Y.WILEVEAU, J. DELAY Andra – National Radioactive Waste Management Agency , Bure, France

1. Stress determination and pore pressure measurements performed at the Meuse/Haute-Marne Underground Laboratory Y.WILEVEAU, J. DELAY Andra – National Radioactive Waste Management Agency, Bure, France

2. Overview • Part 1 • Methodology for regional stress determination • Hydrofrac, HTPF and Sleeve fracturing • Data examples • Stress profile • Part 2 • Pore pressure measurement in clay formation • Pressure profile in the argillite • Comparison and open question

3. Geological setting on Bure’s URL

4. Methodology for stress determination at the Bure site • From shafts • Paleostress • Convergence measurements on several sections • Vertical Mine by Test experiment in the main Shaft of the URL • From boreholes • Deformations of vertical borehole walls • Breakouts and induced fractures in inclined boreholes (Etchecopar, 1997) • Classical hydro-fracturing (Haimson, 1993) • Hydraulic tests on Pre-existing Fractures (HTPF method, Cornet, 1986) • Sleeve fracturing and Sleeve reopening (Desroches, 1999)

5. Convergence measurements in the Oxfordian limestones • H oriented at N155°E • accuracy : 0,1 mm on a 6m diameter of the shaft • maximum convergence measured :  2mm • horizontal stress anisotropy K=H/h: between 1.4 et 1.8 H H Section at 223m H Section at 375m Section at 415m

6. UBI analysis and wall morphology (example for EST 204 borehole) • Breakouts appears in the clay-rich area (less compressive strength) • High dependence on the fluid for drilling (water based mud for EST204) • oil based mud give us better well stability

7. Fracture initiation Breakdown pressure Closure pressure Closure pressure Closure pressure of the induced fracture (Detail of the first hydraulic fracturing cycle) Closure pressure determined from the square root of the shut-in time Induced fractures detected and oriented on FMI image Pressure record during a micro-hydraulic fracturing test Hydraulic fracturing tests in Bure Straddle packer MDT tool (specific configuration for inclined boreholes) Downhole pump

8. General situation of hydraulic fracturing tests at Bure Site • 29 successful tests • in 5 boreholes : • 6 in Oxfordian • 17 in C.Oxfordian • 6 in Dogger

9. In-situ stress in Oxfordian H orientation(°/North) Magnitude (MPa) H h • H oriented in N155°E • Slight rotation at the base of Oxfordian unit • h 8 MPa (average value)

10. Hydraulic fractures mined back during the sinking of the shafts (in clay formation) Induced fracture at 467m (horizontal) Induced fracture at 471m (horizontal)

11. ……but vertical at 499m depth !!! Fractures initiated during Hydrofrac (H direction) H h UBI – acoustical logging after micro-hydraulic tests at depth 499m in EST205 Top view of EST205 borehole at 499m on the ground

12. Vertical stress measured in the Dogger (HTPF method) Selection of a pre-existing lignite layer at 655m depth : possibility to measure v by HTPF method FMI after test FMI before test Induced fracture by packers Direct measurement : v = 14,7 MPa at 655 m depth +Others Pre-existing Fractures have been tested in the argillites (v 12,0 MPa)

13. Q=3 Stress regime: Strike-slip Stress regime: Extension Stress regime: Compression Stress regime: Extension Stress regime: Compression Stress regime: Strike-slip Stress regime: Strike-slip Q=2.5 Q=2 Q=0 Q=1.5 Q=1 Q=0.5 s1 s2 s3 Influence of the shape of the stress tensor on the breakout orientation (from Desroches and Etchecopar, 2005) .. assuming constant orientation of the main stresses

14. Q=3 Q=2.5 Q=2 Q=1.5 Q=1 Q=0.5 Q=0 • Ordering the stresses by breakout analysis inthe argillites (from Desroches and Etchecopar, 2005) Deviated borehole (60°/vert) 2.3 >Q>1.8 sH> sV= sh sh N 60-65 In agreement with hydrofrac results: sh = sV

15. Variation of h with lithology : Orientation Orientations in the Oxfordian turn 40 degrees when approaching the contact with the Callovio-Oxfordian Orientations are roughly constant in the Callovio-Oxfordian and in the Dogger H  N150°E : Major tectonic shortening during the last Alpine Orogeny

16. sh Weight of sediments sV sv ? sh Depth m. sH σh and σv magnitudes : variation with lithology ! • Huge difference between limestone and shales • σh magnitudes are very similar in the limestones surrounding the clays • σh is s3 in the limestones ands2 in the middle of the clays formation • And what’s about σH ? Limestone Shale Limestone

17. Sleeve fracturing and sleeve reopening in the clay formation In order to estimate H • A special test has been performed at 504m • in a sub-horizontal well

18. Estimation of σH Sleeve reopening – Identification of packer pressure for opening of the fracture UBI before test UBI after test H – P0 = 3(v – P0) – (Pr – P0) 12.7 MPa ≤ H ≤ 14.8 MPa

19. Maximum horizontal stress H estimation • by • sleeve reopening • breakouts analysis • shaft convergence • H estimated : •  14-15 MPa • Approximately constant with depth

20. EPG – Long term monitoring at the laboratory location

21. In situ stress profile EPG – pressure profile

22. Conclusions • To determine the complete state of stress in a lithologic sequence • a combination of methods is required • Hydraulic fracturing and image analysis in deviated boreholes are perfectly complimentary • Such a combination allowed the determination of the complete state of stress • In the studied sequence, there is a large difference in the state of stress in the limestones and that in the argillites • The pore pressure profile looks like to stress profile but ….. • Is that a common behavior? How could one predict it?

23. Thank you for your attention !