10.pdf

Geothermics 34 (2005) 99118

Interpretation of a well interference test at theChingshui geothermal field, Taiwan

Kai C. Fan, M.C. Tom Kuo, Kan F. Liang,C. Shu Lee, Shin C. Chiang

Department of Mineral and Petroleum Engineering, National Cheng Kung University, Tainan, TaiwanReceived 29 August 2003; accepted 5 November 2004

Available online 22 January 2005

Abstract

Production in the liquid-dominated Chingshui geothermal field is largely from a fractured zonein the Jentse Member of the Miocene Lushan Formation. The geological data strongly indicate apossibility of linear-flow geometry on a field-wide scale. This was confirmed by re-analyzing theresults of a multiple-well interference test performed in 1979. Radial and linear-flow models wereused in this process. An evaluation of computed reservoir transmissivities and well capacities indicatedthat a linear model fitted the interference test data significantly better than a radial model. The linear-flow model that was developed for the Chingshui reservoir was also instrumental in obtaining animproved estimation of the geothermal fluid reserves (i.e., fluid-in-place). 2004 CNR. Published by Elsevier Ltd. All rights reserved.

Keywords: Geothermal reservoir; Well tests; Chingshui; Taiwan

1. Introduction

Taiwan is located at the western rim of the Circum-Pacific margin, one of the majorgeothermal and volcanic belts in the world. The Taiwanese island lies on a convergent andcompression boundary between the Philippine Sea and Eurasian Plates. The collision ofthese two tectonic plates results in frequent earthquakes and explains the presence of nu-

Corresponding author. Tel.: +886 6 2757575; fax: +886 6 2747378.E-mail address: [email protected] (M.C. Tom Kuo).

0375-6505/$30.00 2004 CNR. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.geothermics.2004.11.003

100 K.C. Fan et al. / Geothermics 34 (2005) 99118

Nomenclature

a formation diffusivity (m2/s)A area (m2)b width of fractured reservoir (m)ct compressibility of fluid (Pa1)FIP fluid-in-place (m3)h formation thickness (m)k permeability (m2)kh permeabilitythickness product (m3)P pressure (Pa)Pi initial pressure (Pa)P pressure change (Pa)PDl dimensionless pressure in linear-flow modelq well volumetric flow-rate at reservoir conditions (m3/s)qm well mass flow-rate (kg/s)Q well capacity (kg/s)t time (s)tDb dimensionless time in linear-flow modelx distance between the production and observation well (m)xD dimensionless distance between the production and observation well

Greek letters viscosity (Pa s) specific volume at reservoir conditions (m3/kg) porosityh porositythickness product (m)

Conversion factors1 bar 105 Pa1 h 3600 s1 darcy (0.9869 1012 m2)

merous volcanoes and geothermal areas. Close to a hundred hot-spring locations have beenidentified in Taiwan and have been classified as volcanic or non-volcanic hot springs. Thenon-volcanic hot springs are found in both the sedimentary province and the metamorphicterrains of the island (Fig. 1). Table 1 summarizes the characteristics of these two typesof hot springs in Taiwan, such as reservoir temperature, predominant lithology, type ofpermeability, and fluid chemistry.

The Chingshui geothermal field is located in the northeast sector of Taiwan, in themetamorphic terrains (Fig. 1). Geothermal exploration in this area began in 1973 (Leeet al., 1980), and consisted of geological, geochemical and geophysical investigations

K.C. Fan et al. / Geothermics 34 (2005) 99118 101

Fig. 1. Thermal springs in Taiwan (Chen, 1985).

Table 1Characteristics of thermal springs in Taiwan

Hot-spring type Volcanic area Sedimentary province, metamorphic terrain

Reservoir temperature 200300 C 100200 CReservoir permeability Fractures in sandstones

and andesitesFractures in sandstones and metamorphic rocks

Major ions SO42; Cl Na+; HCO3pH 25 89


(e.g., Su, 1978; Tseng, 1978; Cherng, 1979; Hsiao and Chiang, 1979; Lee et al., 1980),as well as drilling of a number of gradient (less than 500 m deep) and deeper exploratoryand production wells (Cherng, 1979).

