Geology and Geothermal

Energy Potential in the

San Luis Valley

Paul Morgan

Colorado Geological Surveyfor

Workshop: Geothermal Uses in the

San Luis Valley

February 27, 2010

• General geology (an geologic history) of

Colorado

• What is important for geothermal resources

• The Geology of the San Luis Valley

• Geothermal resources in the San Luis

Valley

Presentation Outline:

. 130 m.y.Paleogeography from

Prof. Ron Blakey, NAU

90 m.y.

75 m.y.

65 m.y.

30-35 m.y.

15-20 m.y.

5-10 m.y.

Geology of Colorado

Heat Flow Map

Blackwell and others, SMU Geothermal Lab,

2004

High Heat Flow

>80 mW/m2

High Heat Flow is generally important

for good geothermal potential

Causes of high heat flow:

1) Thinner lithosphere (plate)

2) Igneous plutons at depth (young volcanism) ?

3) Residual heat (extended geologically-recent

volcanism)

4) Upwelling of deep, heated groundwater –

locally

5) Concentration of radioactive elements ?

Effects of

geological

extension (basin

formation) and

compression

(mountain building)

on heat flow

Deep groundwater circulation

Geothermal Potential of the

San Luis Valley• Regional High Heat Flow (thin lithosphere,

residual heat, concentration of radioactive

elements )

– Gives low-grade geothermal resources, typically

< 200 F in most areas at depths up to 5000 feet

• Upwelling of deep heated groundwater

– May give low-grade geothermal resources at

significantly shallower depths, < 200 F as shallow

as 2000 feet, and higher-grade resources at

currently economic depths, > 250 at < 8,000-

10,000 feet.

Examples of Shallow

Temperatures Studies

Northern San Luis Valley

Heat Flow Data Map

Gradient range:

1.6 to 4.2 F/100 ft,

Predicting ~128 to

~258 F at 5,000 ft

The San Luis Basin

has complex

subsurface

structure that

causes

groundwater to

move up and down

giving cold and hot

spots

A geothermal test well was drilled in the early 1980s

Alamosa Well #1

In general

the basin

becomes a

poorer

aquifer with

depth

Alamosa Well # 1

The test well

demonstrated

encouraging

temperatures

San Luis Valley

Oil-well Bottom-Hole

Temperature Data

confirm high

temperatures at

depth

Typical: 300+ F

at 10,000 feet

From here to there: maximizing the

geothermal potential of the San Luis Valley

• There are some very creative folks in the

Valley – geothermal is a mature resource, but

ideas and technology continue to evolve

• Ground-source heat pumps (geoexchange)

– are the most efficient, clean form of heating, but

swamp cooler are cheaper for cooling in the arid

southwest. Use hot water to make ground-source

heat pump heating even more efficient.

From here to there, concluded

• For direct use (< 200 F) hot water is to be

found everywhere at depth in the valley

– Look for places, upflow zones, where it may be

hotter at a shallower depth

• High-grade resources (>250 F definitely exist

at depth but the permeability may be low.

– As with direct use, the depth to these higher

temperature probably varies with location.

Reservoirs may need stimulation to produce

sufficient fluids to produce electricity.

CGS Geothermal web page:

http://geosurvey.state.co.us

Home page>

Programs & Projects >

Mineral & Energy Resources >

Geothermal

Paul Morgan: paul.morgan@state.co.us

finis

Hydrothermal Systems

<10,000 ft (<3 km)

Enhanced Geothermal

Systems

10,000-30,000 ft (3-10 km)Geothermal Education Association

Hot/Warm

Springs & Wells

Wuanita Hot Spring, Gunnison Valley Yampah Hot Spring, Glenwood Springs

Cottonwood Hot Springs, Buena Vista Mt. Princeton Area, Nathrop

Alligator Farm, Hooper well, San Luis Basin

• Spas & Pools - 18 sites

• Space Heating - 15 sites

• Greenhouses - 4 site

• Aquaculture - 1 sites

• District Heating - 1 site

Heber, CA

Electrical Generation

- 0 sites

• High heat flow

• Quaternary volcanism

• Quaternary faulting

2nd largest heat flow

anomaly in US >100 mW/m2

5 Quaternary volcanoes

>90 Quaternary faults

Colorado is also outstanding in these criteria!

