geothermal well

Note, have standardized downhole / down hole to ‘down-hole’ and airlift/ air lift /

air-lift to’ air-lift’. If this standardization is incorrect, do a find/replace to correct

all.

Procedures for Testing Direct Use Geothermal Wells

S. Ady Candra, Sadiq J. Zarrouk.

Abstract

The well testing and measurement is an important key to predict and investigate the

condition of the well and its characteristics. Rotorua with theiris rich in geothermal

resources, which has enabled a lot ofthe creation of many direct used geothermal

wells, was which are utilized for commercial and domestic puroposes. However, no

should be managed in standard methodology, has been established for management

of the wells, especially in the way that they wellare testeding and measuredment.

Well testing and measurement is key in predicting and investigating the conditions

and characteristics of a well. This study collects and uses data from sSeveral samples

of direct use application geothermal wells data for direct use application in Rotorua

were used as variant in order to classify direct used geothermal wells.

This is then used as the bBasised on those will befor the development ofed a the

standard methodology in for well testing and measurement, in which the

objectiveities are: determining the production rate, estimatinge the reservoir

conditions, and investigating the environmental impact of the geothermal resource

exploitation for direct use of geothermal energy in environmental. During this time

there was no standard practices methodology to conduct the well test and

measurement. Therefore, It is intended that this methodology of well testing and

measurement can be able to be implemented by the Bay of Plenty Regional Council as

authorized inin geothermal resource monitoring in Rotorua.

1

Keywords:

Well test, well measurement, direct use, methodology, completion test, geothermal

energy.

[1] Introduction.

Those are the reason on this study whichI chosen the city of Rotorua as mya

research objectsubject because it is located

Rotorua is an interesting town in New Zealand, which the town sits aton the

top of up-flow and outflow zones belonging to the Rotorua geothermal

system. Thisis condition siting creates has enabled the Rotorua to be

developed to beas a touristm citydestination in New Zealand, because . In

addition to its being able to exploit the geothermal features appearingances

within the city as tourist sight-seeing opportunities,. privateThe residences

and the owner of the motels and hotels are able to utilizezed the geothermal

system underneath beneath them for (power?) (heating?).their place to take

advantages.

Those are the reason on this study which chosen Rotorua as a research object

.

The Geothermal Energy Act from the central government in 1953 states in

activities of take and discharge geothermal fluid should have a permit and license

(Gordon and Mroczek, 2005) (NOTE: the Geothermal Energy Act has been

superseded by the Resource Management Act – you need to update this

sentence accordingly) .

The development of the Rotorua field was developed in an unplanned, manner

and in addition, was pursued without any consideration ofs to theresource

sustainability, of the resource or the impact of the development upon n natural

surface features or and the environment (Steinsa, et al, 2012). Therefore,The

utilizing geothermal wells atin Rotorua should now need to be managed in an

appropriate waymanner., including Such management would require the

implementation of monitoring systems, grant consent permits, and inspection

and investigation utilizing of geothermal resource utilization. As the local 2

administrator and regulator for this area, the Bay of Plenty Regional Council

(BoPRC) is a local administrator and regulator for this area has an important role

to plays to in manage all those things in geothermal systemthis at Rotorua.

One parameter mechanism to for monitoring the utilization ofe geothermal fluid

is periodic well testing and measurement in periodically.

The main objectives of well testing and measurement are:.

Estimating likely well production capability

Identification of the location of permeable zones and their formation

Estimation of formation reservoir pressure.

Checking of well casing conditions

Geothermal well testing and measurements is a mechanism to observe and

investigate the capability of geothermal wells and it can maintain and interpret

the productivity of the geothermal system (DiPippo, 2008). The physical

measurements made in geothermal wells provide the primary information from

which ideas about the underground resource can be developed. Running

downholedown-hole logging techniques can also provide additional information

about rock properties, such as porosity and density, and can help into

determininge detailed information about fracture formations and properties.

Theose can assist in (an overall?) understanding (of the?) the geothermal

resources under consideration (Grant and Bixley, 2011).

The main objective of well testing and measurement:.

Estimating likely well production capability.

Location of permeable zones and its formation.

Estimate formation reservoir pressure.

Checking well casing condition.

1[2] Background research

More thanOver a one thousand geothermal wells were have been drilled in the

BoPRC area, especially the majority of them in Rotorua. Most of them were 3

drilled at in a shallow aquifer consists ofoccurring in (one of?) three regions:

Rhyolitic domes in the north and the south, and an ignimbrite layer at the

bottom of the aquifer with an overlying sedimentary layer (Steinsa, et al, 2012)

(NOTE: I have tried, but have not managed to make this paragraph entirely

clear: It remains ambiguous whether the drilling was in one shallow aquifier

that has three regions , OR in shallow aquifers in three different regions.)

Figure 1 Distribution and density of geothermal bores across the Rotorua geothermal field in

2012. (BoPRC, 2012)

Figure 1 Key: Red dots represent Down-hole Heat Exchangers (DHE)(?) represent non down-hole heat exchangersThe yellow dotted line represents the 1.5km closure zone (note, what is the closure zone / why is it there?)

Figure 1 shows tThe e concentration of wells along Fenton Street (NOTE: how

do we identify Fenton St?) that are associated with motels and hotels. The

impact of the 1.5 km closure zone is immediately apparent with mostly Down-

hole Heat Exchangers (DHEs) located within the zone. The non downholedown-

4

hole heat exchangers in the zone are on limited term resource consents, and

when these expire the abstraction of geothermal fluid must cease (BoPRC,

2005).

