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Recoverable Resource Estimate of Identified 

Onshore Geopressured Geothermal Energy 

in Texas and Louisiana

AAPG 2012 Annual Convention and Exhibition

Ariel Esposito and Chad Augustine

April 24, 2012

NREL/PR-6A20-54999
2 

• Geopressured Geothermal

o Reservoirs characterized by pore fluids under high confining pressures and 

high temperatures with correspondingly large quantities of dissolved 

methane 

o Soft geopressure: Hydrostatic to 15.83 kPa/m

o Hard geopressure: 15.83– 22.61 kPa/m (lithostatic pressure gradient)

• Common Geopressured Geothermal Reservoir Structure

o Upper thick low permeability shale

o Thin sandstone layer

o Lower thick low permeability shale

• Three Potential Sources of Energy

o Thermal energy (Temperature > 100°C – geothermal electricity generation)

o Chemical energy (natural gas)

o Mechanical energy (pressurized fluid)

Geopressured Geothermal Resource
3 

Introduction

Motivation

• The Gulf Coast geopressured geothermal resource is the 

most extensive of any region in the United States

Goals

• Estimate the geopressured geothermal resource in the Gulf 

Coast for combined production of natural gas and electricity

o Total heat in place and recoverable thermal energy

o Total geothermal electricity generation potential 

o Total natural gas that could be recovered with geothermal 

fluid 

• Fully utilize previously published datasets

• Incorporate results from reservoir modeling of geopressured

geothermal reservoirs in the estimate
4 

Background and Methodology

1. Determine geopressured geothermal resource regions within Texas and 

Louisiana

o Five formations identified within Texas: Lower Wilcox, Lower Claiborne, 

Upper Claiborne, Vicksburg-Jackson, and Lower Frio

2. Collect all relevant data on five formations in Texas and geopressured

geothermal region in Louisiana

o Sand and shale thickness, depth to geopressure, porosity, and temperature

3. Complete resource estimate using spatial analysis of Texas formations and 

Louisiana

o Populate a grid of cells (A = 1 km2) region with data

o Estimate geopressured geothermal resource for each grid cell

Background

• Previous work includes detailed multiphase flow reservoir modeling of 

geopressured geothermal fairways in the Frio and Wilcox formations 

(Esposito and Augustine 2011)

• Reservoir modeling provided insight on geothermal brine and natural gas 

flow rate profiles over a long-term time frame, reservoir pressure and 

temperature changes with time, and potential recovery factors
5 

Area

Thickness

Porosity 

& Salinity

Temp 

Gradient

Resource 

Estimate 

per Cell

Geopressured Geothermal Resource Estimate

The total resource and the 

recoverable energy are 

calculated for each cell within 

the geopressured area of the 

formation and then summed 

over the entire formation to 

obtain the formation 

estimates.

Formation 

Total Energy 

Estimate 

Thermal Energy

Methane Quantity

Recovery

Factor

SUM

Ʃ

Recoverable

Resource

per Cell

Ʃ

SUM

Formation 

Recoverable Energy 

Estimate 

Thermal Recovered

Methane Recovered
6 

Texas Geopressured Formation Areas

Formation Geopressured Area 

(km2)

Lower Wilcox 42,534 

Lower 

Claiborne 1,439 

Upper 

Claiborne 5,785 

VicksburgJackson 26,821 

Lower Frio 42,334 

Multiple formations are present at the same 

location but at different depths

Spatial Analysis Criteria

1. Total sand thickness must be 

greater than 30 m

2. A pressure gradient of 

11.3 kPa/m falls above or 

within sandstone

3. Porosity data is available

4. Some regions in formation have 

temperatures above 100°C 
7 

Lower Wilcox Geopressured Area

Thickest
8 

Lower Claiborne Geopressured Area

Very limited 

sand leads to 

small area of 

interest
9 

Upper Claiborne Geopressured Area

Very limited 

sand leads to 

small area of 

interest
10

Vicksburg-Jackson Geopressured Area

Deepest Thickest
11

Lower Frio Geopressured Area

Multiple 

areas of 

thick shale

Includes an 

offshore buffer 

of 10 km
12

Texas Geopressured Formation Summary

Formation Lower 

Wilcox

Lower 

Claiborne

Upper

Claiborne

Vicksburg 

Jackson

Lower Frio

Average Sand 

Thickness 185 8 48 114 123 

Average Shale 

Thickness 725 922 411 1,286 681 

Midpoint

Depth 

Min 1,904 2,795 2,732 2,427 1,814 

Max 5,571 4,217 3,486 6,278 5,712 

Avg 3,436 3,833 3,142 4,524 3,989 

Average Porosity 11.3 17.7 21.3 13.5 12.9 

Total Area (km2) 46,944 28,783 17,741 28,567 117,223 

Area of Interest 

(km2) 42,534 1,439 5,785 26,821 42,334 

Area of Interest

to Total Area 0.91 0.05 0.33 0.94 0.36 

Maximum
13

Louisiana Geopressured Area

Depth to Geopressure (meters) Geopressured Sand Thickness (meters)

