Bsi bs en 01918 4 2016

NORME EUROPÉENNE English Version Gas infrastructure - Underground gas storage - Part 4: Functional recommendations for storage in rock caverns Infrastructures gazières - Stockage souter

BSI Standards Publication

Gas infrastructure — Underground gas storage

Part 4: Functional recommendations for storage in rock caverns

This British Standard is the UK implementation of EN 1918-4:2016 Itsupersedes BS EN 1918-4:1998 which is withdrawn.

The UK participation in its preparation was entrusted to TechnicalCommittee GSE/33, Gas supply

A list of organizations represented on this committee can beobtained on request to its secretary

This publication does not purport to include all the necessaryprovisions of a contract Users are responsible for its correctapplication

© The British Standards Institution 2016 Published by BSI StandardsLimited 2016

ISBN 978 0 580 86102 4ICS 75.200

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 March 2016

Amendments issued since publication

Date Text affected

NORME EUROPÉENNE

English Version

Gas infrastructure - Underground gas storage - Part 4:

Functional recommendations for storage in rock caverns

Infrastructures gazières - Stockage souterrain de gaz -

Partie 4: Recommandations fonctionnelles pour le

stockage en cavités minées

Gasinfrastruktur - Untertagespeicherung von Gas - Teil 4: Funktionale Empfehlungen für die Speicherung in

Felskavernen This European Standard was approved by CEN on 9 January 2016

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E UR O P É E N DE N O R M A L I SA T I O N

E UR O P Ä I SC H E S KO M I T E E F ÜR N O R M UN G

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

Contents

European foreword 3

1 Scope 4

2 Normative references 4

3 Terms and definitions 5

3.1 Terms and definitions common to parts 1 to 4 of EN 1918 5

3.2 Terms and definitions not common to parts 1 to 4 of EN 1918 9

4 General requirements 10

4.1 General 10

4.2 Underground gas storage 10

4.3 Long-term containment of stored products 15

4.4 Environmental conservation 16

4.5 Safety 16

4.6 Monitoring 16

5 Design 16

5.1 Design principles 16

5.2 Geological exploration 18

5.3 Stored product containment 19

5.4 Determination of the maximum operating pressure (MOP) 19

5.5 Cavern stability 20

5.6 Construction parameters 21

5.7 Concrete plug specifications 21

5.8 Connecting caverns to surface 21

5.9 Monitoring systems 24

5.10 Neighbouring subsurface activities 24

6 Construction 25

7 Testing and commissioning 26

7.1 General 26

7.2 First gas filling 27

8 Operation, monitoring and maintenance 27

8.1 Operating principles 27

8.2 Monitoring 27

8.3 Maintenance 28

8.4 HSE 28

9 Abandonment 29

9.1 General 29

9.2 Withdrawing the fluid 29

9.3 Plugging and abandonment of wells and accesses 29

9.4 Surface facilities 30

9.5 Monitoring 30

Annex A (informative) Non-exhaustive list of relevant standards 31

Annex B (informative) Significant technical changes between this European Standard and the previous version EN 1918-4:1998 33

European foreword

This document (EN 1918-4:2016) has been prepared by Technical Committee CEN/TC 234 “Gas infrastructure”, the secretariat of which is held by DIN

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by September 2016 and conflicting national standards

shall be withdrawn at the latest by September 2016

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights

This document supersedes EN 1918-4:1998

This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association

For a list of significant technical changes between this European Standard and EN 1918-4:1998, see Annex B

This document is Part 4 of a European Standard on “Gas infrastructure - Underground gas storage” which includes the following five parts:

— Part 1: Functional recommendations for storage in aquifers;

— Part 2: Functional recommendations for storage in oil and gas fields;

— Part 3: Functional recommendations for storage in solution-mined salt cavities;

— Part 4: Functional recommendations for storage in rock caverns;

— Part 5: Functional recommendations for surface facilities

Directive 2009/73/EC concerning common rules for the internal market in natural gas and the related Regulation (EC) No 715/2009 on conditions for access to the natural gas transmission networks also aim at technical safety including technical reliability of the European gas system These aspects are also

in the scope of CEN/TC 234 standardization In this respect, CEN/TC 234 evaluated the indicated EU legislation and amended this technical standard accordingly, where required and appropriate

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom

1 Scope

This European Standard covers the functional recommendations for design, construction, testing, commissioning, operation, maintenance and abandonment of underground gas storage (UGS) facilities

in mined rock caverns up to and including the wellhead

This European Standard does not cover the technology of lined rock

NOTE 1 Even if not covered in this standard, the lined rock is an available technology

This European Standard specifies practices which are safe and environmentally acceptable

For necessary surface facilities for underground gas storage, EN 1918-5 applies

In this context, "gas" is any hydrocarbon fuel:

— which is in a gaseous state at a temperature of 15 °C and under a pressure of 0,1 MPa (this includes natural gas, compressed natural gas (CNG) and liquefied petroleum gas (LPG) The stored product

is also named fluid);

— which meets specific quality requirements in order to maintain underground storage integrity, performance, environmental compatibility and fulfils contractual requirements

This European Standard specifies common basic principles for underground gas storage facilities Users

of this European Standard should be aware that more detailed standards and/or codes of practice exist

A non-exhaustive list of relevant standards can be found in Annex A

This European Standard is intended to be applied in association with these national standards and/or codes of practice and does not replace them

In the event of conflicts in terms of more restrictive requirements in the national legislation/regulation with the requirements of this European Standard, the national legislation/regulation takes precedence

as illustrated in CEN/TR 13737 (all parts)

NOTE 2 CEN/TR 13737 (all parts) contains:

— clarification of relevant legislation/regulations applicable in a country;

— if appropriate, more restrictive national requirements;

— national contact point for the latest information

This European Standard is not intended to be applied retrospectively to existing facilities

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies

EN 1918-5, Gas infrastructure - Underground gas storage - Part 5: Functional recommendations for

surface facilities

3 Terms and definitions

3.1 Terms and definitions common to parts 1 to 4 of EN 1918

For the purposes of this document, the following terms and definitions apply They are common to parts

cushion gas volume

gas volume required in a storage for reservoir management purpose and to maintain an adequate minimum storage pressure for meeting working gas volume delivery with a required withdrawal profile and in addition in caverns also for stability reasons

Note 1 to entry: The cushion gas volume of storages in oil and gas fields may consist of recoverable and recoverable in-situ gas volumes and/or injected gas volumes

all technical activities connected with the investigation of potential storage locations for the assessment

of storage feasibility and derivation of design parameters

Note 1 to entry: The maximum operating pressure is related to a datum depth and in caverns usually to the casing shoe of the last cemented casing

3.1.26

minimum operating pressure

minimum pressure of the storage reservoir or cavern, normally reached at the end of the decline phase

of the withdrawal profile and for caverns is based on geomechanical investigations to ensure stability and limit the effect of subsidence and normally has to be approved by authorities and has not to be underrun

Note 1 to entry: The minimum pressure is related to a datum depth

3.1.30

permeability

capacity of a rock to allow fluids to flow through its pores

Note 1 to entry: Permeability is usually expressed in Darcy In the SI Unit system permeability is measured in

subsurface safety valve

valve installed in casing and/or tubing beneath the wellhead or the lower end of the tubing for the purpose of stopping the flow of gas in case of emergency

3.1.40

well integrity management

complete system necessary to ensure well integrity at all times throughout the life cycle of the well, which comprises dedicated personnel, assets, including subsurface and surface installations, and processes provided by the operator to monitor and assess well integrity

3.1.41

wellhead

equipment supported by the top of the casing including tubing hanger, shut off and flow valves, flanges and auxiliary equipment, which provides the control and closing-off of the well at the upper end of the well at the surface

3.1.42

working gas volume

volume of gas in the storage above the designed level of cushion gas volume, which can be withdrawn/injected with installed subsurface and surface facilities (wells, flow lines, etc.) subject to legal and technical limitations (pressures, gas velocities, flowrates, etc.)

Note 1 to entry: Depending on local site conditions (injection/withdrawal rates, utilization hours, etc.) the working gas volume may be cycled more than once a year

3.1.43

workover

well intervention to restore, increase production, repair or change the completion of a well or the leaching equipment of a cavern

3.2 Terms and definitions not common to parts 1 to 4 of EN 1918

For the purposes of this document, the following terms and definitions apply which are common to part

4 of EN 1918 only

3.2.1

capillary threshold pressure

pressure needed to overcome the property of a porous rock saturated with a wetting phase (water) to block the flow of a non-wetting phase (gas)

computer simulation of a system

Note 1 to entry: Applied for stability analysis, hydraulic flow pattern around an excavation

rock cavern roof

highest part in a rock cavern average cross section

4 General requirements

4.1 General

This clause gives general requirements for underground gas storage More specific requirements for underground gas storage in mined rock caverns are given in Clauses 5, 6, 7, 8 and 9

4.2 Underground gas storage

4.2.1 Overview and functionality of UGS

The EN 1918 covers storage of natural gas, Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) Because of the relevance of underground gas storage of CNG, the major part of this introduction

is related to this

The underground gas storage is an efficient proven common technology and is in use since 1915 Underground gas storage (UGS) became an essential indispensable link in the gas supply chain for adjusting supply to meet short-term and seasonal changes in demand

Natural gas produced from oil and gas fields is increasingly being used to supply energy requirements

