APPLICATION OF AVO INVERSION TO ESTIMATE BRITTLENESS IN THE BARNETT SHALE

1. APPLICATION OF AVO INVERSION TO ESTIMATE BRITTLENESS IN THE BARNETT SHALE Roderick Perez October 25th , 2010 ConocoPhillips School of Geology and Geophysics The University of Oklahoma

2. OUTLINE • INTRODUCTION • OBJECTIVES • METHODLOGY • Data • Lame parameters (λρ - µρ) • AVO Inversion • Shale Geomechanics • RESULTS • CONCLUSIONS

3. INTRODUCTION Barnett Shale production 1980-2005 • In less than a decade, the Barnett Shale play has become the largest natural gas play in the state of Texas (and maybe in the US). • The Fort Worth Basin is one of about 20 shale gas basins across the United States where total domestic shale gas resources are thought to range from 500 Tcf to 780 Tcf (SLB).

4. INTRODUCTION COMPLEX HETEROGENEITY GEOLOGY HYDRO-FRACTURING Laminated layers of siliceous or carbonaceous material Inches Natural fractures (Not mineral filled) Black organic bulk shale These reseacrh will focus in the mechanical properties of the rock, instead of the depositional environment.

5. PROJECT GOAL Can we estimate ‘BRITTLENESS’ using AVO inversion from prestack seismic data? Find areas in the shale play that are “brittle” is important in the development of a fracture fairway large enough to connect the highest amount of “rock volume” during the hydraulic – fracturing process.

6. METHODOLOGYData • Seismic 3D Survey (P-wave): • Post Stack volume • Pre Stack gathers • Angle Gathers (3°-43°) Production Seismic acquisition PRE STACK POST STACK • Three well logs with dipole logs (DT – DS) • 435 well locations • 308 vertical • 127 horizontal • 435 wells with relative EUR (0-10) 1.325 Upper Barnett Forestburg Time (sec) Lower Barnett 1.475 43 Angle 3

7. METHODOLOGYLame Parameters Theory P-WAVE Uni-axial compressional wave S-WAVE Undeformed porous rock (Goodway, 2010) λ≡ Rigidity – Lame’s constant µ ≡ Incompressibility – Shear Modulus ρ ≡ Density

8. METHODOLOGYLame Parameters Theory STATIC MODULI AND MODULI RATIO DEFINITIONS IN TERMS OF LAME PARAMETERS Young’s Modulus Poisson’s ratio P-wave Velocity S-wave Velocity P-wave Modulus E – ν Relation (Goodway, 2010)

9. METHODOLOGYAVO Inversion Zoeppritz equations WORKFLOW (Fatti et al., 1994) Reflection coefficient Moduli – Density relationship Rs Rp

10. AVO Inversionλρ Well A (GR) ((GPa)*(g/cm3)) 111 Marble Falls Upper Barnett Sh Forestburg Lower Barnett Sh Lower Barnett Shale: λρ 13

11. AVO Inversionµρ Well A (GR) ((GPa)*(g/cm3)) 90 Marble Falls Upper Barnett Sh Forestburg Lower Barnett Sh 24

12. METHODOLOGYGeomechanics Young’s modulus to Poisson’s ratio relationship for the Barnett Shale. • Poisson’s ratio declines with increased Young’s modulus (Grigg, 2004) Results from 2 logs Gale et al., AAPG Bulletin, v. 91, no. 4 (April 2007), pp. 603–622

13. METHODOLOGYGeomechanics • BRITTLENESS is the tendency of a material to fracture or fail upon the application of a stress. • DUCTILITY is the mechanical property that describes a solid material which can be plastically deformed under stress, without fracture Poisson’s ratio (ν): the ability of the rock to fail under stress Young’s modulus (E): capacity to maintain the fracture once the rock fractures.

14. RESULTSFrom well logs High GR 80 Ductile Regions Brittle Ductile 0 100 Results from 2 logs

15. RESULTSFrom Seismic Brittle Ductile

16. CONCLUSIONS • Preliminary results show that the Barnett Shale have relatively low λ’s (incompressibility) and high µ’s (rigidity) • Cross-plotting λρ vs. μρresults from seismic allow the discrimination between ductile and brittle shales in the area of study. • It’s necessary work in conjunction with the Petroleum Engineers in order to calibrate dynamic and static modulus.

17. ACKNOWLEDGEMENTS • Thanks go to Devon Energy for providing the 3D seismic survey for our research and for this publication. Thanks to Schlumberger for providing OU with licenses to Petrel. Finally, my sincere appreciation goes to Dr. Kurt Marfurtfor his continuous support and timely suggestions. • AASPI members

18. METHODOLOGYSummary Computed Measured Static Modulus ρ Zp Zs λ μ λρ μρ E σ Vs GR DT DS Vp 80 0 100 Cluster Anallysis Cluster Analysis Pre-Stack Angle Gathers AVO inversion