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Society of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl
How to Stabilize and Strengthen the Wellbore during Drilling OperationsWellbore during Drilling Operations
Dr Fred GrowcockDr. Fred Growcock
Society of Petroleum EngineersSociety of Petroleum Engineers Distinguished Lecturer Programwww.spe.org/dl
Presentation Outline
The Lost Circulation Problem
Strategy for Managing Lost Circulation
Wellbore StrengtheningWellbore Strengthening
Wellbore Stress Enhancement
Application Strategies on the Rig
Case HistoryCase History
Summary
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The Lost Circulation Problem: High-Risk Operations
eigh
t
Stable Wellbore
Fractured Wellbore
Pressure Gradient / Mud Density
Wei
ght
Mud
We Stable Wellbore
Collapsed Wellbore
Weak zone (depleted)
Frac Gradient
Mud
Mud
W
Well Inclination0 30 60 90
Deviated Wellbores
( p )Weight
Pore Pressure
Depleted ZonesDepleted Zones
Deep Water
The Lost Circulation Problem
• Estimated industry cost in the Gulf of Mexico:$1 billion/yr. Worldwide: ~ $ 2 to 4 billion/yr. y y
• On average, 10-20% of the total cost of drilling anHTHP well is expended on mud losses (U.S.Department of Energy)Department of Energy).
• No consistent approach to manage lost circulation.• Nearly 200 products offered by 50 drilling fluidNearly 200 products offered by 50 drilling fluid
companies to control lost circulation.
A comprehensive Lost Circulation mitigation and prevention program is required. g
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Managing Lost Circulation: A 4-Tiered Strategy
6
Tier I. Best Current or New
Accurate, precise Geomechanics Model, esp.Pore Pressure / Fracture Gradient
Minimum and invariant Equivalent Circulating Density (ECD)• Accurate hydraulics profile for pre-drilling & at well site
• Good hole-cleaning practicesg p
• Optimized solids control equipment
Managed Pressure DrillingManaged Pressure Drilling
Casing While Drilling
Expandable Casing/Liner7
Managing Lost Circulation: A 4-Tiered Strategy
8
Tier II. which Minimize Losses:
WBM:Full pressure shielded from tip by
solids filter cake buildup.
OBM/SBM:Full pressure at fracture tip.
based on Morita et al, SPE 20409
Tier II. which Minimize Losses:
High Low-Shear-Rate Viscosity (LSRV)Reservoir FluidsReservoir FluidsUnderbalanced FluidsAphron and Mixed Metal Fluids
Minimum and Invariant ECDSoluble or Micronized Weighting MaterialTemperature Insensitive RheologyTemperature-Insensitive Rheology
Wellbore IsolationSilicate, Gilsonite Fluids
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Managing Lost Circulation: A 4-Tiered Strategy
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Tier IV. in Pills or Whole MudContingency: losses in high perm zones/fractures
Blends of materials of
Contingency: losses in high-perm zones/fractures
Optimum Bridging Agent Blend for FluidBlends of materials ofdifferent sizes, shapesand properties;
D10 TD50 TD90 T
F0.8
0.9
1.0
Particle size distributionmatches distribution ofopenings in rock
BrandMudA=PuB=PuC=SnD=Om0.6
0.7
ize
Dis
trib
utio
n
openings in rock;
Used in squeeze orsweep treatments; 0.3
0.4
0.5C
umul
ativ
e Pa
rtic
le-S
sweep treatments;
May be used one timeor on regular basis Calc
Avg0
0.1
0.2
C
gwhile drilling ahead.
12
Avg Max 1x10 -2 1x10 -1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 40
Particle Size (microns)
Managing Lost Circulation: A 4-Tiered Strategy
13
vs
Fl kFlakes
Most Fibers Plates
Insoluble Salts
Plates
L i t
MarbleSynthetic Graphite
LaminatesHard,
Granular Fibers
Swellable or Reactive Materials
Soft Granules14
Strategies for Strengthening the Wellbore
• Physical– Wellbore Isolation: Swellable or Reactive Materials
F t Ti I l ti (F t P ti R i t )– Fracture Tip Isolation (Fracture Propagation Resistance)• Chemical
Decrease clay swelling pressure (inhibitors such as K+– Decrease clay swelling pressure (inhibitors such as K+ and invert emulsions)
• Thermale a– Increase temp of drilling fluid above bottom-hole static
temp: stiff formations, high thermal expansion• Mechanical
– Fracture Closure Stress– Hoop Stress Enhancement (Stress Cage)
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Fracture Propagation Pressure (FPP)Original Formation Breakdown Pressure (FBP)
Leak ‐OffPressure(LOP)
FBP after Wellbore Strengthening
e
Fracture Propagation Pressure (FPP)(LOP)
Fracture Gradient (FG)
Pressure Fracture Closure Pressure (FCP)
(= Minimum Horizontal Stress, Shmin)
P
Ti V l P d ( )Time or Volume Pumped (constant pump rate)
Fracture Closure Stress
• High-fluid-loss treatment for existing fractures
A li d hi h fl id l ill h l d• Applied as high-fluid-loss pills or whole mudtreatment (Drill-n-Stress)
• Pill may be water-based in a non-aqueoussystem
• May follow with cross-linked polymer plugs orcement
Fracture Closure Stress
As existing fracture is widened, particles are forced deep within the fracture.
