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Ministerie van Economische Zaken Directie Energiemarkt T.a.v. - … · Ministerie van Economische...
Transcript of Ministerie van Economische Zaken Directie Energiemarkt T.a.v. - … · Ministerie van Economische...
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Ministerie van Economische Zaken
Directoraat-generaal Energie, Telecom & Mededinging
Directie Energiemarkt
T.a.v.
Postbus 20401
2500 EK DEN HAAG
Cc Staatstoezicht op de Mijnen
T.a.v.
Postbus 24037
2490 AA DEN HAAG
Nedmag Industries
Mining & Manufacturing B.V.
BiUitonweg 1
9641 KZ Veendam
RO. Box 241
9640 AE Veendam
The Netherlands
T +31 598 651 911
F +31 598 551 226
E infoiinedmag.nl
I www.nedmag.com
Uw kenmerk
Telefoon
Betreft
Datum
DGETM-EM/14135221
(0598)-651260
Winningsplan Nedmag Industries
Veendam, 30 oktober 2015
Geachte
OJ
OJ
OJ
O a
Conform artikel 6 van het instemmingsbesluit (3 oktober 2014) van het Ministerie van
Economische Zaken aangaande het gewijzigde winningsplan, dient Nedmag een nadere
studie uit te voeren naar het verschil tussen het squeezevolume uit de materiaalbalans en
het volume uit de inversie, en de invloed daarvan op de onzekerheid in de
bodemdalingsvoorspelling.
In mijn brief van 23 juni 2015 heb ik u gevraagd om het onderzoek later te mogen indienen.
In het bijgevoegd rapport is een gedetailleerde studie weergegeven naar de invloeden van
de kritische parameters op de massabalans van Nedmag's zoutwinning. Naast het gevraagde
squeezevolume is ook het ondergrondse pekelvolume berekend.
Bij de opzet van de studie is van het bedrijf NG-Consulting uit
Sondershausen geconsulteerd over de wijze waarop de diverse oplosprocessen verlopen. De
heeft namelijk een uitgebreide expertise op het gebied van
"zoutchemie".
Trade register Groningen 02331543 VAT HD. IML 0049270B4B01
NedMag is ISO 9001. ISO 14001 150 22000 and GMP+ certified
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Het bijgevoegde rapport geeft het volgende aan:
• Het huidige BDS (Brine Data System) model geeft een onvolledige berekening van
het squeeze- en ondergronds volume omdat de geproduceerde magnesiumchloride
pekel artificieel wordt gesplitst in de componenten carnallitische en bischofitische
pekel, en water. Daarnaast is het model opgezet voor berekeningen per individuele
caverne waardoor het squeezevolume onjuist berekend wordt wanneer individuele
cavernes met elkaar verbonden raken.
• Om een separate controle op het BDS model te kunnen uitvoeren is een nieuw
massabalansmodel (MB) opgezet.
• In dit massabalansmodel zijn alle productiedata vanaf 1972 op maandbasis ingevoerd
en zijn onjuiste loogfasen, die in het verleden in BDS zijn gehanteerd, gecorrigeerd
(MB revised).
• acht het zeer waarschijnlijk dat in loogfase 3 het
bischofietvoorkomen direct oplost in plaats indirect. De indirecte oplosroute zou
inhouden dat eerst carnallitische pekel wordt gevormd welke zich daarna omzet tot
bischofitische pekel. Gezien de zeer hoge oplossnelheid van bischofiet zout is een
indirecte oplosroute ergonwaarschijnlijk. De massabalans is hiervoor gecorrigeerd
(MB revised LF 3->2).
• Het model is tot slot aangepast om het effect van clustering van cavernes te bepalen
(MB cluster). Op het moment dat cavernes verbonden raken is er vanuit gegaan dat
het zeer oplosbare bischofiet rond het injectiepunt reeds is opgelost. Door de
verdere loging wordt de gevormde carnallitische pekel onderweg naar de cq in de
producerende caverne omgezet in bischofitische pekel. Dit is dan de indirecte
oplosroute.
