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THE HOT DRY ROCK GEOTHERMAL POTENTIAL OF THE SUSANVILLE (CA) AREA

DONALD W. BROWN, EES-4

GRC 1996 ANNUAL MEETING, 29 SEPT - 2 OCT, 1996 PORTLAND, OR

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THE HOT DRY ROCK GEOTHERMAL POTENTIAL OF THE SUSANVILLE (CA) AREA

Donald W. B r o w

Los Alamos National Laboratoty Earth and Esvironmentai Sciences Division

That portion of northeastern California that lies within the Basin and Range Province repnsents a large, untapped geothermal energy resource in &e fiam of hot, but essentially impermeable, rock at depth. If a means of developing sufficient permeability in the deep, granitic basement in this comer of California can be demonstrated, ?he ek t r i c power generation potential would be considerable ?Ire objective of this study is to look at the specific geographid region extending from northeast to southeast of the village of Etchfield ( 13 miles east of Susanville) to the Nevada border as a target area for the first commercial application of Hot Dry Rock (HDR) reservoir stimulation techniques. The &timate goal is to provide background information that could lead to the creation of a commercial-scale, engineered geothermal reservoir in granitic basement rock of low permeability.

INTRODUCTION

The motivation for this paper is the large potential geothermal energy resource concentrated in northeastern California within the northern Basin aad Range (Great Basin). The focus is on California, because of the existence of a significant HDR resource in this part of the state, a favorable political climate for the development of renewable energy, and the ongoing support from the state government for the development of novel renewable eneagy concepts such as HDR.

Sass (1 995) has noted that with much of the Basin and Range Province having temperatmes of l5OoC or better within easy reach of the drill, one would expect IO or even lo0 times the present geothermal power proctnction level of about 5 10 MW (Benoit, 1996). Sass (1 995) fiuther states that the main reason for the lack of geothermal productiviy in the Great Basin is the absence of significant permeability. In many instances, wells have been drilled into hot but imperraeaM e m k (HDR) within or surrounding known productive reservoirs. However, methods of permeability enhancement have not becn applied to increase the productivity of these resources. I suggest that, by using

reservoir stimulation techniques developed at Fenton Hill during the past 20 years, sufficient permeability could be created in previously impermeable rock to generate a number of additional commerciai-grade geothermal reservoirs within the Great Basin.

The area chosen for this initial HDR evaluation is in the vicinity of Honey Lake, which lies about 20 miles southeast of Susanville, CA (see Figure 1). The Honey Lake area was extensiveiy studied in the late 1970’s and early 1980’s as a source of moderate temperature geothermal fluids (see for example Benson et a]., 1980). Three power plants were ultimately developed in the area. Two of these were small binary geothermal plants developed near existing hot springs; the 0.8 MW Wineagle and the 1.6 MW Amedee Geothermal Venture 1 (Benoit, 1996). The third, about one mile northwest of the village of Wendel, is a hybrid biomass/geothermal plant rated at 35.5 M W which obtains the majonty of its thermal input (abut 95%) fiom the buming of forest wastes (Sanders. 1996).

Figure 1. Location Map (adapted from Zeisloft et ai., 1984).

A number of deep wells have been drilled in association with the hydrothermal development in this area. For example, wells GULF-2-ST, WTN-I, and WIN-2, have penetrated the top of the +tic basement at depths from 4860 to 5050 fi (Zeisloft et al., 1984).

T Brown GEOLOGY

The majority of recent geologic investigations in the Susanville area have been performed by Prof. T. L. T. Grose and his students at Colorado School of Mines working in conjunction with geologists from the California Division of Mines and Geology (Grose et al, 1992; Grose et al., 1991; Roberts, 1985). Other studies have been conducted in direct support of the commercial geothennal developments in the Wendel and Amedee Hot Springs areas (Zeislofi et al., 1984).

The specific area under consideration in this paper is located to the northeast and southeast of the village of Litchfield in Lassen County, California (see Figure 1). According to Grose et al. (1993), the Susanville region is at or near the intersections of 4 distinctive Neogene tectonic provinces defined geologically in the shallow crust as 1) the northern end of the Sierra Nevada block, 2) the southeastern end of the Cascade Range, 3) the southern margin of the Modoc Plateau, and 4) the western margin of the Basin and Range Province. They also identify prominent second-order tectonic features including the Honey Lake depression and the Walker Lane Belt which together compose a transitional northwest-trending boundary between the Sierra-Cascade arc and the Basin and Range-Modoc back arc.

However, the specjfic area under consideration. to the northeast and southeast of Litchfield. appears to lie entirely within the boundary region between the Modoc Plateau and the Basin and Range geologic provinces (Roberts. 1985). According to Grose et ai., (1991), the structural setting consists of northwest to northeast-trending Tertiary to Quaternary normal faulting. However, based on drilling records from several deep wells in the area, only minor offsets on the mapped normal faults have occurred during the Tertiary or Quaternary (Zeisloft et al., 1984).

According to Zeislofi et al. ( 1 984), Jurassic-Cretaceous granitic rocks of the Sierra Nevada batholith form the basement complex in the area. The granitic rocks are overlain uncon- formably by Mid- to Late-Tertiary volcanic rocks. The older volcanic rocks are overlain by or interbedded with Pliocene lake deposits which are in turn overlain by Plio-Pleistocene basalts.

HEAT FLOW AND TEMPERATURE GRADIENT MEASUREMENTS IN THE SUSANVILLE AREA

Figure 2a shows the northeastem portion of California and portions of the two adjacent states. Listed on this figure are the measured heat flow values in the vicinity of Susanville (Mase et aI.. 1982). From this heat flow data. it appears that the area generally northeast to southeast of Susanville has a heat flow in

the range of I00 to 110 mW/m2. This heat flow range was further contbmed by the drilling of the WEN-I well in 1981 (shown on Figures 2a and 2b) with an overall gradient of 71 "C!./km down to 5200 ft and an inferred heat flow of about 1 10 mW/m*.

Figure Zb shows the corresponding geothermal gradient profiles for the Susanville area adapted from Kron et ai., 199 I . This figure shows a very large area in northeastern California with near-& gradients in excess of 6O"C/km. However, the majority of these measurements are from shallow boreholes. and are primarily useful for comparative purposes. Measured heat flow is the m o ~ useful geothermal parameter.

PROJECTED TEMPERATURE AT 4 KM

The recent paper by Sass ( 1995) presents a temperature extrapolation to 4 km (13,100 A) for a region with a 100 mW/m' heat flow and a 1 or 2 km sedimentary cover (see Fig. 3). For the Basin and Range Province, Sass assumes that 4 km represents the current maximum economic drilling depth. Based on the Los Alamos National Laboratory's (LANL's) most recent drilling experience at Fenton Hill - an average of S 152/fi for the depth range fiom 9,000 to 13,000 fi in granitic basement rock (Tester et al., 1989) -- the actual anticipated drilling cost for a 4- km-deep full-size wellbore would be about $2 million. When casing and compietion costs of S800,OOO (Capuano. 199 I ) are included the mtal well cost, for a 7-inch cased well to 12.100 ft. would be $2.8 million.

Assuming that the volcanics and sediments filling the Honey Lake basin down to 5200 ft (1.5 km) have a mean thermal conductivity 50% greater than the 1 km sedimentary blanket in the Sass ( 1995) study ( IL = 1.9 W/m-K). the middle curve of Figure 3 would give a rock temperature of 2 10°C at -1 km. This is a reasonable temperature for electric power generation using either dual-flash steam or binary cycle power plants.

Alternately, one can extrapolate from the measured temperature of 122°C at a depth of 5800 ft ( 1 770 m) in the WIN- 1 geothermal weil (Zeisloft et al., 1984). Assuming a heat floiv value of 110 mW/mz for the region to the northeast and southeast of Susanville (see Figure 1) and a conductivity of 2.5 W/m-K for the basement granitic complex, the temperature at a depth of 4 km would be about 220°C.

PERMEABILITY ENHANCEMENT

Over the past 20 years or so. considerable experience hss been gained in the hydraulic stimulation of the deep. hot. granitic basement at L.44NL.s Fenton Hill HDR test site in the Jemez

Qgc“ Lake

Redding

Sacramento_

I $i

Figure Za. Measured heat flow values for the Susanville area (Mae et at.. 1982).

Nevada City / .Reno I

Sacramento \ Lake T a h o e F *Carson city

Figure 2b. Geothermal gradient profiles for the Susanville area (adapted from Kron et ai.. 199 1 ).

t I

*

Brown

A I 2.5 Wlm-K

0 50 100 150 200 250 Temperature, ‘C

Figure 3. Conductive temperature profiles for the Basin and Range Province illustrating the thermal bknketing effect of basin sediments for a heat flow of 100 m W h 2 (adapted from Sass, 1995).

Mountains of northern New Mexico (Brown. 1995). The results of this testing suggest that in the absence of recently active fault zones, the permeability of the basement crystalline rock at temperatures above about 180°C is extremely low -- of the order of 10-18 m2. We have theorized that the slow. natural convective forces present would ultimately seal even marginally permeable joints or quiescent fault zones by secondary mineralization. given sufficient time. Therefore. to develop a geothermal reservoir with significant permeabilit). under such conditions requires considerable engineering. In December 1983. a 130 million m3 region of fractured rock was created at the Fenton Hill HDR test site by injecting pressurized water into a 6 8 4 (20-m) packed-off section of borehole at a depth of about 11,600 ft (3500 m) and a rock temperature of about 240‘C. Subsequent testing demonstrated a well-flow-connected volume of about 16 million m3 for the HDR reservoir.

This fracturing experiment in 1983. referred to as the Massive Hydraulic Fracturing Test (MHF Test). involved the injection of 5.7 million gallons of water during 62 hours. at a mean injection rate of 1680 gpm ( I I O LIS) and a surface injection pressure of 7000 psi (48 MPa). The projected cost of a similar 5.7-million-gallon reservoir stimulation. if performed today at more reasonable injection rates. would be about 5500.000. For injection pressures up to 2500 psi (17 MPa) at 4 km. which would be more appropriate to the Basin and Range Province (extrapolating to 4 km from the data for Dixie \’alley. NV presented in Hickman and Zoback, 1996), and for an injection rate of 840 gpm, the estimated cost for a IO-day. 1 ?-million- gallon stimulation would be in a similar range (S400.000 io S600.000). These latter hydraulic fracturing conditions probably represent both the pressure range and the kind of effort that would be required to produce a commercial-sized HDR reservoir at 4 km in the vicinity of Honey Lake.

CONCLUSIONS

The region east of Susanville in northeastern California

- and possibly extending to the entire Great Basin -- appears to have a considerable geothermal energy potential if a means for engineering sufficient permeability in the otherwise impermeable deep crystalline basement were available. It is my assertion that by using HDR reservoir stimulation techniques developed by LANL over the past 20 years at the Fenton Hill test site. a proven means of engineering this permeability is presently available. The principal remaining question is whether this permeability can be developed in an efficient and economical manner.

ACKNOWLEDGEMENTS

I wish to thank John Sass of the U.S. Geological Suney and David Duchane of LANL for their comments on the first draft of this paper.

REFERENCES

Benoit, Dick. 1996. “A Review of Geothermal Power Generation in the Basin and Range Provence in 1995.“ Geothermal Resources Council BULLETLY. Vol. 1. NO. 5, pp. 197-201.

Benson, S.. C. Goranson. J. Noble. R. Schroedcr. D. Carrigan. and H. Wollenberg. 1980. “Evaluation of thc Susanville. California. Geothermal Resource.” L R L report - I 1 187-UC-66a.. I00 p.

Brown, D., 1995. “The US Hot Dry Rock Program -- 20 Years of Experience in Reservoir Testing,” in Proc. of the World Geothermal Congress. 1995. Florence. Ita!!. p ~ . 2607-26 1 1.

Capuano. L.E. Jr.. 1991. “Los Alamos National Laboratory Clearlake Hot Dry Rock Project in Lake County. California: Exploration Well Drilling P r o p m and Cost Estimates,” ThermaSource, Inc.

Grose, T.L.T., G.J. Saucedo and D.L. Wagner. 1991. “Geologic Map of the Susanville Quadrangle. Lassen and Plumas Counties. California.” Calif. Di\.. of Mints and Geology Open File Report 9 1-01.

Grose. T.L.T.. G.J. Saucedo and D.L. Wagner. 1992. “Geologic Map of the Eagle Lake Quadrangle. Lassen County, California.” Calif. Div. of Mines and Geo1o-y Open File Report 92- 14.

Grose. T.L.T., D.L. Wagner and G.J. Saucedo. 3993. “Neo- gene Tectonic and Crustal Elements in the Eastern Pan

of the Noxal Transect,” Geological Society of America, Abstracts with Programs, Vol. 25, No. 5 , p. 45.

Hickman, S. and M. Zoback, 1996. %-Situ Stress in a Fauit- Hosted Geothermal Reservoir at Dixie Valley, Nevada,” in Proc. Vmtb International Symposium on Observation of the Continental Crust through Drilling, Tskuba, Japan, R. Ikeda (ed.), National Research Institute for Earth Science and Disaster Prevention, pp. 2 16-22 1.

Kron, A., K. Wohletz, and J. Tubb, 1991. Geothermal Gradient Contour Map of the United States, enclosed with Los Alamos National Laboratory report LA- 12606- MS (July 1993).

Mase, C.W., J.H. Sass. A.H. Lachenbruch, and R.J. Munroe, 1982. “Preliminary heat-flow investigations of the California Cascades,” US. Geol. Survey Open File Rep. 82- 150, 240 p.

Roberts, C.T., 1985. “Cenozoic Evolution of the Northwestern Honey Lake Basin, Lassen County, California.” Colorado School of Mines Quarterly, Vol. 80. NO. 1, 64 P.

Sanders. R.A., 1996. Plant Manager for the HL Power Co. plant. personal communication.

Sass, J.H., 1995. “Mining the Earth’s Heat in the Basin and Range,” Geothermal Resources Council BULLETIN, VOI. 24, pp. 125-129.

Tester, J.W., D.W. Brown and R.M. Potter, 1989. “Hot Dry Rock Geothermal Energy -- A New Energy Agenda for the 21 st Century,” Los Alamos National Laboratory report LA- 1 15 14-MS, 30 p.

Zeisioft, J., B.S. Sibbett. and M.C. Adams, 1984. “Case Study of the Wendel-Amedee Exploration Drilling Project. Lassen County, California: A User-Coupled Confirmation Drilling Program,” report DOE./ID/ 12079- 127 ESL-162, prepared by the Earth Science Laboratory, University of Utah Research Institute. for the USDOE Idaho Operations Office, 97 p.

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