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