On this study was used several sampleOf the direct use geothermal wells

sampled for this study, for direct use which those wells havemost had different

characteristics, and used different technologiesy to extract the geothermal

fluid from the reservoir. Most of them have production casings with a nominal

diameter that ranges nominal between size diameter production casing 100 mm

to 150 mm (4“ to 6”). [It is also including with sample of utilizing hot spring for

direct used of geothermal energy NOTE: This sentence does not make sense]

[Why are the following two paragraphs in Background research rather than

worked into the Introduction? Effectively managing the geothermal field

requires information about the geothermal resource. A variety of different

tools to monitor and predict changes in the field are available to achieve this

which include: a field model, monitoring water level trends, information from

bore construction and testing, and monitoring of chemical and thermal

changes across the field (BoPRC, 2005).

All this time Bay of Plenty Regional Council do not have a standard well test

and measurement methodology for direct used geothermal wells, and it was

conducted in several techniques based on experience practices. Therefore,

data from the measurements have a low level confidence in determining

production capability of geothermal wells.

Therefore, to obtain accurate data from the monitoring resource, it is required

a standard methodology in measurement and well testing. ]

2[3] Direct use of geothermal energy.

Direct use of geothermal energy can vary greatly in size scale and capital value,

depending on the geothermal resource and its applications. Which it was

Ttraditionally, direct use of geothermal energy was used for for domestic 5

purposes, such as bathing, cooking and heating in domestic proposes. Currently

the utiliutilization ofzing geothermal energy has been is being developeding for

industrial proposes such aus agriculture, space heating, and industrial drying

etc, especially for the place wherefur use in locations which have geothermal

resources, such as Rotorua such as in towns in New Zealand.

The main advantages of using the geothermal energy for direct used are low

[overall OR running] costs (when compared with fossil fuels), independence

independenant direct control over the energy source, and mMinimal

eEnvironmental iImpact (Thain, Reyes, & Hunt, 2006).

There are someMost techniques to for extracting the heat from the a

geothermal resource in for direct use application which most of them utilize a

heat exchanger to transfer heat from the geothermal fluid to the secondary

fluid. The secondary fluid acts as a heat caurrier to and distributse the heat

based on its puroposes..

The major components of a direct use system are:

Down-hole and circulation pumps

Transmission and distribution pipelines

Peaking and backup plants

Various heat exchange mechanisms

(Thain, Reyes, & Hunt, 2006).

6

Downhole Pump

Production well

Re-Injectionwell

Main Plate Heat Exchangers

Secondary Plate Heat Exchangers

Primary fluid line (Geo)

Secondary fluid line

Master Valve

Secondary water circulating pumps

3 Classification of Geothermal Wells for Direct Use in Rotorua

Based on the well capability, in direct use can be classified in several

groupsas follows (NOTE: have made this change, because there are only 2

groups below, one with three sub groups):

a. Self discharge (pressurized) wells.

b. Non self discharge(non-pressurized) wells:

[i.] Down holeDown-hole pump wells

[ii.] DownholeDown-hole heat exchanger wells

[iii.] Air liftAir-lift geothermal wells

3.1 Self discharge wells

Many geothermal wells, with water temperatures exceeding 150 ° C, are

known to be self-flowing (Narasimhan & Witherspoon, 1979). The Wwells

has with self discharge capability are usually are in an up-flow zone, such

as in Kirau Ppark, Rotorua, New Zealand which uses well number RR 913

7

Figure 2 typical sSchematic diagram of a dDown-hole pump used in direct use of geothermal energy

as a production well for geothermal direct use in the Rotorua Aquatic

centreer.

AnOother wells have with the capability in self discharge capability are

well number RR 858 and RR 1012,. Those well are used by Queen

Elizabeth Hospital for mineral pools and water heating for health

proposes.

Figure 3. Sample Photo of self discharge well RR 913

Reservoir The enough pressure and the rock permeability have play an

important role to in determininge the capability of well in to self

dischargeing. As a result the Ggood permeability and high pressure at the

reservoir will be result in give good production of from the geothermal

well, with high temperature and fluid enthalpy.

Table 1 sample data of sSelf discharge wells in Rotorua for commercial proposes.

　Classification Well Self discharge wells

Well Number RR 1043 RR 858 RR 1012 RR 758 RR 913

Quantity/Rate 　　　　　

max Flow rate (ton/day) 165 310 310 60 226

Average discharge Temp (oC) 164 145 145　 112 150

Average injected Temp (oC) 158 50 50 　95.5 40　

Max Heat extracted (MWhr 　179 4,644 4,644 174 4,376　

Pressure/WHP (kPa.g) 330 - 400 365 　- -　　-

date drilled 01-Jun-98 01-May-82 -　 01-Apr-77 24-Nov-85

Bore depth (m) 100 129 133.5 141.2 146.5

8

Casing depth (m) 76.3 85 90 90.87 88

Casing diameter (mm) 100 100 125 100 100

Surface Casing Size 　- 200 250 - -　

Depth (m) 　- 15 12.6 -　　-

Intermediate Casing Size 　- 150 150 　- 　-

Depth(m) 　- 32.65 26.9 　- -　

Production casing Size 　- 100 100 -　　-

Depth (m) 　- 85 90 -　　-

Liner Casing 　- no no -　 -　

3.2 Down-hole Pump (DHP) Wells

Fluid eExtractionng fluid from well by using a down holedown-hole pump

is the appropriate system for non self discharging geothermal wells.

