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POSIVA OY

FI-27160 OLKILUOTO, FINLAND

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Jari Pöl länen

Petri Heikkinen

Anne Lehtinen

July 2012

Working Report 2012-13

Difference Flow Measurements in Greenland,Drillhole DH-GAP04 in July 2011

July 2012

Working Reports contain information on work in progress

or pending completion.

The conclusions and viewpoints presented in the report

are those of author(s) and do not necessarily

coincide with those of Posiva.

Jari Pöl länen

Petri Heikkinen

Pöyry Finland Oy

Anne Lehtinen

Posiva Oy

Working Report 2012-13

Difference Flow Measurements in Greenland,Drillhole DH-GAP04 in July 2011

Base maps: ©National Land Survey, permission 41/MML/12

DIFFERENCE FLOW MEASUREMENTS IN GREENLAND, DRILLHOLE DH-GAP04 IN JULY 2011 ABSTRACT To improve the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository of spent nuclear fuel, the Greenland Analogue Project (GAP) has been initiated collaboratively by SKB, Posiva and NWMO. The study site encompasses a land terminus portion of the Greenland ice sheet, east of Kangerlussuaq, and is in many ways considered to be an appropriate analogue of the conditions that are expected to prevail in much of Canada and Fennoscandia during future glacial cycles. The project began in 2009 and is scheduled for completion in 2012. In 2011, deep drillhole DH-GAP04 was drilled at the study site and Posiva Flow Log measurements were carried out in the drillhole. The Posiva Flow Log, Difference Flow Method (PFL DIFF) uses a flowmeter that incorporates a flow guide and can be used for relatively quick determinations of transmissivity and hydraulic head in fractures/fractured zones in cored drillholes. The aim of the measurements was to find high transmissive fractures, which would define the target for water sampling, i.e. the location for the packers in the drillhole. This report presents the principles of the method and the results of measurements carried out in drillhole DH-GAP04 in July 2011. The length of the flow guide in the flow logging measurements was 10 m (section length). Flow into the drillhole or from the drillhole to the bedrock was measured within the section length. The measurements were carried out in both pumped and natural (i.e. un-pumped) conditions. Calculations of the transmissivity (T) and the hydraulic head (h) of the fractures are shown in the results. Measurements were carried out in drillhole length interval 184 – 675 m without pumping. During pumping, measurements were conducted in drillhole length interval 274 – 675 m due to permafrost condition above this level. The risk for the drillhole freezing over in the permafrost area was remarkable. Due to lack of time, the upper part of the drillhole was not measured. The device used also includes a sensor for single point resistance (SPR). SPR was measured in connection with the flow measurements. The electric conductivity (EC) and temperature of the drillhole water were measured as well. Keywords: Greenland, groundwater, flow, measurement, bedrock, drillhole, single point resistance, electrical conductivity, Posiva Flow Log, permafrost.

POSIVA FLOW LOG -MITTAUKSET VIRTAUSEROMITTTAUS-MENETELMÄLLÄ KAIRAREIÄSSÄ DH-GAP04 GRÖNLANNISSA HEINÄKUUSSA 2011 TIIVISTELMÄ Vuonna 2009 Posiva Oy, Svensk kärnbränslehantering Ab (SKB) ja Nuclear Waste Management Organisation (NWMO) Kanadasta aloittivat neljävuotisen tutkimus-ohjelman, Grönlannin Analogia Projekti (GAP) -tutkimuksen Kangerlussuaqissa, Länsi-Grönlannissa. Projektin tarkoituksena on lisätä tietoa jääkauden ja etenkin manner-jäätikön vaikutuksista geologisen loppusijoituksen pitkäaikaisturvallisuuteen. Tutkimus-alue sijaitsee Kangerlussuaqin itäpuolella mannerjäätiköllä ja sen reunan läheisyydessä. Alue soveltuu geologisesti hyvin analogiaksi niin Suomen kuin Ruotsin loppusijoi-tusalueille sekä mahdollisesti myös Kanadalaisten tulevalle alueelle. Vuonna 2011 mannerjäätikön reunan läheisyydessä sijaitsevalle tutkimusalueelle kairat-tiin syvä kairanreikä DH-GAP04 jossa tehtiin Posiva Flow Log -mittaus virtausero-mittausmenetelmällä. Posiva Flow Log -virtauseromittausmenetelmää (PFL DIFF) voi-daan käyttää suhteellisen nopeaan vedenjohtavuuksien ja virtauspaineiden määrittämi-seen raoista tai rakovyöhykkeistä tutkittavissa kairarei’issä. Mittausten tarkoituksena oli löytää kairanreiästä korkean transmissiviteetin omaavat rakovyöhykkeet ja niiden perus-teella määrittää vesinäytteenottopaikat sekä näytteenottolaitteiston tulppien paikat. Tässä raportissa esitetään mittausperiaatteet ja tulokset mittauksista, jotka tehtiin kaira-reiässä DH-GAP04. Virtausmittauksessa käytettiin 10 m mittausväliä. Mittausväleiltä mitattiin veden virtaus reikään tai reiästä kallioon. Tämä tehtiin sekä pumppauksen aikana että luonnontilassa (pumppaamatta). Tuloksiin on laskettu rakojen transmissivi-teetit (T) ja paineet (hfw). Luonnontilassa mitattiin syvyysväli 184 – 675 m. Pump-pauksen aikana mitattiin syvyysväli 274 – 675 m johtuen tämän yläpuolella alkavasta ikiroudasta. Riski siitä, että reikä jäätyy umpeen ikiroutavyöhykkeellä oli merkittävä ja tästäjohtuvat ajan puutteen vuoksi reiän yläosaa ei mitattu.

