Characterizing!Sonic!Anisotropy!for!Geomechanics!and!Geophysics!Applications:!

Case!Study!in!Forties!Field,!UK

Donald!Keir!(Apache),!Adam!Donald*,!Andrea!Paxton,!Ed!Knight!(Schlumberger)

DEVEX!Conference!May!13th ,!2009

Presentation!Outline

• Motivation

• Background

• Workflow

• Single!well!analysis

• Multi"well!analysis

• Conclusions

Forties!Field

Development!of!Mature!Fields• Reducing!drilling!costs!– losses,!pack"offs,!NPT

• Optimum!well!placement!– target!selection!using!seismic!

Wellbore!Stability!Predictions Seismic!Interpretation

0.7!!!!!!!!!!!!!Mud!Weight!!!!!!!!!!!2.2

PP Collapse Losses

Reducing!Uncertainties

• Low!confidence!in!well!–seismic!ties!&!AVO!analysis

• Drilling!challenges!for!landing!casing!above!reservoir!

• Sonic!logs!required!for!input!to!geomechanical &!geophysical models

• Initial!observation!by!petrophysics!is!inconsistentDT!compressional!&!DT!shear

Inclination (degrees)0 16 30 46 60 76 8060

80

100

120

140

180

DT

(us/

ft)

DT!Compressional!displays!decreasing!slowness!with!wellbore!inclination!across!9!wells!in!the!Sele!

Formation!from!the!Forties!Field

Multi"well!comparison

Red!– 1!Degree

Green!– 41!Degrees

Blue!– 61!Degrees

Fast Direction

Slow

Dire

ctio

n

Anisotropy!in!Shale:!Geophysics

Input!to!AVO!analysis,!seismic!calibration

Sele!Fm

Balder!Fm

FortiesAbandonmentUnit

Require!Thomsen!parameters:

!"#$"#%

140!!!!!!!!!DT!!!!!!!!!!!40

Developing!the!anisotropic!velocity!model:!Thomsen!Parameters!Explained

• Epsilon!describes!the!difference!between!the!vertical!and!horizontal!compressional"wave!

• Gamma!describes!the!difference!between!the!horizontally!polarized!and!vertically!polarized!shear"wave

• Delta!describes!the!depth!mismatch!between!logs!or!actual!depth!and!seismic!depth!(most!difficult!one!to!measure)

! =c11 - c33

2c33

% =c66 – c44

2c55

$ =(c13 + c44)

2 - (c33 – c44)2

2c33(c33 – c44)

Where C ij =V2&bulkObtain!these!values!using!a!combination!of!sonic!logs,!core!measurements!and!walk"away!VSP!data

Anisotropy!in!Shale:!GeomechanicsSonic!DT’s!are!affected!by!

bedding!planes

Brevik et al., 2007, TLE

Computation!of!rock!mechanical!properties!vary!with!orientation

Strength

UCS

Stiffness

Young’s!Modulus

Poisson’s!Ratio

Integrated!Project!Workflow

• Single!well!study– Determine!anisotropy!parameters!from!full!core,!sonic!&!VSP!measurements

• Multi"well!study– Integrate!field!wide!compressional!and!shear!data!to!calibrate!parameters!and!account!for!field!heterogeneity

• Correct!all!logs!in!the!field!for!anisotropy!effects!in!Sele!and!input!to!geomechanical!and!geophysical!models

Bands!of!weak/strong!rock!in!Sele

competent!shale

Sele:!weak!&!layered!shale

LWD!Density!Image!&!Core!Photos

Single!Well!Analysis:!Core!Data

Measurements!at!0,!45!&!90!degrees!to!bedding!planes

• Young’s!modulus!(static)

• Poisson’s!ratio!(static)

• Unconfined!compressive!strength!(UCS)

• Thomsen!parameters!using!ultrasonic!stiffnesses!from!the!combination!of!all!orientations!(dynamic)

0 45

90

Ultrasonic!Core!Data:!!"#% &!$

• Comparison!with!published!core!data!for!reference

0.3200.140.272702

"0.0140.190.232699

"0.2160.130.112696

$%!Depth!(mD)

Taken!from!Sayers!(2005),!Geophysical!Prospecting

Stiffness!&!Strength!Static!Core!Data

0

1000

2000

3000

4000

5000

6000

7000

8000

"5 5 15 25 35 45 55 65 75 85 95

Orientation!to!Bedding

Static!You

ng's!M

odulus(M

Pa)