Down holeDown-hole pumps are being used increasingly more often in

low-enthalpy geothermal wells., Wwhich of these pumps are is installed

depends on the physical characteristics of the well, and the chemical

characteristics of the geothermal fluid, the production flow rate, and the

reservoir pressure and permeability (Aksoy, 2007).

Figure 4 Diagram of a cased geothermal well in which a downholedown-hole pump(Aksoy,

9

2007).

A Ssample data was obtained for this study from the Bay of Plenty

Regional Council (BoPRC) data base (shouldn’t this appear as part of the

introduction?).

CThe consent number 64319 was granted to the Wylie Ccourt Mmotel, to

utilizeing DHP for well no RR 910 for commercial use, water heating,

space heating and their drying room. The table below is shows sample

geothermal wells in Rotorua which those are used for direct used

application in commercial proposessettings.

Figure 5 illustration of the downholedown-hole pump well (RR 910) in the Wylie Court Mmotel, Rotorua, NZ

Table 2 sample geothermal well data from wells with downholedown-hole pumps

Classification Well DownholeDown-hole Pump (DHP) Wells

Well Number 910 Surface Casing 200

Quantity/Rate Size 13max Flow rate (ton/day) 178 Depth (m) 　Average discharge Temp (oC) 75 Intermediate Casing 150

Average injection Temp (oC) 　50 Size 　Max Heat extracted (MWhr) 776　 Depth (m) 　Pressure/WHP (kPa.g) 400 Production casing 100

date drilled 14-Aug-85 Size 　Bore depth (m) 104 Depth (m)

Casing depth (m) 82.5 Liner Casing

Casing diameter (mm) 100

10

[3.3] Air liftAir-lifts discharge wells.

The gGeothermal hot water wells which don’t have capability self

discharge capability stillcan have be extracted the geothermal fluid

extracted by air-lift pump. Air-lift pumps work by Bblowing air from the

atmosphere into the well using the an air compressor., The hot water and

air mix in the water pipes and hot water and air are mixed which this can

decreases the density of the hot water, and as a result, the mixed fluids

can be easily pushed out to discharge at the surface to be utilized.for

utilization.

Figure 6 Casing and wellhead details of an air liftair-lift well (left). (Thain, Reyes, & Hunt,2006) & aAir liftAir-lift geothermal well RR 447 at Timothy’s house, Rotorua (right)

The important problem in with air-lift geothermal wells is deposition and

corrosion fouling, which those willcan occur because the introduction of

air will change the (fluid?) chemistry, which and then can then make

cause deposition of solids to become a problem, especially in the plate

heat exchanger., as a result Rraising the ratio of air in to geothermal

water flow solvesd thise problem (Drew, 1988).

The tTable below is shows well samples for taken from air- lift

geothermal wells.

Table 3 sample data Air lift from air-lift discharge wells in Rotorua

11

Sadiq Zarrouk, 11/02/12,

I have sent you are report with better picture

　Classification Well Air liftAir-lifts discharge wells.

Well Number RR 752 RR447

Quantity/Rate 　　

max Flow rate 150 ton/day 2 ton/day

Average discharge Temp (oC) 103 62

Average Injection Temp (oC) 　84 44　

Max Heat extracted (MWhr) 500 6　

Type of use commercial Domestic

date drilled 　　

Bore depth (m) 154 56.3

Casing depth (m) 101.5 　

Casing diameter (mm) 　 100

3.3[3.4] Spring take and discharge.

The appearance of Hhot springs that appear at on the surface can be

utilized for geothermal direct used geothermal. This is the traditional way

direct use of geothermal energy. In an aspect of environments and

reliability of the reservoir is friendly, because the hot water spring naturally

discharges at the surface without pumped or forced. Itn the This mode of

use is economical aspect, as there is no need to it is not required drill a

production well to get hot water. It is also more environmentally friendly,

because the hot water springs naturally discharge at the surface without

needing the water to be pumped or forced. However, a reinjection well for

disposal of the hot spring water is still needed, due to the on this time

regarding with the environment issue, the possibility of dangerous

chemicals in the geothermal fluid. are required a reinjection well to

dispose hot spring water.

12

Figure 7 Concrete cCollection tank of hHot spring water (S 952) in Holliday Iinn, Rotorua, NZ.

.

Table 4 sample data of utilizing spring for direct used in Rotorua

　Classification Well Spring take and discharge.

Well Number S 952 S 623 & S624


max Flow rate 360 ton/day 30 t/day

Average discharge Temp (oC) 89 60

Average Injection Temp (oC) 50 40

Max Heat extracted (MWhr) 2,451　 105　

Type of use commercial commercial

[3.5] DownholeDown-hole Heat Exchanger (DHE) wells.

The adequate DHEs are an (efficient? – ‘adequate’ odd in this context)

method of eExtracting heat from shallow geothermal wells by utilize DHE.

It This is because DHEs can eliminate the problem of disposingal of the

geothermal fluid, since as only heat is removed from the well (Lund,

2003). The DHE consists with of a U tube or pipe laid inside the

geothermal production well. Clean (fresh) water is circulated iInside the

pipe or tube has been circulated with clean water (fresh water) , to

takeand the heat is removed from the geothermal well by natural

13

convection and conduction.

Figure 8 (a) DHE without a promoter, (b) DHE with promoter pipe (US design), (c) DHE

with promoter pipe (NZ design), and (d) DHE with airliftair-lift(Steinsa, et al, 2012)

Figure 9Typical DownholeDown-hole Heat Exchanger Installation (not to scale)(Freeston &

Pan, 1985)

Installing the U-Tube as a downholedown-hole heat exchanger inside of

the geothermal well is more economical, because thisat system is does 14

Sadiq Zarrouk, 11/02/12,

One figure is enough. Take fig 6 out

not required a reinjection well.

