Advanced Seismic Imaging for Geothermal Development

1. Advanced Seismic Imagingfor Geothermal Development John N. Louie University of Nevada, Reno Satish Pullammanappallil Bill Honjas Optim Inc. www.seismo.unr.edu/~louie optimsoftware.com

2. “Integrative” versus “Differential”Geophysical Methods Grav, Mag, MT, Refraction integrate over volumes Seismic Reflection & Radar image point changes

3. Problem: Applying Seismic Exploration for Geothermal Projects • “Cornerstone” of oil & gas exploration and development… • …But until recently, not used for geothermal projects • Lateral complexity prevented accurate velocity modeling • Lack of accurate velocity models prevented focusing of reflection data • Lack of focused reflectors equals poor seismic image • Poor seismic image results in lack of “added value” proposition These problems deprived the geothermal industry of the basic means for economically mapping the subsurface.

4. Solution: Solve the velocity problem • Simulated Annealing Velocity Optimization • Researched at the University of Nevada Seismological Laboratory during the early 1990’s • Commercially developed and released by Optim, under the name SeisOpt®in 1998 SeisOpt iterates through hundreds of thousands of possible velocity solutions to find the single, or “global”, solution that best fits the seismic data, assuming no direction or magnitude of velocity gradient.

5. Advanced Seismic Technology • Proven effectiveness of advanced processing techniques • Build on success of a DOE-funded pilot study in Dixie Valley (Honjas et al., 1997; Grant Number DE-FG07-97ID13465) • Optim has projects underway now at geothermal fields worldwide • Utilize new data acquisition parameters • Designed to enhance results from advanced processing techniques • Image permeable structures at reservoir depth and image tectonic structures beneath geothermal fields • Constrain down-dip geometry of reservoir structures • Characterize features that are significant for evaluating subsurface permeability • Correlate down-dip geometry of features mapped on the surface • Image tectonic structures • To determine their relationship to faults and fractures controlling the reservoir permeability and production

6. Advanced ProcessingTechniques • Nonlinear velocity optimization • Simulated annealing method to produce high resolution velocity models from first arrivals picked off raw shot gathers • Refraction – Integrative • Pre-stack Kirchhoff depth migration • Directly images subsurface structures oriented in any direction • Reflection – Differential

7. Advantages ofPre-stack Kirchhoff Migration • Minimal pre-processing • No need for numerous pre-processing steps common to conventional seismic data processing • Savings on man hours • Directly images structures in depth • Uses velocity models from the optimization technique to place reflectors in their correct location • Avoids unreliable, time to depth conversion, common in conventional data processing • Images structures oriented in any direction • Can handle velocity variations in any direction • Can image flat and moderate to steeply dipping structures • Ideal for imaging in areas with extensive faulting and fracturing

8. SeisOpt®Analysis of Seismic Data for Geothermal Projects • Seismic exploration is necessary for increasing the feasibility of geothermal projects • As an example, volumetric depth models of earth structure have been produced encompassing an 11 square mile area, to a depth of 15,000 feet, at less than half the cost of a single exploration drill hole • Volumetric depth model can be used to reduce risk and increase productivity in all phases of geothermal development • Exploration • Production • Resource management

9. Geothermal Project Case Studies • Dixie Valley, Churchill County, Nevada • Production and Resource Management – Integrative • Coso geothermal field, Inyo County, California • Exploration and Resource Management – Integrative • Pumpernickel Valley, Nevada • Exploration – Differential • Astor Pass, Pyramid Lake, Nevada • Exploration – Differential

10. Dixie Valley Geothermal Field: Production and Resource Management Map showing location of production and injection wells relative to seismic lines. Data along these lines were re-processed using SeisOpt® technology

11. Optimized Velocity Model

12. Dixie 2.5D Model • Further analysis of production related structure revealed a basin-ward synform, or half graben, that directly correlated with location of production and injection wells. • Velocity analysis also revealed less dramatic basinward structure in area of Line 10.

13. Velocity Tomography  Depth Migration

14. Gravity and Seismic Data, Dixie Valley, NV. Map showing surface projection of structure derived from seismic survey (Solid lines). Independent gravity data are also shown as shaded areas, with northwest dipping structure from gravity data shown as hachured areas and southeast dipping structure by stippled areas. The gravity and seismic data correlate well. Gravity Data courtesy of Dr. Dave Blackwell, SMU

15. Velocity Tomography + Depth Migration

16. Velocity Tomography + Depth Migration Okaya & Thompson, 1985

17. Dixie Valley Conclusions A previously unknown basin-ward half graben located by seismic data correlates with production and injection wells within the Dixie Valley geothermal field. • The half-graben was incorporated into the Dixie Valley field injection and production model • Its presence was then confirmed via well tracer tests • The seismic survey settled a basic controversy on whether production and injection within the Dixie Valley field was related solely to the Dixie Valley fault, or controlled by basin-ward structures • The true source of production was unknown prior to revisiting the seismic data with advanced methods.