Pressure buildup and interference tests were conducted for an initial assessment of thefield in 1979 (Chang and Ramey, 1979; Chiang et al., 1979). According to Chang and Ramey,two short, preliminary interference tests were carried out to determine whether detectablepressure responses were observed. A third, 11-day long interference test was completed inNovember 1979. Its main objective was to determine the transmissivity and coefficient ofstorage of the reservoir, parameters that are needed to estimate reservoir deliverability andfluid reserves.

Based on the results of these exploration and reservoir evaluation studies, a 1.5 MWpower plant was installed at Chingshui in October 1977 (Lee et al., 1981). The plant wasreplaced by a larger unit (3 MW), which came on line in July 1981. During its first yearof operation, the average power output was only 1.18 MW. That average dropped morethan 50%, to 0.52 MW, during the third year because of a sharp decline in the productivityof the wells. In 1993, the plant ceased operations when the average power output wasonly 0.18 MW. Fig. 2 shows the field deliverability of geothermal fluids and the poweroutput at Chingshui from 1981 to 1993. There was no re-injection of spent geothermalfluids.

The maximum measured reservoir temperature at Chingshui was about 225 C.Table 2 depicts the chemistry of the geothermal fluids produced at a flowing well-head pressure of 3.92 bars (4 kg/cm2); their pH ranged between 8.5 and 8.8. Non-condensable gases in the produced fluid, primarily CO2, amounted to over 10% byvolume. Scale deposits of CaCO3, NaHCO3, and SiO2 were identified during wellworkovers. Mineral scaling was one predominant reason for the decline of well producti-vities.

The purpose of the study presented here is the re-interpretation of the 1979 interferencetest data in order to calculate the reservoir fluid-in-place, as part of a project to evaluatethe feasibility of resuming commercial exploitation of the Chingshui geothermal system.A conceptual linear-flow model based on geological data was considered in the test datare-interpretation.

Table 2Chemistry of Chingshui geothermal fluids

Water phase Concentrations (ppm)pH K+ Na+ Ca2+ Mg2+ HCO3 Co32 Cl SO42 SiO28.8 36 1149 1.0 0.8 2768 186.0 16.0 23.6 3708.5 36 1095 0.6 0.2 2619 92.5 18.3 32.0 342

Steam phase Composition of non-condensable gases (vol.%)Steam:non-condensable gases (vol.%) CO2 H2S Residue89.70:10.30 97.89 0.46 1.65


Fig. 2. Production history of the Chingshui geothermal field.

2. Geology

The Chingshui geothermal field is an area of hot springs along the Chingshui River,approximately 13 km southwest of Lotung (Fig. 3). Dark-gray and black slates predom-inate. They are from the Miocene Lushan Formation, which can be divided litholo-gically into the Jentse, Chingshuihu, and Kulu members. In general, the Jentse Mem-ber is composed mainly of metasandstones intercalated by slates, while the underlyingChingshuihu and Kulu members consist mostly of slates (Tseng, 1978; Chiang et al.,1979).

The Chingshui geothermal area is located on a monocline structure, which is cut internallyby numerous thrust faults that are lightly curved, and essentially trend NESW, parallel tothe bedding; the most important ones are the Tashi, Hsiaonanao and Hanhsi faults, shown inFig. 4 (Su, 1978; Hsiao and Chiang, 1979). In the field itself, along the Chingshui River, isthe normal, NS striking Chingshuihsi fault. Active tectonic movements most likely created


Fig. 3. Location map of the Chingshui geothermal area.

the numerous faults and well-developed fractures around the Chingshui geothermal area.The best developed fractures in the slates occur near the most convex part of the Hsiaonanaofault, along the Chingshui River.

There is clear evidence that the geothermal reservoir is fracture-dominated. As a result ofthe poor porosity and permeability of the slates, faults, joints, and other extensive fracturesprovide the conduits for the geothermal fluid flow. The predominant joints, which are alignedalmost perpendicular to the strike of the strata, are densely developed within the sandy JentseMember. Fig. 5 shows the rose diagram for 67 joints measured at an outcrop of the JentseMember located near the Chingshui geothermal field (Tseng, 1978). The most prominent set


Fig. 4. Geological map of the Chingshui geothermal area showing the Chingshuihu, Jentse, and Kulu membersof the Miocene Lushan Formation. Triangles and rectangles indicate the up-dipped sides of the reverse faults andthe direction of dip of the normal fault, respectively.

of joints strikes northwest and dips between 65 and 80 to the southwest. A less conspicuousset strikes northeast and dips steeply northwest.