Figure 10 DownholeDown-hole heat exchanger well (RR 1063) in the Alpine Motel Rotorua, NZ

This study used well numbers 10643 and 10644 located at the Alpine

Motel as a examples of DHE geothermal systems to takinge heat from

geothermal wells., which was granted to Alpin motel Rotorua.

Table 5 sample data of from downholedown-hole heat exchanger wells in Rotorua

　Classification WellDownholeDown-hole Heat

Exchanger(DHE) wells

Well Number RR 10643 RR 10644


max Flow rate 0.5 - 2 L/sec 0.5 - 2 L/sec

Average Temp out (oC) 60 60

Average Temp in (oC) 40 40

Max Heat extracted (MWhr) 602 602

Pressure/WHP (kPa.g) 　　

date drilled 16-Jul-07 30-Jul-07

Bore depth (m) 55 55

Casing depth (m) 40 40

Casing diameter (mm) 150 100

Surface Casing Size 250 200

Depth (m) 8 8

Intermediate Casing Size 200 150

Depth (m) 19 19

Production casing Size 150 100

15

　Classification WellDownholeDown-hole Heat

Exchanger(DHE) wells

Well Number RR 10643 RR 10644

Depth (m) 40 40

Liner Casing no 　

3.4[3.6] Reinjection wells.

Reinjection wells is a techniqueare used to bring backreturn geothermal

fluid to the water aquifer beunderneath the reservoir, after the heat has

been extracted., Therefore, regarding withThis is an environmental

consideration, it is the main reason the geothermal fluid after extracted

their heat should be re-injected to reservoir..

There is are three mechanisms to for re-injecting geothermal fluid:

- Re-inject to the shallow aquifer by reinjection well

- Soakage in shallow aquifer

- Discharge the geothermal fluid into geothermal stream.

In order toWhen disposinge of fluid from shallow geothermal direct use

wells, there are concerns to beis the following to consider:

- The dDisposal ofe geothermal fluid to by reinjection well

should be by gravity, and avoiding the use of utilizing

reinjection pumps, because reinjection pumps can give

disadvantages of appearancescause the appearance of hot

springs surrounding the reinjection well.

- The soakage system of dispose geothermal fluid disposal

should be in shallower wells and it is foruse a low flow rate

for reinjecting theon water.

- A venting pipe to release Non Condensable Gas (NCG) should

be installed on re-injection wells.

Monitoring Rreinjection well monitoring has plays an important role to in maintaining the resource of geothermal resources., most of the reinjection geothermal well disposed goethermal water or mixed with surface water

16

in colder temperature. During When reinjecting the colder fluid, its caharacteristics can changeing - particularly in its chemical properties and their behaviors. it Reinjection can causeing the scaling, or the water to become more reactive. In Massive ammmount of water flow rate was reinjected to an aquifer at a high flow rate can became result in a thermal breakthrough to the goethermal system, and sometimes can killing the surface manifestations (NOTE: proofreading this paragraph required a particularly high amount of interpretation on my part, which may have changed the meaning of the words. Please check this paragraph with particular care).

Table 6 sample reinjection well at Rotorua

　Classification Well Reinjection wells.

Well Number RR 1011 RR 680 RR 1050 RR 1059 RR 447-1,2 1054

Quantity/Rate 　　　　　　

max Flow rate (ton/day) 165 310 60 　 2 206

Average injection Temp (oC) 　158 136　 95.5 84 44 40

Pressure/WHP (kPa.g) 　- 330 140 -　 -　 -　

Drilling Method

date drilled -　01-Mar-

74-　 -　 -　 27-Mar-02

Bore depth (m) 115 139 -　 136 shallow 155

Casing depth (m) 90 92 -　 125 -　 130

Casing diameter (mm) 100 100 100 　 -　 100

17

Documents review, signed off by Authorities.

Preparation for Well Testing

Well data

Contractor

Local Authorities

Equipment and Tolls calibrated

Calibration certificates

Well test safetyProcedure

List Equipment

Consent Owner

Well testing execution

Contractors

Local Authorities

Equipment set-up inspection

Data record measurements

Consent Owner

Documents review

Chemical samples

Archives: Hard &E- File


Post Measurements

Technical Authorities

Data Processing and out put

Consent Owner

Documents review

Archives: Hard &E- File


4 Well testing for geothermal direct use.

The main puroposes of well testing and measurement is to determine the wells

characteristics, of wells and the wells’ amount of production well capability.

The results of the activities will beare used to interpret the condition of the

geothermal reservoir, and as a basis for the next decisions and policies for

relating to the ed with sustainability of the resource and the environment

aspect inof the geothermal areas.

Figure 11 latter stages of well testing delivery process for geothermal well direct use application

There Following are techniques to for measuringe geothermal well with

regarding with to the main objective purpose stated in the paragraph aboveof

measurement:.

[4.1] Injectionvity fall-off test.

a. Injection well with cold water

The geothermal well for direct use, it can take in 4-5 hours at constant

flow rate of injection. At that time the well was considered enough

quenching the well. (This does not make sense)

[b.] Injection fall fall-off test

The sequence after conduct injection test is The pressure falloff test is

conducted after the injection test, , which is the well enough to 18

quenching after injection test with cold water and then warming up

after stopped injection of cold water. At this stage, the water level of

well decreasing and follow by pressure drawdown, which it can be

indicated the permeability of the well (This does not make sense).

