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reservoir, boundary, model, Equation, production, parameters, heat, flow, temperature, where, AQUA, using, condition;, with, water, transport, geothermal, field, Zhangzhou, parameter, rate, equation, coefficient, indices, Report, Shengbiao, instead, about, Julong, beat

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• Q~ The United Nations
~ University
GEOTHERMAl TRAINING PROGRAMME
Orkustofnun, Grensasvegur 9,
15-108 Reykjavik, Iceland
DISTRIBUTED PARAMETER MODEL FOR THE
ZHANGZHOU GEOTHERMAL FIELD, CHINA
Hu Shengbiao
Institute of Geology, Chinese Academy of Sciences,
P.O. Box 9825, Beijing 100029,
CHINA
ABSTRACT
Reports 1994
Number 3
A distributed parameter model for the Zhangzhou geothermal field, China, is set up using
the AQUA programme and calibrated by malChing the measured and the calculated
drawdown and temperature datJt from 10 observation wells over the past 8 years. Based on
this, predictions of the reservoir respoosc to the plannod production rates were made up to
the year 20 I O. The flow model indicates that with the present production, the reservoir is
under near steady+state condition. The maximum production rate without injection was
fouod to be about 100 Vs with the condition to keep the Quaterruuy aquifer productive. The
production rate can be further increased if a doublet is employed for injectionlreinjection.
The heat transport model shows that the reservoir temperature will change due to both the
increased production rates and the temperature of the reinjected water in the predicted time
period.
1. INTRODUCTION
The main task of the geothennal reservoir modeller is 10 calibrate the parameters for a geothermal system
using the available field data and to predict the futw'e behaviour of the reservoir during production and
reinjection. A number of cIiff"""t methods for modelling the behaviour of geothermal reservoirs are currently
available to reservoir engineers. such as lumped parameter models and distributed parameter models. The
selection of the proper method for a particular study mainly depends on the amount and quality of field dala
and the objectives of the study.
The Zhangzhou geothermal field in Fujian Province. P.R. China is a typicallow-tcmperab.lre fracture zone
system, where heat is transferred by eonvection, involving deeply penetrating meteoric waters and some salinc
water, from a resource base in the upper crust (thick granodiorite). to the surface, along the intersection of
two deep-cutting faults (!rending northnortheast and westnortbwest) r:w ang et al., 1989). The natural slate
model for i~ has been developed by Hu (1989) and Yang et a!. (1990), and now it is possible to recalibrate
the parameters for the model as a lot of water level-, temperature-, and production data are available.
In the present paper, the AQUA progranune, a distributed parameter model, was used for the calibration of
the reservoir parameters and the prediction of future response of the reservoir with different production and
reinjection rates. Some suggestions for the future development and reservoir management of the Zhangzhou
geothennal field are presented.
Hu Shengbiao 54 Report 3
2. THE AQUA DISTRIBUTED PARAMETER MODEL
AQUA is a programme package developed by Vatnaskil Consulting Engineers (1990), to solve the
groWldwater flow and transport equations using the Galerkin finite element method It is a useful tool for
grothennal and environmental problems, including groundwater flow and contaminant transport modelting.
2.1 Governing equation
Geothermal reservoir modelling involves fluid flow, mass and heat transfer. The following differential
equation is the basis of the mathematical model:
au au a au
a - +b, - + - (eIJ - ) +ju +g '" 0
at Ox, ox, Ox,
The equation is two dimensional, indices i and} indicate x andy coordinates axis, respectively.
2.2 Flow model
For transient flow, Equation 1 is reduced to
au a au
a-+-(e - )+/u+g = 0
at Ox, if Ox,
The parameters in Equation 2 are defmed as
u = h; eif = Tif; f = 0; g = Q + klm (h.-h); a = -S
Using x andy as indices instead ofi and}, Equation 2 becomes
where
a aha ahk oh - (T - )+-(T - )+ - (h - h) +Q • sax =ar ay nay m 0 at
h = Pressure head (m);
Tzz = Transmissivity along principal axis (ml/s);
TYJ' = Transmissivity perpendicular to the principal axis (m2/s);
Q = Pumping/injection rate (m'!s);
(I)
(2)
(3)
klm = Leakage coefficient (lis), where k is the permeability of the semi-permeable layer
and m the thickness;
h. = Pressure head of upper aquifer (m);
S "" Storage coefficient.
