Drilling Fluid Technology
Lesson I
• Introduction and Objectives
– Technical/Scientific Aspects
• Function and Properties
– Wellbore Hydraulics, Cuttings
Transport
– Fundamentals of Rheology
– Drilling Fluids and Borehole
Stability
– Filtration Properties
– Balancing Formation Pressure
– Lost Circulation Problems
– Lubrication/Friction Reducing
– Corrosion Prevention
• Testing Methods/Equipment
• Mud Additives Controlling
Properties
Lesson II
• Solids Control
– Unweighted/Weighted Muds
• Types of Drilling Fluid
Systems
– Waterbased Mud
– Oilbase Mud/Emulsion Systems
• KTB-Experiences
– Strategy
– Pilot Hole
– Ultradeep Hole
• Conclusions
Drilling Mud – Why do we deal with?
Engineers
Drilling Tasks
Scientists
Mud
Mud/Fluids
!Bottomhole Cleaning
Borehole
Logging
Gas
!Borehole Wall Support
Tracers
!Balancing Formation Pressure
Cuttings
!Cooling the Bit
!Hydraulic Power Transmission
!Data Transmission (MWD)
!Reducing Friction
!Corrosion Protection
Mud
Gas
Fluids
Cuttings
Cores
Aiding Scientific Evaluation
!Cuttings Transport
Information Carrier
Technical Key Functions of Drilling Fluids
Rotary Hose
Mud CirculationSystem
Swivel
Hydraulic Optimization
Pump Pressure=f(Pumprate,MudViscosity)
Standpipe
Mud Pumps
Kelly
Charging Pumps
Rotary
Table
Transport of Cuttings
to Surface
Annulus
Shale
Aiding Solids Removal
Shaker
Mud Pits
Casing
Drillstring
Support of
Borehole Wall
Transmission of
Data/Hydraulic Power
Cooling Bit
Protection against
Corrosion
Reducing Friction
Torque/Drag
Balancing Formation
Cleaning the Bottom of the Hole
Pressure
Mud Properties Controlling Technical Key Functions
Functions
Complex Interaction
!Cleaning the Bottom of the Hole
!Transport of Cuttings to Surface
!Hydraulic Power
!Data Transmission
!Cooling the Bit
Properties
1
Rheological Parameters
•Viscosity
•Thixotropy
!Borehole Wall Support/Stabilization
!Balancing Formation Pressure
2
Density
Filtration Parameters
Free Water Capacity
!Reducing Friction/Torque and Drag
3
Lubricity Coefficient
!Protection against Corrosion
4
Chemical Composition
pH
physico-chemical Parameters
!Aiding Cuttings Removal and
Solids Control
5
Solids Content
weighted/unweighted
1
Fundamentals of Cutting Transport
Roundtrip/Circulation Break
Drilling/Mud Circulation
Transporting of Cuttings to Surface
Drill Pipe
Vann: Mud Velocity in Annulus
depends on:
•Pumprate,
Vsett: Cutting Settling Velocity
depends on:
•Mud Parameters
- Rheology (Viscosity)
- Density
•Cutting Parameters
-Density
-Diameter
-Shape
Vann>>Vsett
Basic Law of Cuttings Transport
(Vann-Vsett)/Vann > 50%
Annulus
•Annular Geometry
Drill
Collar
BHA
Drill Bit
Fundamentals of Cutting Transport
Roundtrip/Circulation Break
Drilling/Mud Circulation
Drill Pipe
Holding Cuttings in Suspension
τ0: Yield Strength of Mud
depends on:
•Rheological Behaviour
•Gel Strength, Thixotropy
τcutt: Tangential/Normal Stress
due to Cutting Weight
depends on:
-Cutting Diameter (dc)
-Cutting Density (ρc)
-Cutting Shape
-Mud Density (ρm)
Annulus
1
Drill
Collar
BHA
Drill Bit
τcutt=(dc*g(ρc-ρm))/6
τcutt<τ0
1
Cuttings Transport – The Role of Drilling Fluid Rheology
Circulation/Drilling
Dynamic Carrying Capacity
Rheological Behaviour while Flowing
Viscosity dependent on Shear Rate
Circulation Break/Roundtrip
Static Carrying Capacity
Rheological Behaviour while Stationary
Thixotropy: Fluid
Gel reversible
1
Theory of Fluid Rheology
Shear Stress - Shear Rate Diagram
τ
Vis
co
sity
Slope = Viscosity
ew
ton
ian
ud) e
M
ling r Rat
l
i
r
(D Shea
d
i
Flu t on
c
i
t
as enden
l
p
do dep
u
ity
e
s
s
o
y
P
sit
sc
i
o
c
V
Vis
ity
ia n
s
n
o
o
c
∆γ
wt
s
i
e
V
N
t
Slope = µ
w
n
o
e
L
ar
p
∆τ
Ap
Hig
hN
Viscosity
Shear Stress τ
γ
Typical Drilling Muds are
Shear Thinning
Viscosity decreases with
increasing Shear Rate
Shear Rate γ
Newtonian Fluid (Water, Mineral Oil):
Straight Line with Constant Slope
1
Drilling Mud Viscosity – Measuring Equipment
Rotational Viscosimeter
Marsh Funnel
946 cm3
Determination of Shear Dependent
Viscosity by Measuring Flow Curve at
different Rotational Speeds
Measuring Outflow time (s)
Water: 26 s
1
Measuring Rheological Behaviour of Drilling Fluids
Rotational Viscosimeter
Determination of Flow Model
Measuring Points
Flow Curve
RPM Reading
600
xx
300
xx
200
xx
100
xx
6
xx
3
xx
Reading
Measuring Points
Gel Strength
RPM
Reading
3 after 10 s
xx
3 after 10 min xx
Rotational
Speed (RPM)
Flow Models Describing Pseudoplastic Drilling Fluid Rheology
Shear Stress – Shear Rate Diagram
120
True Viscosimeter Readings
Shear Stress τ (Viscosimeter Reading)
1
100
R@600 RPM
Bingham Fluid
YP: Yield Point= 2*R300-R600
PV: Plastic Viscosity=R600-R300
80
Slope = PV
τ=YP+PV*γ
60
am
h
g
n
i
B
40
gh
i
a
r
St
e
n
i
tL
R@300 RPM
Power Law Fluid
YP
K: Konsistency Index=R300/511n
n: Power Law Coefficient=log(R600/R300)/0.301)
20
τ=K*γn
0
0
100
200
300
400
Shear Rate γ (Viscosimeter RPM)
500
600
Shear Thinning of Drilling Fluids –Impacts on Drilling Process
Low Shear-Range
High Viscosity
Apparent Viscosity µapp (mPas)
1
High Shear-Range
Low Viscosity
µapp= τ/γ
Newtonian Fluid
Bingham Fluid
Power Law Fluid
Annulus -> Cuttings
Transport
Bingham Asymptotic Line
for high Shear Rates µapp-> PV
Drillpipe -> Pressure Loss
Bit Nozzles -> Hydraulic Power at Bit
Solids Control -> Cutting Removal
µapp= µ = const
Shear Rate γ
1
Influence of Yield Point on Cuttings Transport Efficiency
Transport Ratio (%)
Annular Geometry: 5“ Drillpipe/12 ¼“ Hole
Yield Point YP (lbs/100sqft)
Impact of Mud Rheology on Cutting Lag Depth Correction
Hole Depth: 10 km
Mud Density: 1,01 kg/dm3
Cutting Density (kg/dm3)
Mud Rheology:
Rotational Viscosimeter:R(300)=16; R(600)=21
Bingham (YP= 5,3 Pa; PV=5 mPas)
Power Law (K=0,68;n=0,39)
Typical Density Ranges of Rock Minerals
Quarz/Feldspars
Corundum
Amphiboles
Mica
Garnets
Zircon Magnetite
Cutting Diameter: 1 mm
Cutting Shape: Sphere
Lag Depth Correction (m)
Hole Diameter: 8 ½“
Drillpipe Diameter: 5“
Lag Depth Correction (m)
1
1
Gel Building Properties of Drilling Fluids
Pump Pressure necessary for
Breaking Gel
Time dependent Gel Strength
While static: Gel
Drilling Fluids show
thixotropic properties While dynamic: Fluid
100
80
Gel Breaking Pressure
Gel Strength GS (Pa)
Thixotropy: GS@10min-GS@10s
Measured with Rotational
Viscosimeter @ 3 RPM
fragile Gel
desirable
progressive Gel
dangerous
Mining Drilling
5 ½“DP/6“Hole
KTB Pilot Hole
60
g
llin Hole
i
r
ry D 12 ¼“
a
t
Ro “DP/
5½
lling
i
r
D
y
Rotar
“Hole
½
7
1
/
P
5 ½“ D
40
20
0
Initial GS 10
after 10s
Time (min)
30
GS too high
high Surge/Swab Pressures
GS too low
Insufficient Static
Carrying Capacity for Cuttings
Narrow
Annulus
0
2
4
6
8
10
12
14
16
18
20
Gel Strength GS (Pa)
!Excessive Pump Pressures
!Formation Fracturing/Lost Circulation
!Borehole Instability
!Uncontrolled Influx of Formation Fluids
1
Optimizing Drilling Hydraulics
Objective: Maximizing Hydraulic Power at Bit
Pr
es
su
re
Pa
ra
sit
ic
Su
rfa
ce
Lo
ss
HPBit = HPSurface-HPParasitic
Hydraulic Power HP
Rule of Thumb for Rotary Drilling:
2/3 of total Pressure Loss at Bit
Bit
Optimum
Jet Nozzles in a Roller Cone Bit
Drillpipe
Annulus
Surface
Minimizing Parasitic Pressure Losses
PV as low as possible,
YP as high as necessary for Cuttings Transport
Pump Rate
Impact Parameters on Parasitic PL
!Annular Geometry
!Surface Equipment
!Drillpipe Size
!Mud Rheology (YP and PV)
1
Mud Additives Controlling Rheology
Viscosifiers
!Clays
•Bentonite
•Attapulgite
•Sepiolite
•Hectorite
Dispersants/Deflocculants
!Lignosulfonates
!Lignites
!Phosphates
!SSMA (Styrene Sulfonate Maleic Anhydride)
(important for High Temperature Applications)
!Polymers
•Biopolymers
-Xanthan
- Guar Gum
•Polyacrylate/Polyacrylamides
•HEC (Hydroxyethylcellulose)
•CMC (Carboxymethylcellulose)
Mineralogical Structure of Montmorillonite used in Drilling Muds
Faces negatively charged
+Edges positively charged +
+
+
+
Dispersion of Clay in Water
Na+, H20
H20
Cardhouse Structure
Gel
Edge/Face Aggregation
+
+
+
- - -
1
+
+
+
+
+
+
+
Increasing Plastic Viscosity (PV)
Decreasing Filtration Rate, Increasing Water Bonding
Clay
Platelets
dispersed and flocculated
dispersed
reversible
Face to Face
aggregated
aggregated and flocculated
Increasing Yield Point (YP) and Gel Strength
Flocculation
Dispersion
Face to Edge
irreversible
decreasing plastic Viscosity (PV)
Increasing filtration rate, reduced water bonding
State Diagram of Colloidal Montmorillonite Suspension in Water
Aggregation
1
2
Support of the Borehole Wall – Balancing Formation Pressures
While Drilling Open Hole
Mud Column should act as „Hydraulic Casing“
Sufficient Mud Density
Good Filtration Properties
Insufficient Mud Density
Bad Filtration Properties
-Uncontrolled Fluid Entry
-Borehole Instabilities
-Differential Sticking
Balancing Formation Pressures
Pressure of Mud Column
Pmud = Densitymud * g * Depth
Normal Drilling (overbalanced)
Mud Pressure > Formation Pressure
Pressure (MPa
overhydrostatic
subhydrostatic
Formation
Pressure Profile
Depth (km)
2
Sub
hydrostatic
geopressured Aquifer
2
Instruments for Measuring Mud Density
Hydrometer
Mud Balance
2
Weighting Materials for Drilling Muds
Solids Free Salt Solutions
Inert Solids
Mud Density (kg/dm3)
Mud Density (kg/dm3)
Solids Content and Mud Density for Various Weighting Materials
Solids Concentration (Volume Fraction)
2
Mud Density (kg/dm3)
2
Supporting the Borehole Wall – Hydraulic Casing Effect
Mud Properties
!Mud Density -> Pressure Support
!Filtration Characteristics -> Wall Sealing
!Free Water Activity -> Interaction Rock Beginning Filtration Buildup of Filtercake
Pore Pressure
Mud
Mud
Filter Cake
Impermeable
Formation
Mud
Mud Filtrate
Mud
Invasion of:
Wall sealed
Mud Particles
Good Filtration Characteristics
!Quick Filtercake Buildup
!Low Filtration Rate
!Filtercake
-thin
-impermeable
-slick
Pore Pressure
Minimizing Formation Damage
2
Filtercakes and Differential Sticking Mechanism
Overpull required to unstick BHA
Thick
Mudcake
2
Measuring Filtration Properties
Normal Conditions
HTHP Conditions
T: Room Temperature T: 300°F( 149°C)
P: 500 Psi (35 bar)
∆P: 100 psi (7 bar)
∆P: 100 psi (7 bar)
API Filter Press
Parameters measured:
!Filtrate Volume (ml) after 30 min
!Cake Thickness (mm)
2
Measuring Free Water Activity of Drilling Fluids
2
Destabilisation of Red Shale Caused by Contact with Water
CST < 70 s
Original Sample
Sample after 20 min in Water
CST >3600 s
Destabilisation Process is favoured
by High Free Water Activity
High Free Water Activity <-> Low CST
Low Free Water Activity <-> High CST
Sample after 24h in Dehydril HT (2%)
2
Additives Controlling Filtration Properties and Free Water Activity
Bentonite
Polymers
Polymers act as Protection Colloids
Preventing Aggregation of
Clay Particles
!Starch
!Polyanionic Cellulose (PAC)
!Sodium
Carboxymethylcellulose(CMC)
!Hydroxyethylcellulose(HEC)
!Polyacrylates/Polyacrylamides
!Vinylsulfonate/VinylamideCopolymers (VS/VA)
2
Prevention of Lost Circulation – Factors to Consider
Types of Lost Circulation Zones
Preventive Methods
•Reducing Mud Density
•Avoiding Pressure Surges
•Lowering Gel Strength
•Lowering Equivalent Circulation Density
(ECD)
High Permeable Gravel
Fighting Against Lost Circulation
Application of Sealing Material
Natural/Artificial Fractures
Sealing at
Fracture
Face
Sealing within
The Fracture
Proper Size Distribution
Types of Materials used:
Caverneous Formation
•Fibrous (Raw Cotton, Mineral Fibers, Glass Fibers)
•Flaky (Cellophane, Mica, Cotton Seed Hulls)
•Granular (Perlite, Ground Plastic, Nut Shells, Wood)
•Thick Slurry Pills (Bentonite/Polymer, Cement)
Reducing Friction – Controlling Torque/Drag
Borehole Curvature
Dogleg Severity: deg/m
Rotating
Drillstring
Trip In/Out
Drillstring
Normal Force FN
Friction Force FR
FR = µ * FN
Borehole Curvature
3
Drag (Trip In/Out)
Torque (Rotation)
Mud Lubricity Coefficient
3
Lubricity Coefficients of Drilling Muds
4
Inhibiting Corrosion
Pitting Corrosion Inside Drillpipe
Stress Corrosion at DP-Tooljoint
Corrosion is the Major Cause
of Drillpipe Failures
Forms of Corrosion
!Uniform Corrosion
!Localized Corrosion (Pitting)
•Bimetallic Corrosion
•Oxygen Concentration Cells
-Crevice Corrosion
-Air/Water Interface
-Oxygen Tubercles
-Scaling/Sludges
!Corrosion Fatigue
!Stress Corrosion
•Sulfide Cracking
•Hydrogen Embrittlement
Measures
!Raising pH of Mud
!Reducing dissolved Oxygen in
Mud
•Vacuum Degassing
•Oxygen Scavengers
-Sodium Sulfite
-Sodium Nitrite
!Addition of Corrosion Inhibitors
•Filming Amines
•Sulfide Scavengers
•Zinc Carbonate
•Sodium Molybdate
4
Mud Additives for pH and Alkalinity Control
5
Mud Circulation System and Solids Control Equipment
Mud Properties Must Aid
Effective Cuttings Removal
Kelly Hose
Standpipe
Solids Control Equipment
Is the Base for
Cutting Sampling
Swivel
Mixing Hopper
Mud Pump
Centrifuge
Desilter
Desander
Degasser
Suction Pit
Shaker Screen
Mud Return
Flowline