Dit laatste model (MB cluster) geeft de beste benadering weer van de ondergrondse
oplosprocessen en de hierbij ontstane squeezevolumes van de Nedmag
magnesiumchloridewinning.
De belangrijkste conclusies uit dit rapport zijn dat:
• Het berekende squeezevolume 3 % groter is in vergelijking met het huidige BDS
model.
• Het ondergrondse pekelvolume met 11 % is toegenomen in vergelijking met het
huidige BDS model.
Nedmag heeft gevraagd om bijgevoegd rapport inclusief de
massabalansberekeningen te toetsen. Nedmag heeft, op dit moment, nog geen bevestiging
gekregen dat hij deze opdracht wil uitvoeren.
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De invloed van het toegenomen squeeze- en ondergronds volume op de huidige en
toekomstige bodemdaling is beperkt gezien de bovengenoemde beperkte afwijkingen ten
opzichte van de huidige waarden in BDS. Voordat wij hieraan verdere conclusies verbinden
stellen wij voor om eerst de onderstaande lopende acties af te wachten zodat er een totaal
beeld ontstaat van alle huidige en toekomstige effecten van onze zoutwinning. Eveneens
vinden wij het belangrijk om een reactie van Staatstoezicht op de Mijnen te krijgen op dit
rapport.
Lopende acties
Aangezien het squeezevolume bepalend is voor de optredende bodemdaling hebben wij het
volume uit de ontstane bodemdalingskom over de periode eind 2003 t/m medio 2010 laten
bepalen met behulp van de INSAR techniek. Deze pilot study is ingediend bij het
Staatstoezicht op de Mijnen (21 augustus 2015) en op 20 oktober 2015 besproken met
Als vervolg op deze pilot study wil Nedmag de
bodemdaling over de gehele squeezeperiode 1993 t/m 2015 door SkyGeo laten bepalen.
Zoals met het Staatstoezicht op de Mijnen is besproken op 20 oktober is het van belang dat
de INSAR meetdata goed worden geïnterpreteerd en verwerkt. Hiervoor is nog een nadere
bespreking nodig tussen het Staatstoezicht op de Mijnen, Nedmag en SkyGeo. Indien alle
partijen het eens zijn over een goede verwerking en interpretatie van de INSAR meetdata zal
Nedmag deze studie laten uitvoeren. Het voordeel van deze INSAR analyse is dat ook het
komvolume berekend kan worden en vergeleken kan worden met de resultaten uit het
bijgevoegde rapport voor de periode 1993 t/m 2015. Een belangrijk punt van dit onderzoek
is de wijze waarop de correctie wordt gemaakt voor de bodemdaling door gaswinning welke
rond de zoutwinning Nedmag optreedt.
Staatstoezicht op de Mijnen laat de door Nedmag uitgevoerde abandonneringsstudie (onze
brief van 2 april 2015) reviewen. De verwachting is dat deze review in het voorjaar van 2016
gereed is. Deze abandonneringsstudie en de review zullen antwoord geven op de vraag welk
effect het ondergrondse pekelvolume heeft op de toekomstige bodemdaling na
abandonnering van de cavernes.
Samenvattend
In het tweede kwartaal van 2016 zal zowel de review van Staatstoezicht op de Mijnen als
ook de bovenstaande acties zijn afgerond. Met de uitkomst hiervan en de genoemde
conclusies uit de massabalans studies kunnen effecten van de huidige en toekomstige
zoutwinning bepaald worden. Deze resultaten zullen met het Staatstoezicht op de mijnen
worden besproken.
Hopende u hiermee voldoende te hebben geïnformeerd.
Hoogachtend,
NEDMAG INDUSTRIES
turing B.V.