Figure 12 injection falloff test plotting curve

b.[c.] Determine injectivity

The technique to predict a geothermal well’s production rate from a geothermal well is measure injectivity (J) measurement. With the constants injection usually quoted with flow range which it can be change with higher flow rate or often longer times during injectivity test (this sentence does not make sense). Injectivity tests areis conducted by varyingiation of the injection pressure (p) with and changing the injection flow rate (Q)

J= ΔQΔp…………………..¿

Where : J = Injectivity (ton/hr/bar)

ΔQ = Injection flow rate (ton/hr)

ΔP = Injection pressure (bar)

c.[d.] Interpreting data record and analysis

When the falloff pressure declines, it will should be followed by

measuring and recording the well’s water level at the well after shut in

injection cold water in real time. The differences of water level at well

can indicate the declining of hydrostatic pressure in interval time.

Applying the hydrostatic pressure equation, it can determine the

declining pressure of water level at the difference water level.

Analyzing permeability can be used semi log plot method. There are

19

tc

four type semi log plot :

Miller Dyes Hutchinson (MDH) Plot

Pressure vs log Δt

Horner Plot

Pressure vs log (tc+ Δt)/ Δt

Agarwal Time Plot

Superposition Time Plot

Because in injectivity test used only for a falloff preceded by a constant

rate injection period, so Semi log plot method with horner plot will be

selected in this case for geothermal direct used application.

Determining the horner time uses equation below and plot the

pressure with log horner:

Horner time=tc+∆ t∆ t

Where : tc = circulating time (second)

∆ t = delta time (second)

The curve of plotting Log horner time with Pressure can be analyzed by

finding the slope value in part of semilog curve. Determining slope

value at semi log curve can be selected at the uniform line curve.

1.000 1.500 2.000 2.500 3.000 3.500 3000

3200

3400

3600

3800

4000

4200

Log time (sec)

Pres

sure

(Pa)

Figure 13 Semilog practical aspect in determining SloOverall in order

conduct the injectivity falloff test, there are considerations should be

manage and prepare before Operational testing:20

Not Uniform part of curve

Uniform part of curve

Y = mx + C

DrainGeothermal

Well

Injection waterTanks

P WHP

Injection pump

Flow Meter

– Surface facility constraints, which related with the capacity

of injection water and the adequate waste storage or

drainage system.

– Offset well considerations

– Recordkeeping, it is maintain an accurate record of

injection rates and real time record

– Well calibrated and condition of instrumentation and

pressure gauge

Below the standard schematic diagram for set up injection falloff test

Figure 14 simple injection falloff test well head set-up

Based on the sample well on Rotorua, which the main proposes is for

commercial direct use application, therefore the injection falloff test

can be came optional when conducting well testing and

measurement. The reason is the formation condition of reservoir in

this place has similarity and has common characteristic. As a result

the objective of this test had been known and don not have change

in several year.

4.1[4.2] Temperature profile measurements

The temperature profile of shallow well can be conducted by simple tolls,

such us downholedown-hole thermometer/thermocouple with a string

cable complete with meter scale.

By running the thermometer as long as the depth of well, it can be record

21

the temperature in each meter depth. From the record data of

temperature can be plotted at a graphic temperature versus depth.

Figure 15 Example of plotting Temperature profiles (Steinsa et al, 2012)

Regarding the temperature profile, it can be interpreted the formation of

permeable and feed zone at the reservoir.

4.2[4.3] Flow rate measurement (output discharge) test

4.2.1[4.3.1] Vertical discharge

Measuring flow rate geothermal well can be done by vertical

discharge method, especially for self discharge well and/or which

has two phase fluid. This method called with the lip pressure

method (James, 1965). The Method of flow measurement is used a

pipe with small hole of 6 mm diameter at 6 mm below the pipe lip

where the pressure is measured. This technique of measurement is

used in an empirical correlation to calculated flow rate. But for the

vertical discharge measurements should be consider the enthalpy of

fluid based on the fluid enthalpy at the main zone temperature

(Helbig & Zarrouck, 2012). Therefore determining the mass flow rate

can be described with Russell James formula:

¿¿¿

Where: m = mass flow rate (kg/s)

22

P WHP

Discharge toAtmosphere

Drain

Cold waterSupply

Calorimeter Tank

V1 ; T1

V0 ; T0

3-WayValve

GeothermalWell

Cold water

Mixing water

h = Enthalpy of the discharge fluid (kJ/kg)

A = Lip pressure pipe cross sectional area (m2)

P = lip pressure (kPa.abs)

Regarding the range nominal size diameter of geothermal well on

this study is the maximum 150 mm (6 inch) which the vertical

discharge can be done for minimum nominal size diameter is 8 inch,

therefore samples geothermal well on this study cannot done

measure flow rate by vertical discharge.

4.2.2[4.3.2] Total flow Calorimeter

As cited in Helbig & Zarrouck, 2012, the total flow calorimeter is

common used in direct used geothermal well with the maximum

flow rate 10 kg/s and the maximum enthalpy 950 kJ/kg (Sitonen,

1986).

Figure 16 As cited in Helbig & Zarrouck, 2012, Schematic diagram

calorimeter set-up (modified from Sitonen, 1986)

The disadvantages of this method are required mobilization and

demobilization the mountain truck calorimeter. An others

disadvantages are:

Heat may be lost from the sides of tank to the air

The limitation size of the Tank because the tank should be in

23

Wellhead Pressure(Bar.g)

Flow rate (ton/hr)m2 m1

P2Trend line curve

Plotting dataP1

transportable

Water may splash out of the tank because of flow

Steam may be lost from the tank

The size of piping from the well may effected flow rate.