Liquid leaks from the slurrythrough the fracture walls or tip.
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Fracture Closure Stress
As the slurry deliquifies, it consolidates.
The residual solid plug supports the fracture and isolates the tipisolates the tip.
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Hoop Stress Enhancement
• Wellbore is pre-fractured and sealed to preventsubsequent fracturing
• Mathematical models are used to design the : calculate the required fracture width and particle size q pdistribution of
• is added at moderate concentration whileis added at moderate concentration whiledrilling (involves solids control management):Continuous addition is much more effective than pillsp
• The formation is pressured every stand to build hoopstress or ECD is raised to desired levelstress, or ECD is raised to desired level
Hoop Stress Enhancement
As fracture is widened, large particles are forced inand wedged in the fracture mouth to create bridge
Smaller particles come in behind the bridgeand seal the openingg
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Hoop Stress Enhancement
Trapped fluid filtersthrough permeable walls of fracture
The pressure drops and compressive p p pforces are transferred to WSM
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Hoop Stress Enhancement Application Cycle
Suitability of Treatment Data CollectionModeling of FractureCreation and Fillingg
Output:-Fracture dimensions-Formulation of LossPrevention MaterialLessons Learned
Fluids Program-Type of treatment:
*Pills*ContinuousData Collected
-Handling WSM-Fluid property management-Monitoring tools
• Slot Tester• Sieves
-Mud Pump restrictionsD h l t l t i ti
ProgramImplementation
Data Collected&Analyzed
-Downhole tools restriction-Lost circulation contingency
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Design of Hoop Stress Enhancement
• Fracture Width required to achieve desired wellbore pressure – elastic model:
Desired Equiv. Circ. Density, or Wellbore Pressureq y
Rock Properties – Poisson’s Ratio, Young’s Modulus, Minimum Horizontal Stress (or Fracture Gradient)
Well Geometry – Depth, Inclination, Hole Size
• Acceptable types of WSMp yp• WSM particle size distribution (PSD) and
concentration
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AcceptableLarge, Tough and GranularLarge, Tough and Granular
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Unacceptable
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Continuous Addition of to whole mud is best
• For short intervals, bypass the shale shakers
• For long intervals screen out the WSM with the shakersFor long intervals, screen out the WSM with the shakers
• The most effective solution: an WSM Recovery System
Screens out drilled cuttingsScreens out drilled cuttings
Recovers and l WSMrecycles WSM
Screens out fines
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Screens out fines
Monitoring Hoop Stress Enhancement
• Techniques to be used at the rigsite:– Permeability Plugging Testsy gg g– Wet Sieve Analysis– Sand kit determination
• Techniques available at shore bases:Techniques available at shore bases:– Laser Light-Scattering Particle Size
Distribution– Fracture Sealing and Wellbore
Strengthening tests
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eepwater Gulf of Mexico, Above and Below Salteepwater Gulf of Mexico, Above and Below SaltCase History – Deepwater Gulf of Mexico
Major challenges• Mud losses…> 15,000 bbl/well
on previous wells especially in
SALTSALT
on previous wells, especially inintervals below the salt!
• Wellbore stability
S l tiSALTSALT Solution• Strengthen five intervals- One above the Salt
O i th S ltDrilling ECD exceeds min Frac Gradient
- One in the Salt- Three below the Salt• Shakers dressed with
14/20 mesh screens14/20 mesh screens• [WSM] ~ 15 to 30 lb/bbl• WSM Design
Si ed Marble- Sized Marble- Granular Synthetic Carbons
Case History – Deepwater Gulf of Mexico
No losses in 2900 ft sand section above salt No losses in 7500 ft salt section, screened upNo losses in 9200 ft sand section below salt (where majority of losses occurred in offset wells)(where majority of losses occurred in offset wells)
Savings• Total cost for the WSM ~ $ 0 7 MM Previous mud• Total cost for the WSM ~ $ 0.7 MM. Previous mud
losses ~ $ 2.7 MM. Net savings ~ $ 2.0 MM on materials alone.
• On subsequent 4 wells, similar net savings of ~ $ 2.0 MM on materials alone.
The 4-tier strategy for managing lost circulationSummary
must be an integral part of well planning
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