Algemeen directeur
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OUIAIQBN
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Mass balance study of the Nedmag caverns
Modelling of magnesium salt dissolution and calculated squeeze volumes
NEDMAG
Author
Version
Date
1
30-10-2015
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ni NEDMAG Mass balance of the Nedmag caverns v1
1. INTRODUCTION
On 26 March 2013 NEDMAG Industries Mining & Manufacturing B.V. in Veendam
(Nedmag) has requested the Minister of Economic Affairs for approval of a modified
production plan for potassium and magnesium salts. The plan announces a study into
best practices to abandon the caverns after final production stop ^\
On 3 October 2014 the Minister of Economic Affairs has approved of the modified plan
under certain conditions, among others article 6, stating that Nedmag will investigate the
discrepancy between the squeeze volume calculated on basis of a mass balance and the
volume derived from inversion of the soil subsidence and the influence on soil subsidence
predictions.
After pre-feasibility study and discussions with magnesium salt solution mining expert
a study proposal was presented to State Supervision of Mines and
TNO-Utrecht on 25 March 2015. The proposal was to do a history match of the Nedmag
brine field from 1972 with the aim to improve the accuracy of the calculated squeeze
volume. The study includes the following:
A mass balance model will be developed and expanded with the salt lithology to
quantify the amount of inert material and bulking effects.
- The existing BDS model will be scrutinized with respect used leaching phase and
other assumptions.
The effect of direct versus indirect dissolution of bischofite will be studied.
- The effects of connectivity of caverns will be incorporated.
This note describes the results of these investigations followed by conclusions regarding
the accuracy of calculated squeeze volumes.
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2. THE NEDMAG SOLUTION MINING PROCESS AND ITS MODELLING
2.1 The Nedmag solut ion mining process
Nedmag produces magnesium brine by solution mining of magnesium at a depth of
1300 to 1800 m in the Zechstein II formation. The first four caverns VE-1 to 4 have
been developed from WHC-1, the caverns TR-1 to 9 were developed from WHC-2.
Process water or dilute brine is injected into the bischofite/carnallite containing ZE-I
l b layer. In the early years also salt was produced from the carnallite containing ZE-I
2b/3b layer.
' I l l
1 n i l j r /
MOB n K . i j l
D lOOOm I r i n
I « M B
_ .
IMOm
Z3 =J I I I
Vtfm II
1
VWH),,,
1
/..».!
Kkt
Metfcl
I I . l l l l I
Figure 1: Typical salt lithology of a Nedmag cavern
In the development of the caverns the following 6 leaching phases are distinguished:
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Cluster operation
Figure 2: Leaching phases of Nedmag caverns
In leaching phase 1 water or dilute brine is directly injected into the carnallite layer
underlying the bischofite salt. In this phase a sump is prepared and a carnallitic (KCI-
rich) brine is produced while sylvite precipitates. To prevent uncontrolled upward
leaching the top of the cavern is protected with an oil blanket.
The leaching paths can be represented below by line OPC in the thermodynamic
phase diagram (Figure 3). From O to P carnallite dissolves congruently, thereafter
from P to C more carnallite dissolves while sylvite precipitates.
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Figure 3: The MgCla/KCI phase diagram
After the desired sump volume is obtained the oil blanket and/or the injection level
are raised and the upper lying bischofite salt is contacted and leaching phase 2 sets in.
In leaching phase 2 the injection fluid contacts the bischofite salt and bischofitic brine
is directly formed along direct path OQB. In addition the carnallitic brine present in
the sump is displaced by more dense bischofitic brine and also enriches to bischofitic
brine.
After further upward displacement of the oil blanket and/or injection point in leaching
phase 3 the injection fluid first contacts the overlying carnallite salt and carnallitic
brine is formed and sylvite precipitates. The carnallitic brine "floats" on top of the
denser bischofitic brine. Since the volume of the formed carnallitic brine exceeds the
volume of the formed cavity the excess carnallitic brine is pushed into the bischofitic
area and further enriches towards bischofitic brine. As a result secondary carnallite,
kieserite and halite precipitate. In leaching phase 3 the dissolution path OPCOB is
followed and bischofitic brine is formed indirectly. The specific volume effects of
indirect formation of bischofitic brine are significantly smaller than for direct
formation as described in leaching phase 2.
One major assumption in the BDS model (section 2.2.1) in leaching phase 3 is that
insoluble tailings fall to the bottom of the cavern as well as part of the formed sylvite.