Over all even the total flow calorimeter has several disadvantages,

but this method is the adequate way to measure flow rate of self

discharge geothermal well for direct use application.

The result of measurement with this method, there are data of flow

rate in several pressure at the wellhead. Based on this data flow rate

and wellhead pressure, it can be plot as curve characteristic the well

regarding with different pressure.

Figure 17 typical flow rate Vs wellhead pressure as a result total flow rate

calorimeter measurement

4.2.3[4.3.3] Plotting pump performance curve.

Conducting well test and measurements, especially for production

capability; it can use the existing downholedown-hole pump.

If there is a figure of centrifugal pump performance curve, it can easy

to determine the production flow rate based on the well head

pressure.

By plotting wellhead pressure in the Centrifugal Pump Performance

24

Mass Flow rate (kg/sec)

(kPa)Head Pressure

Qm1

P1

pressure versus flow rate, we can determine the figure of flow rate.

Figure 18 Example Characteristic of pump performance in

constant speed and fixed diameter of pump impeller

4.2.4[4.3.4] Count filing time with bucket and stopwatch

By small water vessel complete with volume scale and stop watch to

measure time. Those can measure the flow rate from low production

well, which on this study sample is Timothy’s house with their air

liftair-lift discharge geothermal well. When the well discharging, by

small measured vessel and count the time when filling the vessel, it

can determine the flow rate of air liftair-lift discharge well.

4.2.5[4.3.5] Weir Box measurements

Measurement flow rate by weir box is simple method and has good

accuracy. Installing weir box at the discharge well is common in

geothermal fluid flow. There are so many type of weir box type

based on the shape on discharge side.

Regarding different type of shape, also have different approach to

determine the flow rate, below same equation to determine flow

25

Rectangular weir90o – V notch weirSuppressed weir

b

h h h

rate in each type weir box:

– Rectangular weir mw=6000 x b xh1.5

– 90o – V notch weir mw=4720 xh2.5

– Suppressed weir mw=6290 x b xh1.5

(Simplified for water at 98oC)

Figure 19 Ttypical weir box with several type of discharge shape side

There are considerations when measuring the flow rate with weird

box:

- The weir box should be design and manufactured in standard

design

- The portable weir box installed in vertical and stable condition

- The cleanness of weir box should be consider

- There is density correction when the density at the weird box

and density at the measuring point are different.

hweirbox=hmeasuredρmeasuredρwirbox

4.3[4.4] Geothermal fluid Chemical sample test.

Taking sample fluid of geothermal well is one key to monitor

characteristic of chemistry fluid from reservoir. Based on the chemical

properties geothermal fluid including with gasses and solid dissolved,

it can determine its behavior in different temperature and pressure.

Therefore laboratories analysis is key point to determine chemical

properties of geothermal fluid from the production well and fluid

before injected to the reservoir.

Monitoring survey of chemical properties by taking sample of

26

geothermal well can be conducted minimum in one times in one year

geothermal production time.

4.4[4.5] Casing condition Survey

The production casing string in a geothermal well is the primary

conductor of the geothermal production fluids from the formation to

the surface and is thus subject to extreme conditions both from

thermally induced stress conditions and from continuous exposure to

formation fluids both internally and externally (Hole, 2008).

Therefore, The production casing condition should be surveyed in

periodically time to monitor the well capability and to make sure the

safety condition of well. There are some problem occure in

production casing during their operation such as, scaling, thermal

deformation, internal and external corotion.

Running downholedown-hole measurement, mechanical caliper is one

way to measure thecondition of inner diameter of casing geothermal

well. Regarding with limitation of size mechanical caliper, which the

smallest size diameter of mechanical caliper is 4 inch, as a result the

geothermal which have smaller than 4 inch cannot running

mechanical caliper to survey the condition of inner casing of well.

5 Methodology well testing and measurements in each classification of wells

On this study will be gave the several techniques in well testing and

measurement, which the testing was adjusted for direct used geothermal

well in Rotorua according with the sample data well. It was categorized in

several well depend on the well’s characteristic and resources of geothermal

energy.

5.1 Self discharge wells

In order to measure and assess self discharge geothermal well

especially for production capability, it can adopted from methodology 27

Temperature Vs Depth

InjectivityPressure profile (Pressure Vs Depth)Semi log chartPermeability thickness

Specific Enthalpy discharge fluidWell head pressure (WHP)Mass flow rate in every WHPMass flow rate Vs WHP chart

Laboratory analysisChemical properties of fluid report

Preparation

Production output (flow rate) test Vertical Discharge test, orTotal flow calorimeter testGeo. fluid chemical sample testMinimum 1time in a year

Record data base in E-file and hard copyAnalyzing and interpreting resultFinal Report

Temperature Profile Measurement

in standard measurement and well test for geothermal well for power

generation.This is because the well has similarity in self discharge.

There sequence in measurement self discharge geothermal well for

direct used application:

5.1.1 Injectivity falloff test (Optional test)

5.1.2 Temperature profile measurements.

5.1.3 Flow rate measurement

5.1.3.1 Vertical discharge (depend on the wellbore size, the

minimum is 6 Inch)

5.1.3.2 Total flow Calorimeter

5.1.4 Geothermal fluid Chemical sample test

On this stage was recommended to conduct one time in a single

year production period.

5.1.5 Casing condition survey(Optional)

Figure 20 Flowchart sequences in self discharge well testing and measurement

28

[5.2] DownholeDown-hole Pump (DHP) Wells

In order well test and measuring Geothermal well for direct used which

utilizing DHP to extract hot water is different with self discharge well.

