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Underground Storage
InRock Caverns
November 9th2009
Rajan K Pillai
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Going UndergroundGoing Underground
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Types of Underground Storages
Salt Leached Caverns.
Aquifers or Depleted fields
Disused mines.
Underground Rock Caverns (Unlined & lined)
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Salt Dome
Salt Leached Caverns
Borehole
Water injection Brine
Several
hundredmeters Tens of
meters
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Aquifers
Impermeable stratum
Porous & Permeable
Geological formation
Hydrocarbon Storage
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Disused Mines
Water table
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The finished rock cavern for LPG at Visakhapatnam
Example of an Underground Unlined Rock Cavern
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Comparison of Depths of LPG andCrude Caverns
-30 m
-162 m
SALPG LPG Cavern ISPRL Crude CavernMean Sea Level
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Example of cavern using a rampfor Access
Inclined Ramp
Water
Curtain
Main Storage GalleriesOperation Shafts
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Access Ramp (AR)
Upper Connection (UC)
Intermediate connection
(IC)
Upper Shaft Connection (USC)
Access Shaft (AS)
Operation Shaft (OS)
Lower Shaft Connection(LSC)
Water Gallery Operation
Shaft Connection (WOC)
Water Gallery Access
Shaft Connection (WAC)
Water Curtain Gallery
(WCG
Sump which houses the
submersible pumps
Lower connection (LC)
Example of Cavern Using Vertical Shaftfor Access
Source : SALPG
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Equipment lowering throughShaft
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Systems required for
access & mucking in
case of Shafts
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Mean Sea Level(MSL)
Water Curtain
Boreholes Water curtain tunnels
Storage Caverns
Separation of differentproducts to be stored
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Design for light Products andCrudes (Flat Invert)
- Caverns for light products & crudes can be designed to
have flat inverts with water beds (water bed not required
for LPG)- These caverns have no heating systems.- Can be made for products which do not have major
sludge problems
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- Caverns are designed to have a slope for ensuring a proper
flow towards the sumps.- Heating system provided for heating and circulation of the
product stored.- The design permits storage of heavy oils and heavy crudes.
Design for Heavy Products and Crudes(Sloping Invert)
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Storage Caverns
Inertisation of caverns (products other than LPG)
Connecting the vapour spaces can reduce the requirement of inert
gas.
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Storage capacity
Cost/
m3o
fstorage
Caverns in less
favorable geological
conditions
Caverns in favorable
geological conditions
Lower Marginal Costs For larger volumes
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Large size- Need for benching
For large caverns there is a need to
excavate the caverns in steps. The topheading is completed first followed by
benching
Ten story
building
30 M
20 M
Top Heading
Benches
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Excavation method adopted forlarge caverns
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Need for Access to Various Levels inLarge Caverns
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Excavation Using Drill & Blast (For Hard Rock)
Two Boom Jumbo (Used for drilling in hard rock)
D illi & Bl ti M th d f E ti
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Drilling & Blasting Method of Excavation
Holes are charged
with explosives afterdrilling andcontrolled blastingcarried out
Jumbo used fordrilling holes inrock
D illi & Bl ti M th d f E ti
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Pull
Drilling & Blasting Method of Excavation
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Excavation using Road Headers(For Soft Rock)Road Headers (Used in case of soft to medium hard rock Limestone,
Chalk etc)
Example of Rock Cavern constructed using road headers for top heading &
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Example of Rock Cavern constructed using road headers for top heading &
blasting for benching followed by trimming by road headers. Cross section is
85 sq m
Source : Geostock
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Crude
Tankers
Crude
Cavern
Boiler
For
Horticulture
For Water Curtain
Inert Gas
Booster Station
Heat Exch.
Stage 1 Stage 2Carbon
Filter
ETP
Booster
Pumps
Flare
Submersibl
e Pumps
Typical Scheme for CrudeCaverns All aboveground facilities will
be as per standard Oil industry
practices. Layout shall be asper OISD guidelines
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Lined Rock Caverns
These types of storage facilities can be used for small or medium sized caverns.
The lining can be steel or plastics. In the depths are large the linings have to be
designed to counter the hydrostatic pressure or the can get
Steel or
plastic lining
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Over breaks and rock falls
Over breaks as shown can slow down progress to a
large extent. Also a major safety issue.
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Method of addressing poor rockconditions
To ensure there is good stability of the cavern, rock bolts need to be installed
and shortcrete applied. Poorer the rock strata, larger is the support
requirement.
Rock bolts
Shotcrete
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Example of Poor RockConditions
Large number of cracks and fissures in the rock could
lead to large over breaks .and excessive supports
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Example of a water bearingzone
Water bearing zones could result in large water ingress
if pre-grouting is not resorted to. The time taken up by
grouting could delay excavation.
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Pre-Grouting in excessive waterbearing zones
Pre-Grouting involves
drilling a number of
holes on the face and
pumping cement paste
under pressure into
them till sealing is
achieved.
High permeability and water bearing strata could
result in higher grouting and slow excavation
progress.
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Water Table Monitoring
Water table
Typical Excavation progress curves for
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Typical Excavation progress curves forUnderground caverns
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Advantages of going underground
Product is located at a depth and is fully isolated.
External Fires will not affect Storage
Maximum security. Safety hazards on account of sabotage, storms,
earthquakes and explosions are minimized.
Surface land requirement is low
Caverns by their very nature require very low maintenance.
Beyond certain capacities the capital cost per ton of storage is low.
Environment benefits. The rock debris generated can be used for
infrastructure development.
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