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Keuper Gas Storage
Project
Preliminary Study of Gas Cavity
Design Capacity
November 2015
Application Reference No: EN030002
INEOS
KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE
DESIGN CAPACITY
IEL / R / J / 0002
MAIN PURPOSE OF THE REVISION AND TYPE OF MODIFICATIONS
SUBJECT REVISION
0 Original issue.
GEOSTOCK
2, rue des Martinets – CS 70030 - 92569 Rueil-Malmaison Cedex - France
Tél : +33 1 47 08 73 00 – Fax : +33 1 47 08 73 73– 434023032 RCS Nanterre
TVA FR84434023032 – SAS au capital de 1 500 000 €
www.geostockgroup.com
CHECKED (NAME, VISA)
T. YOU / B. COLCOMBET
APPROVED (NAME, VISA)
A. REVEILLERE
REVISION: 0 DATE: 31 JULY 2014 STATUS: RFA PAGES: 3
IEL-0011-tt-SHA / 31 July 2014
ISSUED (NAME, VISA)
M. KARIMI-JAFARI
Mehdi KARIMI JAFARI2014.07.3116:09:28+02'00'
Date:2014.08.04 10:27:55 +02'00'
ArnaudREVEILLERE2014.08.0718:50:06+03'00'
BrunoColcombet2014.08.0717:46:17+02'00'
IEL-0011-tt-SHA / 31 juillet 2014
1. EXECUTIVE SUMMARY 5
2. INTRODUCTION 6
3. CAVERNS LAYOUT 7
4. CAVERNS GEOMETRY 10
LEACHING INTERVAL 10 4.1
CAVERN FREE VOLUME 10 4.2
5. CAVERNS OPERATING PARAMETERS 11
6. WORKING AND CUSHION GAS 12
IEL-0011-tt-SHA / 31 juillet 2014
LIST OF APPENDICES
1 Cavern implementation plan
2 Design rules and geometry of the cavern
3 Caverns free volume estimate
4 Total working gas volume estimate
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
IEL-0011-tt-SHA/ 31 July 2014 5
IEL / R / J / 0002 REVISION 0
1. EXECUTIVE SUMMARY
Keuper Gas Storage Limited (KGSL), a wholly owned subsidiary of INEOS Enterprises Group
Limited (INEOS), is looking to develop a new gas storage project (the Keuper Gas Storage
Project, or‘KGSP’) in the southern part the Holford Brinefields and the surrounding area to the
north of Middlewich.
Cavern locations proposed by KGSL have been verified on the basis of preliminary
geotechnical rules (pillar over diameter ratio).
Cavern geometry and, in particular, cavern height have been set up using geological data
derived from the seismic campaign data shot by TESLA Exploration International Ltd (England)
under the supervision of Geostock in November 2013 and Geostock standard practices on
solution mining. The results of the seismic surveys are included in Geostock Report
IEL-Y-J-0002-revA issued in July 2014.
Cavern operating parameters (pressure and temperature range) have been set on the basis of
preliminary design rules and Geostock experiences.
Based on all the above assumptions, the working and cushion gas volume of the KGSP have
been estimated.
At this stage of the KGSP, the gas volume estimates should be regarded as being accurate to
within ±20 %.
The total working and cushion gas volume (19 new caverns) estimated in this study are listed
in the following table:
Total gas capacity
(Msm3)
Total working gas volume
(Msm3)
Total cushion gas volume
(Msm3)
716 446 270
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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2. INTRODUCTION
KGSL requested Geostock to estimate the gas storage design capacity of up to 19 caverns for
the KGSP in the southern part of the Holford Brinefield.
The proposed KGSP cavern implementation plan is presented in Appendix 1.
The salt formation depth levels (top and bottom level) have been derived from the Seismic
Campaign Interpretation Report prepared by Geostock (Report IEL-Y-J-0002-rev A).
The following documents and data have been reviewed for this study:
■ KGSP cavern’s implementation plan.
■ Geology of Byley.
■ Seismic campaign interpretation.
■ ELAN interpretation of well Drakelow 2A.
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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3. CAVERNS LAYOUT
As presented in the map 13-03-01/HOL/60/228-P1, up to 19 caverns are proposed for the
KGSP.