The methodology for this type well still has similarity with self

discharging well, but need adjustment in output production testing.

Because the type of this well utilize downholedown-hole pump, so in

order to measure temperature profile and conducting injectivity falloff

test, the complete set of downholedown-hole pump and its accessories

should be pulled out from the well.

After conducting the both of test, the downholedown-hole pump set can

be installed If the well to conduct flow rate measurement and taking fluid

sample.

Below list sequences of well testing for downholedown-hole pump

geothermal well:

5.1.6[5.2.1] Injectivity falloff test (Optional)

5.1.7[5.2.2] Temperature profile measurements.

5.1.8[5.2.3] Flow rate measurement

It can be plotting wellhead pressure at pump performance curve

to determine the flow rate.

5.1.9[5.2.4] Geothermal fluid Chemical sample test

It is conducted minimum one time in one year.

29



Preparation

I n j e c ti v it y F a ll o ff T e s t ( O p ti o n a l) 4 - 5 h o u r i n j e c ti o n w a t e r i n c o n s t a n t fl o w r a t e S h u t i n i n j e c ti o n f o ll o w b y f a ll o ff t e s t M e a s u r e d e c li n i n g o f w a t e r l e v e l i n r e a l ti m e P r e s s u r e p r o fi l e m e a s u r e m e n t

Geo. fluid chemical sample testOne time in a year




Figure 21Flowchart sequences in downholedown-hole pump well testing and

measurement

[5.3] Air liftAir-lifts discharge wells.

Based on the sample geothermal well at Rotorua which using air liftair-lift

to extract hot water, most of them have lower production rate rather

than the other type. It is because the air liftair-lift well has limitation in

pull out the water with pressurizing air in vertical pipe.

Well testing for airliftair-lift geothermal well basically has not difference

with well test and measuring in downholedown-hole pump geothermal

well. The sequences for this type well are:

5.1.10[5.3.1] Injectivity falloff test (Optional)

5.1.11[5.3.2] Temperature profile measurements.

5.1.12[5.3.3] Flow rate measurement.

Regarding the flow rate of air liftair-lift discharge well is lower and

small, therefore in measuring flow rate of production it can be

conducted by:

- Bucket water and count filing time.

30



Well DataCalibrated instrumentation an checked tools Set-up tolls and equipments

G e o . fl u i d c h e m i c a l s a m p l e t e s t O n e ti m e i n a y e a r



Injectivity Falloff Test (Optional)4-5 hour injection water in constant flow rateShut in injection follow by falloff testMeasure declining of water level in real timePressure profile measurement

- Measuring water level at the weir box

5.1.13[5.3.4] Geothermal fluid Chemical sample test one time in a year

Figure 22 Flowchart sequences in air liftair-lift well testing and measurement

[5.4] DownholeDown-hole Heat Exchanger(DHE) wells

Methodology well testing and measuring on this well can be applied the

well testing at non self discharging geothermal well for direct used. But

because the wells not discharge the geothermal well, therefore

production output test cannot conduct.

There are steps for well testing are:

5.1.14[5.4.1] Injectivity falloff test(Optional)

5.1.15[5.4.2] Temperature profile measurement

5.1.16[5.4.3] Geothermal fluid Chemical sample test.

5.1.17[5.4.4] Casing condition Survey

At this stage, it is also checking the condition casing of borehole

and the external condition of downholedown-hole heat exchanger

tube.

31




Preparation

Well DataList calibrated Tool & EquipmentsSet-up tolls and equipments


Injectivity Falloff Test(Optional)4-5 hour injection water in constant flow rateShut in injection follow by falloff testMeasure declining of water level in real timePressure profile measurement

Geo. fluid chemical sample test one time in a year

Record data baseAnalyzing and interpreting resultFinal Report

Figure 23Flowchart sequences in DHE well testing and measurement

5.2[5.5] Reinjection wells.

As mention before about the reinjection well, basically function of the

well is to dispose the geothermal fluid after used and transferred its heat

for heating system or domestic proposes.

The reinjection well testing and measuring is also important in order to

manage and monitor condition of reservoir.

Below the methodology to testing and measure:

5.2.1[5.5.1] Injectivity falloff test(Optional)

5.2.2[5.5.2] Measurement of temperature profile

5.2.3[5.5.3] Casing condition Survey.

5.2.4[5.5.4] Geothermal fluid Chemical sample test

Taking sample fluid before injection to the well is key point to obtain

the accurate condition of fluid properties. The geothermal fluid from

the production wells and fluid which expect to dispose in reinjection

well have differences. Therefore considering the differences, taking

sample fluid before injected to reinjection well also gives the great

advantages.

The differences of characteristic fluid which will be injected to

reinjection well because of:32


Preparation

Well DataList calibrated Tool & EquipmentsSet-up tolls and equipments

G e o . fl u i d c h e m i c a l s a m p l e t e s t o n e ti m e i n a y e a r

R e c o r d d a t a b a s e A n a l y z i n g a n d i n t e r p r e ti n g r e s u lt F i n a l R e p o r t

Diameter Well logging data

Condition casing survey (Optional)


Injectivity Falloff Test (Optional)4-5 hour injection water in constant flow rateShut in injection follow by falloff testMeasure declining of water level in real timePressure profile measurement

The difference temperature of fluid

The geothermal fluid was introduced with air for air liftair-lift

discharge well

The geothermal fluid mixed with the other fluid in processing

for heating system or for mineral pool.

Geothermal fluid was contacted with other materials; it could

be carrying out the chemical properties troughthe fluid before

injected to reinjection well.