18. Dixie ValleyThe low-angle fault is why there is no resource to the south! NBMG Map 151

19. Southern Dixie ValleyThe low-angle fault may not tap deep enough into the crust to channel geothermal fluids.

20. Geothermal Project Case Studies • Dixie Valley, Churchill County, Nevada • Production and Resource Management – Integrative • Coso geothermal field, Inyo County, California • Exploration and Resource Management – Integrative • Pumpernickel Valley, Nevada • Exploration – Differential • Astor Pass, Pyramid Lake, Nevada • Exploration – Differential

21. Coso Geothermal Field: Exploration and Resource Development Generalized geologic map showing the study area. Modified from Duffield and Bacon, 1979.

22. Reservoir boundaries Optimized Velocity Model

23. Coso 2.5D Volumetric Model • Interpolate between velocities along individual 2D lines • Reveals 3D geometry of features observed along 2D lines

24. Slices through the 3D volume reveal the emergence of distinctive zones of permeability within the geothermal field. Unlike other geophysical methods, SeisOpt reveals target depth. 2000 foot slice 3000 foot slice 2500 foot slice 4000 foot slice 3500 foot slice Coso 2.5D Volumetric Model

25. East West East West Coso: Prestack Kirchhoff Migration

26. Coso Conclusions The seismic survey identified discrete thermal reservoir areas within the Coso geothermal field. • Defined boundaries of two distinct reservoirs within a volcanic pile • Imaged brittle-ductile transition • Predicted orientation and location of fracture system • Imaged deep, “bright lens” reflector which is thought to be created by high-temperature thermal brines.

27. Conclusions of Early Projects • Seismic exploration can be used to reduce risk and increase productivity in all phases of geothermal development • Exploration • Production • Resource management • Seismic exploration is economic and feasible • Significant added value • Cost effective, providing a volumetric model encompassing several square miles, and extending to depths of exceeding 8,000 feet, for less than 1/2 the cost of a single exploration drill hole • Seismic exploration is the only geophysical method that can directly sample the subsurface to depths exceeding 8,000 feet • Can be used to calibrate and corroborate MT and gravity data.

28. Geothermal Project Case Studies • Dixie Valley, Churchill County, Nevada • Production and Resource Management – Integrative • Coso geothermal field, Inyo County, California • Exploration and Resource Management – Integrative • Pumpernickel Valley, Nevada • Exploration – Differential • Astor Pass, Pyramid Lake, Nevada • Exploration – Differential

29. Pumpernickel Valley, Nevada

30. Pumpernickel Valley Raw Record

31. Pumpernickel Valley Velocity Line 3

32. Pumpernickel Valley Prestack Migrated Line 3

33. Pumpernickel Valley Preliminary Line 3

34. Pumpernickel Valley Velocity Line 4

35. Pumpernickel Valley Prestack Migrated Line 4

36. Pumpernickel Valley Preliminary Line 4

37. Pumpernickel Valley Velocity Line 5

38. Pumpernickel Valley Prestack Migrated Line 5

39. Pumpernickel Valley Preliminary Line 5

40. 3 4 5 Pumpernickel Valley - Preliminary interpretation of seismic data Only the range-front fault is manifested at the surface

41. Pumpernickel Valley, NevadaPreliminary fault traces based on seismic only

42. Pumpernickel Conclusions The seismic survey imaged hidden basin-ward step faults directly as seismic reflectors. • Network of 2-D lines explored prospect at a fraction of the cost of 3-D • Acquisition specially designed for best SeisOpt® velocity results • Good velocity info allowed imaging faults and alluvial stratigraphy • NGP is proceeding with drilling soon

43. Geothermal Project Case Studies • Dixie Valley, Churchill County, Nevada • Production and Resource Management – Integrative • Coso geothermal field, Inyo County, California • Exploration and Resource Management – Integrative • Pumpernickel Valley, Nevada • Exploration – Differential • Astor Pass, Pyramid Lake, Nevada • Exploration – Differential

44. Upper 2 km 10-25 m V.R. Up to 240 channels Lines 2-7 km long Source-receiver spacing 17-67 m Astor Pass: 2-D WAZ Acquisition

45. Astor Pass: Fault Discoverywith Direct Fault-Plane Images

46. Astor Pass: Imaging Volcanic Stratigraphy

47. Now that we have direct fault images, we can analyze: • Seismic attributes- amplitude, phase, frequency, edges, shadows, etc. • AVO- amplitude versus offset, Poisson’s ratio • AVA- amplitude versus azimuth, fracture orientation • Seismic inversion- separate Dr, Dl, Dm

48. Astor Pass Conclusions The seismic survey discovered new fault sets. • Fault-plane image quality depends on survey orientation- 3-D imaging in process • Excellent imaging of Tertiary volcanic stratigraphy- domes versus flows • Faults and stratigraphy verified from new wells • Fault imaging allows seismic attribute, AVO analysis of geothermal reservoir

49. Nevada Is Looking for anAsst. Professor of Geological Engineering • https://www.unrsearch.com/postings/9727 • The Department of Geological Sciences and Engineering seeks a full time tenure-track assistant professor of Geological Engineering. • The chosen candidate must be committed to both undergraduate and graduate instruction and will be expected to develop an externally funded program of research in their specialty. • Specialty areas are open, but existing and emerging critical needs for the State of Nevada include: • Geothermal resource development • Hydrologic and geohydrologic resource development and conservation • Minerals and minerals industry sustainability, and • Recognition and mitigation of geological hazards. • Minimum requirements are Ph.D. completion and at least one degree in geological engineering or a closely related engineering discipline. • Application deadline November 21, 2011!