Greatest depth to geopressure near coast

Data on any shale present in the 

geopressured region was not available. In 

this analysis, the formation only consisted of 

sandstone.
14

Temperature Estimation at Reservoir Midpoint

• Input Data:

• AAPG bottom hole temperature (BHT) measurements

o More than 27,000 data points for United States

• Correct BHT using the Kehle correction up to 3,930 m

 ∆T = -1.73 x 10-10 Z3 – 1.28 x 10-7 Z2 + 7.97 x 10-3 Z -0.565 [°C] 

• After 3,930 m use linear equation (Blackwell et al. 2010)

 ∆T = 19 + 3.28 x 10-4*(Z-3,930) [°C] 

• Temperature Interpolation (MATLAB):

• Fluid temperature is calculated at the grid cell midpoint

1. Delaunay triangulation of the scattered data locations

o Input: x, y, depth (z), and corrected BHT

2. Linear interpolation of temperature to midpoint of grid cell

o Temp (x, y, z) Gridded: x, y, midpoint (z) points
15

Temperature Data

Location of data points from AAPG BHT database selected for 

analysis
16

Midpoint Temperature Estimate - Texas

Lower Wilcox 

Vicksburg-Jackson

Lower Frio 

Lower Claiborne

Upper Claiborne

Maximum temperature of 273°C occurs 

in southern Vicksburg Jackson

The midpoint temperature in all five formations increases towards the coast due to 

the significant dipping in each formation.
17

Resource Estimate Assumptions

• Sand and shale thickness is uniform throughout the grid 

cell area of 1 km2

• Sandstone is located in center of formation and bounded 

by upper and lower shale 

• Pressure gradient at midpoint depth is 15.83 kPa/m

Heat Capacity, Enthalpy, and Entropy calculations:

6th order polynomials in terms of temperature 

Fluid Density at Reservoir Conditions (ρR):

ρR = ρ0 (1 - (PR - P0)/E)/(1 + β(TR - T0)) [kg/m3 ]

o E : bulk modulus for water (2.1 x 109 Pa)

o β : volumetric temperature expansion coefficient (0.0004 m3/m3 oC) 

o P0 : reference pressure | PR : reservoir pressure

o T0 : reference temperature |TR = reservoir temperature

o ρ0 : reference fluid density
18

Texas: Total Heat in Place (Sandstone and Shale) 

Formation Total (J)

VicksburgJackson 2.67E+21

Lower Wilcox 1.78E+21

Lower Frio 1.74E+21

Upper 

Claiborne 1.89E+20

Lower 

Claiborne 1.10E+20

0

100

200

300

400

500

600

700

Total Heat in Place (1018J) 

Temperature (°C)

Lower Wilcox Lower Frio Upper Claiborne

Lower Claiborne Vicksburg_Jackson

Heat in Place Method

1. Total mass (mT):

mT = φ·ρ·A·(zsand+zshale) 

2. Heat in place (JT):

JT = mT·cP ·(TR-T0) 

with T0 = 25 °C 
19

Total Recoverable Energy Calculations

1. Recoverable Mass (mwh )

mwh = RF·VT ·φ ·ρ

RF : recovery factor

VT : total volume

φ : porosity

ρ : fluid density

2. Exergy (E) 

E = mwh[hwh-h0-T0(swh-s0)]

hwh : fluid enthalpy

h0 : reference enthalpy

T0 : reference temperature

swh : fluid entropy

s0 : reference entropy 

3. Electricity Generation 

Potential (We) 

We = E·ηu ηu : utilization efficiency

y = 0.0032x - 0.16

y = 0.4

0

0.1

0.2

0.3

0.4

0.5

0.6

50 100 150 200 250 300 350

Utilization Efficiency [

η

u ]

Temperature ( °C)

Geothermal Power Conversion* 

*Williams et al. 2008
20

Texas: Recovery Factors from Reservoir Modeling

Frio Recoverability Factors:

