Sign In Sign-Up

Welcome!

Close

Would you like to make this site your homepage? It's fast and easy...

Yes, Please make this my home page!

No Thanks

  Don't show this to me again.

Close

R. K. Goel, A. K. Dube

The energy shock of 1973 saw petroleum prices rising by hours rather than weeks and months and exposed the world economy’s vulnerability to petroleum exporting countries. The importing countries of the world forced to rethink and revaluate their strategies to meet the crisis. The world economy had still not recovered from the shock when the second shock of 1979 completely put the petroleum industry in disarray. The petroleum importing countries, whileputting their house in order to effectively face the situation both in political and economic fronts, thought of various strategies to create sufficient reserves to at least combat the immediate situation till a more lasting solution could be found.

Demand of oil, LPG and LNG for industrial and domestic uses is increasing world-over. India is not an exception. We contemplate growing demand and subsequently means to store it safely and economically ensuring environmental congeniality and safety. In our oil fields, gas is available but it is not sufficient to cater our needs. In view of this growing demand and the widening gap between demand and supply, a new strategy is needed for exploration, exploitation and storage.

As far as storage of petroleum and LPG and other products are concerned, every country has its own policy of storage of strategic products. Besides, the strategic considerations, the operational storages are voluminous. These storages in the conventional steel spheres and tanks require large space and other safety mechanism. The storage of petroleum products has to be built-up because of the following reasons:

(i) Operational requirements

(ii) Strategic needs

(iii) Gaining advantages of fluctuating oil prices

(iv) Unforeseen circumstances like political disturbances and political instability

In India, the oil installations are either within the populated areas or nearer to them, and are thus a potential hazard and danger to the population.

Social tensions, riots, terrorists attacks, etc. are unpredictable in nature and any fire occurring due to it may be devastating. Wars are also not ruled out and the surface tanks are sitting ducks for enemy attack.

The surface tanks under fire are difficult to save. The underground storages are free from fire hazards. Various advantages of going underground are as follows:

India today has steel tanks for crude and other petroleum products and the steel spheres for LPG as the usual modes for storages at the terminals, refineries distribution and consumption centers. The refineries have storages between 100,000 to 300,000 tonnes of crude in tanks of various sizes. Similarly the products from crude are also stored in tanks. However, the LPG in the steel spheres may have a total storages between 20,000 to 30,000 tonnes in refineries.

The crude and products are transported through pipelines between main centers. However, distribution for consumptions is usually done by tank wagons of railways and on road by oil tankers. The transportation net work draws oil from the storage within the refinery complex or the jetties near the import terminals. These locations are most suitable for construction of the underground storages. Underground storages can not be constructed at every location. They invariably need good rock formations.

India so far not has underground storage facility because of some or the other reasons. Currently, Hindustan Petroleum Corporation Ltd. (HPCL) are planning to have underground storage facility for LPG in Visakhapatnam area. Indian Oil Corporation Ltd. (IOCL) is also planning to have underground storage of crude oil. This shows that the awareness for the usefulness of underground storage of LPG and oil has increased recently.

In India the rocks of the western coast, the Aravalli system, Deccan plateau and Bundelkhand granites are broadly suitable for the underground storages (Figure 1).

The SMPL (Salaya Mathura Pipe Line) connects the following important towns along its route: Mathura, Bharatpur, Daosa, Tonk, Bhilwara, Nathdwara, Pindwara, Abu Road, Palanpur, Mehsana, Viramgram, Surendranagar, Rajkot, Jamnagar, and Narabeghet.

In a detailed examination of the feasibility of underground storage by a team constituted by the Govt. of India, emphasis was given to sites in the vicinity of Salaya and Bombay while other locations and modes were also examined. These are discussed in detail below.