As the gas supply from these fields does not match with the variable market demand natural gas is injected into subsurface storage reservoirs when market demand falls below the level of gas delivery or

if there is an economic incentive for injection Gas is withdrawn from storage facilities to supplement the supply if demand exceeds that supply or withdrawal is economically attractive

The primary function of UGS is to ensure that supply is adjusted for peak and seasonal demand Apart from this, the storage facilities can provide stand-by reserves in case of interruption of the planned supply Increasingly, UGS is applied for commercial storage services

Thus, in summary underground gas storage facilities can be used for:

— security of supply;

— providing flexibilities;

— balancing of seasonal demand variabilities;

— structuring of gas supply;

— provision of balancing energy for the optimization of transport grids;

— trading and arbitrage purpose;

— stand-by provisions and strategic reserves;

— structuring renewable energy sources – power to gas;

— storage of associated gas as service for production optimization and resultant environmental conservation

4.2.2 Types of UGS

For storage of natural gas, several types of underground gas storage facilities can be used which differ

by storage formation and storage mechanism (see Figure 1):

— pore storage:

— storage in aquifers;

— storage in former gas fields;

— storage in former oil fields

— caverns:

— storage in salt caverns;

— storage in rock caverns (including lined rock caverns);

— storage in abandoned mines

For LPG storage, only salt or rock caverns can be applicable

The UGS type applied is dependent on the geological conditions and prerequisites as well on the designed capacity layout

4.2.3 General characterization of UGS

UGS are naturally or artificially developed reservoirs respectively and/or artificially developed caverns

in subsurface geological formations used for the storage of natural gas or LPG An UGS consists of all subsurface and surface facilities required for the storage and for the withdrawal and injection of natural gas (or storage of LPG) Several subsurface storage reservoirs or caverns may be connected to one or several common surface facilities

The suitability of subsurface geological formations have to be investigated individually for each location, in order to operate the storage facilities in an efficient, safe and environmentally compatible manner

In order to construct a storage facility, wells are used to establish a controlled connection between the reservoir or cavern and the surface facilities at the well head The wells used for cycling the storage gas are called operating wells In addition to the operating wells, specially assigned observation wells may

be used to monitor the storage performance with respect to pressures and saturations and the quality

of reservoir water as well as to monitor any interference in adjacent formations

For the handling of the gas withdrawal and gas injection, the surface facilities are the link between the subsurface facilities and the transport connection point, comprising facilities for gas dehydration/treatment, gas compression, process control and measurement

Gas is injected via the operating wells into the pores of a reservoir or into a cavern, thus building up a reservoir of compressed natural gas or LPG

Gas is withdrawn using the operating wells With progressing gas withdrawal, the reservoir or cavern pressure declines according to the storage characteristic For withdrawal, re-compression may be needed

The working gas volume can be withdrawn and injected within the pressure range between the maximum and minimum operating pressures In order to maintain the minimum operating pressure it

is inevitable that a significant quantity of gas, known as cushion gas volume, remains in the reservoir or cavern

The storage facility comprises the following storage capacities:

— working gas volume;

For specific elements of an underground gas storage facility, e.g wells and surface installations, existing standards should be applied

4.2.4 Storage in mined caverns

Generally spoken, a mined cavern storage facility comprises subsurface facilities of access works by tunnel or/and shaft, one or several galleries, excavated in hard rock, operation shaft and related surface facilities for handling of the stored product

Unlined mined cavern technology is widely used in the field of underground storage for:

— liquids (crude oil, distillates, etc.);

— liquefied petroleum gas (LPG)

Within a limited scope, this technology is adapted for underground storage of compressed natural gas (CNG) in lined or unlined rock caverns

Recently Lined Cavern technologies have been developed extending the field of application of the underground storage technics to Compressed Natural Gas (LRC CNG) and Membrane Lined Rock Cavern for Liquefied Natural Gas (MLRC LNG) For both concepts (LRC CNG and MLRC LNG), product tightness

is provided by a steel liner For MLRC, the steel liner is completed by a thermal insulation and a water drainage system when necessary This functional recommendation focus on the design, construction and operation principles of underground storage in unlined mined caverns for LPG and CNG products (see Figure 2) It does not cover gas storage Lined Rock Caverns nor Membrane Lined Rock Cavern Underground storage in mined caverns is an alternative to underground storage in salt leached caverns especially where the local geological conditions do not provide salt or where the salt does not offer suitable characteristics for solution mining

The main advantage of this technology relies on its adaptability to several geological conditions allowing implementing the storage capacity close to needs

Most favourable geological conditions for implementing an unlined mined cavern are typically igneous, metamorphic or hard sedimentary rocks such as granite, gneiss, andesites, shales, limestones, rock salt

Another compulsory prerequisite for LPG storage in unlined mined caverns is the presence of a favourable hydrogeological context to ensure the hydrodynamic containment conditions of the stored product Water curtain systems and grouting works could be developed in order to improve the natural conditions and control the hydraulic containment of the stored product during the lifetime of the storage facility

