SGP-TR-109-23
PROCEEDINGS
TWELFTH WORKSHOP
GEOTHERMAL RESERVOIR ENGINEERING
January 20-22, B87
*Sponsored by the Geothermal and Hydropower Technologies Division of the U.S. Department of Energy, Stanford-DOE
Contract No. DE-AT03-80SF11459and Contract No. DE-AS07-841D12529
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PROCEEDINGS,Twelfth Workshop on Geothermal Reservoir Engineering
Stanford University, Stanford, California, January 20-22, 1987
SGP-TR-109
DEVELOPMENT DRILLING, TESTING AND INITIAL PRODUCTION
OF THE BEOWAWE GEOTHERMAL FIELD
V. T. Hoang, E. D. James, I. J. Epperson
Chevron Resources Company
San Francisco, California
ABSTRACT
The Beowawe geothermal field in north
central Nevada is generating 16MW using two
production wells (Ginn 1-13 and 2-13) and one
injection well (Batz).
Drilling the second
production well (Chevron Ginn 2-13) in 1985
led to the discovery of a second productive
strand of the Malpais fault zone. The wells
a r e completed in the Malpais fault zone and
a r e capable of producing 420+oF geothermal
fluid at rates exceeding 1,000,000 Ibs/hr.
Initial testing suggests that the completion
zones of the two production wells have no
pressure communication, therefore providing
what is essentially a second production zone
for future development. Injection of produced
fluids into a fault parallel with the Malpais
shows no pressure communication with other
wells. One year of production in the system
shows no pressure depletion or enthalpy
decline in the producing area.
t h e Malpais fault (MFZ) system, charges
permeable horizons along the way and finally
discharges at the surface.
Figure 1. Well locations and surface features.
INTRODUCTION
BEOWAWE GEOTHERMAL FIELD
EVALUATION
The Beowawe a r e a has been well known for
many years due to the geysers, fumaroles, and
boiling springs that exist there.
These
numerous geothermal surface manifestations
led Magma Power Company and Sierra Pacific
Power Company to drill I 1 shallow wells in t h e
sinter terrace a r e a from 1959 through 1965.
Chevron acquired t h e leases in 1973-1975 and
began an extensive geologic study of the area.
Chevron drilled five more wells, starting with
Ginn 1-13 in 1974 to a depth of 9563 feet, and
numerous shallow temperature holes in the
evaluation and development process.
This paper presents a n overview of the
Beowawe development drilling, testing and
initial production of the 16 M W power plant.
The 16 M W plant utilizes two production wells:
the Ginn 1-13, drilled by Chevron in 1974
(Layman, 1984; Epperson, 1982 & 1983); and
t h e Chevron Ginn 2-13, drilled during the
The Ginn wells are
summer of 1985.
completed in separate strands of the Malpais
fault zone (MFZ).
The Beowawe geothermal field is located in
north-central
Nevada, about 50 miles
southwest of t h e town of Elko. The field is in
the Basin and Range province at the boundary
between a plateau of volcanics to the south
and the downfaulted Whirlwind Valley to the
north. Active surface manifestations in "The
Geysers" a r e a cover one-half square mile, and
include a large sinter terrace, geysers,
fumaroles, and hot springs (Figure 1). The
reservoir is thought to b e in lower Paleozoic
carbonates at depths of perhaps 20,000 to
30,000 feet.
No wells have penetrated t h e
carbonates, but the low salinity, sodiumbicarbonate nature of t h e Beowawe thermal
water suggests that these rocks a r e t h e
ultimate deep reservoir.
Geothermal fluid
flows upward from the deep reservoir through
Magma conducted the first Beowawe well
tests o n four of their wells on the sinter
terrace.
During a year long flow, visual
checks of the discharge indicated an apparent
decrease in flow r a t e and temperature. Based
o n these data, it was concluded that t h e
Beowawe reservoir was depleting and being
invaded by cold water. Recent Chevron data
indicates that t h e reduction in flow r a t e and
temperature is due to t h e cooler fluid contribution from a high permeability fault below
t h e main fault feeding these wells (Epperson,
1983).
-159-
Chevron began a n extensive testing program
t o e v a l u a t e t h e reservoir with t h e completion
of Beowawe 33-17 o n t h e s i n t e r t e r r a c e in
1979. During 1981, a f t e r drilling Beowawe 8518, Chevron conducted numerous flow tests
and monitored pressure i n t e r f e r e n c e e f f e c t s in
several surrounding shut-in wells to e v a l u a t e
t h e d e g r e e of continuity between wells.
A
summary of Chevron flow test results prior to
1985 is presented in Table 1. N o t e t h a t all
wells e x c e p t Rossi 21-19 flowed at r a t e s of
about 300,000 Ibs/hr t o t a l mass. T h e relative
low flow r a t e s a r e d u e to mechanical
completion restrictions.
T h e permeabilitythickness (kh) f o r most Beowawe wells is in
t h e range of 200,000 to 800,000 md-ft., thus
indicating t h e e x t r e m e l y prolific n a t u r e of t h e
reservoir.
SIMPLE FAULT MODEL
GEOTHERMAL SYSTEM
Mapping of t e m p e r a t u r e in t h e MFZ shows
t h a t 4200F w a t e r s at depths g r e a t e r than 9000'
in Ginn 1-13 rise obliquely up t h e MFZ towards
t h e northeast where t h e r e i s a n abrupt, u p d i p
diversion of flow at t h e prominent bend in t h e
MFZ.
This upwelling f e e d s t h e s u r f a c e
discharge at t h e Geysers.
Variations in permeability within t h e MFZ and
siliceous vein filling in t h e cuttings f r o m low
kh wells suggest t h a t p a r t of t h e f a u l t zone i s
sealed-off. The region of t h e MFZ p e n e t r a t e d
by Ginn 1-13, 85-18 and wells on t h e sinter
t e r r a c e is open and very permeable. However,
t h e MFZ at t h e Rossi and Batz wells is less
permeable t h a n o t h e r areas.
Rossi w a s
apparently drilled into t h e low permeability
c a p of t h e fault. A t Batz, t h e MFZ does not
s e e m to be in pressure communication with
any o t h e r wells. T h e MFZ is tight at B a t z
probably
d u e t o silica sealing.
The
t e m p e r a t u r e and permeability d a t a indicate
good potential f o r expansion of t h e producing
a r e a down-dip of t h e MFZ f r o m t h e 85-18 and
Ginn 1-13 wells, and along s t r i k e south west of
Ginn 1-13 (Figure 3).
-
TABLE 1
BEOVAWE FLOW TEST SUMMARY
Gim
Number of f l o w l e i t i
M ~ X . I I ~ Itemp.,OF
~C
Flow rate, Mlblhr
Kh. md-11
I
6
I
3
3
365
360+
3601
386
240
30J
320
240
280.
800,000 150,000 780,000
8.953
285
8,900
'Flow w i t h nitrogen gar lift.
BIQ
u20
232,000
PI. Ibihrlpri
u
R-i
21-19
200,000
7,800
**lnlution rate.
24,000
300
x Upper injection
200"
850,000~
27,070
zone.
R-47-E
I
BEOWAWE
Models proposed f o r thermal w a t e r flow in
Beowawe system a r e varied, but all involved in
t h e Malpais f a u l t zone. T h e c u r r e n t model
(Layman, 1984) incorporated t e m p e r a t u r e
profiles, drilling history, c u t t i n g description,
and kh distribution to show t h e importance of
t h e MFZ as a primary conduit at Beowawe and
provided a simple model to l o c a t e producing
zones in t h e Beowawe field. Geologic mapping
indicated t h a t a simple planar f a u l t c a n b e
constructed through MFZ i n t e r c e p t s in wells
and t h e s u r f a c e trace. T h e f a u l t dip appears
c o n s t a n t at 65-700 to t h e depth of t h e deepest
well a t 9563'.