For long tcnn exploitation, storage of the reservoir is controlled by compressibility of the water and the rock
in tenns of the elastic storage coefficient and by the delayed yield effect. So the equation for the transient
flow is
Report 3 55 Hu Shengbiao
(4)
where
" : IlK and K is the time constant (s);
~ = Effective porosity.
For steady-state conditions, Equation 1 is reduced to
a au - re -)+fu+g : 0
aX j IJ ox, (5)
The parameters in Equation 5 are defined as
u = h; 'if = Tif; f= 0; g = Q+kim(h,-h)
and using x and y as indices instead of i andj, Equation 5 becomes
a aha ahk
-(T -)+-(T - )+ - (h -h)+Q : 0
ax J:::rax ay "'ay m D (6)
The following boWldary conditions are allowed in AQUA:
8. Dirichlet boundary condition; the pressure head, the piezometric head or the potential ftmction are
prescribed at the boundary as a function of time;
b. Von Neumann 00undary condition; the flow at the boundary is prescribed by defining source nodes
(recharge or pumping) at the no flow boundary nodes;
c. Cauchy boundary condition; the flow rate is related to both the normal boundary derivative and the
head.
2.3 Heat transport model
For heat transport. the parameters in Equation 1 are defmed as follows:
u=T; a=#R/t; bj=vjb; et/= - bKIj; /=y+Q; g=yTo-QTw
By using x, y instead of the indices i, j, Equation 1 reads
a aTa aT aT aT aT
-(~hD -)+-(~hD -)-vh--vh- • "hR'-at +q>hR,AT- (T,-1)y-Q(T.-1) (7) or IQ: or ay YY oy 11: Or Y ay
The heat dispersion coefficients K"", Kyy are defmed by
Hu Shengbiao 56
K -a v"-+D.,
"" r ,
The heat retardation coefficient R" is given by
with the retardation coefficient ~b. as
where
T - Temperature ('Cl;
c, p .-, C
I
T. - Temperature of vertical inflow (' C);
C, - Specific beat capacity of the fluid (kllkg'C);
C, - Specific beat capacity of the porous mediwn (kllkg'C);
D. - Heat diffusivity (m'/s).
Report 3
(8)
(9)
(10)
(11)
Other parameters are previously dermed.. For heat transport:. there are two boundary conditions allowed:
a. Dirichlet boundary condition; the temperature is specified at the boundary;
b. Von Neumann boundary condition; the temperature gradient is set to be zero indicating convective
transport of beat through the boundary.
3. MODELLING OF THE ZHANGZHOU GEOTHERMAL FIELD
The conceptual model ofZbangzhou was proposed by Wang et a1 (1989). Based on i~ the nwnerical model
is set up for the AQUA progranune and calibrated by matching the computed and the measW"ed data.
3.1 Geological background
The Zbang;d1ou geothennaI6eld, lies in the southeastern part of an artesian basin, the Zbangzhou rbom-busshaped fault basin, in Fujian Province, China It is surrounded by a large catchment and drained by the Julong
River (Figure I). The basin is about 1000 km2 and has an average elevation of 30 m a.s.1. The outer terrain
in the north aod northwestern sectors stands about 500 to 1500 m above sea level. The Zbangzhou thermal
area lies close to the Julong River and most of it is located inside the city. The production wells are 7-10 m
a.s.1. At Zhangzhou the Julong river is close to sea level. and the water level in the river fluctuates with
variations in the rainfall. Subsequently changes in subsurface water level and temperature are observed
(Figure 2).
Report 3
The basement rocks
surrounding Zhang-zhou
basin consist mainly of
Mesozoic granodiorite and
metamorphic rocks of
Jurassic age covered by thin
(<30 m) Quaternary
sediments inside the basin.
The whole catchment is dissected by two sets of steeply
dipping old faults striking
northeast and northwest,
respectively. Within the
basin. sets of younger faults
have been mapped !rending
northnor theas t and
westnorthwest (Figure 3). It
has been postulated that the
hot water in the Zhangzhou
prospect ascends along highly
permeable segments of the
younger faults, especially at
the intersection of the faults
(W 80g et al., 1989).