The minimum cavern spacing between these new caverns varies from 275 m to 534 m as
presented in the following table:
Cavern Adjacent
cavern
Cavern
spacing (m) Cavern
Adjacent
cavern
Cavern
spacing (m)
H501 H510 315 H511 H509 275
H502 H505 309 H512 H504 277
H503 H517 276 H513 H512 300
H504 H505 275 H514 H507 278
H505 H504 275 H515 H516 276
H506 H516 279 H516 H515 276
H507 H504 275 H517 H503 277
H508 H511 836 H518 H519 300
H509 H511 275 H519 H518 300
H510 H502 295
The P/D ratio is calculated as follows:
■ P: Minimum pillar width between two neighbouring caverns.
■ D: average diameter of two neighbouring caverns.
At this stage of the KGSP, we consider that a minimum P/D of 1.75 m (as for “Holford” gas
storage caverns) is required. Holford project geotechnical models and simulations described
in Geostock reports BYL/R/J/0003 and BYL/R/J/0005 have shown that caverns complying
with this requirement and operated within allowable pressure range meet the main
geotechnical stability criteria:
Criterion 1: the no-tension criterion
Although salt can sustain moderate tensile stresses (salt tensile strength is limited to 1.5 –
2 MPa), its behaviour becomes brittle under tension load and it is recognized that a sound
design should not lead to its occurrence in the simulations. Cavern roof stability and integrity
near the well cementation may particularly be challenged under this condition.
Tensile stresses can result from over pressurization of the cavern or from a thermal shock due
to gas cooling during a production period. Another possible reason for the occurrence of
tensile stresses would be the roof sagging as a result of excessively large cavern roof span.
For the sake of conservatism, no tensile stress is acceptable on the cavern wall.
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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Criterion 2: the creep strain criterion
The magnitude of the creep strain in the rock salt must not exceed a given limit in the long
term. Laboratory experiments show that salt is highly ductile when submitted to compressive
loading at slow strain rate and under lateral confinement. Samples can sustain large
deformation without failure. However, for design purposes, it is recommended to limit the
creep strain at the salt pillar in the range of 5 % to 10 %.
The creep strain in the rock salt around the casing shoe should be limited to 0.3 %.
Criterion 3: the dilation/damage criterion
It is now widely accepted that rock dilation, i.e. an increase in the volume of rock submitted to
deviatoric stresses, is an excellent indicator of damage. Onset of dilation is given by a stress
criterion.
In general, the dilation criterion is expressed in terms of the second invariant of the deviatoric
stress tensor and the first invariant of the stress tensor. As a simple criterion, deviatoric
stresses in the salt pillar must be limited to approximately 20 MPa.
Criterion 4: Gas permeation
The risk of gas permeation into the rock mass is evaluated based on the value of the
tangential stresses along the cavern wall during operation. It is generally admitted that the gas
permeation can occur when the tangential stresses at the cavern wall are less compressive
than the normal stress (equal in magnitude to the gas pressure) acting on the wall of the
cavern.
Assuming a design diameter of 100 m, the minimum distance between cavern wellheads must
be 275 m.
The wellheads (or casing shoes if known) of the adjacent field caverns (Holford Gas Storage
and Stublach Gas Storage) are beyond 275 m from the proposed KGSP caverns.
Stublach Gas Storage caverns are located at a distance greater than 305m from the proposed
nearest KGSP caverns, and the Holford Gas Storage caverns are at least 294m away.
Cavern Adjacent cavern Cavern spacing (m)
H502 H406 294
H508 H408 330
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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In the current layout of the KGSP caverns, the smallest salt pillars are related to Holford gas
storage caverns H406 and H408. The maximum diameter of H406 and H408 caverns based
upon recent sonar measurements are presented in the following table:
G1 Cavern Maximum cavern diameter (m)
H406 102
H408 104
Assuming a design cavern diameter of 100m for new KGSP caverns and considering the
‘worst case' orientation of Holford caverns (i.e the widest dimension of the Holford cavern is
oriented towards the KGSP cavern); cavern H508 and H509 satisfy the minimum required
pillar width.
Pillar Pillar width Required pillar width
(P/D=1.75) Safety factor
H502 - H406 193 176.7 1.1
H508 - H408 228 178.5 1.3
Thus, the proposed KGSP cavern layout complies with the geomechanical preliminary rules.
