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UNDERGROUND STORAGE OF NATURAL GAS - AN OVER VIEW. Overview. A vailability of energy at a steady rate and at a reasonable cost are vital for sustainable economic development of India . Two basic reasons, why the use of natural gas as fuel source is expected to increase:

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  • Availability of energy at a steady rate and at a reasonable cost are vital for sustainable economic development of India.
  • Two basic reasons, why the use of natural gas as fuel source is expected to increase:
    • Natural gas is environment friendly
    • Reserves of natural gas are comparable to those of crude oil with much lower consumption levels, accordingly, natural gas could last longer than crude oil.


  • With about 8% current energy consumption contributed through natural gas, the projected demand is estimated to grow about 5% per annum upto 2025.
  • Projected demand for power generation and fertiliser plants is expected to grow manifold.
  • Energy outlook of India is on a definite transformation owing to recent gas finds.

Projected Gas Demand

Source: : IRADe-PwC Report Fuelling India’s Future (Early 2008 figures)


Energy Security

  • Intensive exploration for oil & gas through NELP
  • Exploration by national oil companies
  • Increasing recovery of oil & gas from existing fields by EOR technique
  • Exploring for alternative sources of hydrocarbons such as CBM, Gas Hydrates etc.
  • Acquisition of equity oil abroad
  • Augmentation of gas supply through import of LNG & trans national gas pipelines
  • Creating strategic & commercial reserves

Why Strategic & Commercial Storage of Natural Gas?

  • Spurt in development & usage of CNG, both for transportation sector and domestic markets.
  • Disruptions in gas supply through proposed trans national pipelines
  • In line with the energy security mandate of common minimum programme of Govt. of India.
  • Strategic & commercial storageof natural gas will cater fluctuation in demand, besides providing a buffer against natural disasters, war or similar events that may affect the production or supply of natural gas.

Gas Infrastructure Drivers

  • Industrial sectors
  • Automotive sectors
  • Residential + Commercial sectors
  • Gas based power generation
  • Fertilizer plants

Studies, so far

In pursuance of the objective of creating strategic storage of natural gas, Ministry of Petroleum & Natural Gas (Govt. of India) has already initiated action.

Engineers India Ltd. was assigned the task of preparation of the Pre-Feasibility Report. The PFR has been submitted to MoPNG /OIDB and is under active consideration on Govt. of India for further progress on the subject.


International Scenario

  • Over 400 Natural gas storages in U.S.A.
  • Over 600 Natural gas storages world wide
    • 450 nos. in Depleted Reservoirs
    • 80 nos. in Deep Aquifers
    • 70 nos. in Salt Caverns

USA Gas Storage Capacity – Volume Distribution

  • Total Storage Capacity, MMcf 8,255,042
    • Salt Caverns 2.9% 239,990
    • Aquifers 15.0% 1,238,158
    • Depleted Fields 82.1% 6,776,894
  • Total Withdrawal Capacity, Bcf/d 76
  • Total Number of Active Fields 393
    • Salt Caverns 7.6% 30
    • Aquifers 11.0% 43
    • Depleted Fields 81.4% 320

USA Gas Cavern Working Capacity

Source: US Energy Information Agency


USA Gas Cavern Inventory Levels

Source: US Energy Information Agency


Surface Vs. Underground Storage


  • Do not meet safety requirements to withstand enemy attacks during wars
  • Vulnerable to fire hazards as a result of mal-operations and accidents
  • Occupy large area of valuable land


  • Have inbuilt safety to withstand attacks during wars
  • Resistant to fire hazards
  • Economical for larger capacities

Types of Sub-surface Storage of Gas

Sub-surface storage of Gas

Natural Gas

Coal Gas

H2, CO2 , CO, etc.

Porous Media

Void Space

Abandoned Mines

Depleted Reservoirs

Deep Aquifers

Salt Domes

Salt Layers

Oil Fields

Gas Fields

Mined Caverns

Dissolved Caverns


Underground storage of Natural Gas

  • Total gas storage capacity is the maximum volume of natural gas that can be stored at the storage facility.
  • Base gas (also referred to as cushion gas) is the volume of gas that is intended as permanent inventory in a storage reservoir to maintain adequate pressure and deliverability rates throughout the withdrawal season.
  • Working gas capacity is the total gas storage capacity minus the base gas.