The trend of the Chingshui River runs almost parallel to that of the joints. Its bed has cutthrough the slates, which present well-developed fractures. There are numerous hot springsand fumaroles along the river within the geothermal field. It is reasonable to infer that theriver bed is the area where the major open fractures reach the surface.

Subsurface data indicate that geothermal production at Chingshui comes largely from afracture zone within the steeply dipping Jentse Member (Hsiao and Chiang, 1979). Structuralanalyses show that this member presents predominant, well-developed, steeply dippingjoints that strike between N 25W and N 40W. Outcrops near the area of the thermalmanifestations also reveal that the faults run parallel for almost 100150 m, striking betweenN 30W and N 35W (Tseng, 1978).


Fig. 5. Rose diagram for 67 joints in the Chingshui geothermal area (Tseng, 1978).

3. Well drilling, completion and development

The drilling fluid used at Chingshui was bentonite slurry treated with chrome lignosul-fonates. In order to prevent wellbore cave-ins, the mud was always maintained at a specificgravity of 1.10 to 1.25 and at a Marsh funnel viscosity of 40 s. Heavy circulation lossesoccurred when the drill bit penetrated major fracture zones. During completion, fresh waterwas injected into the well to wash out the drilling mud and remaining drill cuttings.

The casing program for the production wells was: 50.8 cm (20 in.) conductor, 34 cm(13 38 in.) surface casing, 24.4 cm (9 58 in.) production casing, and 17.8 cm (7 in.) or 11.4 cm(4 12 in.) slotted liner. The slotted liners hung between 490 and 1048 m depth, depending uponthe depth of the high-temperature production zone; the length of the liners varied between950 and 2160 m. All casings, except the liners, were cemented. Table 3 summarizes the com-pletion and capacity data for all the Chingshui production wells (i.e., 4T, 5T, 9T, 12T, 13T,14T, and 16T). Well-production capacities were measured using the James method (1966).

4. Interference test

Identification of the prevalent reservoir fluid flow model is a pre-requisite for reachinga correct evaluation of well test data, and thus of fluid-in-place, and for developing drillingand field management programs.


Table 3Well capacity and completion data for wells in Chingshui geothermal reservoir

Well Elevation(m asl)

Well capacity Well completion

Steam rate(l03 kg/h)

Hot water rate(l03 kg/h)

Total flow-rate(l03 kg/h)

Total depth(TD) (m)

Depth ofliner shoe(m)

Depth oflinerhanger (m)

Temperatureat TD (C)

4T 257.95 28.6 98.1 126.7 1505 1503 498 2015T 269.54 6.0 34.0 40.0 2005 1998 493 2209T 260.67 18.7 55.3 74.0 2079 2074 490 20512T 260.67 6.9 40.0 46.9 2003 1998 1048 22313T 269.54 10.4 60.1 70.6 2020 2015 505 21914T 281.50 22.0 66.0 88.0 2003 1995 947 21516T 272.58 30.3 85.9 116.2 3000 2990 830 225

In this paper we describe a new interpretation of the data of the November 1979 wellinterference test. In the original interpretation by Chang and Ramey (1979) the authorsassume a radial flow model. We will show that the use of a linear-flow model is moreappropriate for the Chingshui reservoir.

As mentioned earlier, the geothermal reservoir presents well-developed joints and faults.All the wells drilled into the Jentse Member, the producing formation, have rather high-angle inclinations of up to 35, and all are deviated almost parallel to the joints observedat the surface (Hsiao and Chiang, 1979). The deviations in some wells changed abruptly,turning sharply back in a direction almost parallel to the joints, with loss of mud circulationwhenever a highly productive fractured zone was encountered.

On the basis of the trend of the fractures in the production zone, a linear-flow model shouldmore accurately represent the geothermal reservoir and the flow regime between wells thana radial flow model, which assumes either primary porosity or a random distribution andorientation of joints and fractures.

During the 1979 test, well 16T was put into production, and pressure responses wereobserved in wells 4T, 5T, 9T, 12T, 13T, and 14T (Chang and Ramey, 1979). Fig. 6 showsboth surface and bottom-hole locations of these wells. Since the drill bit in all the wellsdrifted in the direction of the geologic structures, the distance between the bottom-holelocations had to be estimated in order to interpret the interference test data, the distancesbetween wells corresponding to the distance between pairs of feed zones.

The data relative to the 11-day interference test are presented in Table 4. Hot waterproduction rate, measured in a weir, ranged from 80,000 to 83,500 kg/h during thetest. The total fluid (water + steam) production rate was calculated from the hot waterproduction rate using energy-balance considerations for flashing water. For the 11-dayinterference test, the wellhead pressure, water production rate and total fluid produc-tion rate of flowing well 16T stabilized at 3.59 bars, 80,000 kg/h, and 105,000 kg/h,respectively. Wellhead pressures were monitored at all the observation wells, but datafrom wells 5T and 13T appear to be unreliable because of equipment malfunction. Thetheory and interpretation of the interference test results will be presented in Sections5 and 6.

108K.C.F

anetal./G

eothermics34(2005)99118

Table 4Interference test in Chingshui geothermal field (Chang and Ramey, 1979)Time (h) Observation wells Flowing well

4T 9T 12T 14T 16 T

WHPa (bar) Pb (bar) WHP (bar) P (bar) WHP (bar) P (bar) WHP (bar) P (bar) WHP (bar) Hot waterrate(103 kg/h)

Total fluid rate(103 kg/h)

0.0 11.86 0.00 9.51 0.00 12.89 0.00 9.17 0.00 17.79 0.0 0.018.5 11.79 0.07 9.45 0.07 12.76 0.14 9.17 0.00 4.76 24.0 30.842.5 11.58 0.28 9.31 0.21 11.17 0.34 8.96 0.21 4.00 83.5 108.766.5 11.45 0.41 9.17 0.34 12.55 0.34 8.62 0.55 3.86 83.1 108.490.5 11.45 0.41 8.96 0.55 12.41 0.48 8.62 0.55 3.86 83.1 108.4

114.5 11.38 0.48 8.96 0.55 12.34 0.55 8.48 0.69 3.86 82.0 107.0138.5 11.31 0.55 8.96 0.55 12.27 0.62 8.34 0.83 3.86 82.4 107.5162.5 11.31 0.55 8.89 0.62 12.20 0.69 8.27 0.90 3.72 82.4 107.8186.5 11.24 0.62 8.83 0.69 12.13 0.76 8.20 0.97 3.72 81.0 106.0210.5 11.17 0.69 8.76 0.76 12.07 0.83 8.20 1.03 3.65 80.0 104.8234.5 11.17 0.69 8.76 0.76 12.07 0.83 8.07 1.10 3.59 80.0 105.0258.5 11.10 0.76 8.69 0.83 12.07 0.83 7.93 1.24 3.59 80.0 105.0

a WHP: wellhead pressure.b P: pressure change.


Fig. 6. Well locations and inferred temperature distribution (C) at 1500 m depth in the Chingshui geothermalarea (from Chang and Ramey, 1979).

5. Theory

There are a number of books and reports discussing the theory and practice of ana-lyzing data from tests performed in different types of wells (groundwater, oil and gas,geothermal). The test data can be analysed by means of curve fitting techniques or


computer-aided approaches (e.g., McLaughlin et al., 1995; Horne, 1995; OSullivan et al.,2005).

5.1. Radial ow model

The most commonly used analytical solutions for interpreting an interference test isthe Theis solution (Theis, 1935) and the line source solution (van Everdingen and Hurst,1949), for use in groundwater and petroleum engineering, respectively. The line sourcesolution corresponds to an infinite-acting, isotropic reservoir, and assumes a constantproduction/injection rate in which only one (liquid) phase is involved. This is themodel used by Chang and Ramey (1979) in their analysis of the 1979 interference testdata.

5.2. Linear-ow model

We have developed a conceptual linear-flow model of the Chingshui geothermal reser-voir, based on the geological data of the area (see previous sections). Fig. 7 is a sketch ofthe linear-flow model in which the geothermal reservoir is represented by a parallelepiped.Fluid flow is parallel to the main strike of the joints and the lateral boundaries of the prism.The cross-section of the parallelepiped is assumed to be a rectangle with a height h anda width b. The production well is represented by a planar source. The diffusivity equa-

Fig. 7. Sketch of a linear-flow model for a fractured reservoir.


tion governing fluid flow in an infinite linear reservoir for the constant-rate case is givenby:

P

t= a

2P

x2(1)

subject to the following initial and boundary conditions:t = 0, P = Pi for x 0

and

t > 0,P

x= q

2bhkfor x = 0 and lim

xP(x, t) = Pi for x

where a= k/ct, the formation diffusivity.Miller (1960) investigated unsteady influx of water in linear reservoirs for the constant-

rate case and an infinite-acting reservoir using the equations given above. Miller adaptedthe Carslaw-Jaeger (1959; p. 75) solution of heat conduction to pressure drawdown in linearreservoirs as follows:

p(x, t) = pi q2khb

[2at

exp

( x

2

4at

) x erfc

(x

2at

)](2)

Millers solution [Eq. (2)], is similar to that developed by Jenkins and Prentice (1982) toanalyze aquifer tests in fractured rocks assuming linear-flow conditions. The Miller solutionwas previously applied to a steam reservoir for interference analysis (Ehlig-Economideset al., 1980). To apply Millers solution to a fractured hot water reservoir using SI units, thefollowing dimensionless variables are defined:

PDl = 2khPq

(3)

xD = xb

(4)

tDb = khthctb2

(5)

where k is permeability (m2); h is formation thickness (m); P is pressure change (Pa); q isvolumetric well flow-rate at reservoir conditions (m3/s); is viscosity (Pa s); x is distancebetween the production and observation wells (m); b is width of the fractured reservoir (m); is porosity; ct is compressibility of fluid (Pa1); and t is time (s). The well volumetricflow-rate at reservoir conditions can be calculated by multiplying the well mass flow-ratewith the specific volume of geothermal fluid at reservoir conditions, or, q= qm where qmis well mass flow-rate (kg/s); and is specific volume of geothermal fluid at reservoirconditions (m3/kg).


Table 5Type-curve matching using van Everdingen and Hurst (1949) solutionaRadial flow model Observation wells

4T 9T 12T 14T

Match pointPD (P= 0.6895 bars) 0.95 0.77 0.78 0.43tD/r

2D (t= 100 h) 1.5 0.95 1.2 0.75

Distance (m) 175 300 90 330kh (darcy m) 9.24 7.49 7.59 4.18h (m) 425 185 1650 108

a qm = 105,000 kg/h, = 1.188 103 m3/kg, = 0.12 103 Pa s, ct = 1.45 104 bar1.

Eq. (2) can then be written in terms of the dimensionless variables defined above:

PDlxD

= 2

tDb

x2Dexp

( x

2D

4tDb

) erfc

(xD

2tDb

)(6)

Eq. (6) can be used to calculate a loglog type-curve, PDl/xD versus tDb/x2D, for linear-flow.If practical units (i.e., darcy, bar, and hour) are used instead of SI units, Eqs. (3) and (5)

become:

PDl = 0.0007106khPq

(3a)

tDb = 0.0003553khthctb2

(5a)

The CarslawJaegerMiller solution assumes that one half of the produced fluid comesfrom each side of the production plane/well; for this reason, Fig. 7 shows only one side fora production well along the direction of fluid flow and the main strike of the joints.

6. Interpretation of interference test data

Fig. 8 is a match of the well 4T pressure versus time data against the vanEverdingenHurst radial flow solution. Fig. 9 shows similar matches for wells 9T, 12Tand 14T. Table 5 summarizes the curve matching results for all the well pairs assuming theradial flow model.

Fig. 10 is a match of the well 4T pressure versus time data against the Miller linear-flowsolution. Fig. 11 shows the match for wells 9T, 12T and 14T. The linear-flow type-curvematching results for all pairs are given in Table 6.

As can be seen from Tables 5 and 6, porositythickness products obtained from the radialflow model varied over a wide range, from 108 to 1650 m, while the range obtained fromthe linear-flow model was significantly smaller (i.e., 279956 m). To apply the linear-flowmodel, the width of the Chingshui geothermal reservoir was estimated to be around 300 m,


Fig. 8. Well 4T. Type-curve match using the radial flow model.

Table 6Type curve matching using Miller (1960) solutionaLinear-flow model Observation wells

4T 9T 12T 14T

Match pointPDl/xD (P= 0.6895 bars) 4.8 1.6 2.9 1.4tDb/x2D (t= 100 h) 13 3 7.5 3.4

Distance (m) 175 300 90 330kh (darcy m) 85.5 48.9 26.6 47.1h (m) 468 396 956 279

a qm = 105,000 kg/h, = 1.188 103 m3/kg, = 0.12 103 Pa s, ct = 1.45 104 bar1, b= 300 m.

based on the bottom-hole locations of the production zones of the seven wells (4T, 5T, 9T,12T, 13T, 14T, and 16T) shown in Fig. 6.