An expert group was assigned the task of examining the possibility of utilizing existing subterranean caverns along the routes of the Salaya-Viramgam-Koyali and Viramgam- Mathura pipeline and also to examine the rock formations at Salaya with a view to creating mined caverns for storage. The scope of this Sub-Group was to find out locations of abandoned mines or other subterranean caverns along the pipeline route satisfying the following criteria: (i) it should have a capacity of approximately 1 million m³, (ii) it should preferably be located below water table and have a depth below water table of approx. 20 metres; and (iii) it should not block any future potential mineable areas.

The constraints in items (i) and (ii) above can be relaxed somewhat in case the required number of suitable mines of smaller capacity are available in the vicinity, or if the water head is less but the capacity is large. The same criteria as applied for mines would also be applicable for other subterranean caverns.

Two members of the Expert Group made field visits and held discussions with concerned Central and State Government organisations knowledgeable in the geology of the region.

A number of observations were made regarding the potentially suitable areas for crude oil storage:

The general conclusion is that abandoned mines of the capacity and water table requirements would not be available in these areas and also most of the old mines may be reopened at a future date. A number of mica mines are available in the Bhilwara area which could be considered for crude oil storage. However, the total volume of mica mines is very small compared to the volume required for the purpose of crude oil storage.

Studies have concluded that no abandoned mines or caverns are available in the general vicinity of the pipeline route.

The geology of the rock formations indicates that the area in the vicinity of the marine terminal at Salaya predominantly consists of basalts. However, very little drilling has been carried out in this area. The nearest place where drilling data is available is in the Chotila hill area. This shows basalt with inter-trappeans having a thickness of two to seven metres. These beds are localised in character.

In this area bore holes have been drilled up to depths of 30 m. The cores show that the top six to eight metres comprises weathered basalt followed by hard, fine textured basalt. Visual examination of open wells shows that below six metres, hard massive basalt occurs. It would require detailed drilling to determine the nature and type of the underlying rock strata.

The water level in the various wells was examined with a view to determining the permanent ground water table. In all the wells that were studied, the water level was observed to be within 6 to 8 m below ground level. It was concluded that due to the vicinity of the sea the ground water table is close to the mean sea level.

In general it can be said that the basalt is quite thick in this area. The water table is also suitable. Consequently, this area would be potentially suitable for creation of mined caverns for storage of crude oil.

The area in the vicinity of Chotila hill was also investigated for its suitability for creating mined caverns in inter-trappean beds. On examination it was found that the inter-trappean beds are isolated in nature and of very limited thicknesses. They are, consequently, likely to pose problems as compared to mining caverns in massive basalt.

This island is the main oil unloading/loading terminal for the BP and HP refineries. The geology of the area is similar to that on the main island as it comprises mainly of basalt rock. It is connected by submarine pipelines to BP and HP refineries. Although the rock formations on Butcher Island may be suitable, the area required for creation of mined caverns would not be available on this island. Also due to the close proximity to the sea, water inflow rates may be very high if the bed rock is fractured. Consequently, it is felt that an onshore area near the refineries will be more suitable.

The quantity of crude oil that could be stored in these caves is extremely limited - the maximum storage possible in the largest cave is only about 10,000 m³.

In the vicinity of the Grind-Well factory area near Uran, 0.5 to 1.0m thick dykes trending E-W and dipping 30° due North occur, cutting across the basaltic flows are present. The top 15 m cover at the quarry site is weathered and highly jointed. Four flows are present, with gentle dips due west and the basalt is dense and amygdaloidal in character; spheroidal weathering is noticed in dense flews. Dykes with NW-SE and WNW-ESE orientation are present. Near Borivili, a fault trending N 20°W and vertically disposed is present in a road-cut in the inter-trappean beds. In the quarry site behind the HP refinery near Trombay, dense and amygdaloidal basalts are seen. Seepage from junctions of flows has been observed and the weathering zone is about 6 m. On the basis of geological and engineering studies, the Deccan Traps exposed in the hills lying between HP refinery and Bhaba Atomic Research Centre, Trombay, are considered to be suitable for storage of crude oil in underground mined rock caverns. Large scale mapping, drilling and possibly geophysical surveys will be required for detailed design and feasibility studies.