Laite sisältää myös maadoitusvastusanturin (single point resistance, SPR). SPR:ää mitattiin aina virtausmittauksen yhteydessä. Myös reikäveden sähkönjohtavuus (EC) ja lämpötila mitattiin. Avainsanat: Grönlanti, pohjavesi, virtaus, mittaus, peruskallio, kairareikä, maadoitus-vastus, sähkönjohtavuus, Posiva Flow Log, ikirouta.

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TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ

1 INTRODUCTION .................................................................................................... 2

2 PRINCIPLES OF OPERATION .............................................................................. 5

3 INTERPRETATION .............................................................................................. 10

3.1 Hydraulic head ..................................................................................................... 10

3.2 Transmissivity and hydraulic head ....................................................................... 10

4 EQUIPMENT SPECIFICATIONS ......................................................................... 13

5 EXECUTION OF MEASUREMENTS ................................................................... 15

6 RESULTS ............................................................................................................. 16

6.1 Flow logging and single point resistance (SPR) ................................................... 16

6.2 Flow rate, transmissivity and hydraulic head in fractures ..................................... 16

6.3 Flow: Theoretical and practical measurements limits .......................................... 17

6.4 Hydraulic head, water level, air pressure and pumping rate ................................ 18

6.5 Drillhole water: electrical conductivity and temperature ....................................... 18

6.6 Comments on the results ..................................................................................... 18

7 SUMMARY ........................................................................................................... 19

REFERENCES ............................................................................................................. 20 APPENDICES Appendices 1.1 – 1.11 Flow rate and single point resistance Appendix 2 Transmissivity and head of detected fractures Appendix 3 Table of transmissivity and head of detected fractures Appendix 4 Hydraulic head in the drillhole Appendix 5 Air pressure, water level in the drillhole and pumping rate during flow logging Appendix 6 Electrical conductivity of drillhole water Appendix 7 Temperature of drillhole water

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1 INTRODUCTION

A deep geological repository for spent nuclear fuel needs to be designed to keep spent nuclear fuel isolated from mankind and the environment for hundreds of thousands of years. Within this time frame, glaciated period(s) are expected to occur and the effects of the glaciation cycles on a deep geological repository need to be evaluated during the site investigation process. To advance the understanding of processes associated with glaciation and their impact on the long-term performance of a deep geological repository, the Greenland Analogue Project (GAP) has been initiated. As a part of GAP, Posiva Flow Log (PFL) was used in drillhole DH-GAP04 in July 2011 in the Kangerlussuaq area, West Greenland. The location of the drillhole is shown in Figure 1-1. A carefully designed and fast measuring programme was carried out due to permafrost condition in the area. The aim of the measurements was to find high transmissive fractures, which would define the place for water sampling, i.e. the location for the packers in the drillhole. Detailed information and the drilling, heating and measuring schedule of DH-GAP04 is presented in Table 1-1. In permafrost-free areas, PFL measurements are in a new drillhole normally conducted a week after the end of drilling in order to let the groundwater situation to recover in the drillhole. However, in the case of DH-GAP04, the investigation and equipment installation schedule was tight due to the freezing of drillhole water as a result of the presence of permafrost (Table 1-1). The field work was conducted by Petri Heikkinen (Pöyry Finland Oy) and Juha Taskinen (Posiva Oy) and the subsequent data interpretation by Pöyry Finland Oy. The section length was 10 m in the flow logging measurements. Flow into the drillhole or from the drillhole to the bedrock was measured within the section length and carried out in both pumped and natural (i.e. un-pumped) conditions. Calculations of the transmissivity (T) and the hydraulic head (hf) of the fractures are shown in the results. Measurements were carried out in drillhole length interval 184 – 675 m without pumping. During pumping, measurements were carried out in drillhole length interval 274 – 675 m due to permafrost condition above this level. The risk for the drillhole freezing over in the permafrost area was remarkable. Due to lack of time, the upper part of the drillhole was not measured. The device used also includes a sensor for single point resistance (SPR). SPR was measured in connection with flow measurements. The EC (electric conductivity) and temperature of the drillhole water were measured as well.