7. Discussions

The main objective of the study of the Chingshui field was to identify a model thatmost appropriately describes the geology and flow behavior of the fractured geothermal


Fig. 9. Wells 9T, 12T, and 14T. Type-curve match using the radial flow model.

reservoir. A realistic model is an important tool in our analysis of interference test data andin estimates of the geothermal fluid-in-place.

The capacity of a geothermal well depends on a number of factors, such as permeability-thickness product, well skin, and well completion. According to Darcys law, undersimilar conditions of well completion and skin, well capacity is proportional to thepermeabilitythickness product.

In our interpretation of the interference test data, we applied both the radial and the linear-flow model, and compared their results. The permeabilitythickness products estimatedwith these two models were compared and correlated to well capacities in order to selectthe appropriate model. As shown in Table 7, the kh products estimated using the linear-flow

Table 7Comparison of well capacity with permeabilitythickness product

Well number Well productivity totalfluid rate, Q (10 3kg/h)

Permeabilitythickness product, kh (darcy m)Linear-flow model Radial flow model

4T 126.7 85.5 9.249T 74 48.9 7.4912T 46.9 26.6 7.5914T 88 47.1 4.18


Fig. 10. Well 4T. Type-curve match using the linear-flow model.

model appeared to correlate with well capacities, whereas this was not the case for the radialmodel.

Figs. 12 and 13 illustrate a least-square fit of well capacities versus permeabilitythickness products for the radial and linear-flow models, respectively. The small valueof the sample correlation squared regression coefficient (i.e., R2 =0.1362) correspond-ing to the radial model (Fig. 12) indicates that the two parameters are not well correlated.On the other hand, the same coefficient is quite high (i.e., R2 = 0.9146) for the linear-flowmodel (Fig. 13). In this case, the regressed equation would be quite useful in predictingwell capacity from the permeabilitythickness product, i.e.,

Q = 1574kh (7)where Q is well capacity (kg/h) and kh is the permeabilitythickness product (darcy m).

Because the thickness of Chingshui geothermal reservoir is not known, we were unableto separate the average permeabilitythickness product of 52 darcy m (or the averageporositythickness product of 525 m) into effective permeability (or porosity) and net thick-ness with accuracy. However, a range of thickness may be considered to estimate effectivepermeability and porosity values. For example, if the net reservoir thickness is assumed to be2500 m, then the effective permeability and porosity would be approximately 21 millidarcysand 0.20, respectively, for this liquid-dominated system. A porosity of this order of mag-


Fig. 11. Wells 9T, 12T, and 14T. Type-curve match using the linear-flow model.

Fig. 12. Regression lines between well capacities and permeabilitythickness products obtained using the radialflow model.


Fig. 13. Regression lines between well capacities and permeabilitythickness products obtained using the linear-flow model.

nitude appears high, so the indication is that the net reservoir thickness may exceed2500 m.

The main importance of the porositythickness product obtained from interference test-ing is that it can provide an estimate of the fluid-in-place. Based on the isotherms map(Fig. 6), the area of the Chingshui geothermal reservoir is estimated to be around 2 km2.The fluid-in-place can be calculated by a volumetric method using the following equation

FIP = hA (8)where FIP is fluid-in-place (m3); h is porositythickness product (m); and A is area (m2).Therefore, the fluid-in-place for Chingshui geothermal reservoir is slightly higher than109 m3 (i.e., 525 m 2 km2).

8. Conclusions

The application of a linear-flow model in the interpretation of data from an interfer-ence test carried out in the Chingshui geothermal field was discussed. The analysis showedthat the data can be matched to type curves for either the radial or the linear-flow model.However, when the values of permeabilitythickness products are correlated with the wellproductivities, the correlation is poor for the radial flow model and very good for thelinear model. As initially indicated by geologic and well drilling information, the in-terference data analysis confirms that the flow regime in the reservoir is predominantlylinear.

