Acknowledgements

1. Introduction to seismic structure interpretation methods and assessment of trap integrity in exploration and baffles to production. forPESA by Dr Peter Boult GINKGO ENPGNG October / November 2009 In requesting the services of GINKGO ENP GNG the client agrees that GINKGO ENP GNG is acting in an advisory capacity and shall not be liable or responsible for any loss, damages or expenses incurred by the client, or any other person or company, resulting from any data or interpretation presented in this report. PJ Boult

2. Acknowledgements Graham Yielding (Badleys Geoscience) Brett Freeman (Badleys Geoscience) John Walsh (FAG Dublin) Quentin Fisher (Leeds RDR) SANTOS Rodinia Oil Corp (Calgary) Meridian Petroleum (UK) Adelaide Energy Permission to reproduce material in this PESA DL course has been granted by PJ Boult

3. Seismic Structure Introduction Basic fault and fold terminology. Why do some rocks fold while others fracture? Using 3D folds axial surfaces of to get better 2D maps Locating axial surfaces in seismic sections A novel (better?) interpretation workflow for folds in 2D data Lessons - mapping folds Introduction to faults Why and how do they form What do they look like Normal faults Reverse fault Strike-slip faults Relays Duplexes Exercise Seismic structural interpretation in complex faulted settings Interpretation workflow recommendations Geometric considerations Seismic processing considerations Checking your interpretation for geological plausibility Kinematic considerations Exercise Fault seal classification Lithification: Rock deformation – brittle or ductile? Fault seals in exploration Primary analysis – juxtaposition Secondary analysis Fault rock analysis Fault reactivation / top seal failure Case study Fault seals in production Methods for incorporating faults into production simulation models Case study Exercise Calibration Asking the right questions Evidence-based approach to fault seal analysis Validation Exploration Production Concluding remarks Workshop 1 Workshop 2 PJ Boult

4. Seismic Structure inPetroleum Exploration & Production? Structural traps make up 95% of reservoirs Fold and fault mapping is a crucial, though very underrated step in the structural geological workflow in exploration and production. Provides the foundations for all subsequent analysis and modelling PJ Boult

5. Why is Fault and Fault Seal Analysis important? • Faulting issues impact on >70% of reservoirs • Petroleum Exploration • Faults often form one of the main seals for reservoirs • Faults are often invoked as conduits for petroleum migration • Faults may allow the leakage of petroleum through top seals • Petroleum Production • Faults can severely retard fluid flow resulting in compartmentalisation • Many companies have had to lower their reserve estimates due to fault-related compartmentalisation • Effective production strategies require understanding of fault behaviour PJ Boult

6. Why do some rocks fault while others fold? Substance Minerals Porosity Temperature Confining pressure Strain rate Ductile Stress Elastic Brittle Elastic Strain Transition from elastic to ductile OR brittle depends on:- PJ Boult

7. Seismic Structure - folds • Using 3D folds axial surfaces of to get better 2D maps • Locating axial surfaces in seismic sections • A novel (better?) interpretation workflow for folds in 2D data • Lessons - mapping folds In requesting the services of GINKGO ENP GNG the client agrees that GINKGO ENP GNG is acting in an advisory capacity and shall not be liable or responsible for any loss, damages or expenses incurred by the client, or any other person or company, resulting from any data or interpretation presented in this report. PJ Boult

8. Folds in seismic sections γ1 = γ2 T2 = T1 γ1 < γ2 T2 > T1 Folds can be classified based on whether or not the thickness of stratigraphic layers changes over various dip domains OR across axial surfaces PJ Boult Diagrams from Shaws et al, 2005

9. Fold models and processes γ1 = γ2 T2 = T1 Flexural or bedding plane slip Ductile γ1 < γ2 T2 > T1 PJ Boult Diagrams from Shaws et al, 2005

10. Locating axial surfaces in seismic sections Migration moves dipping reflectors upward and laterally to properly image the fold geometry. Reflections on non-migrated OR UNDERMIGRATED sections do not accurately represent fold shape. However, the axial surfaces can still be interpreted by mapping the truncations of the HORIZONTAL reflections Diagrams from Shaws et al, 2005 PJ Boult

11. Axial planes propagate from discontinuities of rigid basement. Not a fold just a bend in the seismic Compression of domino basement blocks – with some strike-slip movement Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

12. But how should we create a map out of data like this? Aliasing problem! Not a fold just a bend in the seismic Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

13. At half the line spacing the gridding bulls eyes have almost gone. 4800 x 4800 2400 x 2400 Lots of bulls eyes 1200 x 1200 PJ Boult

14. But individual structures bear little resemblance to folds 4800 x 4800 PJ Boult

15. Put the fold axes on So what’s the best way to deal with this situation? Not a fold just a bend in the seismic Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

16. Correlate fold axes Add horizon axial traces Line fold axial traces up in 3D Not a fold just a bend in the seismic Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

17. Using horizon axial traces as well as 2D horizons give more control when gridding Not a fold just a bend in the seismic Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

18. Top reservoir horizon Not a fold just a bend in the seismic Data courtesy of Rodinia Oil Corp / Officer Basin Energy Pty. Ltd. PJ Boult

19. Map using horizon axial trace control 600 x 300 PJ Boult

20. 600 x 300 45 degs rotation with fold axes – BUT NO Z DATA 1200 x 600 45 degs rotation with fold axes – BUT NO Z DATA 2400 x 1200 45 degs rotation with fold axes – BUT NO Z DATA Just for comparison – using the horizon based fold axial traces – BUT NO Z DATA PJ Boult

21. Lessons - mapping folds Correlation should be done in True Perspective 3D Consider en-echelon nature of folds IN OUTCROP Line up fold axes and extract horizon-based axial traces Need to grid at the correct scale Normally ½ 2D line spacing BUT when fold axis are used, can go down to much smaller grid without bulls eyes. BEST to use a grid cell with its longer dimension along structural grain However, EVEN BETTER to combine above with use of Z data on horizon-based axial traces Z data best created in 3D interpretation package PJ Boult