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As a resuit a larger cavity is created in the overlying carnallite giving less carnallitic
brine overflows to the lb bischofite section.
AV p r o d u c t l o n A
fall
AV in ject ion
Sylvite •
Inert Halite, Kieserite
Precipitates Seconday carnallite, halite, kieserite 9
Figure 4: Schematic fall-out of inert material and sylvite in leaching phase 3
In leaching phase 4 the injection point and oil blanket are raised to the lower 2b
carnallite layer. The carnallitic brine formed moves through the borehole to the top of
the lb section and transforms to bischofitic brine as in leaching phase 3 with indirect
formation of bischofitic brine.
In leaching phase 5 the injection point and oil blanket are raised to the upper 3b
carnallite layer and the production is raised to the lower 2b carnallite layer. In this
phase carnallitic brine is produced according to the same dissolution path as in
leaching phase 1.
Until the year 1993 the caverns were operated close to litho-static pressures with a
"room and pillar" solution mining approach. After successful demonstration of the
squeeze concept between 1993 and 1995 the TR wells, except TR-9, are producing
under 60 - 80 bar sub-lithostatic conditions
Soon after start-up in October 1982 a pressure connection was found to be between
TR-1 and TR-2. In the period from November 1996 onwards more TR caverns gradually
interconnected into one large cluster. In September 2009 VE-4 also connected to the
TR cluster. During the last VE-3 workover in November 2006 a connection with VE-2
was noticed.
Currently the Nedmag caverns consist of two clusters and two separate caverns:
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- The TR cluster consisting of TR-1/2/3/4/5/6/7/8 & VE-4.
- The VE cluster consisting of VE-2 & VE-3.
VE-1 developed in the 2b/3b section only.
- TR-9 in development since May 2012.
In the cluster operation which is currently applied to the TR cluster water or brine
typically are injected into the shallower l b sections, the carnallitic brine formed
migrates through connections within the l b bischofite layer to a deeper l b cavern.
During its migration towards the production point the carnallitic brine contacts
bischofite salt and enriches into a bischofitic brine.
2.2 Nedmag mass balance models
2.2.1 The BDS model
The Brine Data System (BDS) model was developed in 1995 and is in use to
monitor the development of the various volumes due to the Nedmag solution
mining process since 1972. It is primarily based on a mass balance with inputs of
measured: injection and production brine volumes and concentrations per cavern.
At a given leaching phase BDS calculates the quantities of dissolved salt, and
precipitate as well as the squeeze volume and the total underground brine
volume. The squeeze volume is defined as the volume of brine coming to surface
in excess to what could be expected from the injection fluid without cavern
convergence.
One characteristic BDS feature is that it assumes that all brine compositions can
be represented by a mixture of the three components: saturated bischofitic brine,
saturated carnallitic brine and water. In addition it is assumed that the caverns are
filled by a two phase system of saturated carnallitic brine floating on top of a
saturated bischofitic brine with compositions independent on depth. In case of the
production under-saturated brine it is assumed that part of the injection water
shortcuts directly to the brine production flow.
The BDS calculations are set-up for a single cavern operation. The interconnection
of caverns creates a mismatch between injection fluid and brine production per
cavern. Therefor realistic squeeze volumes and underground brine volume can
only be obtained by summating the values of the individual caverns.
The accuracy of the BDS model calculations for the total underground brine
volume has been estimated by Renier His main findings were that the selected
leaching phases were not always correct and that the choice for indirect or direct
formation of bischofitic brine has a significant effect on the volumes calculated.
Renier recommended to study the following:
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o
o
The effect of depth (temperature) on saturated brine compositions and
densities. A variation analysis for the total height difference between the
caverns showed that this introduces an inaccuracy of 4 % of the calculated
squeeze volume. This result has been reported by Nedmag in 2012
The effect of pressure, depth and shape on cavern convergence. This is
part of the Nedmag Abandonment study .
The effect of brine exchange between interconnected caverns, which is
part of this study.
