advanced seismic imaging for geothermal development

Copyright © 1998-2011 Optim Inc. and University of Nevada

John N. LouieUniversity of Nevada, Reno

Satish PullammanappallilBill HonjasOptim Inc.

www.seismo.unr.edu/~louie

optimsoftware.com

Advanced Seismic Imagingfor Geothermal Development

“Integrative” versus “Differential”Geophysical Methods

Grav, Mag, MT, Refraction integrate over volumes

Seismic Reflection & Radar image point changes



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.


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.


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


Advanced Processing Techniques

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


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


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


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


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


Optimized Velocity Model


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.


Velocity Tomography Depth Migration


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


Velocity Tomography + Depth Migration


Velocity Tomography + Depth Migration

Okaya & Thompson, 1985


Dixie Valley ConclusionsA 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.


NBMG Map 151

Dixie Valley

The low-angle fault is why there is no resource to the south!


Southern Dixie Valley

The low-angle fault may not tap deep enough into the crust to channel geothermal fluids.


Coso Geothermal Field: Exploration and Resource Development

Generalized geologic map showing the study area. Modified from Duffield and Bacon, 1979.


Optimized Velocity Model

Reservoir boundaries


Coso 2.5D Volumetric Model

• Interpolate between velocities along individual 2D lines

• Reveals 3D geometry of features observed along 2D lines


Coso 2.5D Volumetric Model

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 2500 foot slice 3000 foot slice

3500 foot slice 4000 foot slice


Coso: Prestack Kirchhoff Migration

West WestEast East


Coso ConclusionsThe 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.


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.


Pumpernickel Valley, Nevada


Pumpernickel Valley Raw

Record


Pumpernickel Valley Velocity Line 3


Pumpernickel Valley Prestack Migrated Line 3


Pumpernickel Valley Preliminary Line 3


Pumpernickel Valley -

Preliminary interpretation of

seismic data

5

4

3

Only the range-front fault is

manifested at the surface


Pumpernickel Valley, Nevada

Preliminary fault traces based on

seismic only


Pumpernickel ConclusionsThe 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

Astor Pass: 2-D WAZ Acquisition 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: Fault

Discoverywith

Direct Fault-Plane

Images


Astor Pass: Imaging Volcanic Stratigraphy


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


Astor Pass ConclusionsThe 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


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 !

https://www.unrsearch.com/postings/9727

https://www.unrsearch.com/postings/9727

advanced seismic imaging for geothermal development

Documents

velocity problem

seismic exploration

university of nevadajohn

university of nevadaproblem

university of nevadasolution

depthuses velocity models

possible velocity solutions

magnitude of velocity