Criteria for geothermal power potential:

Machette, 2003, USGS OFR 03-417

Quaternary

Faults

Quaternary

Faults

&

Neogene/

Quaternary

Volcanic

Deposits

Thermal Point Distance to Quaternary Faults

Unique Spring and Well Areas

29

15

8

14

10

17

0

5

10

15

20

25

30

35

0-10 10-20 20-30 30-40 40-50 >50

Distance (miles)

Nu

mb

er

of

Th

erm

al

Po

ints

Thermal Point Distance to Quaternary FaultsUnique Spring and Well Areas

Thermal Point Distance to Recent Volcanism (<23Ma)

Unique Spring and Well Areas

30

12

6 53

37

0

5

10

15

20

25

30

35

40

0-10 10-20 20-30 30-40 40-50 >50

Distance (miles)

Nu

mb

er

of

Th

erm

al

Po

ints

Thermal Point Distance to Neogene Volcanism (<23Ma)

Unique Spring and Well Areas

Thermal Points Temperature vs Distance to Quaternary Fault

All Springs and Wells

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Distance (miles)

Tem

pera

ture

(d

eg

C)

Temp vs Distance to Quaternary

Faults

Thermal Points Temperature vs Distance to Recent Volcanism (<23Ma)

All Springs and Wells

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100

Distance (miles)

Tem

pera

ture

(d

eg

C)

Temp vs Distance to Neogene

Volcanics

Temperature Relationships

50°C

25 mi

from Dueker, Yuan, & Zurek, 2001

Tomographic P-wave velocity

variationsMap at 100 Km Depth

Yellow/red = Low

Velocity Material

South North

ASPEN YSTN

100

200

300

400

0

500

-200 0 100 200 400 600-400-600-800

Distance (km)

D D’

Depth

(km

)

from Dueker, Yuan, & Zurek, 2001

Tomographic P-wave velocity variationsCross-Section View

Interpretive Heat Flow Map

Heat Flow Map – Mt. Princeton

Heat Flow Map – Rico

Heat Flow Map – Trinidad

Bottom Hole Temps – Denver Basin

Denver

Bottom Hole Temps – San Juan Basin

Durango

• Colorado is prospective

• Multiple lines of evidence

• The more we look …

… the better the prospects

In Summary:

Geothermal Gradient Map

>50 C/km

or

>2.7 F/100 ft

San Luis Basin at Alamosa

Back of the Envelope Analysis I

• Like most sedimentary basins in Colorado,

San Luis Valley has high geothermal

gradients (~ 2.4 ̊F/100 ft; ~50 ̊C/km) – good

geothermal prospects.

• Porous/permeable sediments are relatively

thin (1500 ft; 500 m) around Alamosa –

deeper volcanic fill is low permeability.

• Effects of Alamosa horst and its faults are

relatively unknown.

Back of the Envelope Analysis II

• Hindsight: Alamosa Geothermal Well # 1

(early 1980s) may have had more success

if logs could have been run on the hole to

find a permeable zone

• Techniques are now more advanced to

increase permeability, primarily

hydrofracing – expensive, but high returns

• This is one of the directions of the future!

Isostatic Gravity Anomaly Map

(from Oshetski and Kucks, 2000; USGS OFR-00-42)

Table 2.2. High-grade EGS areas (>200 C at depths of about 4 km)

MIT Study - Enhanced Geothermal Systems

from Tester and

others, 2006

MIT Study - Enhanced Geothermal Systems

from Tester and

others, 2006

6.5 km

10 km

3.5 kmFor EGS, Colorado has the

one of the best high temp resources in the

US.