Keuper Gas Storage Project - kgsp KEUPER GAS STORAGE PROJECT PRELIMINARY STUDY OF GAS CAVERN STORAGE...

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



IEL-0011-tt-SHA / 31 July 2014 6


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.



IEL-0011-tt-SHA/ 31 July 2014 7


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.



IEL-0011-tt-SHA / 31 July 2014 8


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



IEL-0011-tt-SHA/ 31 July 2014 9


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.



IEL-0011-tt-SHA / 31 July 2014 10


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.



IEL-0011-tt-SHA/ 31 July 2014 11


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



IEL-0011-tt-SHA / 31 July 2014 12


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


IEL / R / J / 0002 REVISION 0 PAGE 151

APPENDIX

IEL-0011 | SHA | 31 July 2014

DESIGN RULES AND GEOMETRY OF THE CAVERN


IEL-0011 | SHA | 31 July 2014

INEOS

DESIGN RULES AND GEOMETRY OF THE CAVERN


IEL / R / J / 0002 REVISION 0 PAGE 172

APPENDIX

IEL-0011 | SHA | 31 July 2014

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CAVERNS FREE VOLUME ESTIMATE


IEL-0011 | SHA | 31 July 2014

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Topsalt

Base

Salt

SaltInterval

Distance

TopSaltto

Casin

gShoe

Casin

gShoe

Cavern

neck

length

Topcavern

Base

Cavern

Bottom

margin

Start

Leaching

Cavern

Interval

Max

diam

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Max

radius

Roof

Angle

Bottom

angle

Ratio

Excavated/

Geom

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Insolubles

(%)

Bulking

Factor

Cavern

Geom

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Volume

Diam

(m)

(m)

(m)

(m)

100

3702

8036

9293

484

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281

134

618

1563

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100

50.0

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26.0

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575

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1.5

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037

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3690

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681

328

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415

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312

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3692

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3689

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610

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615

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650

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2800

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037

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866

625

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515

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611

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770

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856

515

580

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TOTAL WORKING GAS VOLUME ESTIMATE


IEL-0011 | SHA | 31 July 2014

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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

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