The specific complementary prerequisite for CNG storage in mined caverns is a proven gas tightness of the rock mass The proof of the tightness has to take into account the presence of fractures

Underground storage in mined caverns is a safe way to create reserves of oil and gas products in the immediate vicinity of producing, importing or consuming centres such as:

— refineries, import or export terminals;

— petrochemical complexes for which LPG constitutes a feedstock;

— regional feedstock for resale;

— stockpiling

The hydraulic containment principle for LPG storage in unlined mined rock caverns relies on the groundwater pressure prevailing in the adjacent rock mass The cavern is located at such a depth that the water naturally present in the surrounding rock flows everywhere towards the cavern preventing the stored product from migrating into the rock mass The favourable effects of the capillary threshold pressure are considered as an additional safety term

The product, lighter than and hardly miscible with water, is in this way hydraulically contained within the storage space

The water which is collected in the cavern during operation is removed by pumping, treated and disposed of or recycled

Furthermore, depending on the required commercial product specifications, coalescers and/or dryers are implemented at the surface if necessary for the product during withdrawal Stripping units are implemented before disposal or recycling if necessary for the seepage water

The control of the gas containment conditions for CNG storage in unlined mined rock caverns is provided by the capillary pressures and/or hydraulic potentials of the host rock mass

Key

1 LPG outlet 10 concrete plug (shaft)

3 seepage water outlet 12 rock mass

4 ground level 13 concrete plug (tunnel)

5 water inlet for water curtain 14 access tunnel

6 operation shaft 15 LPG, liquid phase

8 water curtain boreholes 17 LPG pump

9 water curtain gallery 18 water pump

Figure 2 — Cross section of a typical unlined rock cavern for LPG

4.3 Long-term containment of stored products

The storage facility shall be designed, constructed and operated to ensure the continuing long-term containment of the stored fluids

This presupposes:

— adequate prior knowledge of the geological formation in which the storage is to be developed and

of its geological environment;

— demonstration that the storage is capable of ensuring long-term containment of the stored fluids through its hydraulic and mechanical integrity

All operations adjacent to a storage facility shall be compatible with the storage activity and shall not endanger its integrity

All new storage projects shall take into account existing adjacent activities

In addition to the usual safety rules and recommendations applicable to all comparable industrial installations, measures shall be taken to reduce the risk and consequences of blow-out and leakages

A safety management system should be applied

Proven technology shall be used for analysis and calculations All relevant data should be documented Technology proven in the oil and gas and mining industry should be used where possible

The design shall be based on written procedures and shall be carried out by competent personnel and companies

The key parameters governing the design, construction and the safe operation of a mined rock cavern underground storage include:

— long-term stability;

— containment of the stored product;

— absence of detrimental environmental impact;

— absence of impact on product quality during storage time The product stored is delivered after the storage period in a state compatible with the users' requirements

Specific monitoring devices and procedures are implemented during construction and operation periods for checking the key parameters

Usually, an unlined mined rock cavern storage facility for LPG (see Figure 2) comprises one or several galleries, excavated from an access shaft or ramp and located at sufficient depth to reach the suitable rock mass level and to ensure the hydraulic containment of the product to be stored

The access works are first used for the excavation of the caverns and may consist of:

— an inclined tunnel;

— one or several shafts with extraction equipment;

— a combination of one or several shafts and an inclined tunnel

The storage cavern is made up of main galleries of variable sections, according to rock type and depth The gallery length depends upon the configuration of galleries and the required storage capacity

Connection galleries, generally of smaller sections, may connect the main galleries They allow for easy disposition of personnel, materials and equipment and for ventilation during the construction phase Furthermore, they provide circulation of water and stored product between the galleries during the operation phase and contribute to the storage capacity

If deemed necessary for improving and controlling the hydrogeological conditions of the site, a specific water curtain system composed of water galleries and water injection boreholes, is installed above or/and at the periphery of the storage cavern

The most commonly used excavation method in hard rock is drilling and blasting Alternative methods include road headers or tunnelling machines The choice of method is determined mainly by the rock mass properties and the size of the excavations but also by the cost and availability of equipment

The storage cavern equipment for operation, such as casings and tubings for stored product, water casing pumps and other instrumentation devices, are generally run in dedicated operation shafts

Before the storage facility is put into operation, the cavern galleries are isolated from the access shaft and/or ramp by concrete plugs located near the cavern entrance A concrete plug is installed at bottom

of the operation shaft, close to rock cavern roof

The access shaft and/or ramp, water curtain systems and operation shaft are flooded with water prior storage cavern commissioning and operation start-up

Emergency procedures should be developed

Adherence to the safety and environmental requirements shall be monitored

During the design phase, the following activities and reviews related to safety will be carried out, including but not limited to: