Improvements In Oil Base Mud Technology Enhances Drilling
Efficiencies On Extended Reach Wells
-A Wellsite Perspective-
Hole Stability - What Mud Weight Is Required?– Pore Pressure– Fracture Gradient– Hole Inclination
Formation Characteristics– Lithology– Mechanical Strength– Chemical Reaction
Developing The Mud ProgramFactors to Be Considered For ERD
smax
smin P
WellboreCollapse
TensileFracturing
Developing The Mud ProgramFactors to Be Considered For ERD
HoleCleaning
Formation
ROP
Cuttings Size
Hole Angle
Section Length
Flow RegimeAnnular Velocity
Fluid Rheology
Pipe Eccentricity
Velocity Profile
Pipe Rotation
Mud Weight
Wellbore Path– Rate Of Build /
Drop– Max. Angle– Azimuth Changes– Section Lengths– How Much
Steering?
Developing The Mud ProgramFactors to Be Considered For ERD
Lubricity– Torque & Drag
» DP Make-up Torque Ratings
» Computer Simulations
– Top Drive Rating (Do You Have a Top Drive?)
– COF Of The Mud– COF Of Formations
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
OBM
Synthetics
WBM
Coefficient Of Friction
Avg. COF of Various Fluids
Lubricant Enhanced
Hydraulics– Pressure Requirements/Limitations– Pumping Capability
» Number of Pumps» Pressure Rating
– ECD Concerns– Motors, Downhole Tools– Drillpipe Size (65/8, 5½, 5)– Mud Rheology (Minimization of
PV’s)– Liner Instead of Casing?
Developing The Mud ProgramFactors to Be Considered For ERD
Hydraulic Analysis6-5/8” vs 5” DP
0
1000
2000
3000
4000
5000
6000
7000
8000
Pre
ssu
re (
psi
)
6-5/8"+5" DP 5" DP 5" DP850 GPM 850 GPM 650 GPM
AV = 196 fpm
AV = 166 fpm
AV = 127 fpm
Daily Operational Cost Logistics Rig Mud Mixing System Displacements Procedures Completion Technique Environmental Issues
– Marine Toxicity– HES– Discharge Restrictions
Developing The Mud ProgramFactors to Be Considered For ERD
Selection of Mud SystemWhat To Use?
WATER BASE – Inhibition
» KCL, Salts» Glycols (DCP Product Line)
– Lubricants– Rheologically Engineered
INVERT EMULSION– Arctic Diesel– #2 Diesel– Low Toxic Mineral Oil– Synthetic– Lubricants
Hole Stability
Wellbore Trajectory
Lubricity
Hole Cleaning
Hydraulics
Safety
Logistics
Marine Environment
Formation Damage
Invert SystemsOil-Based Muds
Advantages– Shale Stability– Lubricity– Temperature
Stability– Drill Solids
Tolerant– Chemical
Contamination Tolerant (CO2, H2S)
– Re-usable– Reduce Sticking
Potential– Near Gauge Hole– Corrosion
Protection– Cost Effective
(Drilling and Mud Cost)
Disadvantages– Lost Circulation
» Promotes Fracture Propagation
» Reduced Re-opening pressure
» Slow Self Healing» Expensive (Especially
Synthetics)– Potential Disposal
Problems– HES Concerns– Environmental Discharge– Elastomer Compatibility– Kick Detection (Gas
Solubility)– Cleanliness
Synthetic Fluid Options• BAROIDPETROFREE - (Henkel Ester)
XP07 Linear Parafin Oil• M-I NOVADRIL - Polyalfaolefin (PAO)
ESTERDRIL - Ester (finagreen)NOVALITE - Linear Olefin (LAO)NOVAPLUS - Internal Olefin (IO)
• ANCHOR AQUAMUL II - AcetalAnchogreen - (Pronova Ester)
• B.H.I. BIO-MUL - LAB (Phasing out In UK)SYNTEQ - IO
• DOWELL Finagreen - EsterULTIDRIL - LAO/IO
• B.W. MUD ECODRIL - LAO/PAO
Regulatory Authorities > Commercial > Technical
Base Fluid PropertiesFLUID DENSITY
(SG)VISCOSITYcst @ 40°C
FLASH POINT °C
POUR POINT °C
ANALINE POINT °C
ESTER 0.85 5-7 179 -30 25
PAO 0.80 5-7 175 -65 107
LAO (16/18) 0.78 3.08 146 3 N/A
IO (16/18) 0.78 3.1 137 -24 81
LAO (14/16) 0.78 2.1 114 -12 69
ETHER 0.83 6 166 -10 40
LTOM 0.80 2-3 100 -18 76
DIESEL 0.85 3-4 66 -10 65
HES Issues - Oil Vapours
New Norwegian GuidelinesOil Mist 1 mg/m³, Oil Vapour 50 mg/m³
Vapors Collected @ 65°C For 30 Minutes
2.3
0.9
37
7.3
28
160
0.0 50.0 100.0 150.0 200.0
FG Ester
PAO
LAO 1416
IO 1618
HDF 200
#2 Diesel (5 min.)