The amount of reservoir fluid-in-place is significant (more than 109 m3); however, un-less scaling is controlled, the long-term electricity generating capacity of the Chingshui


geothermal system may remain at the 12 MW level. Scaling control and re-injection ofspent geothermal liquids would help increase the productive lifetime of the geothermal field.

Acknowledgments

This research was funded by the Energy Commission, Ministry of Economic Affairsand National Science Council of Taiwan (NSC-93-2623-7-006-006-ET). The authors aregrateful for the valuable comments and suggestions of the reviewers, especially Dr. SabodhGarg and Dr. Marcelo Lippmann, who helped to improve the paper.

References

Carslaw, H.S., Jaeger, J.C., 1959. Conduction of Heat in Solids, 2nd ed. Oxford, University Press.Chang, C.R.Y., Ramey, H.J., 1979. Well interference test in the Chingshui geothermal field. Paper presented at

Fifth Geothermal Reservoir Engineering Workshop, Stanford University, Stanford, CA, pp. 6476.Chen, C.H., 1985. Chemical characteristics of thermal waters in the central range of Taiwan. R.O.C. Chem. Geol.

49, 303317.Cherng, F.P., 1979. Geochemistry of the geothermal fields in the slate terrane. Geotherm. Resour. Counc. Trans.

3, 107111.Chiang, S.C., Lin, J.J., Chang, C.R.Y., Wu, T.M., 1979.A preliminary study of the Chingshui geothermal area, Ilan

Taiwan. Paper presented at Fifth Geothermal Reservoir Engineering Workshop, Stanford University, Stanford,CA, pp. 249254.

Ehlig-Economides, C., Economides, M.J., Miller, F.G., 1980. Interference between wells in a fractured formation.Geotherm. Resour. Counc. Trans. 4, 321324.

Horne, R.N., 1995. Modern Well Test Analysis, 2nd ed. Petroway Inc, Palo Alto, CA.Hsiao, P.T., Chiang, S.C., 1979. Geology and geothermal system of the Chingshui-Tuchang geothermal area, Ilan,

Taiwan. Petrol. Geol. Taiwan 16, 205213.James, R., 1966. Measurement of steam-water mixtures at the speed of sound to the atmosphere. N. Z. Eng. 20

(1), 437441.Jenkins, D.N., Prentice, J.K., 1982. Theory for aquifer test analysis in fractured rocks under linear (nonradial)

flow conditions. Ground Water 20 (1), 1221.Lee, C.R., Lee, C.F., Cheng, W.T., 1980. Application of roving bipole-dipole mapping method to the Chingshui

geothermal area, Taiwan. Geotherm. Resour. Counc Trans. 4, 7376.Lee, C.S., Chang, P.T., Hsu, J.B., 1981. A model approach for the geothermal fields in slate terrain of Taiwan.

Geotherm. Resour. Counc. Trans. 5, 181184.McLaughlin, K.L., Barker, T.G., Owusu, L.A., Garg, S.K., 1995. DIAGNS: An interactive workstation-based

system for well test data diagnostics and inversion. Proceedings World Geothermal Congress, Florence, Italy,vol. 4, pp. 29412944.

Miller, F.G., 1960. Theory of unsteady-state influx of water in linear reservoirs. Report. Stanford University,Stanford, CA, p. 45.

OSullivan, M.O., Croucher, A.E., Anderson, E.B., Kikuchi, T., Nakagome, O., 2005. An Automated Well TestAnalysis System (AWTAS). Geothermics 34, 325.

Su, F.C., 1978. Resistivity survey in the Chingshui prospect, I-lan, Taiwan. Petrol. Geol. Taiwan 15, 255264.Theis, C.V., 1935. The relation between the lowering of the piezometric surface and the rate and duration of

discharge of a well using ground-water storage. Trans. Am. Geophys. Union 16, 519524.Tseng, C.S., 1978. Geology and geothermal occurrence of the Chingshui and Tuchang districts, Ilan. Petrol. Geol.

Taiwan 15, 1123.van Everdingen, A.F., Hurst, W., 1949. The application of the Laplace transformation to flow problems in reservoirs.

Trans. AIME 186, 305324.

Interpretation of a well interference test at the Chingshui geothermal field, TaiwanIntroductionGeologyWell drilling, completion and developmentInterference testTheoryRadial flow modelLinear-flow model

Interpretation of interference test dataDiscussionsConclusionsAcknowledgmentsReferences

Documents

10.pdf