57
OS 94 12.0676 HuS
Hu Shengbiao
CJ Zha~hou SaW.
0IIJl Catchment
~ COastal plain
-"Model boundary
t N
I
o 20 km
FIGURE I: Location of the Zb8Ogzhou geothermal field
and the boundary of the model
9-,--------------------- BOO
--...~ River level Rainfall
600.
.1, ! 4001
... ~ .,
8
7
200:
• 0 ·1 35
~
'" ~ • ,
25 ..
K
'" E ~
~ • ·2
-'-..
~ ·3
j ·4
.LLL.L.l..l.JLL-6-LL.l.J...LTL~-'-?-'-·~'~.J'"_'fLi-'-"-'-~J'JU_ZRL! ~1.2.L' -'..J_'LL' 1.1 -'-, .LLL-'--'-'- 15
1986 1987 1988 1989 1990 1991 1992
Time (Year) OS 94.12.oen HuS
FIGURE 2: Time variation of river level, rainfall. subswface water table and temperature
Hu Shengbiao 58 Report 3
os !to\.12 0619 "IuS
More than 100 shalIowweUs « 100 m) bave been drilled
in the Zbangzhou prospect over an area of25 km2, and
all the wells stand in granitic rocks. lsotemperature
cootoors alSO m devth indicate an inner reservoir (about
0,5 km') where the temperatures are greater than 60'C
(Figure 3), The highest temperatures (120'C at 90 m)
have been found in two shallow wells near the centre of
the inner reservoir.
LEGENO
__ Fault
ZR16 Mon/Iomg wells
• .od w.n number
iPl T.m~!ur. contour iC)
U al SOm deplh o "'00 m ,
FIGURE 3: Temperature distribution at
50 m depth in the Zhangshou geothennaI
field and location of faults and wells
o os 94.12.0679 HuS
o ... IwIUo. dopth ,,~
o =,
(0)
"" o
lR21 SI&oo
o 0
""
817;
0
"''' 0 ""', 0 " 0
"''' o
=,
o %R2. S1113 ZR1ZR33
o 0 0 0 .,
Mi .. dl»'colOo._tor
with i'Mgh Cl c" .. u ...... tion
3.2 Conceptual reservoir model
Stable isotope data (0" and D) indicate that all thermal
fluids are meteoric waters whose isotopic composition
lies close to the meteoric water line (Wang et al" 1989),
The absence of any 0" shift indicates that temperatures
of less than 200°C prevail at the deepest level of fluidrock interaction. The thennal water in the inner
reservoir is highly mineralized (up to to g/kg total
solids), being a slightly alkaline Na-CI type. Most of the
mineralization is probably due to mixing of a less
mineralized deep hot water with saline pore fluids which
=, for example, in cold wells lying to the east of the
thermal prospect. Shallow wells elsewhere in the basin
produce groundwater with less than 0.3 gIl total solids.
S'91
o "''' o
,.,
~,
o (0)
The geothermometers indicate
a reservoir temperature of
about 145'C (Wang et aI"
1989), The origin and
variation of the chloride
concentration of the thermal
water in the prospect is
explained in Figure 4, It has
been inferred that meteoric
water in the catclunent
perx:trates to depths of 3.5 to 4
km. sweeping heat along
radially inward-directed paths
with hot fluids ascending
thmugh a fractured reservoir
of vertical, cylindrical sbape,
The hot fluids from the deep
level are cooled down at a
shallow depth by conduction
and mixing with the cold
groundwater.
Conel11trlrtio" of Chlotid. (ppm)
In this work, a 5000 km2 near
rectangular area is established
for the reservoir modelling
area, its boundaries are FIGURE 4: Relationship between Cl concentration and temperature
of the bedrock water in wells
Report 3 59 Hu Shengbiao
determined by the surface water division and set as no flow boundaries. The model was created with 2386
nodes and consists of 4736 elements. As to the initial state prior to production, it was assumed that the
reservoir water head was constant so that there was no hydraulic gradient in the model area. Since the W -NW
faults were believed to be more penneabJe, the anisotropy angle was set to be 1500 along the faults.