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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4. CAVERNS GEOMETRY
LEACHING INTERVAL 4.1
As a general rule, the cavern roof depth is set about one cavern radius below the top salt
level.
The casing shoe of the KGSP caverns is set below the G1 marl band (around 130 m below the
salt top). This is due to a number of factors, including the presence of marl layers in the upper
salt and a limited free volume creation, if mined.
A minimum cavern neck height of 15 m is required between the casing shoe and the cavern
roof.
A minimum length of 10 m is required between the cavern bottom (leaching start depth) and
the salt bottom level.
These design rules and the geometry of the cavity are summarized in Appendix 2.
Based on the seismic campaign results, the salt top and bottom depth and chosen leaching
interval for each cavern are presented in Appendix 3.
The location of the casing shoe and leaching start depth could vary up to 10 m for each cavern
from current estimates.
CAVERN FREE VOLUME 4.2
Based on site experience, the following assumptions have been made to estimate the cavern
free volume:
■ average insoluble content in the leaching interval: 26 %.
■ insoluble bulking factor: 1.5.
■ cavern roof angle: 20°.
■ cavern bottom angle (dissolution angle): 35°.
■ shape factor (irregular leached cavern volume over regular geometry envelope): 0.8.
■ free volume ratio (Gas physical volume over free leached cavern volume including
remained brine): 0.98.
Cavern estimated free volumes are presented in Appendix 3.
Depending on geological conditions and the actual results of the solution mining phase, the
caverns shape factors could vary from 0.75 to 0.85 but for the base case estimates, the value
of 0.8 has been taken.
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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5. CAVERNS OPERATING PARAMETERS
Based on Geostock standard practice and experience, at this preliminary stage of the KGSP,
operating pressure limits of caverns are set as follows:
■ The maximum cavern pressure is set to 0.185 bar/m x casing shoe depth limited to
75-80 % of the natural least compressive stress.
■ The minimum cavern pressure is set to 0.06 bar/m x cavern 2/3 depth (at least 30 % of
Pmax).
These figures have been used and validated in many projects and are consistent with the
operating pressure limits currently in use at the Holford gas storage, which is operating next to
the KGSP location and has similar characteristics (same salt strata and same cavity design).
As a preliminary rule, gas operations must be within these pressure limits to satisfy the criteria
set out in section 3.
The vertical stress at the casing shoe is calculated as the weight of the overlying rock column
at the casing shoe depth. From the log density measurement performed in the Drakelow 2A
well that is located within the cavern field area for KGSP (13-03-01/HOL/60/228-P1), the
specific weight of the overburden and the salt layer were estimated at respectively
0.0244 MPa/m and 0.0216 MPa/m.
The maximum and minimum operating pressure of all KGSP caverns as a function of their
depth is presented in Appendix 4. As shown in the appendix, the maximum pressure at casing
shoe varies between 93 bar for H519 to 122 bar for H512.
These pressure gradient limits will be validated by geomechanical modeling using updated
data from laboratory tests in the later stage of the KGSP.
Based on experience, cavern maximum and minimum temperature are assumed to be as
follows:
■ Tmax = 40 °C
■ Tmin = 5 °C
Simulation will be completed during the detailed design phase of the project.
The gas composition considered for this study is as follows:
Compound Methane Ethane Propane Butane Pentane Hexane CO2 Nitrogen
Molar fraction
(%) 87.22 5.66 1.73 0.61 0.17 0.08 1.4 3.13
INEOS KEUPER GAS STORAGE PROJECT
PRELIMINARY STUDY OF GAS CAVERN STORAGE DESIGN CAPACITY
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6. WORKING AND CUSHION GAS
The base case for the caverns physical free volume and working / cushion gas volume have
been estimated using the above presented assumptions and parameters.
The total physical volume of caverns is estimated at 5 973 000 m3.
The total working gas as shown in Appendix 4 is estimated at 446 Msm3 or 15.8 bcf.