• Data were collected for five fairways

o Developed 9 unique reservoir models

• Recovery factor was calculated:

o 20-year average: 0.325%

o RF 100-year average: 0.486%

• Frio 20-year average RF of 0.325%

was also applied to Vicksburg Jackson

Wilcox Recoverability Factors:

• Data were collected for six fairways

o Developed 12 unique reservoir models 

• Recovery factor was calculated:

o 20-year average: 0.685%

o 100-year average: 0.870%

• Wilcox 20-year average RF of 0.685% was 

also applied to Lower and Upper Claiborne

Recoverability Factor (RF) = Volume Recovered/Total Pore Volume

Source: 

Esposito and 

Augustine 2011
21

Texas: Electricity Generation Potential

Formation

Total 

Elecricity

(MWe) 

VicksburgJackson 1,032

Lower Wilcox 939

Lower Frio 429

Lower 

Claiborne 54

Upper 

Claiborne 46

0

50

100

150

200

250

300

Total Electricity Generation Potential (MWe) 

Temperature (°C)

Lower Wilcox Lower Frio Upper Claiborne

Lower Claiborne Vicksburg Jackson
22

Heat in Place Method: Only Sandstone

1. Total mass (mT):

mT = φ·ρ·A·(zsand) 

ρ = 0.25

2. Heat in place (JT):

JT = mT·cP ·(TR-T0) 

with T0 = 25°C 

0

10

20

30

40

50

60

70

80

90

100

<100

100-110110-120120-130130-140140-150150-160160-170170-180

Total Heat in Place (1018J) 

Temperature (°C)

Louisiana: Heat in Place (Sand)

Louisiana: Heat in Place (Only Sandstone)

Formation Total (J)

Louisiana 3.47E+20 

1) Multiple regions in Louisiana resource 

region have temperatures less than 100°C 

2) Large portion of resource below 100°C
23

Louisiana Recoverable Energy Estimates

Louisiana recovery factor is much 

higher from the sandstone based 

on available data from Bassiouni

(1980) than from Frio and Wilcox 

reservoir modeling

RF = -3E-11(VT·φ) + 0.2516

R2 = 0.6915

0%

5%

10%

15%

20%

25%

1.E+09 3.E+09 5.E+09 7.E+09

% of Sandstone Volume Recovered

Sandstone Pore Volume (m3) 

% Sandstone Volume Recovered 

vs. Sandstone Pore Volume

Evaluation by Bassiouni (1980):

• For the top 63 prospects, recovered electrical 

energy was provided

• For the top 15 prospects sandstone pore volume 

was estimated using sandstone thickness

Recovery Factor Estimate:

The total volume recovered for the top 15 prospects 

was estimated using assumptions presented in 

Bassiouni (1980). Recovery factors were estimated 

by dividing the estimated volume recovered by the 

sandstone pore volume.
24

Louisiana Recoverable Energy

0

100

200

300

400

500

600

700

800

Total Electricity Generation Potential (MWe) 

Temperature (°C)

Louisiana: Total Electric Energy

Formation Total ( MWe) 

Louisiana 2620 

Summary: 

Due to high recovery factors 

for Louisiana based on results 

from Bassiouni (1980), the 

electric energy potential is 

equivalent to the five 

formations in Texas. This is 

true even though the 

resource is at on average a 

lower temperature and 

covers a smaller surface area.
25

Natural Gas Recoverability Estimate

0.0%

2.5%

5.0%

7.5%

10.0%

12.5%

15.0%

17.5%

20.0%

22.5%

0 100 200 300 400 500 600 700 800 900 1000

Percent 

Produced Gas Water Ratio (GWR) (scf/bbl)

Distribution of the Produced Gas Water Ratio 

from results of fairway reservoir modeling

Anomalous outliers

Summary:

• 10% < 45 scf/bbl

• 90% < 170 scf/bbl

• 53% between 45–85 

scf/bbl

Natural Gas (VNG) 

VNGA = mwh·ρ-1·GWRave

• ρ: density

• Density is a function of 

depth, pressure, and 

temperature (lb/bbl)

• GWRave : average 

produced gas water ratio 

from reservoir modeling 

results for all fairways at 

83 scf/bbl 

Results from 19 of the 21 reservoir models excluding the two 

anomalous outliers were used to calculate GWRave

Source: 

Esposito and 

Augustine (2011)
26

Gulf Coast Total Recoverable Natural Gas

Formation Total Natural

Gas (scf) 

Total Mass 

Produced (kg)

Average Flow 

Rate of Gas

(MMscf/D)