ppm Vapor
Oil-Base Fluids DevelopmentRheological Engineered Systems
Early - Mid 80’s, ERD Wells Drilled With OBM Experienced Severe Problems:– Using Existing Mechanical Technology
» No Top Drive» No MWD» Etc.
– Hole Cleaning» “Mud Engineer, Increase That Yield Point!”
– Barite Sag» Static Problem» “Mud Engineer, Increase That Yield Point!”
Gotta Raise ThatYP and Gels!
Conclusions Of Study– Annular Velocity (No Substitute For The Pump)– Pipe Rotation Critical (Hard to Clean Without It!)– Elevated Low Shear Rate Reduces Cuttings Bed
Thickness– High Viscosity Sweeps DO NO GOOD!– Turbulent Flow Sweeps Agitate Beds– Turbulent Flow Cleans Better IF....– If Turbulence Is Not Achievable, Go Laminar
With Elevated LSRV.
Cuttings Move In Helical Flow Pattern– Viscoelastic Coupling Of Mud & Pipe Rotation
Rule Of Thumb: LSRV = 1.0 to 1.5 * Hole Dia.
Oil-Base Fluids DevelopmentHole Cleaning Studies - MI’s ERL
Oil-Base Fluids DevelopmentRheological Engineered Systems
LSRV Modifier Development
1
10
100
1 10 100 1000Shear Rate (1/sec)
Sh
ea
r S
tre
ss
(D
ial R
ea
din
g)
Conventional OBM
Rheo. Modified OBM
Measured @ 120°F
Oil-Base Fluids DevelopmentBarite Sag - MI’s ERL
14.0
15.0
16.0
17.0
18.0
0 20 40 60 80 100 120 140
Circulating Time, min.
Mu
d W
eig
ht,
pp
g
Mud Weight = 15.9 ppbSample Taken At Shaker
Conclusions Of Sag Study– Phenomena Independent of Mud Type
» Occurs In OBM & WBM– Dynamic Settling A Major Contributing Factor
» Previously Thought To Be A Static Problem– Sag Is NOT SOLELY A MUD RELATED PROBLEM
» Slow Circulation Rates (Coring, Liner On Bottom)– Elevation Of LSRV & Gel Strengths Are Helpful In
MINIMIZING The Problem
Development of Field Testing Procedures– Viscometer Sag Test (VST)– Sag Index (VST, MW, Angle, Hole Dia. & Length, Flow
Rate)
Oil-Base Fluids DevelopmentBarite Sag - MI’s ERL
Oil-Base Fluids DevelopmentRheology Testing - Fann Model 70 HTHP Viscometer
1
10
100
1 10 100 1000Shear Rate (rpm)
Dia
l R
ead
ing
50°C Fann 35
50°C / 0 Bars
50°C / 103 Bars
65 °C / 220 Bars
90°C / 483 Bars
120°C / 703 Bars
150°C / 828 Bars
ERD Experience With OBMSouthern Norwegian Sector - North Sea
Platform Set In 1981 Geology
– Overpressured Shale– Weak “Gas Cloud” Section In the Shale
(Low Frac)– Depleting Chalk/Limestone Reservoir
» 7.2 ppg In the Center» 14.5 ppg In the Flanks
– Subsidence In the Overburden (Stressed) Early Drilling History
– Started With Water-Based Fluids– Quickly Turned to OBM
» Stuck Pipe» Unstable Hole Conditions
Early Experiences With OBM
Diesel Þ Low Toxic Mineral Oil No Major Problems When Drilling Low
Angle Wells Major Difficulties With Angles Over
50°– Hole Cleaning– Barite Sag
Rotating Mud CompaniesMud
Mud Weight Requirements
0500
1000150020002500
300035004000
45005000
8 9 10 11 12 13 14 15 16
Mud Weight, ppg
Measu
red
Dep
th (
Mete
rs)
Mud Weight Pore Pressure Fracture
Introduction Of NewOBM Technology
Begin Hole Cleaning Studies Identify Hole Cleaning
Parameters– Elevated LSRV– Rotation
Rheological Modifiers– Improves Hole Cleaning
Reduce Sagging Tendencies
1989
Continuous OperationLast 5 Years
All Wells Now Horizontal Through The Reservoir
Casing Deformation Due To Subsidence
– Casing Pulling/Window Milling - Sidetracks
TVD vs. MD Typically 1:1.5 to 1:2.8– Max. 2500 mTVD 7200 mMD
Integral Part Of Drilling Team With Other Contractors
Max. Input Into Drilling Programs Incentive Drilling Program
Lessons LearnedERD With OBM
Hole Cleaning– LSRV 16” Hole 15-20 12¼” Hole 11-15 8½”
>10– Maintain minimum pump rate of 850 GPM
» Interrupt Drilling» Circulate & Rotate
– Do Not Orient More Than 2 Joints Per Stand» Back Ream/Rotate (100-150 rpm)....Continue
To Drill– Circulate A Minimum Of 1.5 Times B/U Before
POOH» May Circulate Up To 3-4 Times B/U
– Max. usage of 6-5/8” DP» More Flow, More AV, Less Pressure
– Pump Pills IF NECESSARY!» Lo-Vis/Hi-wt
<850 gpm DON`T DRILL
Drilling Practices– When POOH....
» Begin By Just Pumping » If Tight Hole Encountered...Begin
Backreaming– When Backreaming
» Start With 3m/min.....increase gradually» Bring Up RPM`s Slowly to 120 - 150» Start Pumping In A Controlled Manner
– No Arbitrary Wiper Trips» Only As Hole Conditions Dictate
Lessons LearnedERD With OBM
Platform Practices– Monitoring Of Drilling Parameters
» Plotting Torque, Drag Againts Predicted & Measured Values
– Monitoring Of Cuttings Return Parameters» Done With Cuttings Injection System (Predicted vs.
Measured)– Gunk Squeeze Pill Ready As Depleted Chalk Formation Is
Approached» Pump Gunk Immediatedly When Losses Are
Encountered “Do Not Try To Establish Circulated”» 2-3 Gunk Squeezes Maybe Required (100% Success
Rate)– Gilsonite Additions Aids When Sliding In 8-1/2” Hole
Section» May Improve Wellbore Stability in 12-1/4” Hole Section?
– Barite Sag Minimized If...» 3 RPM > 10» 10s Gel > 15
Lessons LearnedERD With OBM
Experienced Personnel Is The Key
The Learning Curve Very Expensive!
Hard Lesson LearnedERD With OBM
Improved Hydraulic Calculation– Virtual Hydraulics (Temp. & Press. Accountability)– Base Oil Specific
Lubricant Development– OBM & Synthetic Fluids
Drag Reducers– Improve Hydraulics (Pressure Reduction, Hole
Cleaning)
Hole Cleaning & Barite Sag– Non Rotation, Slow Annular Velocities– Ultra-Low Shear Rate Viscosity Analysis (Oil Base
FLO-PRO)
Product Development (Elevated LSRV, Low PV)
– Basic Emulsifier Package– Low shear Rate Modifiers
Future DevelopmentOBM For ERD Wells