Ehni Enterprises, Inc. - images2.loopnet.com€¦ · Ehni Enterprises, Inc. P. O. Box 4228 Carson City, NV 89702-4228 November 2008 Background Wabuska Hot Springs is located in Lyon

Ehni Enterprises, Inc. Geologic Consulting, Prospecting & Evaluation P. O. Box 4228, Carson City, Nevada 89702 • (775) 883-1107 FAX (775) 883-7279 email: [email protected]

Geologic Evaluation of the Geothermal Potential of Wabuska Hot Springs Lyon County, Nevada

By:

Wm. J. Ehni Geologist

November 24, 2008

McCabe/Fleeman, Wabuska Hot Springs Page 2 of 13

Ehni Enterprises, Inc. P. O. Box 4228 Carson City, NV 89702-4228 November 2008

Scope and Purpose

The purpose of this report is to provide a cursory geologic evaluation of the geothermal potential

of acreage located near Wabuska Hot Springs in sections 21 and 22 of Township 15 North Range

25 East (MDB&M), Lyon County, Nevada, with an emphasis on the McCabe/Fleeman land as

outlined on Figure 1. Information used to evaluate the prospect consisted of exiting public

domain data. A partial list of data and reports used for this process is included at the end of the

report. It is not within the scope of this report to provide a detailed explanation of the

commercial uses of geothermal resources or to provide a detailed discussion of the techniques

used for geothermal development. The user of this report should be casually familiar with the

project area and have a layman’s concept of geothermal systems.



Figure 1: Location map of Wabuska Hot Springs and the McCabe/Fleeman parcel in

sections 21 and 22 of T15N R25E; Lyon County, Nevada.



Background

Wabuska Hot Springs is located in Lyon County, Nevada. A power plant using geothermal brine

produced from two wells was built in 1984 and expanded in 1987 to its current configuration.

The Wabuska power plant (currently operated by Homestretch Geothermal LLC) has the

distinction of being the first geothermal power plant to be built in Nevada. In addition, the inlet

temperature and production rates of the wells have not declined over this period of time,

something that has plagued numerous other geothermal power plants in Nevada. However,

naturally occurring hot springs in the area have dried up indicating inadequate recharge to the

system. According to information available from the Nevada Division of Minerals

http://minerals.state.nv.us/ogg_nvgeorespro.htm the plant is currently generating approximately

0.7 net megawatts (6221 MWH in 2007). The inlet temperature is approximately 220 degrees

Fahrenheit. The binary electrical generators are supplied by hot water from two production

wells, PW1 and PW2. PW1 is 488’ deep, had an Initial Production (IP) rate of 700 gallons per

minute (gpm). PW2 had an Initial Production rate of 800 gpm and is 500’ deep. The combined

IP of the two wells is 1500gpm which equates to 2.16 million gallons per day. All produced

fluids are currently discharged on the surface. Current discharge rates are reported to be 1.9

million gallons per day. Prior to the startup of the Wabuska power plant, surface discharge from

natural hot springs in the area was approximately 50 gallons per minute (72,000 gallons per day).

Geology

A northeast trending fault running from Wabuska Hot Springs to Kribs Hot Spring (see Figure 2)

is the controlling structure for the Wabuska Geothermal System. The Wabuska Fault, as

identified in Figures 2 and 3, parallels the “Wabuska Lineament”. This fault is part of the



extensional tectonic setting associated with the northwest striking Wabuska Lineament and the

right lateral faulting associated with the Walker Lane. In 1988, Stewart recognized the northeast

trending “Wabuska Lineament” and other researchers (Trexler and others, GSA 2000) have

noted the relationship between the Wabuska Lineament and the right lateral Walker Lane fault

system.

The existing geologic model for the Wabuska geothermal system focuses on this east dipping

high angel normal fault as providing increased permeability and the conduit for hot water to

migrate from deeper higher temperatures as depicted in Figure 2 and on cross section A-A’ in

Figure 3. The existing production by Homestretch from production wells PW1 and PW2 is from

the footwall side of the fault as interpreted in this report. Production temperatures of PW1 and

PW2 are only slightly higher than the original surface temperatures of the hot springs as reported

by Mariner in 1974. Wabuska Hot Springs subsequently “dried” up after production from this

shallow outflow zone from PW1 and PW2 was initiated. Accurate historical groundwater table

elevation data is not available for the area; however, some wells that used to be artesian no

longer flow and therefore it appears that the water table is dropping due to production of

geothermal fluid in the absence of any recharge.

The existing production wells produce from a shallow outflow zone on the northwest side

(footwall) of the Wabuska fault zone. Using the east dipping geologic model for this geothermal

system, and assuming that the fault zone will be the best production zone, the optimum drill sites

should be in the east (hanging wall) side of the fault. Higher temperatures will be encountered at

shallower depths on the east side of the fault also. The geochemistry of the historical Wabuska



Hot Spring suggests that these are “mature” unmixed waters, supporting the interpretation that

springs emanate from this fault.

Figure 2: Contoured temperature gradient map of the Wabuska Geothermal System



In 1988, the operator of the power plant attempted to locate a recharge zone. Although it is not

clear in the existing documents, this effort probably coincided with decreased flow of surface hot

springs, and possibly the cessation of artesian flow from some wells. The attempt to identify a

useable injection zone to recharge the system was limited to a very small portion of the resource.

As a result of limiting the areal extent of the investigation, the operator was unable to find a

satisfactory injection zone and continued with surface discharge.

Figure 3: Contoured isothermal cross section showing the southeast dipping Wabuska fault



The original natural flow rate of Wabuska Hot Springs is not well documented; however, based

on descriptions by earlier investigators it appears that the natural flow rate, prior to the start up of

the geothermal power plant in 1984, was about 50 gallons per minute (gpm). White and

Williams (USGS Circular 726; Assessment of Geothermal Resources of the United States -

1975) reported “Several hot springs of low natural discharge”. Waring (USGS professional

paper 492, 1965; Thermal Springs of the United States on other Countries of the World - A

Summary) did not comment on the flow, even though he tabulated the flow for most hot springs

included in his summary. The area in which the old hot springs existed has been inspected by

this author, and based on surface features and the areal extent of the extinct springs, it has been

concluded that the original natural flow of the hot spring system was probably about 50 gallons

per minute.

Other “first hand” descriptions of the springs include one by Russell (1885, p. 48, 49), where he

states that “the springs occur along an east-west line that coincides with the course of a post-

Lahontan fault, which is plainly shown by an irregular scarp, in some places 6 m high. The

springs occur in circular mounds; the water is collected in small basins and evaporated,

reportedly forming a saline deposit, ….”. In 1937, Stearns and others reported that the “Hot

springs, about 1.6 km north of Wabuska, range in temperature from 59 to 72°C and occur over a

large area in Secs. 14, 15, 16, 23, Tl5N, R25E. Gas bubbles issue from the pools with a faint

odor of H2S”. These quotes were referenced at

http://www.nbmg.unr.edu/geothermal/site.php?sid=Wabuska%20Hot%20Springs (21Nov2008).

The USGS sampled Wabuska Hot Springs in 1974 and reported a temperature of 97C (Mariner).

In 1978, the USGS sampled the springs again and reported the surface temperature as 93.3C.



The eastern portion of the Wabuska geothermal anomaly was explored in 1988 by Yankee Power

Inc. The results were encouraging and temperature gradient holes (28-11 and 68-11) from this

exploration effort are included on Figure 2. Yankee Power’s exploration appears to have been

focused on the northeast extension of the Wabuska fault. A hot spring located in the northwest

quarter of section 14, T15N R25E, and referred to as Kribs Hot Spring in Yankee’s 1988 report,

is interpreted as being on the Wabuska fault (Figure 2). This hot spring was also noted on the

geologic map by Moore (NBMG Bulletin 75) in 1969. A well located in the NW/4 of the NE/4

of section 14, T15N R25E, referred to as the Gadda Well by Yankee Power, has a reported

flowing (surface) temperature of 86 Degrees Fahrenheit, is 145 feet deep (NBMG Bulletin 91)

and is also on trend with the Wabuska fault.

Resource Temperature

The resource temperature can be estimated by analyzing the composition of water produced from

the hot springs or wells in the area. Fournier’s 1977 silica geothermometer predicts an

equilibrium temperature of the Wabuska geothermal system to be 326 degrees Fahrenheit, using

155 ppm Si02 (silica) as reported on the Nevada Bureau of Mines and Geology web site:

http://www.nbmg.unr.edu/geothermal/databases.htm for sample number “108 N15 E25 16D 1

spring”. Other analyses of the geothermal fluids at Wabuska suggest equilibrium temperatures

of about 300 degrees Fahrenheit; therefore, on Figure 3 the minimum resource temperature is

estimated to be 300 degrees Fahrenheit. It should be noted that estimating the temperature of a

geothermal resource is a very complex process and although Fournier’s 1977 silica

geothermometer is an important component, it should not be used as a definitive tool. Other

geothermometers (eg: alkali), mixing models and resource information needs to be incorporated



into the final estimate; however, as a “qualitative” tool to compare various prospects, the silica

(SiO2) concentration is a useful measure of the geothermal system.

Resource Management and Development

Other important components of a geothermal system include resource management. In one of

the largest geothermal fields in the United States (The Geysers, California) the management of

the resource was neglected by not re-injecting fluid to maintain a balanced system. The Geysers

is a dry steam field and over time, because the field was produced without injection, production

declined. A major effort was undertaken to obtain fluid to re-inject after production rates from

wells dropped so low that it could have forced the closure of some power plants. Operators at

The Geysers are now injecting fluid to support the geothermal system.

Currently at Wabuska, the produced fluid is discharged on the surface, and not re-injected into

the system. As a result, the surface manifestations (hot springs) have disappeared due a drop in

the water table associated with the geothermal production and surface discharge. The power

plant has been operating with surface discharge, producing from a relatively shallow portion of

this resource, with basically no decline in well head temperature. However, if production rates

are increased, and there is no reinjection of fluid to maintain resource pressures (which is directly

related to elevation of the water table); it could have long-term detrimental affects to the

geothermal resource.

Development and expansion of the Wabuska geothermal resource should include injection wells,

strategically designed to maintain reservoir pressures and not impact production temperatures.



Failure to incorporate injection wells into any expansion of the Wabuska geothermal

development will result in an additional drop in the water table, which will require wells to be

drilled deeper in order to produce hot water.

The fact that the Wabuska geothermal system has been in production since 1984 and has not seen

a decline in production temperatures or a significant decline in reservoir pressures, even with

only surface discharge, indicates that this a relative large geothermal system. Developing the

deeper and hotter portion of this resource could double the efficiency for producing electricity.

The existing shallow lower temperature production at Wabuska averages 1273 gallons per

minute of brine at 220 degrees Fahrenheit per megawatt; whereas, if the 300 degree Fahrenheit

resource was developed it would only take about 670 gallons per minute to generate 1 megawatt

of electricity.

location MW gpm (field) gpm/Mw Temperature

No of wells gpm/well

Wabuska 1.2 1528 1273 220 2 764 empire 3.6 4769 1325 280 3 1590 steamboat 60 26921 449 325 14 1923 Stillwater 13 5625 433 338 4 1406 Soda Lake 16.6 5185 312 340 5 1037 Brady 21 9074 432 355 6 1512 Desert Peak 10 1829 183 410 2 915 Beowawe 16.7 4421 265 415 3 1474 Dixie Valley 66 11088 168 480 7 1584

Table 1: Comparison of the performance of several geothermal power plants in Nevada



Development of the McCabe/Fleeman parcel should target the 300 degree Fahrenheit resource.

Wells drilled on the northwest side of the property could encounter the fault zone at about 3500

feet below ground level. Shallower production could be established; however, establishing

production from the primary fault zone should maximize the productivity. The recommended

location for an exploratory production well is in the northwest quarter of the northwest quarter

(NW/4 NW/4) of section 22 Tl5N, R25E, drilled to a total depth of 3500 feet, or until the fault

zone (and loss circulation) is encountered. Produced fluid should be injected back into a

recharge zone for pressure maintenance. The injection well(s) should be located far enough

from the production wells in order to limit cooling of the production well(s); however, the

injection wells need to close enough to the production wells in order to maintain reservoir

pressures. A likely area for locating an injection well on the McCabe/Fleeman parcel would be

in the northeast quarter of the southeast quarter of section 21 Tl5N, R25E. At this location, the

injection well should be drilled to a total depth of 4750 feet, with 500 feet of slotted liner at the

bottom of the well. After drilling the production and injection wells, prudent development of the

geothermal resource on the McCabe/Fleeman parcel should proceed with a long term flow test

with tracers in the injection well. The results from this flow test would be used to design future

wells and the power plant.

Production from the shallower geothermal resource on the McCabe/Fleeman parcel is not

recommended at this time due to probable degradation of the resource by over production

(without injection) at the facility operated by Homestretch to the north.



Partial List of References

DATE Month/Day/Year description Notes

1974 USGS OFR May 1974 Chemistry of Wabuska Hot Springs

1979 Bulletin 91; NBMG Discussion of Wabuska Hot Springs

1981 Nevada Department of Energy Geothermal Resource Area 5

1987 EG&G News Wabuska Development 4/1/1972 Well Drillers Report Log No. 12652 8/28/1981 Well Drillers Report Log No. 23216 11/18/1981 Well Drillers Report Log No. 23501; permit 43572 2/22/1985 Well Drillers Report permit 47645; Log No. 61233

3/11/1985 TAD's to Department of Minerals GDA Report

1/12/1987 Well Drillers Report Log No. 30007; permit 47644 2/12/1988 Yankee Power/DWR exploration program

4/6/1988 GDA to Department of Minerals

Completion report 15-15 and 15-15A

4/20/1988 28-11 Gradient hole log 4/20/1988 67-11 Gradient hole log

5/19/1988 GDA to Department of Minerals Notes on PW-2, 15-15A

12/27/1994 GDA to Department of Minerals Completion report ST-1

3/8/1995 Well Drillers Report Log No. 47231 3/9/1995 Well Drillers Report Log No. 47230 8/21/1996 Well Drillers Report Log No. 54964 (MW-1) 8/21/1996 Well Drillers Report Log No. 54963 7/23/1997 Completion Report 25-15 well

Documents

Ehni Enterprises, Inc. - images2.loopnet.com€¦ · Ehni Enterprises, Inc. P. O. Box 4228 Carson City, NV 89702-4228 November 2008 Background Wabuska Hot Springs is located in Lyon