Louisiana 9.52E+13 1.75E+14 13,040 

Lower Wilcox 1.37E+13 2.49E+13 1873 

Lower Frio 6.92E+12 1.25E+13 948 

Vicksburg 

Jackson 6.82E+12 1.21E+13 934 

Upper 

Claiborne 1.98E+12 3.66E+12 272 

Lower 

Claiborne 9.52E+11 1.51E+12 114 

Total 1.25E+14 2.29E+14 1.71+04 

Assumptions: 

1. All fluid is fully 

saturated with 

natural gas at 

reservoir conditions

2. Some free phase gas 

is present in the pore 

space representing 

between 1%–5% of 

pore volume

3. Presence of potential 

gas layers is not 

included in estimate
27

Results and Conclusions

• Estimated recoverable electricity generation potential:

o Texas: 2.5 GW

o Louisiana: 2.6 GW

• Highest quality resource is in southern Vicksburg Jackson 

due to collocation of high temperatures and thick sands

o Total of ~1,000 MW electricity generation potential

• Large quantity of natural gas could be produced in 

conjunction with geopressured geothermal resource

o 1.25 x1014 scf of natural gas

• More data for each formation as well as data on 

sandstone permeability would improve overall analysis

• Louisiana estimate is quite high and is based on limited 

data on recovery factors. Should be treated as less certain 

than estimate for Texas.
28

Ariel Esposito

ariel.esposito@nrel.gov

303-275-4694 

Chad Augustine

chad.augustine@nrel.gov

303-384-7382 

THANK YOU!

This work was funded by the Department of Energy Geothermal Technologies Program. 

We would like to acknowledge Arlene Anderson for her input and support. 

We would also like to recognize Billy Roberts for his significant contribution to the spatial analysis and 

cartography.

References and data sources for spatial analysis:

• American Association of Petroleum Geologists (AAPG). (1994). CSDE, COSUNA, and Geothermal Survey Data_Rom. 

• Bassiouni, Z. (1980). "Evaluation of Potential Geopressure Geothermal Test Sites in Southern Louisiana.” Petroleum Engineering Department. Baton Rouge, LA: 

Louisiana State University.

• Bebout D.G.; Weise, B.R.; Gregory, A.R.; Edwards, M.B. (1982). "Wilcox Sandstone Reservoirs in the Deep Subsurface Along the Texas Gulf Coast: Their Potential 

for Production of Geopressured Geothermal Energy." Report of Investigations No. 117. Bureau of Economic Geology. Austin, TX: University of Texas.

• Bebout D.; Loucks, R.; Gregory, A. (1983). "Frio Sandstone Reservoirs in the Deep Subsurface Along the Texas Gulf Coast: Their Potential for Production of 

Geopressured Geothermal Energy." Bureau of Economic Geology. Austin, TX: University of Texas. 

• Esposito, A.; Augustine, C. (2011).“Geopressured Geothermal Resource and Recoverable Energy Estimate for the Wilcox and Frio Formations, Texas.” 

Geothermal Resource Council Transactions (35); pp. 1563–1571.

• Galloway W. E.; Hobday, D.K.; Magara, K. (1982). "Frio Formation of the Texas Gulf Coast Basin-Depositional Systems, Structural Framework, and Hydrocarbon 

Origin, Migration, Distribution, and Exploration Potential." Report of Investigations No. 122. Bureau of Economic Geology. Austin, TX: University of Texas.

• Gregory, A.R.; Dodge, M.; Posey, J.; Morton, R. (1980). "Volume and Accessibility of Entrained (Solution) Methane in Deep Geopressured Reservoirs-Tertiary 

Formations of the Texas Gulf Coast." Final report. Bureau of Economic Geology. Austin, TX: University of Texas. 

• Loucks, R.G.; Dodge, M.M.; Galloway, W.E. (1979). “Sandstone Consolidation Analysis to Delineate Areas of High-Quality Reservoirs Suitable for Production of 

Geopressured Geothermal Energy Along the Texas Gulf Coast.” Final Report. Bureau of Economic Geology. Austin, TX: University of Texas. 

• Wallace R.; Kraemer, T.; Taylor, R.; Wesselman, J. (1978). "Assessment of Geopressured-Geothermal Resources in the Northern Gulf of Mexico Basin." U.S. 

Geological Survey, Circular 790; pp. 132–155.

• Williams, C.F; Reed, M.J.; Mariner, R.H. (2008). “A Review of Methods Applied by the U.S. Geological Survey in the Assessment of Identified Geothermal 

Resources.” USGS Open-File Report 2008-1296

.