Interference tests conducted at Beowawe
before completion of Ginn 2-13 show pressure
communication
between
all
the
wells,
excepting t h e Batz well (drilled by Magma.)
Response t i m e s a r e less than o n e hour, irrespective of t h e distance between wells.
Analyses of t h e i n t e r f e r e n c e d a t a verifies t h e
calculated kh f r o m t h e individual drawdown
and build-up analyses.
These results a r e
illustrated in Figure 2.
1-13
33-17
a w a vul-2
----
FOR
"
I2
R-48-E
8
7
0
2000
9
4000
FEET
Figure 3. Permeability and elevation of the Malpais F.Z.
Figure 2. Interference response. December 1981.
-160-
DEVELOPMENT O F THE 16 M W POWER
PLANT
trace. A wellhead performance test showed
t h a t Ginn 2-13, after clean up of drilling
damages, would provide over one million Ibs/hr
of fluid f o r t h e power plant.
Pressure
monitored during t h e test and during t h e plant
start-up period indicated no interference
between Ginn 2-13 and t h e other wells
completed in t h e main Malpais f a u l t trace.
In 1985, Chevron drilled a second production
well, Ginn 2-13, to supply s t e a m for a 16 MW
power plant which was built by C r e s c e n t
Valley Energy Company.
The well was
programmed to p e n e t r a t e t h e MFZ northeast
of t h e Ginn 1-13. The well t e s t e d t h e concept
t h a t t h e MFZ was open over t h e large interval
between t h e Ginn 1-13, Rossi wells to t h e west
and t h e sinter t e r r a c e a r e a to t h e east. T h e
well, however, encountered a major lost circulation zone 500 feet above t h e t a r g e t MFZ
which was interpreted as a second fault. This
f a u l t t r a c e is parallel with t h e main Malpais
f a u l t t r a c e which was intersected in both t h e
Ginn 1-13 and Rossi wells (Figure 4). Minor
lost circulation and siliceous alteration mark
t h e second f a u l t in these wells.
T h e discovery of t h e second f a u l t has greatly
extended t h e development potential of t h e
Beowawe field.
A t present, t h e t w o production wells, Ginn 21 3 and 1-13, supply 1.3 million Ibs/hr of 420°F
fluid to a 16 M W dual flash power plant. The
produced fluid contains a relatively low TDS (k
1,200 PPM) and noncondensible gases (2 550
PPM Co2). The unflashed geothermal fluid
returned f r o m t h e plant is pressurized for
injection at t h e plant and is transported via a
10" d i a m e t e r two-mile insulated pipeline to
t h e existing Batz well (Figure 5). A t t h e Batz
well, t h e fluid is injected i n t o a shallow, cool
zone of high permeability above t h e MFZ
intercept. This zone is interpreted as a rangef r o n t f a u l t parallel with and hydrologically
unconnected to t h e MFZ (Figure 61, but is
believed to be connected to t h e carbonate
reservoir.
During one year of operation, no
injection effects w e r e observed in t h e
monitoring wells, indicating this range-front
f a u l t is a n a t t r a c t i v e t a r g e t f o r f u t u r e
injection wells.
SE
NW
2000'
,
- - 50OO'
Figure 4. Geologic cross-section A-A'.
Figure 5. Plant and surface facilities.
A short flow test soon a f t e r completion
evaluated Ginn 2-1 3 productivity and reservoir
properties.
The Ginn 1-13 was monitored
during t h e test t o evaluate interference
effects between t h e t w o f a u l t strands.
A
J a m e s t u b e instrument was installed to g a t h e r
d a t a f o r flow r a t e and enthalpy estimation.
Bottomhole flowing pressures w e r e measured
using helium filled capillary tubing and expansion
chamber
with
a surface q u a r t z
transducer.
The test results indicated t h a t
Cinn 2-13 encountered a very permeable zone,
kh= 340,000 md-ft
containing 4202OF geothermal fluid. Ginn 1-13 produces t h e s a m e
t e m p e r a t u r e fluid f r o m t h e main Malpais f a u l t
During t h e October 1986 Beowawe power plant
shutdown f o r maintenance and inspection, a
small a m o u n t of c a l c i t e scale was recovered in
t h e upper portion of t h e producing wells.
However, t h e scale deposit did not affect t h e
wells'
performance significantly.
Well
performance tests, a f t e r t h e scale was milled
out, indicated t h a t Ginn 2-13 and Ginn 1-13
w e r e capable of producing 1.2 million Ibs/hf
and 800,000 Ibs/hr of fluid respectively at 102 psia wellhead pressure.
Ginn 1-13
bottomhole pressure built up rapidly t o t h e
reservoir
initial
pressure
after
shut-in
indicating no pressure depletion in t h e
producing area.
Enthalpy of t h e produced
,
-161-
fluid, measured during t h e plant shutdown,
showed no change from the value obtained
before t h e plant start-up. The production data
gathered during the first year of operation
reconfirms the prolific nature of the Beowawe
reservoir.
COLLINS
B
-
4000
-
3wo
-
A
After one year of production no pressure
depletion or enthalpy reduction has been
observed within the producing area.
4.
The minimum potential of t h e proven
reservoir at Beowawe is 200 M W , based
on 10 MW/well and 40 a c r e spacing
between wells in the two fault zones.
.
-------
-------
ACKNOWLEDGEMENT
The authors would like to thank Chevron
Resources Company for permission to publish
this paper.
-------
Y
+
3.
8'
2000-
$
Injection of produced fluid into a rangefront fault parallel with the Malpais
shows no pressure communication with
other wells. This fault is a n attractive
target for additional future injection.
SE
NW
5wo
2.
1000-
Y
Y
SL-
-2000
-Iwo-
REFERENCES
-
7
LOCATION
P M J -mW'
.LO*C STIINL
8"
See Figure 4
for lithology.
-3000-
0
1.
Epperson, I. J. (1982), "Beowawe,
History and
Nevada, Well Testing:
Results; CRC Trans., Vol. 6, p. 257-260.
2.
Epperson, I. J . (1983), "1981 Interference
Well Testing: Beowawe, Nevada:'
Trans., Vol. 7, p. 413-416.
INJECTION ZONE
7
GRC
Kx)o*
3.
Epperson, I. J. (19831, "Beowawe Acid
Stimulation," GRC Trans., Vol. 7, p. 409411.
4.
Layman, E. 8. (1984), "A Simple Basin
and Range Fault Model for the Beowawe
Geothermal System, Nevada,"
CRC
Trans., Vol. 8, p. 451-457.
5.
Swift, C. M. (19791, "Geophysical Data,
Beowawe Geothermal Area, Nevada,"
GRC Trans., Vol. 3, p. 701-703.
Figure 6. Geologic cross-section B-B.
An important question to b e answered is the
estimated size of t h e reservoir and t h e
ultimate development potential of t h e field.
Due to the geologic complexity of Beowawe,
this question can only b e partially answered
now. A semi-steady state analysis of t h e long
term flow test data by Chevron indicates an
extremely large fluid volume (in excess of
1010 bbls). The steady-state performance of
Beowawe 33-17 after about 200 hours of flow
in a 1980 test is indicative of a infinite
reservoir or perhaps a constant pressure
"boundary" (IJE 1983). Flow d a t a from other
Beowawe wells indicate fluid volume in excess
of 1012 bbls. None of t h e tests have ever
indicated a flow barrier or reservoir boundary,
so these fluid volume estimates a r e only
minimum values. The proven productive area
of the two faults indicate a development of at
least 200 MW.
CONCLUSIONS
1.
Wells completed in t h e two strands of
the Malpais fault zone a r e highly
productive with potential to produce
4200F fluid at rates exceeding 1,000,000
Ibs./hr. Testing indicates that t h e two
faults are essentially separate production zones, thus providing a large a r e a
for future development.
- 162-