2.2.2 The mass balance model
Since BDS relies on the physically incorrect assumption that all brine compositions
can be split into: saturated carnallitic and bischofitic brine and water a more exact
mass balance model was prepared. In this model it is assumed that the undiluted
brine composition is representative for the entire cavern content. This avoids the
use of a standard bischofitic brine composition. However the use of standard
saturated carnallitic brine remains necessary in the case of indirect dissolution in
leaching phases 3 and 4. The model equations are given in Appendix I and have
been described previously
3. MODEL CALCULATIONS
3.1 BDS and mass balance model with the same input data and assumptions
Using the same monthly based input data-set for the period of 1972 till June 2015 the
volume calculations were repeated with the mass balance model. All leaching phases
as well as fall out of tailings/sylvite in leaching phase 3 were kept identical to the ones
used in the original BDS calculations. The summated volumes for the two single
caverns and the two clusters are reported below.
Cavern/Cluster Squeeze volume, m^ Total underground brine volume, m^
BDS MB BDS MB
VE-1 21,646 31,115 197,531 165,637
TR-9 56,426 138,493 192,560 132,637
VE-2/3 219,954 424,544 684,396 665,202
TR-1/8, VE-4 5,696,586 6,389,158 4,747,297 4,317,038
Total 5,994,612 6,983,311 5,821,784 5,280,514
It is shown that the improved mass balance produces 16 % more squeeze volume and
9 % less total underground brine volume than BDS. This is besides imperfections in
the BDS mass balance, which is not closed because of brine splitting, mainly due to
the large negative squeeze contributions that arise in BDS when in case of injection
into a cavern without brine production.
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3.2 Mass balance model with revised leaching phases
The designation of leaching phases in the BDS data was checked against the actual
injection depth as reported in historical monthly reports in relation to the salt
lithology per cavern. It was found that there were a number of months in which was
injected into the lb bischofite (leaching phase 2) instead of the overlying lb carnallite
(leaching phase 3) as used in BDS. This means that there has been more direct
production of bischofitic brine than accounted for in the original BDS calculation. After
revision of the leaching phases for this (MB revised) the following volumes were
calculated:
Cavern/Cluster Squeeze volume, m^ Total underground brine volume, m^ Cavern/Cluster
MB original MB revised MB original MB revised
VE-1 31,115 31,115 165,637 165,637
TR-9 138,493 36,361 132,637 327,345
VE-2/3 424,544 226,705 665,202 986,054
TR-1/8, VE-4 6,389,158 5,914,734 4,317,038 5,005,945
Total 6,983,311 6,208,914 5,280,514 6,484,981
Because in direct dissolution mode of bischofite more brine is formed than by indirect
dissolution the non-squeeze contribution to the production flow is increased. As a
result the squeeze contribution reduces by 0.78 Mm^ and the total underground brine
volume increases by 1.20 Mm^.
3.3 Mass balance model with revised leaching phases and direct dissolution from lb
only
In the view of consultant Norbert Grüschow complete indirect dissolution of
bischofite in leaching phase 3 for a single cavern is highly unlikely. This is mainly due
to the mixed nature of the overlying bischofite and carnallite salt and the brine
convections flows. To quantify the effect of direct bischofite dissolution the
calculations with revised leaching phases were repeated with all leaching phases 3
replaced by leaching phase 2.
Cavern/Cluster Squeeze volume, m^ Total underground brine volume, m^ Cavern/Cluster
MB revised MB revised LF 3 - > 2 MB revised MB revised LF 3 - > 2
VE-1 31,115 31,115 165,637 165,637
TR-9 36,361 36,361 327,345 327,345
VE-2/3 226,705 197,875 986,054 1,021,098
TR-1/8, VE-4 5,914,734 5,470,444 5,005,945 5,802,750
Total 6,208,914 5,735,795 6,484,981 7,316,829
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In the extreme situation of direct bischofite dissolution only when injected and
produced from the lb section the squeeze volume drops by 0.47 Mm^ and the total
underground brine volume increases by 0.83 Mm^.