3.3 Production History
The hot w_ in Zltangzhou geothennal field was exploited aod utilized for bathing a loog time ago, but only
on a small scale until the 1990s when the Wuzhong Central Delivery Thermal Plant and several fish fanns
were built (Table 1). In that plant, the hot water with a temperature of 80-85°C is reinjected by a doublet.
At present, the production is still small but there is a great potential for further development.
TABLE 1: Production and reinjection history in Zbangzhou geothermal field
Site Production (mJ/day) R.einjection (ml/day)
Rate Month Initial Rate Month Year
Wenquan Public Bath 400 Dec. to Feb. 1986 200 Mar. to Sept.
Oazhong Public Bath 400 Dec. to Feb. 1986 200 Mar. to Sept.
Gongren Public Bath 85 Dec.to Mar. 1986 30 June to Sepl
50 Other time
Wenquan Hotel 300 Dec. to Feb. 1993.1100 Other time
Reruning Ladies Bath 6 Det. to Jan. 1986 Gongren Sanatorium 35 Year-round 1986 Wuzhong Central Delivery 1500 Year-round 1990.11 1500 Year-round 1992.10
Thermal Plant
The Swimming Pool 200 June to Ocl 1990 Xiazhuang Fish Farm 500 Year-round 1992.9Xingtang Fish Farm 600 Dec. to Apr. 1991.12
425 Other time 28 wells were used for observation wide or outside the production area. The drawdown in September 1993,
relative to the natural state in September, 1986 (Figure 5) shows changes with time due to the increasing
production and the doublet reinjection which started in October, 1992.
3.4 Calibration of aquifer parameters using the AQUA model
The process of simulation is a trial and error process, i.e. adjusting the parameters within some limits in order
to match the calculated val ues with the measured ones.
Hu Shengbiao 60 Report 3
-L--'\-'-\-;~12500
:-'--'-<::1-12000
1500
1000
0500
FIGURE 5: Observed changes of drawdown (m) with time
3.4.1 Flow problem
The water level data from 10 selected observation wells (Figure 3) were used for calibrating the reservoir
parameters including the transmissivity, storativity and porosity. Those data are based on observation for a
period of8 years, 1986-1993, respectively.
The calibration was satisfactory when good matching had been achieved between the measured and the
computed data. The transmissivity inside the Zhangzh.ou basin of the model area turned out to vat)' from
5xI0" to O. 15 m'ls (Figure 6). The fractw-ed zones are highly penneable, and the background transmissivity
outside the basin is 3xl(}"J m2/s. The storage coefficient inside the basin for the model is in the range from
5xlO-4 to lxlO-2 (Figw-e 7). In the area outside the basin the storage coefficient is 2.5xlO-4. The porosity is
assigned to be 10% for the fracturc zonc and 1~2% for the outer granite.
The multiplier for Sqrt(T Jf.J is 0.447, i.e. the transmissivity aJong the westerly to northwesterly trending
faults is 5 times greater than in the other direction.
The good fit with the measured drawdown (Figure 8), using the equation for delayed yield, shows that the
reservoir is controlled by two different storage mechanisms. At the start of production. storage is controlled
by liquid/formation oompressibility and later by the mobility of the free surface, thc delay yield time constant
is 2800 days. The resulting flow field in the model is obviously controlled by the production and reinjection.
Report 3 61 Hu Shengbiao
,
N
b:!I 0.1-0.15
QS,OE-2
htWH S.OE·3
1:::::::1 3.0E-3
FIGURE 6: Transmissivity distribution (m'lls) in the Zbangzhou geotbennal field
N
~1 .0e- 2
111'17.5 E.2
! 0 HMMH 5.0E·4
k::J 2.5E·4
() 500 1000 m
FIGURE 7: Storativity distribution in the Zbangzhou geothennal field
3.4.2 Heat transport
Before calculating the heat transport, the initial temperature, the temperaurre of the vertical inflow into the
aquifer and the thickness of the aquifer have to be known. The initial temperature is not constant but varies
over the area. The vertical inflow temperature, i.e. the injection temperature is 80°C for the present injection
well and 40°C for a plarmed future injection well. The longitudinal dispersivity, aL, is assumed to be 200 rn,
and the multiplier for Sqrt(aT/aL) to be 0.447. The aquifer thickness is 1000 m.