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Table 1-1. Detailed information on DH-GAP04.

DH‐GAP04

coordinate system UTM/D_WGS84

Northing (WGS84) 74.49004

Easting (WGS84) 54.0732

Elevation 525.66*

Length 687 m

Dip 70

Drilling 18‐28.6.2011

Deviation measurement 29.6.2011

Heating of the drillhole 29.6.‐1.7.2011

Posiva Flow Log measurements 1‐2.7.2011

*Ground surface, ellipsoidal elevation

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Figure 1-1. Location of the investigation site on the west coast of Greenland.

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2 PRINCIPLES OF OPERATION

Unlike conventional drillhole flowmeters, which measure the total cumulative flow rate along the drillhole, the PFL DIFF probe measures the flow rate into or out of defined drillhole sections. The advantage gained by measuring the flow rate in isolated sections is improved detection of incremental changes in flow along the drillhole. As these are generally very small, they can easily be missed when using conventional flowmeters. Rubber sealing disks located at the top and bottom of the probe are used to isolate the flow of water in the test section from flow in the rest of the drillhole, see Figure 2-1. Flow inside the test section is directed through the flow sensor. Flow along the drillhole is directed around the test section by means of a bypass pipe and discharged at either the upper or lower end of the probe. The entire structure is called the flow guide. Generally two separate measurements with two different section lengths (e.g. 2 m and 0.5 m) are used. In this case, only a 10 m setup was used due to the presence of permafrost, which gave a short time window to conduct the PFL measurements. Flow rates into or out of the test section are monitored using thermistors, which track both the dilution (cooling) of the thermal pulse and its transfer by the moving water. The thermal dilution method is used for measuring flow rates because it is faster than the thermal pulse method, and the latter is only used to determine the flow direction within a given time frame. Both methods are used simultaneously at each measurement location. In addition to incremental changes in flow, the PFL DIFF probe can also be used to measure: The electrical conductivity (EC) of both drillhole water and fracture-specific water.

The electrode used in EC measurements is located at the top of the flow sensor, see Figure 2-1.

The single point resistance (SPR) of the drillhole wall (grounding resistance). The electrode used for SPR measurements is located between the uppermost rubber sealing disks, see Figure 2-1, and used for high-resolution length determination of fractures and geological structures.

The prevailing water pressure profile in the drillhole. Located inside the watertight electronics assembly, the pressure sensor transducer is connected to the drillhole water through a tube, see Figure 2-2.

The temperature of the water in the drillhole. The temperature sensor is part of the flow sensor, see Figure 2-1.

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WinchPumpComputer

Flow along the borehole

Rubberdisks

Flow sensor-Temperature sensor is located in the flow sensor

Single point resistance electrode

EC electrode

Measured flow

Figure 2-1. Schematic of the probe used in PFL DIFF.

FLOW TO BE MEASURED

FLOW ALONG THE BOREHOLE

RUBBERDISKS

FLOW SENSOR

PRESSURE SENSOR (INSIDE THE ELECTRONICSTUBE)

CABLE

Figure 2-2. The absolute pressure sensor is located inside the electronics assembly and connected to the drillhole water through a tube.

PRESSURE SENSOR (INSIDE THE ELECTRONICS ASSEMBLY)

Flow along the drillhole

FLOW ALONG THE DRILLHOLE

RUBBER SEALING DISKS

Rubber sealing disks

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The principles behind PFL DIFF flow measurements are shown in Figure 2-3. The flow sensor consists of three thermistors (Figure 2-3 a). The central thermistor, A, is used both as a heating element and to register temperature changes (Figures 2-3 b and c). The side thermistors, B1 and B2, serve as detectors of the moving thermal pulse caused by the heating of A. Flow rate is measured by monitoring heat transients after constant-power heating of thermistor A. The measurement begins with constant-power (P1) heating. After the power is cut off, the flow rate is measured by monitoring transient thermal dilution (Figure 2-3 c). If the measured flow rate exceeds a certain limit, another constant-power heating (P2) period is started after which the flow rate is re-measured from the following heat transient. Flows are measured when the probe is at rest. After transferring the probe to a new position, a waiting period (which can be adjusted according to the prevailing circumstances) is allowed to elapse before the heat pulse (Figure 2-3 b) is applied. The measurement period after the constant-power thermal pulse (normally 100 s each time the probe has been moved a distance equal to the test section length and 10 s in every other location) can also be adjusted. The longer (100 s) measurement time is used to allow the direction of even the smallest measurable flows to be visible. The flow rate measurement range is 30 mL/h–300 000 mL/h. The lower limit of measurement for the thermal dilution method is the theoretical lowest measurable value. Depending on the conditions in the drillhole, these limits may not always prevail. Examples of possible disturbances include drilling debris entrained in the drillhole water, bubbles of gas in the water and high flow rates (some 30 L/min, i.e. 1 800 000 mL/h or more) along the drillhole. If the disturbances encountered are significant, the limits for practical measurements are calculated for each set of data.

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-5 0 5 10 15

0

50

100

150

200

Po

we

r (m

W)

AB1 B2

Flow sensor

Constant power in A

-5 0 5 10 15Time (s)

0

10

20

30

40

dT

(C)

Flow rate (mL/h)1020

3060

6090

13300

27700

57200

135000

297000

Thermal dilution methodTemperature change in A

P1

P2

a)

b)

c)

Figure 2-3. Flow rate measurement.

The top length reference point is at the top of the casing tube (length 0 m). The lower length reference point is situated in the PFL DIFF probe at the upper end of the test section. The length parameter in the results is the distance along the drillhole between these two reference points. When assessing the location of anomalies in the measured drillhole, there are always some errors. They can be caused by the following reasons:

1. The cable stretches under tension. When the probe is lifted upwards ca. 1000 m, tension can be ca. 175 kg. When it is lowered over the same drillhole length, the tension can be ca. 75 kg. This difference could cause a length difference of ca. 3 m between the measurements over a length of ca. 1000 m. The tension values

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here are estimates and can vary greatly depending on the device setup and hole properties. Length errors have been determined in drillholes where there are known length marks on the wall of the drillhole. The error has been approximately 1 m (before the length correction based on the length marks) over a length of ca. 1000 m.

2. If the length increment for flow measurement is x, a worst case length error of ± x can potentially occur for a fracture location.

3. The length of the test section is not exact. The specified section length denotes the distance between the nearest upper and lower rubber sealing disks. Effectively, the section length can be larger. At both ends of the test section, there are four rubber sealing disks. The distance between them is 5 cm. This will cause rounded flow anomalies: a flow may be detected already when a fracture is situated between the four rubber sealing disks. These phenomena can cause an error of ± 0.05 m when the short step length (0.1 m) is used. A similar error can occur when flow along the hole is measured.

The total error in the worst case can be estimated. In the worst case, all the errors are in the worst possible direction. With a 2 m point interval, the worst case error for a fracture location would be:

E = ±(2 + d·0.002)

where E (m) is the total estimated worst case error and d (m) is the drillhole length. Note that this is only a rough estimate and subject to change.

Fractures nearly parallel to the hole may also be problematic. The fracture location may be difficult to define accurately in such cases. In this case, the point interval during flow logging was 2 metres. Due to that, the worst case error of the fracture location is quite high. The length error can be decreased essentially if there are known depth marks on the drillhole wall that can be synchronized with the PFL DIFF log. A length mark can be an artificial widening of the drillhole diameter or they can be geological features seen in the drillcores and on the drillhole wall. Usually the Single Point Resistance (SPR) log in PFL DIFF is used for depth correlation. SPR is measured at 0.01 m point intervals. The depth correlation described above is not carried out for the results presented in this report.

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3 INTERPRETATION

3.1 Hydraulic head The absolute pressure sensor measures the sum of air pressure and hydrostatic pressure in the drillhole. Air pressure is also registered separately. Hydraulic head along the drillhole under natural and pumped conditions can be determined from the measured data. The air pressure recorded on the site is first subtracted from the absolute pressure measured by the pressure sensor and the hydraulic head can then be calculated. The hydraulic head (h) at a certain elevation z is calculated using the following expression:

h = (pabs - pb)/(ρ g) + z 3-1

where

h is the hydraulic head (masl)

pabs is absolute pressure (Pa)

pb is barometric (air) pressure (Pa)

ρ is unit density 1000 kg/m3

g is standard gravity 9.80665 m/s2 and

z is the elevation at the measurement location (masl)

An offset is subtracted from all absolute pressure results. Exact z-coordinates are important in hydraulic head calculation as a 10 cm error in the z-coordinate leads to a 10 cm error in the calculated head.

3.2 Transmissivity and hydraulic head The interpretation of data is based on Thiem’s or Dupuit’s formula, which describes a steady state and two-dimensional radial flow into the drillhole (Marsily 1986): hs – h = Q/(T·a) 3-2 where h is the hydraulic head in the vicinity of the drillhole and hs is the hydraulic head at the radius of influence (R), Q is the flow rate into the drillhole, T is the transmissivity of the test section,

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a is a constant that depends on the assumed flow geometry. For cylindrical flow, the constant a is: a = 2·/ln(R/r0) 3-3 where: r0 is the radius of the drillhole and R is the radius of influence, i.e. the zone inside which the effect of pumping is felt. If measurements of flow rate are carried out using two levels of hydraulic head in the drillhole, i.e. natural and pump-induced heads, then the undisturbed (natural) hydraulic head and the transmissivity of the drillhole sections tested can be calculated. Equation 3-2 can be reformulated in the following two ways: Qs0 = Ts·a·(hs- h0) 3-4 Qs1 = Ts·a·(hs- h1) 3-5 where: h0 and h1 are the hydraulic heads in the drillhole at the test level, Qs0 and Qs1 are the measured flow rates in the test section, Ts is the transmissivity of the test section and hs is the undisturbed hydraulic head in the tested zone far from the drillhole. In general, since very little is known about the flow geometry, cylindrical flow without skin zones is assumed. Cylindrical flow geometry is also justified because the drillhole is at a constant head, and no strong pressure gradients along the drillhole exist except at its ends. The radial distance R to the undisturbed hydraulic head hs is not known and must therefore be assumed. In this case, a value of 500 for the quotient R/r0 is selected. The hydraulic head and the transmissivity in the test section can be deduced from the two measurements: hs = (h0-b·h1)/(1-b) 3-6 Ts = (1/a) (Qs0-Qs1)/(h1-h0) 3-7 where: b = Qs0/Qs1

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The transmissivity (Tf) and hydraulic head (hf) of individual fractures can be calculated provided the flow rates at the individual fractures are known. Similar assumptions to those employed above must be used (a steady-state cylindrical flow regime without skin zones). hf = (h0-b·h1)/(1-b) 3-8 Tf = (1/a) (Qf0-Qf1)/(h1-h0) 3-9 where: Qf0 and Qf1 are the flow rates at a fracture and hf and Tf are the hydraulic head (far from the drillhole) and the transmissivity of the fracture, respectively. Since the actual flow geometry and any skin effects are unknown, transmissivity values should only be considered as an indication of the prevailing orders of magnitude. As the calculated hydraulic heads do not depend on geometrical properties but only on the ratio of the flows measured at different heads in the drillhole, they should be less sensitive to unknown fracture geometry. A discussion of potential uncertainties in the calculation of transmissivity and hydraulic head can be found elsewhere (Ludvigson et al. 2002).

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4 EQUIPMENT SPECIFICATIONS In the PFL DIFF method, the flow of groundwater into or out of a drillhole section is monitored using a flow guide, which employs rubber sealing disks to isolate any such flow from the flow of water along the drillhole. This flow guide defines the test section being measured without altering the hydraulic head. Groundwater flowing into or out of the test section is guided to the flow sensor, and flow is measured using the thermal pulse and thermal dilution methods. The measured values are transferred to a computer in digital form. The main parts and features of the equipment are listed in Table 4-1. Table 4-1. Equipment and features.

Part/Feature Description

Flowmeter PFL DIFF probe

Measurable drillhole diameters 56 mm, 66 mm and 76 mm (or larger)

Length of test section The flow guide length can be varied

Method of flow measurement Thermal pulse (direction) and thermal dilution (rate).

Additional measurements Temperature, Single-point resistance, Electrical conductivity of water, Water pressure

Winch Mount Sopris Wna 10, 0.55 kW, Steel wire cable 1500 m, four conductors, Gerhard -Owen cable head.

Drillhole length determination Based on a digital distance counter.

Logging computer PC (Windows XP or Windows 7)

Software Based on MS Visual Basic

Total power consumption 1.5 - 2.5 kW depending on the type of pump employed

The range and accuracy of the sensors used are shown in Table 4-2.

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Table 4-2. Range and accuracy of sensors.

Sensor Range Accuracy

Flow 30 – 300 000 mL/h ± 10 % curr.value

Temperature (central thermistor) 0 – 50 C 0.1 C

Temperature difference (between outer thermistors) -2 – (+2) C 0.0001 C

Electrical conductivity of water (EC) 0.02 – 11 S/m ± 5 % curr.value

Single point resistance 5 – 500 000 ± 10 % curr.value

Groundwater level sensor 0 – 0.1 MPa ± 1 % full-scale

Air pressure sensor 800 – 1060 hPa 5 hPa

Absolute pressure sensor 0 – 20 MPa ± 0.01 % full-scale

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5 EXECUTION OF MEASUREMENTS The measuring programme in drillhole DH-GAP04 included:

1. Dummy logging for drillhole stability/risk evaluation 2. Flow logging without pumping (Length of section = 10 m, step = 2 m). 3. Flow logging with pumping (Length of section = 10 m, step = 2 m, pumping rate

10.0 - 16.5L/min). 4. The EC and temperature of drillhole water with pumping.

The measurements are listed in Table 5-1. The results are discussed in more detail in Chapter 6. Table 5-1. Activity schedule.

Started Finished Drillhole Activity

Average speed of

measurement (m/h)

2011-07-01 7:35 2011-07-01 9:35 DH-GAP04 Dummy logging. 700

2011-07-01 11:23 2011-07-01 18:07 DH-GAP04 Flow logging without pumping, section 10 m. 73

2011-07-01 20:01 2011-07-02 1:09 DH-GAP04Flow logging with pumping, section 10 m,

drawdown ≈ 12 m. 78

2011-07-02 1:12 2011-07-02 2:33 DH-GAP04Drillhole EC and temperature with

pumping. 495

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6 RESULTS

6.1 Flow logging and single point resistance (SPR) The measuring programme contains two flow logging sequences. The flow results were collected into the same diagram with the SPR results (right-hand plot), see Appendices 1.1 – 1.11. SPR has usually a lower value of resistance in a fracture where flow is detected. Many other resistance anomalies result from other fractures and geological features. As the electrode of the SPR tool is located within the upper rubber sealing disks of the probe, the locations of resistance anomalies associated with leaking fractures coincide with the lower end of the flow anomalies. Detected fractures are shown on the drillhole length scale together with their positions. As they are interpreted on the basis of flow curves, they represent flowing fractures. A long line represents the location of a leaking fracture and a short line indicates that the existence of a leaking fracture is uncertain. A short line is used if the flow rate was less than 30 mL/h or if flow anomalies are overlapping or unclear because of noise. Coloured triangles show the magnitude and direction of flows. Triangles have the same colour as the corresponding curves. Flow logging measurements were conducted using a device setup with a 10 m section length when the drillhole was not pumped and in pumped conditions. In these measurements, the probe was deployed in 2 m steps.

6.2 Flow rate, transmissivity and hydraulic head in fractures

An attempt was made to evaluate the magnitude of fracture-specific flow rates. In cases where the distance between fractures is less than ten metres, it may be difficult to evaluate flow rates. In such cases, a stepwise increase or decrease in the flow data plot is equivalent to the flow rate of a specific fracture (filled triangles in the Appendices). The hydraulic head and the transmissivity (Tf) of fractures can be calculated from the flow data using the method described in Chapter 3. The plotted results of these calculations are shown in Appendix 2. The hydraulic head in measured fractures is stated in the plots if both of the flow values at the same drillhole length are not zero. Transmissivity is stated if either of the flows is not zero. The measured flow rates, transmissivities and hydraulic heads for each detected fracture are presented in Appendix 3. Some fracture-specific results were classified as “uncertain”. The basis for this classification is either a minimal flow rate (< 30 mL/h) or unclear fracture anomalies. Fracture anomalies are considered to be unclear if the distance between them is less than half a metre or if their nature is unclear because of noise.

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6.3 Flow: Theoretical and practical measurements limits

The theoretical minimum for measurable flow rate in overlapping measurements is some 30 mL/h. The upper limit of the flow measurements is 300 000 mL/h. As these upper and lower limits are determined by flow calibration, it is assumed that flows can be reliably detected between the upper and lower theoretical limits in favourable drillhole conditions. In practice, the minimum measurable flow rate may be much higher. Drillhole conditions may have an influence on the flow base level, i.e. the noise level. Noise levels can be evaluated in intervals along the drillhole where there are no flowing fractures or other complicating structures, and may vary along the drillhole. There are several known reasons for increased noise in the flow:

1) Roughness of the drillhole wall

2) Solid particles such as clay or drilling debris in the water

3) Gas bubbles entrained in the water

4) High flow rate along the drillhole

Roughness in the drillhole wall always results in high levels of noise, not only in the flow results, but also in the SPR results. The flow curve and SPR curves are typically spiky when the drillhole wall is rough. Drilling debris usually increases noise levels. This kind of noise is typical for both natural (un-pumped) and pumped conditions. Pumping results in lower pressure in the drillhole water and in the fracture water located near the drillhole. This may lead to the release of dissolved gas and increase the quantity of gas bubbles entrained in the water. Some fractures may produce more gas than others. Sometimes, when the drillhole is being measured upwards, increased noise levels are observed just above certain fractures. The reason for this is assumed to be gas bubbles. The effect of a high flow rate along the drillhole can often be seen above fractures with a high flow. Any minor leakage in the seal provided by the lower rubber sealing disks will appear in the measurement as increased levels of noise. A high level of noise in a flow will mask the “real” flow if it is smaller than the noise. Real flows are registered correctly if they are about ten times larger than the noise, but are totally invisible if they are some ten times smaller than the noise. Experience indicates that real flows between one-tenth of the noise level and 10 times the noise level are summed with the noise. Noise levels could therefore be subtracted from measured flows to get real flows. This correction has not yet been carried out because the cases to which it is applicable are unclear.

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6.4 Hydraulic head, water level, air pressure and pumping rate The hydraulic head, as described in Section 3.3, in the drillhole during the measurements is presented in Appendix 4. Air pressure, water level in the borehole and pumping rate during flow logging are shown together in Appendix 5.

6.5 Drillhole water: electrical conductivity and temperature

Appendix 6 presents the electrical conductivity (EC) profile of the drillhole water, and Appendix 7 the temperature measurements carried out simultaneously. The results marked “Measured with lower rubber disks” are not the most representative values of the drillhole water. The problem with measurements performed without removing the lower rubber sealing disks is that the flow guide carries some water with it and the results obtained in this configuration may therefore not be representative. The EC values quoted have been temperature corrected to 25 C to make them more comparable with other EC measurements (Heikkonen et al. 2002).

6.6 Comments on the results The sum of all the measured flows without pumping was 3.6 L/min (Appendix 3). There was only one “negative flow” (flow out from the drillhole). The sum of the measured flows in an unpumped drillhole should normally be zero. The explanation is that the drillhole was artesian, leaking at the top. The sum of all the measured flows during pumping was 8.4 L/min. The pumping rate ranged from 16.5 L/min (at the top) to 10.0 L/min (at the bottom). There can be flows at the unmeasured parts of the drillhole, but the largest flows were probably found. The measurements were carried out partially in transient state. Flow measurement began two days after drilling. During the pumping phase, there was no time to wait for steady state. Constant drawdown was applied and the pumping rate decayed (Appendix 5). Based on the decay curve, the main time constant for the decay is less than four hours. The length errors could be possible decreased by length correlation between core logs and the Single Point Resistance Log.

19

7 SUMMARY As a part of the Greenland Analogue Project, difference flow measurements were performed using the PFL DIFF method. The measuring campaign was conducted in July 2011. The aim of the PFL measurements was to find transmissive fractures (fractures with flow into the drillihole) for water sampling in drillhole DH-GAP04. This objective was achieved. Suitable fractures for water sampling with positive hydraulic head (flow direction into the drillhole when the drillhole is at rest) were found in drillhole length section 540 m to 640 m. The frequency of transmissive fractures was low in the measured part of the drillhole. The electrical conductivity and temperature of the drillhole water were also measured successfully. Temperature was in the permafrost part of the drillhole near the freezing point during the measurement.

20

REFERENCES Heikkonen, J., Heikkinen, E and Mäntynen, M., 2002. Mathematical modelling of temperature adjustment algorithm for groundwater electrical conductivity on basis of synthetic water sample analysis (in Finnish). Helsinki, Posiva Oy. Working report 2002-10. Ludvigson, J.-E., Hansson, K. and Rouhiainen, P., 2002. Methodology study of Posiva difference flow metre in borehole KLX02 at Laxemar. SKB Rapport R-01-52. Marsily, G., 1986. Quantitive Hydrology, Groundwater Hydrology for Engineers. Academic Press, Inc., London.

21 Appendix 1.1

100 101 102 103 104 105 106

Flow rate (mL/h)

200

195

190

185

180

175

170

165

160

155

150

Len

gth

(m)

102 103 104 105

Single point resistance (ohm)

Flow 0 without pumping (L = 10 m, dL = 2 m), 2011-07-01

Flow 1 with pumping (drawdown = 12 m, L = 10 m, dL = 2 m), 2011-07-01 - 2011-07-02

Lower limit of flow rate

Greenland, drillhole DH-GAP04Flow rate and single point resistance

Interpreted fracture-specific flows:Flow 0 (Flow into the hole)

Flow 0 (Flow into the bedrock)

Flow 1 (Flow into the hole)

22 Appendix 1.2

100 101 102 103 104 105 106

Flow rate (mL/h)

250

245

240

235

230

225

220

215

210

205

200

Len

gth

(m)

102 103 104 105









23 Appendix 1.3

100 101 102 103 104 105 106

Flow rate (mL/h)

300

295

290

285

280

275

270

265

260

255

250

Len

gth

(m)

102 103 104 105









24 Appendix 1.4

100 101 102 103 104 105 106

Flow rate (mL/h)

350

345

340

335

330

325

320

315

310

305

300

Len

gth

(m)

102 103 104 105









25 Appendix 1.5

100 101 102 103 104 105 106

Flow rate (mL/h)

400

395

390

385

380

375

370

365

360

355

350

Len

gth

(m)

102 103 104 105









26 Appendix 1.6

100 101 102 103 104 105 106

Flow rate (mL/h)

450

445

440

435

430

425

420

415

410

405

400

Len

gth

(m)

102 103 104 105





415.7





27 Appendix 1.7

100 101 102 103 104 105 106

Flow rate (mL/h)

500

495

490

485

480

475

470

465

460

455

450

Len

gth

(m)

102 103 104 105









28 Appendix 1.8

100 101 102 103 104 105 106

Flow rate (mL/h)

550

545

540

535

530

525

520

515

510

505

500

Len

gth

(m)

102 103 104 105





548.0





29 Appendix 1.9

100 101 102 103 104 105 106

Flow rate (mL/h)

600

595

590

585

580

575

570

565

560

555

550

Len

gth

(m)

102 103 104 105





551.6

584.6





30 Appendix 1.10

100 101 102 103 104 105 106

Flow rate (mL/h)

650

645

640

635

630

625

620

615

610

605

600

Len

gth

(m)

102 103 104 105





600.2

638.4

604.0





31 Appendix 1.11

100 101 102 103 104 105 106

Flow rate (mL/h)

