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Underground Rock Cavern Storages Challenges and Project ManagementR K Pillai, CEO, Indian Strategic Petroleum Reserves Limited (ISPRL)

With rapid economic growth and the increasing energy requirement of Indian households, the issue ofEnergy Security has assumed importance. In view of the countrys high dependence on imported crudeoil, volatility of oil prices in the international market as well as perpetual political instability in some ofthe major oil exporting nations/regions, the Indian Government appointed Indian Strategic PetroleumReserves Limited (ISPRL), a special purpose vehicle (SPV), to build and commission strategic storageof crude oil at three locations (Visakhapatnam, Mangalore, and Padur) to ensure uninterrupted supply ofcrude oil to the countrys large and well spread energy supply chain. R K Pillai, CEO, Indian StrategicPetroleum Reserves Limited (ISPRL), details the challenges and geological risks while excavating theunderground rock caverns storages. He also describes the magnitude of works, project management, andbidding process in successfully commissioning the underground caverns. Edited excerpts from Pillaispresentation delivered during the Oil & Gas World Expo 2014.

In January 2006, the government approved the financial plan for the strategic reserves to create 5 millionmetric tonnes (MMT) of crude oil storage. The capacity is almost 75 days of the entire crude oilproduction of ONGC. This storage was to be in underground rock cavern. The client ISPRL wasrequired to create the largest underground caverns, ever excavated, in the country, without any technicalexpertises, the necessary land acquisition, environment clearance and supporting infrastructure, within atimeline of six years. The height of the caverns is almost equivalent to a ten story building and the mainstorage galleries as long as 913 meter.

Risk & Challenges Involved in Underground Works It is noted that storage in rock caverns is akin to storage ofhydrocarbon and porous vessels. Hence there were challengeswith respect to containment of products. Unlike aboveground

works where it is possible to a large extent to determine the timelines required for different activities,determination of timelines for underground works is not easy because geology can change very rapidlyin underground works.

Drilling & blasting method for excavation in underground works can vary depending upon the rockquality. When the rock quality is good, it is possible to excavate large quantum of rock, but when therock quality is poor, excavation can be painfully slow. This is because the support requirements forstabilising the cavities are different.

This is a major factor in deciding the timelines for underground project and can also be a major issuewhile deciding the performance of a contractor. A good contractor despite his best effort can end upbeing slow in excavation when he encounters poor rock condition. Geological risks during constructionof underground cavern include wedge failures that can cause fatalities and slow down the progress of theproject.

Fault can cause a rock slide, hidden behind the bench. When the bench is excavated because of theweight of the rock, a rock slide can occur, and huge quantities of rock can come crashing down,resulting in accidents and delays.

Water bearing zones or aquifers could result in large water ingress into caverns or shafts, resulting in aslow down of works. Such problems were encountered by ISPRL in cavern projects in Vishakhapatnam.Water jetting out of the joints of the caverns with a speed as high as 17/18 kg per square centimeter cancreate problems for the progress of the underground works.

Large number of equipment are deployed for excavation of caverns in underground works and handlingthese equipments like loaders, huge excavators PC 200 can be risky because these are louveredthrough shafts.

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Magnitude of Works in Caverns A typical process scheme of crude cavern is included theconstruction of both underground and aboveground facilities(Figure 1). Aboveground facilities are to be constructed as perstandard oil industry practice and layout shall be as per OilIndustry Safety Directorate (OSID) guidelines.

For the underground facilities, the quantum of excavationmade by ISPRL is shown in Figure 2.

In Figure 2, the encircled highlights that the total tunnelingrequirement was approximately 30 km, drilling of borehole of water curtain was to the extent of 76 kmand rock excavation was almost 22 million tonnes. The excavated rock debris can fill almost 2.5 millionstandard 10 ton trucks.

For the underground facilities, the quantum of material usedby ISPRL is shown in Figure 3.

Figure 3 shows that the amount of concrete used was around1,77,000 cubic meter, shotcrete around 94,000 cubic meter,rock bolts around 7,000 tonnes, reinforcement steel around10,000 tonnes and explosive around 8,300 tonnes.

The aboveground facilities were also a complex task; and packages and systems used by ISPRL inaboveground facility included:

In-shaft facilitiesDCS, Metering skids and instrumentationHot oil circulation system including boilers & heatexchangersDiesel/Fuel oil storage facilitiesFlare systemNitrogen system

Effluent treatment plantElectrical substation, switchyard and distribution systemStandby generatorCompressed air supply system

The quantum of work involved in the aboveground facility was equal to a crude unit in a medium sizerefinery.