The estimated total cushion gas is about 270 Msm3 or 9.5 bcf. At this stage of the project, the
gas volume estimates should be regarded as being accurate to within ±20 %
APPENDICES
CAVERN IMPLEMENTATION PLAN
APPENDIX 1 IEL / R / J / 0002 | REVISION 0 | PAGE 14
IEL-0011 | SHA | 31 July 2014
INEOS
CAVERN IMPLEMENTATION PLAN
KEUPER GAS STORAGE PROJECT
IEL / R / J / 0002 REVISION 0 PAGE 151
APPENDIX
IEL-0011 | SHA | 31 July 2014
DESIGN RULES AND GEOMETRY OF THE CAVERN
APPENDIX 2 IEL / R / J / 0002 | REVISION 0 | PAGE 16
IEL-0011 | SHA | 31 July 2014
INEOS
DESIGN RULES AND GEOMETRY OF THE CAVERN
KEUPER GAS STORAGE PROJECT
IEL / R / J / 0002 REVISION 0 PAGE 172
APPENDIX
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CAVERNS FREE VOLUME ESTIMATE
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XY
Topsalt
Base
Salt
SaltInterval
Distance
TopSaltto
Casin
gShoe
Casin
gShoe
Cavern
neck
length
Topcavern
Base
Cavern
Bottom
margin
Start
Leaching
Cavern
Interval
Max
diam
eter
Max
radius
Roof
Angle
Bottom
angle
Ratio
Excavated/
Geom
etric
Insolubles
(%)
Bulking
Factor
Cavern
Geom
etrical
Volume
Diam
(m)
(m)
(m)
(m)
100
3702
8036
9293
484
765
281
134
618
1563
375
510
755
123
100
50.0
2035
0.8
26.0
1.5
3270
0010
037
0788
3694
6048
776
627
913
261
915
634
756
1075
612
210
050
.020
350.8
26.0
1.5
3250
0010
037
1332
3697
4444
969
925
011
156
015
575
689
1068
911
410
050
.020
350.8
26.0
1.5
2940
0010
037
0832
3690
2252
681
328
813
866
415
679
803
1080
312
410
050
.020
350.8
26.0
1.5
3340
0010
037
1003
3692
3849
777
928
313
563
115
646
769
1076
912
310
050
.020
350.8
26.0
1.5
3290
0010
037
1300
3692
8748
274
926
612
360
515
620
739
1073
911
810
050
.020
350.8
26.0
1.5
3110
0010
037
1103
3689
7750
878
327
512
963
715
652
773
1077
312
110
050
.020
350.8
26.0
1.5
3210
0010
037
0196
3702
0741
869
627
813
154
915
564
686
1068
612
210
050
.020
350.8
26.0
1.5
3240
0010
037
1075
3702
4242
466
023
610
252
615
541
650
1065
011
010
050
.020
350.8
26.0
1.5
2800
0010
037
0590
3692
4051
780
528
913
965
615
671
795
1079
512
510
050
.020
350.8
26.0
1.5
3350
0010
037
0978
3705
0040
866
625
811
752
515
540
656
1065
611
610
050
.020
350.8
26.0
1.5
3020
0010
037
0915
3687
5853
280
327
112
665
815
673
793
1079
312
010
050
.020
350.8
26.0
1.5
3160
0010
037
1187
3686
3150
976
625
711
662
515
640
756
1075
611
610
050
.020
350.8
26.0
1.5
3010
0010
037
1368
3688
9349
274
825
611
660
815
623
738
1073
811
510
050
.020
350.8
26.0
1.5
3000
0010
037
1605
3690
3648
174
726
512
260
415
619
737
1073
711
810
050
.020
350.8
26.0
1.5
3100
0010
037
1578
3693
1147
274
627
512
960
015
615
736
1073
612
110
050
.020
350.8
26.0
1.5
3200
0010
037
1575
3696
1244
770
725
911
856
515
580
697
1069
711
610
050
.020
350.8
26.0
1.5
3040
0010
037
1750
3698
5641
266
825
611
552
715
542
658
1065
811
510
050
.020
350.8
26.0
1.5
3000
0010
037
2024
3699
7836
265
629
414
350
515
520
646
1064
612
610
050
.020
350.8
26.0
1.5
3400
00
TOTAL WORKING GAS VOLUME ESTIMATE
APPENDIX 4 IEL / R / J / 0002 | REVISION 0 | PAGE 21
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GEOSTOCK
2, rue des Martinets – CS 70030 – 92569 RUEIL-MALMAISON Cedex – France
Tél : +33 1 47 08 73 00 – Fax : +33 1 47 08 73 73 – 434023032 RCS Nanterre
TVA FR84434023032 – SAS au capital de 1 500 000 €
www.geostockgroup.com