Underground storage of Natural Gas

  • Physically unrecoverable gas is the amount of gas that becomes permanently embedded in the formation of the storage facility and that can never be extracted.
  • Cycling rate is the average number of times a reservoir’s working gas volume can be turned over during a specific period of time. Typically the period of time used is one year.


Schematic Diagram for Storage Types

The principle of storage in depleted reservoir is simple, because the reservoir formerly contained gas or oil. Hence it satisfies the permeability & porosity conditions required for storage.

However, before developing a gas storage in a depleted field, it is indispensable to check whether it corresponds to required withdrawal rate and imperviousness of the cap rock.


Schematic Diagram for Storage Types

The predominant type of underground storage of natural gas consists of depleted gas / oil reservoir.

This type of storage is the cheapest and easiest to develop, operate and maintain.

The cushion gas for depleted reservoir storage option is high (about 50%).




Schematic Diagram for Storage Types

The principle of storage in salt caverns involve dissolving salt with fresh water and removing the brine through a process, called as Solution Mining.

However, before developing a gas storage in a salt formation, establishment of its geologic characteristic features determining its suitability is important.


Schematic Diagram for Storage Types

Underground salt formations both salt domes / bedded salt formations offer option of natural gas storages called as salt cavern storages.

Though the process of creating the cavern is relatively expensive, once created the salt caverns offer a high deliverability. The cushion gas component in this option is low (about 30%).




Schematic Diagram for Storage Types

The principle of storage in deep aquifers is to create an artificial gas field by injecting gas into the voids of an aquifer formation.

Therefore, geologic conditions such as an anticline with sufficient closure, a porous and permeable reservoir and excellent quality cap rock are prime requisites.


Schematic Diagram for Storage Types

Deep Aquifer formations need confirmation to be used as natural gas storage.

As these facilities are more expensive than the depleted reservoir types, the deep aquifer storages are usually taken up in areas where there are no depleted reservoir options and that the sub-surface geology of the area suits the requirements.



Underground storage of Natural Gas

  • underground storage of natural gas is mainly located within Sedimentary Basins

Source : DGH

Sedimentary Basins of India

  • Sedimentary Basins of India occupy 3.14 M Sq.Km.
  • 0.39 M Sq. Km. is in Offshore up to 200m water depth.
  • 1.35 M Sq. Km. is in deep waters beyond 200m.
  • 1.40 M Sq. Km. is in Onshore.
  • India is endowed with 26 major sedimentary basins of an estimated 50,000m thick Sediments.

Aspects for Storage Performance

  • Verification of Inventory (Capacity)
  • Containment against Migration (Operating Parameters)
  • Assurance of Deliverability (Efficiency)

Approach for Regional Assessment

  • Reconnaissance Survey
  • Regional Geological Setting
  • Regional Ground Water Table

Parameters vis a vis Types of storages

  • Anticlinal Geometry
  • Stratigraphic Lenses
  • Faults / Structural Traps
  • Deep Aquifers
  • Salt Caverns
  • Depleted Reservoirs
  • Self Healing Salt Formations
  • Depleted / Marginal Reservoirs

Reservoir Characteristics

  • Porosity
  • Directional Permeability
    • Vertical Migration
    • Horizontal Migration

Reservoir Characteristics

PorosityPermeabilityin %in millidarcies

  • Storage Media 6-35 0.01-7,000
      • Sand Stone
      • Fractured Limestone
  • Impervious Caprock 1-12 zero-0.0001
      • Shale
      • Limestone
      • Anhydrite

Critical Issues for Deep Aquifers/Depleted Reservoirs

  • Geometric Shape
    • Inverted Saucer preventing vertical and lateral migration
  • Caprock Matrix
    • Permeability, Porosity and Threshold Pressure
  • Continuity
    • Freedom from anomalies
  • Leakage Detection
    • Tracer Study

Salt Cavern Storage

  • Features
    • Large volume
    • Hydrocarbon liquids & gas, compressed air, hydrogen
    • Impermeable containment
  • Advantages
    • Less costly (larger scale)
    • Excellent physical security
    • Lower environmental impacts
  • Disadvantages
    • Geological limitations
    • Longer to construct

Salt Cavern Storage

  • Benefits for natural gas storage
    • Salt provides an impervious barrier
    • Very high deliverability
    • Good [ working gas : total gas ratio ]

Key Design Elements - salt cavern storage

  • Cavern and well integrity
  • Geomechanical stability
  • Salt creeping and convergence
  • Cavern separation
  • Surface subsidence
  • Maximum operating pressure
  • Minimum operating pressure
  • Cavern shape, roof span
  • Web or pillar width