Hu Shengbiao 62 Report 3
E • ,
;;
K
E
~
O ~--------------------------r=~----,
(ZR17 )
-5
I
i f •
~
-10
------
Measu!1ld
--7- Calculated (Ca .. 1)
--B--- Calcua.t.d (Case 2 I
--&- Calculated (Case 3)
----;,- CalculaWd (Case 4)
-15
OS 94. 12.0683 HuS
1990 1995 2000 2005 2010
Time (y .. r)
FIGURE 8: Measured and computed drawdown in wen ZR17 and futw"e predictions
for different production cases
55
( ZR'7 )
50 -
fA .
: ~
------ -~ ....
45
40 - Calculated (CaM 1)
-- Caleulnld (Case 2)
- - Calculated (CaM 3)
........... C.leulflted (C ... 4)
OS 94 .12.0684 HuS
I I I I
35
1990 1995 2000 2005 2010
TirM (Yur)
FIGURE 9: Measured and computed temperatures for different
production and reinjcction rates in well ZR-17 and future
predictions for different production cases
The retardation constant,
i.e. the ratio of the heat
capacity of the rock to
that of the water. is 0_2\3_
The measured and
calculated temperatures as
well as the predicted
temperatures in well ZR·
17 are shown in Figure 9.
Report 3 63 Hu Shengbiao
4. FUTURE DEVELOPMENT AND RESERVOIR MANAGEMENT
4.1 Future development
,.a.o,) Drawdown con1our (ml . , f I
- F\ow d~ec'lion --...:... " 0
As the Zhangzhou geothennal field is
located in the Zhangzhou City, a larger
scale development of the thermal water
can be expected. 10 this work, on the
basis of the present production and
reinjection, four additional assumed
production wells have been planned and
sited (Figure 10) to assess the response
of the reservoir to increased production
and reinjection rates. The planned new
thennal plant A, (Figure 10), a main
producer in the downtown area, is
designed to proouce hot water. Here five
cases are demonstrated, with constant or
increasing production, with or without
reinjection (Case 1 to 4 in Table 2).
Producers B and C have the same
production rates as the Ziazhuang fish FIGURE 10: The drawdown in the year 2010 foe
case 2 (Table 2), and the planned new production wells
TABLE 2: Proposed design for the new thennal plant A
Production rate Yearly increase Reiojection
Case 1 1500 m'/day 0 0
ease 2 1000 m'/day 10% 0
Case 3 1500 m'/day 0 100%
Case 4 1000 m'/dav 10% 100%
fann in Table 1, and producer D the same as the Zingtang fish farm. All the new production wells are
assumed to start producing in 1995, and the predictions are carried out to the year 2010. For cases 1 and 3
(Figure 11a), the average production rates increase from the present 40 Vs to 70 lis. For cases 2 and 4
(Figure lIb), the average production rate increases from 70 lis to 110 lis in the year 2010 (Figures lla and
lib)
4.2 Future prediction
The future predictions deal with the responses of the reservoir to designed future production and reinjection.
In this work, the draw-down and temperatures are predicted with different production and reinjection rates.
4.2.1 Drawdown
The drawdown will drop abruptly at the beginning and then increase continuously, no steady state condition
can be reached in the year 20 10 under the planned production rates. Case 2 has the largest drawdown and the
steepest response (0.6 mIyear). In the year 2010 it will have reached 13 m in the production area (Figure 10),
Hu Shengbiao 64
100 -r-------------r------------------------,
..
90
eo 70
60
50
40
'"
20
10
o ;.. ~10
c ~
g .20 .J-----
'c -30
&
A 1990 1995 2000 2005 2010
Time (Year)
12O-r------------,-----------------------,
110
100
00
80
70
60
50
40
'"
20
10
o ~ -10 -j-________ __
·20 -g
~
'E' -50
;j!