3.4 Mass balance model with revised leaching phases and clustering
The general conception is that inter-cavern connections arise in the continuous more
soluble bischofite layers. Caverns are assumed to be connected when their pressures
start to correlate. However pressure communication gives no clue about volumetric
exchange between caverns. This can only be deduced by comparing volumetric
balances of injection and production per cavern. Unfortunately the balances are also
affected by squeeze flows which are not known for the individual caverns. However in
practice the connections in the TR cluster are actively used with in general injection
into the more shallow lb caverns and production from the deepest l b caverns, but
the actual flow paths are uncertain.
The mass balance model was used to determine the effect of a cluster operation on
the calculated volumes. It was assumed that up to the point of connection caverns
can be treated as single caverns using revised leaching phases and the assumption
that there is only direct dissolution when injected and produced from the lb section.
From the onset of connection the connected caverns are represented by one big
cavern with mixed injection and mixed production flows.
In the cavern development over time the following 9 clusters can be defined:
Figure 5: Time development of connections between the Nedmag caverns
For the connected cluster it is assumed that all bischofite in the injection zone already
has been consumed in the pre-connection period and that additional injection results
in the formation of carnallitic brine. The carnallitic brine migrates through the cluster
and somewhere contacts bischofite to form bischofitic brine. This type of leaching can
be described by leaching phase 4.
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Cavern/cluster Squeeze volume m^ Total underground brine volume, m' Cavern/cluster
MB revised LF 3 - > 2 Cluster MB revised LF 3 --> 2 Cluster
VE-1 31,115 31,115 165,637 165,637
TR-9 36,361 36,361 327,345 327,345
VE 2/3- 197,875 218,891 1,021,098 449,516
TR 1-8/VE-4 5,470,444 1,621,421 5,802,750 1,828,331
Cluster 1-9 4,270,717 3,703,218
Totaal 5,735,795 6,178,504 7,316,829 6,474,046
As a resuit of an increased indirect dissolution contribution in the cluster approach
the squeeze volume increase by I
total underground brine volume.
the squeeze volume increase by 0.44 Mm^ with an associated decrease of 0.84 Mm^ in
4. DISCUSSION
In 2011 an inversion study was carried out by TNO '̂ on the subsidence measurements
for the period of 1993 till 2010. From this study a mismatch of about 15 % was found
between the BDS calculated squeeze volume and the squeeze volume as determined
by inversion. According to TNO this discrepancy can be due to either an error in the
geomechanical model or a positive structural error in the determination of the total
squeeze volume from production data.
In the table below the calculated squeeze and underground brine volumes are
summarised.
Case Squeeze Underground
volume brine volume
3
m m^
BDS 5,994,612 5,821,784
MB 6,983,311 5,280,514
MB revised LF's 6,208,914 6,484,981
MB revised, LF 3 - > 2 5,735,795 7,316,829
MB cluster approach 6,178,504 6,474,046
Under the assumption of a constant factor of 85 % for the whole production period of
1972 till June 2015 an inversion volume of 5.09 Mm^ is expected on basis of the BDS
squeeze volume. In none of the above calculations with the mass balance model such
a low value is approximated even with direct bischofite dissolution giving a minimum
value of 5.74 Mm^.
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Since the cluster approach gives a more realistic representation of the multiple cavern
operation a squeeze volume of 6.18 Mm^ is considered to the more likely value with
an associated total underground brine volume of 6.47 Mm^.
5. CONCLUSIONS
Mass balance calculations for the Nedmag caverns incorporating revised leaching
phases and the effects of cavern connections gives a most likely squeeze volume of
6.18 Mm^ and a total underground brine volume of 6.47 Mm^ for the period 1972 till
June 2015. This squeeze volume is only 3 % higher than the 5.99 Mm^ found with the
current BDS model. Since this disagreement is far less than the accuracy of
subsidence measurements a correction on soil subsidence predictions is not
reasonable.
However a squeeze volume of 6.18 Mm^ is 21 % higher than the expected inversion
squeeze volume of 5.09 Mm^ for the same period. This discrepancy cannot be
explained by the physical solution chemistry and the followed leaching paths of
dissolving carnallite and bischofite but must be due to inaccuracies in the subsidence
measurements or geomechanical effects that prevent part of the underground
volume reduction to come to surface.
