARE NOT ALWAYS SUFFICIENT TO IDENTIFY THE PROBLEMS
EXPLAIN WHAT HAPPENED.
% spacer in mixture
Integrated Mud and Cement Design

21. Surfactants are Temperature Dependent, Very Critical in Deep Water
Temperature effect on compatibility
180
20 deg C
160
52 deg C
85 deg C
140
120
100
Rotational viscometer, 100 RPM, lb/100ft sq 80 60 40 20
TO COMPOUND THE PROBLEM SPACER EFFECTIVENESS IS TEMPERATURE DEPENDENT. THIS IS PARTICULARLY IMPORTANT IN DEEP WATER. THE ABOVE SHOWS THE ABILITY OF THE SURFACTANT TO PREVENT VISCOUS EMULSION OCCURRING IS DEPENDENT ON THE TEMPERATURE.
THIS IS ANALOGIES TO WASHING AT HOME WHERE TO BE EFFECT AT LOW TEMPERATE YOU NEED DIFFERENT DETERGENTS, E.G. WASHING UP A GREASY PLATE IN COLD WATER.
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

22. Mud contamination of cement
Acceleration by brines
Retardation by WBM (lignins/HEC/citrates/
borates)
Impact on strength/acoustic impedance
WBM
CONTAMINATION OF THE CEMENT CAN HAVE SERIOUS IMPACTS
SMALL QUANTITIES OF OBM REDUCE THE PUMPING TIME DUE TO THE BRINE PHASE IN THE OBM.
> 10% CONTAMINATION WILL HAVE A SIGNIFICANT IMPACT ON COMPRESSIVE STRENGTH. TWO IMPACTS ARE THAT THIS MAY IMPACT DRILL OUT / PRESSURE TESTING THE SHOE OR THE EVALUATION SINCE ACOUSTIC IMPEDANCE WHICH MOST LOGGING TOOLS DETERMINE IS DIRECTLY PROPORTIONAL TO STRENGTH.
SBM
Integrated Mud and Cement Design

23. 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
TO DISPLACE DRILLING FLUID ESSENTIALLY THE SUM OF THE PRESSURE FORCE DUE TO THE RHEOLOGY PROFILE OF THE DISPLACING FLUID AND THE DENSITY DIFFERENTIAL MUST EXCEED THE RESISTANCE (NORMALLY CONSIDERED TO BE THE GEL STRENGTH).
IN VERTICAL WELLS THE BUOYANCY IS VERY EFFECTIVE HOWEVER IN HIGH ANGLE WELLS YOU MUST RELY ON PRESSURE AS THE DISPLACING FORCE NB
TURBULENT FLOW IS BY FAR THE MOST EFFECTIVE DISPLACEMENT MECHANISM HOWEVER IT IS UNLIKELY THAT ANY BARITE WEIGHTED SPACER CAN BE PUMPED IN TURBULENT. IF A WASH CAN BE PUMPED (DETERMINED BY WELL CONTROL RESTRICTIONS) THIS IS VERY EFFECTIVE.
Integrated Mud and Cement Design

24. 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 ineffective
spacers and poor
centralisation
Thicker gelled muds
displaced with lighter
fluids with poor
centralisation
TO IMPROVE MUD DISPLACEMENT
MAXIMISE DENSITY DIFFERENCE
REDUCE MUD RHEOLOGY (BEFORE RUNNING PIPE)
MAXIMISE CENTRALISATION
ADDITIONAL ENERGY
PUMP FASTER
MOVE PIPE
DO NOT FORGET THERE ARE TWO INTERFACES SPACER MUD AND CEMENT SPACER, BOTH NEED TO BE ASSESSED.
Variables to Improve Displacement
* Density Difference * Rheology of Pill and Mud * Pipe movement
* Flow Rate * Volume / Contact Time
Integrated Mud and Cement Design

25. Predicted effect of rotation on annular velocity
Axial Velocity
(m/s)
7” liner in 8.5” hole
Stand Off = 40%
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
10 RPM
PIPE ROTATION CAN BE BENEFICIAL PARTICULARLY IF THERE IS A LOW STAND OFF (CASING ECCENTRIC) HOWEVER HIGH RATES MAYBE NEED TO MITIGATE THE LOW FLOW RATE ON THE LOW SIDE OF THE ANNULUS (PROBABLY >50 RPM WHICH MAY NOT BE SUITABLE FOR THE CONNECTIONS ON THE PIPE) .
No Rotation
25 RPM
Integrated Mud and Cement Design
GQS37586_30

26. 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.
IN SUMMARY
INDUSTRY GROWING TO UNDERSTAND THAT CEMENT PAYS A LARGE PART IN THE NUMBER OF WELLS THAT SHOW SCP
CEMENT PLACEMENT IS ONE OF THE PRIMARY CAUSES OF PROBLEMS AND INTEGRATION OF THE MUD AND CEMENT DESIGNS IS CRITICAL FOR SUCCESS
DEEPWATER IS DIFFERENT AND STANDARD CEMENT DESIGN PRACTICE NEED TO BE ADAPTED
CEMENT PROPERTIES AFTER SETTING CAN BE COMPROMISED DURING WELL OPERATION AND PARTICULARLY IN HPHT WELLS MODELLING OF THE IMPACT OF THE OPERATING CONDITIONS ON THE CEMENT SHEATH IS MODELLED AND TESTED AT REAL DOWNHOLE CONDITIONS.

27. END