B 1990 1995 2000 2005
11me (Year)
FIGURE I I: Production and reinjection for a) cases 1 and 3;
b) cases 2 and 4
2010
Report 3
which is going to
exhaust the Quaternary
aquifer smce the
bottom of the
Quaternary layer in the
production area is just
20 m below the surface.
Therefore, the
production rate for case
2 can be taken as the
maximum rate without
future remJection.
Figures 12·14 show the
predicted drawdown for
the different cases in
three wells. Case I has
less drawdown (0.1
m/year) than case 2.
Because of relatively
small production in the
later year.; (Figure Ila
and lib). Its
drawdoWIl in the year
20 10 is about 8 ID, so
the production rate for
ease 1 can be taken as
the co~ative or
proper rate without
future reinjection.
Cases 3 and 4, which
share the same 100%
remJection at the
plarutcd new thermal
plant, have exactly the
same drawdown Gust 5
m in the year 2010)
corresponding to 0.08
mJyear. It is obvious
when comparing cases
I and 2 with cases 3
and 4 that reinjection is
necessary in order to
increase the production
rate without having too
much drawdown.
Report 3
I
i j
~
I
i j il 65
o~------------------------------~~ ____ -,
(ZR'. )
-5
-'0
-'5
--e- Musured
~ Calculated (Cue: 1)
-e- Calculllttd (CaM 2)
---rr- CaIcuIMed (Case 3)
--+- C.IcuLated (Case 4)
'990 '995 2llOO
TimelY .. "
OS 94.12.0687 HuS
2005 20'0
FIGURE 12: The predicted drawdown with time in well ZRI6
o~-----------------------------------,
-5
-10
-15
~ ..........
--e- CalcuinMt (Case 1)
-e- C«IcuLated (CaM 2)
---rr- Calcu'-*' (Cue 3)
--+- CaIcuINd tc- 4)
1990 1995 2llOO
Tirne{V .. "
OS 94.12.0688 Hu$
2005 2010
FIGURE 13: The predicted drawdown with time in well ZR18
Hu Shengbiao
Hu Shengbiao 66
o~------------------------------===------.
-5
E
I
B
-10
-15
4.2.2 Temperature
---.- ..... , ...
-'T- C.leulated (Cae1)
--e-- C.leua.t.d (cu. 2)
---tr-- C.leua.ted (cas. 3)
----;,- C.lcus.t.d (CaH 4)
1900 1995 2000
Time(y .. ..,
( ZR26 )
OS 94. 12.0689 HuS
2005 2010
FIGURE 14: The predicted drawdown with time in well ZR26
o Temperature
(1 ..... contour ("Cl
o BOOm
~
Report 3
The predicted temperatures show some decline (<3°C)
due to the production but obvious changes (as much as
1 O°C) occur in some areas owing to the injected water
with a temperature of SO°C at the present thermal
centre (Wuzhong central delivery thermal plant in
Table I) and 40'C at the planned new thenna! plant A,
respectively. The temperature distribution in the year
2010 (Figw-e 15) is quite similar to the present one
(see Figw-e 3) except for the injection sites. The
production area, has a lower temperature than the
injection water. The temperature there is going to
increase with time. and can increase as much as 10°C
under the present and planned injection temperatures
(Figure 16). For the recharge area with higher
temperature, it will cool slightly down throughout the
prediction time period (Figw-e 17). For the area
outside the production area, the temperature will
change very little.