700

695

690

685

680

675

670

665

660

655

650

Len

gth

(m)

102 103 104 105





670.0

682.0





32 Appendix 2

513 517 521 525 529 533 537

Head (m)

700

650

600

550

500

450

400

350

300

250

200

150

Len

gth

(m)

10-10 10-9 10-8 10-7 10-6 10-5 10-4

Transmissivity (m2/s)

Head 0 in the drillhole without pumping (L= 10 m, dL= 2 m)2011-07-01

Head 1 in the drillhole with pumping (L= 10 m, dL= 2 m)2011-07-01 - 2011-07-02

Fracture head (0-1)

Greenland, drillhole DH-GAP04Transmissivity and head of detected fractures

Transmissivity of fracture (0-1)

33 Appendix 3

Area: Greenland Drillhole: DH‐GAP04 Drillhole Diameter (mm): 76 Inclination: 70 ZGround: 525.66, Ztoc: 526.16 Description of reference length (Length = 0): Top of casing tube (Ztoc) Date of measurement without pumping (Flow0): 2011‐07‐01 Date of measurement with pumping (Flow1): 2011‐07‐01 ‐ 2011‐07‐02 Description of columns: Length (m) = Length along the drillhole from reference drillhole length to the fracture (m) Head0 (m) = Head in the drillhole without pumping (m) Flow0 (mL/h) = Flow from the fracture to the drillhole without pumping Head1 (m) = Head in the borehole with pumping (m) Flow1 (mL/h) = Flow from the fracture to the borehole with pumping T (m2/s) = Transmissivity of the fracture Head of fracture (m) = Head in the fracture Comments = Additional information

Length (m)

Head0 (m)

Flow0 (mL/h)

Head1 (m)

Flow1 (mL/h)

T (m2/s) Head of fracture (m)

Comments

415.7 526.41 ‐ 514.35 103 2.35E‐09 ‐ *

548 527 3340 515.05 8390 1.16E‐07 534.90

551.6 526.98 16300 515.01 50500 7.86E‐07 532.69

584.6 527.09 73500 515.2 182000 2.51E‐06 535.14

600.2 527.23 119000 515.67 257000 3.29E‐06 537.20

604 527.18 1040 515.25 3570 5.82E‐08 532.08 *

638.4 527.34 214 515.43 653 1.01E‐08 533.15

670 527.53 ‐ 515.61 68 1.57E‐09 ‐ *

682 528.1 ‐179** 516.25 140 7.40E‐09 521.45 * * Uncertain fracture. The flow rate is less than 30 mL/h or the flow anomalies are overlapping or they are unclear because of noise. ** Negative flow means flow out from the drillhole

34 Appendix 4

513 515 517 519 521 523 525 527 529Head (m)

700

650

600

550

500

450

400

350

300

250

200

150

Len

gth

(m)

Head(m)= (Absolute pressure (Pa) - Airpressure (Pa) + Offset) /(1000 kg/m3 * 9.80665 m/s2) + Elevation (m) Offset = Correction for absolut pressure sensor

Greenland, drillhole DH-GAP04Head in the drillhole during flow logging

Head 0 without pumping (during flow logging), 2011-07-01

Head 1 with pumping (during flow logging), 2011-07-01 - 2011-07-02

35 Appendix 5

Greenland, drillhole DH-GAP04Air pressure, water level in the drillhole and pumping rate during flow logging

Without pumping (during flow logging, L = 10 m, dL =2 m)

With pumping (during flow logging, L = 10 m, dL = 2 m)

Without pumping (after flow logging)

2011-07-01 9:36

2011-07-01 12:00

2011-07-01 14:23

2011-07-01 16:47

2011-07-01 19:11

2011-07-01 21:35

2011-07-01 23:59

2011-07-02 2:23

Year-Month-Day

512

516

520

524

528

Wat

er le

vel

DH

-GA

P04

(m

)

95

96

97

Air

pre

ssu

re

(kP

a)

0

10

20

Pu

mp

ing

ra

te

(L/m

in)

36 Appendix 6

0.01 0.1 1Electrical conductivity (S/m, 25 oC)

700

650

600

550

500

450

400

350

300

250

200

150

100

50

0

Len

gth

(m)

Greenland, drillhole DH-GAP04Electrical conductivity of drillhole water

Measured with lower rubber disks:Without pumping downwards, 2011-07-01

With pumping downwards, 2011-07-01 - 2011-07-02

Without pumping upwards, 2011-07-02

37 Appendix 7

0 1 2 3 4 5 6 7

Temperature (oC)

700

650

600

550

500

450

400

350

300

250

200

150

100

50

0

Len

gth

(m)

Greenland, drillhole DH-GAP04Temperature of drillhole water

Measured with lower rubber disks:Without pumping downwards, 2011-07-01

With pumping downwards, 2011-07-01 - 2011-07-02

Without pumping upwards (after flow logging), 2011-07-02

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