Typical Salt Cavern Storage Characteristics

Bedded Salt Caverns

  • Size
    • 50 000B to 1 MMB
  • Depth
    • Top of Salt: 500’ – 1,000’
    • Depth to Roof: 500’ – 3,000’
  • Short and Squat
    • Cavern Height: 30’ - 300’
    • Diameter: 75’ – 300’

Domal Salt Caverns

  • Size
    • 2 to 15 MMB (& larger)
  • Depth
    • Top of Salt: 500’ – 2,000’
    • Depth to Roof: 2,000’ – 4,000’
  • Tall & Slender
    • Cavern Height: 500’ – 2,500’
    • Diameter: 75’ – 300’

Attributes of Underground Storage

  • Large Aquifer offers the maximum potential storage capacity.
  • Deliverability from a Salt Cavern Storage is rated higher than other options
  • Therefore, when the two storage attributes, the Inventory (capacity) and the Deliverability are considered in relation to specific requirements of energy markets, it is clear that both Aquifer storage and Salt cavern storage command their respective justifications in economic desirability.





Trans-National Pipelines

Underground Strategic / commercial Storage

Regional Underground Storage Hubs

Trans-shipment of LNG Through Sea Port


Underground Storage of Gas


Strategic /Commercial Storage of Natural Gas

  • Present consumption is about 65 MMSCMD (as of 2008) of natural gassupplied to the consumers.
    • About 40% of NG is used for power generation,
    • 28 % for fertilizer and balance
    • 32% for uses such as industrial, residential etc.
  • The 10th Plan document predicted increase in natural gas consumption from present 65 MMSCMD to 130 MMSCMD- double the consumption level in five years.
  • Vision 2025 document envisages consumption level of Natural Gas is expected to rise to 391 MMSCMD.

National Gas Grid

  • Development of Strategic / Commercial Gas Storage along with National Gas Grid will cater to energy integration of the nation.

Pre-Feasibility Studies

  • Based on the geology of the Indian sub-continent, and with a design basis that all strategic gas inventories should be located as near as practical to existing and planned gas transmission pipelines, initially ten prospective areas were identified :
  • Based on the desk studies of available literatures, geological maps etc. seven sites were retained for further studies.
  • The seven sites were comparatively ranked using a weighted scale of evaluation factors, where in the first four sites have been subsequently selected and are ranked as follows:
  • 1.North Gujarat (Depleted / Marginal Reservoirs)
  • 2.Bikaner (Salt Cavern)
  • 3.Kota (Deep Aquifer)
  • 4.Bhubaneswar (Deep Aquifer)

Pre-Feasibility Studies

  • In order to maximize the storage capacities at each of the candidate sites to the extent possible, with the intention of storing the proposed 3 BSCM of natural gas at each site, an assessment was made through the PFR studies.
  • The study revealed that while it is possible to store 3 BSCM in salt caverns at Bikaner and in depleted reservoirs in North Gujarat individually, the maximum capacities at Kota & Bhubaneswar are of the order of 1250 MMSCM.
  • While a published report from Geological Survey India outlines a detailed account of the bedded salt formation reported in the North Western part of Rajasthan, a recent study by ONGC reveals the details of salt formation in and around Sri Ganganager Dist. Rajasthan.

Pre-Feasibility Studies

  • An attempt was made in this study, to identify the depleted reservoirs that could be made available for storage of natural gas. However, several operators have declined to part with the reservoirs in the anticipation of enhanced oil recovery.
  • Thus it has been suggested by MoPNG that a mechanism should be in place so as to define the depleted reservoirs through a due diligence and subsequent relinquishment.
  • As of the salt cavern storage, the MoPNG / OIDB observed that the possibility of locating both the crude oil and natural gas storages at Bikaner should be explored further.


  • In India, interest in under ground gas storage, which is a relatively recent technique, has been developing rapidly. It can become an essential part of the gas chain.
  • Stimulated by the changes taking place in the gas market, application of underground storage of natural gas is expected to intensify.
  • The expected growth in gas demand, increased dependence on imports and the growing need for flexibility will strongly influence future storage requirements.
  • In addition, the storage infrastructure is gradually offering new opportunities (new services, storage for third parties, storage for transit), enabling the owners of the facilities to strengthen their position on the market.