FIGURE 15: The predicted temperature
in 2010 for case 4 (see Table 2)
Report 3 67
"-.---_._-- -- ._-- --------=:=
(ZR18 )
1
1 ti:
t ! I ti:" j JO tm,J~~~I-! - -J -e-- =:,::~::: (c.w "
, -- Calculated (Case 21
~ Calculated (Cue )J
20 I -, -, - , ,Ca:CUI,lIrd (Cur 4)
1990 1995
Time (Ynr)
.Q~~. '~:0&9\~S i
2005 2010
F[GURE [6: The predicted temperature with time in well ZR[6
so ( ZRt8 )
'" -
,. •
E

- .. --.:;--.:::
~ '" -~
E
~
45 - -e-- _wNd
-- calcula*! (c...1)
-- C.IcuLdad (e- 2)
40 - -- CaIcuLmd (Cue 3)
--.. CakwLNcl (Cue 4)
35
OS 94.12.0692 H1.15
I I I I I
1990 1996 ""'"
Tirne(Y .. .,
F[GURE 17: The predicted temperature with time in well ZR[ 8
5. CONCLUSIONS AND RECOMMENDATIONS
Hu Shengbiao
The prime objective of this study was to create a mcxlel estimating the natural conditions of the Zbangzhou
gccthermaI field. The reservoir model was calibrated using the water level and temperature observatioo data
from monitoring wells, for the last 8 yeaB. Based on the calibrated med.[, the predictioos ofboth drawdown
and temperature were made. Some preliminary conclusions and recommendation are:
1. The results of the calibration show that the transntissivity is much higher in the fractured zooe than
outside it The good fit with the measured drawdown, using the equation for delayed yield, shows
that the reservoir is controlled by two different storage mechanisms. At the start of production.
storage is oontrolled by liquid/formation compressibility and later by the mobility of the free surface,
the delay yield time constant is 2800 days.
Hu Shengbiao 68 Report 3
2. The flow model indicates that the reservoir is under steady-state conditions with the present
production and injection rates, but for the four calculated cases of the planned production, a steadystate condition in the reservoir cannot be reached in the year 2010. The drawdown in the year 2010
will be 13 m for case 2; 8 m for case I and 5 m for cases 3 and 4.
3. The transport model shows that the temperature pattern can be affected by both the reinjection and
the production depending on the hydrogoologicallocation. The greatest decline in temperature for
case 2 is about 3°e in the recharge area. The temperature in the area near the injection well with
higher injection temperature will increase as much as looe.
4. For long time development, reinjection is necessary so that the Quaternary aquifer will remain
productive. With no reinjection, case 2 represents the maximum production rate (about 110 lis in
2010) and case I shows the proper production rate to keep the Quaternary productive. The
production can be increased if reinjection is going to be made. The most optimum geotbennal
development in Zbangzhou field is doublet production and reinjection, especially for the higher
temperature fields in the downtown area.
5. The long-term monitoring 'WOrk for the development of the Zhangzbou field must be continued, and
a few of the pn:xluct:ion wells should be used for observation wells, but the monitoring frequency can
be cut down to 1-2 times a month. The production rates for every well need to be recorded more
accurately, which will affect the results of the modelling, especially the results of the prediction.
6. The geothennal reservoir engineering work should be included in any feasibility study for future
development.
ACKNOWLEDGEMENTS
The author is grateful to the supervisors, Dr. Snorri Pall Kjaran and Mr. Sigurdur Larns Holm, for their
guidanoc and help. I would like to thank Dr. Ingvar Birgir Fridleifsson, the director of the UNU Geothennal
Training Programme for providing me with the opportunity to attend the course and for his kindness. My
thanks also goes to Mr. Ludvik S. Georgsson, and Ms. Margret Westlund for their help and kindness and to
the ladies in the drawing office for drawing of the figures used in this report. I am vel)' grateful to all the
lecturers for their comprehensive lectures. Finally, the author is grateful to Dr. Pang Zhonghe, a former
fellow, and Prof. )Gong Liangping for providing all the data which were used in the report.
REFERENCES
Hu Shengbiao. 1989: Reservoir modelling o/the Zhangzhou low-temperature, fractured-zone system,
FUjian Province, P..R. China. Geothennallnstitute of Auckland University, New Zealand, Project Report
89.10.
Vatnaskil Consulting Engineers, 1990: AQUA, user 's manual. Vatnaskil, Reykjavik.
Wang Jiyang, Pang Zhonghe and Xiong Liangping, 1989: Genesis analysis of Zhangzhou Basin geothennal
system.lGAS, China Ocean Press, Advances in Geoscience, ], 409-417.
Yang Zbongke, Hu Shengbiao and Hochstein, M.P., 1990: Conceptual model of the Zhangzhou lowtttnpaaturo system and its surrounding eatcluncnt (Fujian Province, PK China). Proceedings of the J 5th
Workshop Geothermal Reservoir Engineering, Stanford University. USA., 97-102.

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