REFERENCES
1. Winningsplan kalium- en magnesiumzoutwinning 2013, Nedmag Industries Mining &
Manufacturing B.V., Winningsvergunning Veendam, 26 maart 2013.
2. Gedrag van Magnesiumzouten tijdens de Winning in de Concessie van Nedmag te
Veendam en een daaruit volgende volumebepaling van het Complex van Cavernes van
WHC-2. MSc Thesis TU Delft, 1 september 2006.
3. Het ondergronds pekelvolume en onzekerheidsanalyse hiervan bij de Nedmag
zoutwinning. Interne Nedmag notitie, Veendam, 25 april 2012.
4. Abandonment study Nedmag caverns. Cavern squeeze modelling and geophysical
analysis of brine permeation and containment. Well Engineering Partners B.V.,
, Hoogeveen 31-3-2015.
5. Nauwkeurigheidsanalyse BDS modelberekeningen. Interne Nedmag Notitie, ,
Veendam, januari 2013.
6. Nedmag Veendam inversie bodemdaling TNO-rapport (060-UT-2011-00687).
, Utrecht, 8 april 2011.
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APPENDIX I
Leaching phase 1
The development of a cavern starts with the creation of an undercut in the lower section of
the l b carnallite salt. Dissolution of the overlying bischofite salt is prevented by installing an
oil blanket. In phase 1 water or diluted brine (Mi) is injected and the salts: carnallite (C),
halite (H), kieserite (K) go into solution forming brine (M). Due to the incongruent
dissolution behaviour of carnallite the sylvite {Si) precipitates simultaneously. Typically a
carnallitic brine is formed typically wi th: 27 % MgCb, 5.2 % KCl, 2 % NaCl and 1.3 % MgSOa
and a density of 1.33 t /m^ (PCB) at saturation.
For phase 1 the following mass balance equations are valid:
Total mass M i + C + H + K = M + S| (1)
Magnesium chloride m i M i + mcC = mM (2)
Potassium chloride SiMi + ScC= sM + Sj (3)
Sodium chloride balance h i M i + H = hM (4)
Kieserite balance k i M i + kkK = kM (5)
The symbols: m, s, h and k represent the dissolved mass concentrations of MgCb, KCl, NaCl
and MgS04 in the injection fluid (subscript 1) or of the brine formed. The symbols mc, Sc and
kk represent the MgCIa content in carnallite, the KCl content in carnallite and the MgS04
content in kieserite respectively.
Combination of eqn's (2), (3), (4) and (5) and substitution in eqn. (1) yields:
M = M l (1-mi/mc - h i - k M / ( I - m/mc - h - k/k^) (6)
Insertion of known mass of injected water or brine and measured concentrations of injection
and product brine allows the calculation of the mass of brine (M) formed. Insertion of M in
eqn's (2) till (5) quantifies the mass of the dissolved salts: C, H, K and precipitate SJ..
The net volume of the carnallite cavity for litho-static pressure conditions, i.e. in the absence
of cavern convergence, is calculated using the respective salt densities through:
AV ccav = C/pc + H/PH + K/PK - Si/psy (7)
Finally the volume of brine produced under litho-static conditions is calculated through:
AVprod = M / PCB - AVc,cav (8)
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\i NEDMAG
Mass balance of the Nedmag caverns vl
Carnallite Bischofite Kieserite Halite Sylvite
p, t /m3 1.60 1.60 2.57 2.14 1.99
MgCl2,% 34.28 46.86
KCl, % 26.84
NaCl, %
MgS04, % 86.98
Leaching phase 2
After an undercut has been developed the oil blanket is withdrawn allowing contact of the
injected water or brine with bischofite salt. As a result bischofite dissolves (B) from the l b
section and a bischofitic brine is produced typically containing: 36.8 % MgCb, 0.32 % KCl, 0.48
% NaCl and 0.45 % MgS04 and a density of 1.38 t /m^ (PBB) at saturation.