0

5

10

15

20

25

30

35

"5 5 15 25 35 45 55 65 75 85 95

Angle!to!Bedding!Planes!(degrees)

UCS!(M

Pa)

Unconfined!Compressive!Strength

• Horizontal!~!vertical!strength

• 85%!reduction!@!45!deg

• Wells!drilled!at!45!deg!are!more!prone!to!collapse

Young’s!Modulus

• Horizontal!>!vertical!stiffness

• Consistent!with!ultrasonic!data

Traditional!correlations!between!strength!and!stiffness!do!not!work!when!shale!bedding!planes!are!weak

3D!Anisotropy!from!Sonic:!%• Shear!derived!from!dipole!

and!Stoneley!waveforms

• DT!shear!measured!along!borehole!axis!&!rotated!to!bedding!plane!axis

• C66!~!SH &!C44!~!SV!% =!0.6!"0.7

Higher!than!ultrasonic!core!values,!difference!associated!to!stress!effects!

Sele!Fm.!C66>C44

Multi"Offset!VSP:!! &!$

• Slowness!/!Polarization!Inversion

• Best!fit!model! =!0.254$ =!0.006

Consistent!with!ultrasonic!core!values

Multi"well!Study!Workflow

1. Identify!all!logs!with!processed!compressional!(125)!&!shear!(9)2. Take!average!shear!and!compressional!slowness!across!the!Sele!Fm3. Plot!slowness!(P&S)!against!relative!dip!with!anisotropic!velocity!model!

(Norris!&!Sinha,!1993)4. Calibrate!the!anisotropy!parameters!(!"#$"#%)!using!the!multi"well!data5. Apply!the!calibrated!parameters!and!apply!to!all!logs!to!obtain!P&S!

values!for!vertically!propagating!waves

Example!of!phase!slowness!curves!for!the!Bakken!Shale!formation

Illustrates!variation!in!SV,!SH &!P!slownesses!as!a!function!of!relative!dip

Forties!Bravo!Platform:!Compressional!Phase!DT

! =!0.28,!$ =!0!using!multi"well!data

! =!0.254,!$ =!0.006!using!VSP!data

! =!0.21,!$ =!0.03!using!average!core!data

High!confidence!in!! and!$ for!Bravo!platform

Same!method!applied!across!field!with!similar!results

80

90

100

110

120

130

140

150

160

0 10 20 30 40 50 60 70 80 90 100

Relative!dip!(degrees)

Ave

rage

!DT!Co

mpression

al!(u

s/ft)

Average DTc’s in Sele

Anisotropic DTc Velocity Model

Forties!Field:!P!&!S!Phase!Slownesses

• Multi"well!calibration!of!% ~!0.7!for!9!wells

• Consistent!with!shear!sonic!log!from!Bravo

• Lower!confidence!with!shear!due!to!lower!data!concentration!&!extrinsic!effects!such!as!stress!

Phase Slowness Curves

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80 90

Relative dip (degrees)

Aver

age

shea

r slo

wne

ss (u

s/ft)

100

115

130

145

160

175

190

Ave

rage

com

pres

sion

al s

low

ness

(u

s/ft)

Comparison!of!uncorrected!and!corrected!compressional!slowness!values

Inclination (degrees)0 16 30 46 60 76 80

60

80

100

120

140

180

DT

(us/

ft)

Uncorrected DT Compressionaldisplays decreasing slowness with

wellbore inclination

180

DT

(us/

ft)

Inclination (degrees)0 16 30 46 60 76 80

60

80

100

120

140

Stable slowness with wellboreinclination after anisotropy correction

applied to DT Compressional

Summary

• Combination!of!single!&!multi"well!data!to!develop!a!field!wide!anisotropic!velocity!model!for!the!Sele!Fm

• Compressional!data!well!constrained,!more!uncertainty!with!the!shear!data

• Update!calibration!of!seismic!ties!and!refine!wellbore!stability!models

Acknowledgements

• Thanks!to!Apache!for!permission!to!publish

• Klaas Koster,!Brett!McIntyre!with!Apache!

• Wes!Martin!at!TerraTek!in!Salt!Lake!City,!US

• Tom!O’Rourke,!Anzar Syed,!Chang!Liu!with!Schlumberger