Attenuation of rock salt:

Gulf of Mexico core measurements and a VSP survey

Jingjing Zong1,2, Robert R. Stewart2, Nikolay Dyaur2

1. National University of Singapore

2. University of Houston

Outline

Introduction and motivations

Field Q estimations

A VSP survey in Markham salt dome, TX

Conclusions

Ultrasonic lab Q measurementsGulf coast salt cores

2

Attenuation mechanism

Source

signal

• Geometrical spreading

• Scattering

• Intrinsic attenuation or anelasticity

Q: quality factor1

𝑄=

∆𝐸

2𝜋 ∙ 𝐸=

∆𝐴

𝜋 ∙ 𝐴

3

Motivations of the salt study

Seal rock

studyblue.com

Storage

© KBB Underground Technologies

Mining

saltassociation.co.uk

4

Attenuation modeling

P wave front

S wave front

sourcereceiver

5

Synthetic wave propagations in rock salt

0 m 6000

2500

Q estimation – spectral ratio method

𝐴 𝑓 = 𝐺 𝑥 𝑒−𝛼 𝑓 𝑥𝑒𝑖(2𝜋𝑓𝑡−𝑘𝑥)

(Johnston, 1978)

ln𝐴

𝐴0= −

𝝅𝒕

𝑸𝑓 + ln

𝐺

𝐺0

ln𝐴

𝐴0= −

𝝅

𝑸(𝒕𝟎 − 𝒕)𝑓 + ln(

𝐺

𝐺0)

Aluminum

𝑸𝟎 ≈ +∞

Sample

𝑸

𝑸

Measurement Slope Intercept

𝑙𝑛𝐴

𝐴0=

𝜋𝑡0𝑄0

−𝜋𝑡

𝑄𝑓 + 𝑙𝑛

𝐺

𝐺0

(a) Aluminum standard

(b) Multi travel lengths

6

GoM rock salt core

Examples of the measured rock salt samples

96.1%

NaCl

99.6%

NaCl

Hockley, TX Bayou Corne, LA

7

8

Experimental apparatus for ultrasonic measurements

Source transducer

Sample

Receiver transducer

Center frequency

1 MHz

gcts.com

Benchtop measurements:H1 - Qp: 32 ± 4 , Qs: 34 ± 3

H2 - Qp: 43 ± 6 , Qs: 34 ± 4

𝑄0 𝑄

𝑄0 ≈ +∞

Aluminum

ln𝐴

𝐴0= −

𝝅𝒕

𝑸𝑓 + ln

𝐺

𝐺0Measurement Slope Intercept

Attenuation of GoM rock salt – spectral ratio method

9

Attenuation of GoM rock salt – spectral ratio method

Aluminum

Benchtop measurementsQp: 57 ± 13 , Qs: 41 ± 2

ln𝐴

𝐴0= −

𝝅

𝑸(𝒕𝟎 − 𝒕)𝑓 + ln(

𝐺

𝐺0)

Measurement Slope Intercept

𝐴0

𝐴

𝑄

10

Temperature dependence – Bayou Corne, Louisiana

11

Relative Q variations under varying temperature

Pressure dependence – Bayou Corne, Louisiana

12

Relative Q variations under varying pressure

Attenuation – pressure and temperature dependence

Vp vs. Pressure, Temperature Qp vs. Pressure, Temperature

13

Pressure (psi) Pressure (psi)0 4000 8000 12000 0 4000 8000 12000

4.4

4.5

4.6

0

100

200

300

Vp

(km

/s)

Q

CT Scanning of the test sample

before and after pressure loading

Pressure healing & thermal cracking

before

after

Thermal cracks on the surface of rock salt under

increasing temperature (Chen et al., 2015)

14

50oC in oven, over 24h 110oC in oven, over 24h

140oC in oven, over 24h 200oC in oven, over 24h

4.4 4.45 4.5 4.55 4.6 4.65

Vp (km/s)

0

50

100

150

200

250

300

Qp

Q p vs. V p

23.9oC(75

oF)-Unloading 37.8

oC(100

oF) 65.6

oC(150

oF) 93.3

oC(200

oF)

Qp vs. Vp

𝑙𝑛𝑄𝑃 = 53 ∙ 𝑙𝑛𝑉𝑃 − 33𝑅2 = 0.84

Attenuation – pressure and temperature dependence

Qs vs. Vs

𝑙𝑛𝑄𝑠 = 28 ∙ 𝑙𝑛𝑉𝑠 − 10𝑅2 = 0.4

15

A typical GoM salt dome

© John Perez Graphics & Design LLC.16

Resistivity (ohmm) Density (g/cc) Temperature (̊C)

Gamma Ray (API)

Caliper (in)16 26

0 100

0.2 200 1.5 2.5 70 80

Well A (KB = 25.9 m)

Me

asu

re d

ep

th

fro

m K

B (

m)

1000

1200

1400

1600

1800

2000

Top of

salt

Bottom

of salt

Heterogeneous

Layer

Neutron Porosity (%)55 -35

RadialDirect

S-w

ave

— Interval velocity

Check-shot data – velocity profile

S: ~2560 m/s

In saltP: ~4570 m/s

In salt

17

1 2

P-wave first arrival picking and

velocity profile

Check-shot data - Qp

247.7

-76.8

71.1

Flattened down-going P-waves Spectra ratio and

Q estimation

3 4 5

18

1 2

S-wave first arrival picking

and velocity profile

Check-shot data - Qs

31.6

10.9

-19.7

83.4

16.5

Flattened down-going S-waves Spectra ratio and

Q estimation

3 4 5

19

Qp vs. Vp

Attenuation – pressure and temperature dependence

20

Qs vs. Vs

Conclusions

• Increase pressure elevates both velocity and Q;

• Increase temperature decreases velocity and Q;

• Q vs. V: 𝑙𝑛𝑄𝑃 = 53 ∙ 𝑙𝑛𝑉𝑃 − 33; 𝑙𝑛𝑄𝑠 = 28 ∙ 𝑙𝑛𝑉𝑠 − 10.

21

✓A better understanding of the elastic behaviors of rock salt is provided;

✓Empirical values and relationships are summarized for direct application.

Arthur Cheng, Yunyue (Elita) Li, NUS;

Fred Hilterman and Geokinetics Inc., Houston;

Joel Warneke, Texas Brine Corp. and United Salt Corp.;

Di Jiao, Craig Whitney, Core Laboratories Inc.;

Scott Leaney, Alan Champbell, Ali Sayed, Schlumberger;

Stephan Gelinsky, Long Huang, Shell;

Leon Thomsen, Sharon Cornelius, Yukai Wo, UH;

Acknowledgements