For this phase the following mass balance equations are valid:
Total mass
Magnesium chloride
Potassium chloride
Sodium chloride
Kieserite
M i + C + B + H + K = M
m i M i + mcC + mBB= mM
SiMi + ScC= sM
h iMi+ H = hM
k iM i + kkK = kM
(9)
(10)
(11)
(12)
(13)
The symbols: m, s, h and k represent the mass concentrations of MgCl2, KCl, NaCl and MgS04
in the injection fluid (subscript 1) or in the brine formed. The symbol mg represent the MgCb
content of bischofite salt.
Combination of eqn's (2), (3), (4) and (5) and substitution in eqn. (1) yields:
M = M l (1- Si/sc*(l-mc/mB)- mi/mg - h i - ki/kk) / ( 1 - s/sc*(l-mc/mB)m/mB - h - k/kk) (14)
Insertion of the known mass of injected water or brine and measured concentrations of
injection and product brine allows the calculation of the mass of brine (M) formed. Insertion
of M in eqn's (10) till (13) allows the calculation of mass of the dissolves salts: B, C, H, K.
The net volume of the cavity without for litho-static pressure condition convergence, is
calculated using the respective salt densities through:
AV B.cav = C/pc + B/PB + H/PH + K/PK (15)
Finally the volume of brine produced under litho-static conditions is calculated through:
AVprod = M/PBB - AVB.CSV (16)
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ni NEDMAG Mass balance of the Nedmag caverns vi
Leaching phases 3 and 4
After the bischofitic cavern had reached its optimum diameter the injection point was raised
either into the l b carnallite layer above the bischofite salt (phase 3) or the 2b/3b carnallite
layer (phase 4). As a result the injected water or brine initially forms a carnallitic brine in a
carnallite cavity. The carnallite dissolution process is identical to phase 1 described by eqn's:
(1) to (7). The part of the carnallitic brine that doesn't fit into the carnallitic cavity overflows
to the underlying l b bischofite cavity according to:
AVoverf low = M / pCB " A V c ,( (17)
In the bischofite cavity the carnallitic brine (M i = AVoverfiow * PCB) dissolves bischofite salt and
a bischofitic brine is produced. As a result of the increased MgCb concentration part of the
carnallite (C|), kieserite (K|) and halite (H|) precipitate. The effects of the carnallitic brine
transformation can be described by:
Total mass balance:
Magnesium chloride balance:
Potassium chloride balance
Sodium chloride balance
Kieserite balance
M i + B = M + Ci + Ki + H i (18)
m i M i + mBB= mM + mcCi (19)
SiMi = sM + ScCi (20)
h i M i = h M + H i (21)
k iM i = kM + kkKi (22)
After some manipulation of eqn's (19), (20), (21) and (22) followed by substitution in eqn.
(18) gives:
M = M l (1- Si/sc*{l-mc/mB)- mi/mg - h i - k M / ( I - s/sc*(l-mc/mB)m/mB - h - k/kk) (23)
This equation is identical to equation (14).
Insertion of known mass of injected water or brine and measured concentrations of injection
brine allows the calculation of the mass of the overflow AVoverfiow The underlying assumption
is that a saturated carnallitic brine. Inserting the overflow as M i allows the calculation of the
bischofite brine formed (M). With eqn's (19) till (22) the mass of the dissolved B and
precipitates: C|, H i , K l is calculated.
Leaching phase 5
The volume effects resulting from production of carnallitic brine though injection and
production from the 2b/3b layer can be fully described are identical to the ones derived for
leaching phase 1.
Calculation of squeeze volume
The net volume of the cavity without for litho-static pressure condition convergence for the
l b bischofite section is calculated using the respective salt densities through:
AVB.cav = B/PB - Ci/pc - Hi/pH - Ki/pK
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ni N E D M A G Mass balance of the Nedmag cavems vi
The volume of brine produced that would be produced under litho-static conditions is
calculated through:
AVprod = M / PBB - AVB,cav
The squeeze volume is defined as the excess of brine coming to surface over the calculated
litho-static contribution:
AVsqueeze ~ AVjurface " AVprod
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f \ 1