Over all the differences of fluid should be monitor and manage due

to introduce the new chemical to the reservoir can give significant

breakthrough to the reservoir and the environment surrounding. The

recommende taking saple of geothermal fluid is minimum one time

in a year

Figure 24 Flowchart sequences in reinjection well testing and measurement

5.3[5.6] Hot Spring takes and discharge.

Utilizing Hot spring for direct used basically do not required a well, and

also reinjection well. In order to dispose hot water after used, it can be

discharged to the stream. Therefore methodology measurement and

testing absolutely have different with the others.33

Temperature fluid data

Discharge pump pressure Mass flow rate in every pressure discharge


Preparation

List calibrated Tool & EquipmentsSet-up tolls and equipments

Temperature Measurement

Production output (flow rate) test Plot the Pressure in pump performance curve

Geo. fluid chemical sample test one time in a year


Below sequences testing and measuring production for Hot spring take

and discharge for direct use:

5.3.1[5.6.1] Measure temperature at the surface of Hot spring

5.3.2[5.6.2] Flow rate measurement.

Measuring production capacity in taking hot spring for direct use

can used the existing pump, which the pump used to lift

geothermal water from hot springs.

The methodology at this stage has similarity in measure flow rate at

geothermal well with downholedown-hole pump to extract the hot

water from the well.

Thus by plotting the discharge pressure in pump performance

curve, it can be determined the flow rate of the pump in extracted

hot water spring.

5.3.3[5.6.3] Geothermal fluid Chemical sample test one time in a year

Figure 25Testing and measurement flowchart for hot spring take and discharge

6 Conclusion

Regarding the well testing and measurement for the direct used geothermal

well in Rotorua, which each type well have different stages in testing, the

following table is the summary stages and methodology in each well: 34

Table 7 Summary stages of measurement in each type of well

Self

discharge

wells

DownholeDown-

hole Pump (DHP)

Well

Air liftAir-

lifts

discharge

wells

DownholeDown-

hole Heat

Exchanger wells

Reinjecti

on wells

Spring

take

and

discharg

e

Injectivity falloff test. Optional Optional Optional Optional Optional No

Temperature profile

measurementsYes Yes Yes Yes Yes Yes

Flow rate measurement

(output discharge) testYes Yes Yes Yes No Yes

Vertical discharge Yes1 No No No No No

Total flow Calorimeter Yes No No No No No

weir box No No Yes No No No

Bucket and stopwatch No No Yes No No No

Existing pump

performance curveNo Yes No Yes No Yes

Geothermal fluid

Chemical sample test2.Yes Yes Yes Yes Yes Yes

Casing condition Survey

with Mechanical Caliper

Optional Optional Optional Optional Optional Optional

Over all methodology of testing in each well is depending with the

characteristic of the wells. The objective of the methodology well testing and

measurement in each type of well is to measure the production capacity and

estimate the capability of the well by conduct the testing to estimate well

condition and productivity. The result of the analysis record data can be used

to monitor and manage the geothermal resource in Rotorua, especially for

direct use geothermal application.

Another important key for measurement and well test methodology will give

the standard well testing for the regulator, in this case is BoPRC, in order

conduct well test for new concession or re-new concession for geothermal

direct used in their area.

1 depend on size diameter of borehole2 Minimum one time in a year

35

Acknowledgements.

We would like to thank:

The Bay of Plenty Regional Council for the data provided, and ;

especially in particular Miriam Robertson and, Janine Bbarber for their

support, time and help.

The consent holders which forwho gave both their time, and chance

the opportunity to visit their geothermal well facilities; Garry at the,

Alpin <motel; Peter Brownbridge of, Rotorua District Council;

Maureen Gray at the, Holiday Inn Rotorua; and Timothy Richard.

Many thanks also to Ridwan Febrianto, which who give gave his time

and preparing the trip at around Whakatane, Rotorua and Taupo.

References.

Aksoy, N. (2007). Optimization of downholedown-hole pump setting depths in liquid-dominated geothermal systems: A case study on the Balcova-Narlidere field, Turkey. Geothermics 36 , 436–458.

DiPippo, R. (2008). Geothermal Power Plants : Principles, Applications, Case Studies and Environmental Impact (2nd edition ed.). London: Butterworth-Heinemann.

Drew, S. R. (1988). Direct-Use Projects Equipment and Controls. Geothermics , XVII, 141-171.

Environment, B. R. (2005). Rotorua Geothermal Field Management Monitoring Update: 2005. Whakatane: Bay of Plenty Regional Council.

Grant, M. A., & Bixley, P. F. (2011). Geothermal reservoir engineering (2nd edition ed.). Burlington: Elsevier.

Helbig, S., & Zarrouck, S. J. (2012). Measuring two-phase flow in geothermal pipelines using dharp edge orifice plates. Geothermic 44 , 52-64.

Hole, H. (2008). Geothermal Well Completion Tests. Workshop #26 , 1-5.Lund, J. W. (2003). The use of downholedown-hole heat exchangers. Geothermics

32 , 535-543.Narasimhan, T., & Witherspoon, P. (1979). Geothermal Well Testing. Journal of

Hydrology , 537-553.Steinsa, C., Bloomerb, A., & Zarrouk, S. J. (2012). Improving the performance of the

down-hole heat exchanger at the Alpine Motel, Rotorua, New Zealand. Geothermics 44 , 1-12.

Thain, I., Reyes, A., & Hunt, T. (2006). A Practical Guide to Exploiting Low Temperature Geothermal Resources. Lower Hutt, NZ: Institute of Geological and Nuclear Sciences Limited.

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geothermal well

Technology