Large number of railway tunnels in the Berghat section between Karjat and Khandala stations are located in amygdoloidal basalts, and in most of them only short spans are lined. Groundwater seepages in the tunnels along joints and contacts of flows. In the Bombay-Nasik sector there are a few short lengths of abandoned tunnels. In all these cases the caves have extremely limited volume for storage of crude oil and are far away from the refineries and marine terminal.

The Borra Caves, located about 100 km NNW of Visakhapatnam are in crystalline limestones of pre-Cambrian age belonging to the Khondalite group of rocks of the Eastern ghats. Prominent stalagmites occupy a part of the floor space of the main cave. There are a few stalactites also.

The main accessible part of the cave is roughly conical in shape with a diameter of about 33 metres and a height of about 20 m. Excluding the space occupied by the stalagmites, the volume of this accessible part of the cave works out to be about 5000 m3. There is a prominent shear zone on the southern side of the cave.

In view of the distance from the Visakhapatnam port (which will necessitate a 100 km pipeline for transporting stored crude to the refinery), the joints and the sheared nature of the limestone and the very small storage volume available, this cave is not suitable for storage of crude oil.

Oil Industry Development Board (OIDB) through Oil and Natural Gas Corporation Ltd. (ONGCL) has given a scientific study for the feasibility of underground storage of oil and gas in the areas near Vadodara, Delhi, Mathura and Jamnagar to Central Mining Research Institute (CMRI).

On the basis of the study at 10 locations in above four areas, CMRI has developed a site selection rating (SSR) criteria for the primary identification of the underground storage sites. SSR criteria was developed using the following five parameters:

(i) The Rock Mass Rating (RMR) obtained from the geomechanics classification (ii) Ground water condition

(iii) Nearness to petroleum network

(iv) Land use

(v) Nearness to rail / road networks

CMRI in its study has prima-facie found that almost all the four sites are suitable for the underground storage of crude oil and gas. However, the final decision shall be taken on the basis of the detailed feasibility study.

This method of storage can be traced back to the years 1939 to 1945. During World War II attacks against surface oil installations became commonplace and surface storage tanks were prime targets. Consequently, it was considered advisable to build these installations below ground, protected by a substantial rock cover. The first attempt at storage underground was by building steel tanks in caverns excavated in massive rock formations. Those types of tanks are still in existence and are being operated in Sweden and some other European countries. However, the inherent cost involved in building first a rock cavern and then a steel tank inside it has led to the abandoning of this method in favour of less expensive methods like using abandoned mines or mined unlined caverns for storage of crude oil or refined petroleum products. The basic principle is that because oil is lighter than water and does not mix with it, the underground cavern must be located wholly below the permanent groundwater table. This ensures that the oil is retained there because the groundwater present in the surrounding rock exerts pressure at all points greater than the hydrostatic pressure of the oil stored.

Increasing use of underground caverns, either natural or mined, is being made all over the world for storage of crude oil, petroleum products, liquefied natural gas and liquid ammonia. For the storage of LPG two techniques, i.e., refrigerated and pressurized caverns storage are being adopted world over. It is reported that in areas of earthquake risk the underground storage is virtually invulnerable provided pipes and fittings are flexibly anchored to the rock walls. As a rule of thumb, earthquake forces in underground structures may be taken as 50% of those at the surface. Following Table 1 gives an idea of some of the LPG (propane and Butane) and LNG underground storage facilities.

LPG, or liquefied petroleum gas, is a collective term for a number of petroleum gases in liquefied form. To keep these gases liquefied, they must either be stored far down in rock under high pressure and at ambient temperatures or closer to the surface, refrigerated under low pressure and low temperatures.

In the case of pressurized storage, the cavern has to be located deep enough to achieve a higher groundwater pressure around the cavern than the pressure from the gas inside the cavern. The LPG is stored at a pressure and boiling point corresponding to the temperature of the surrounding rock.

The ambient rock temperature is therefore of importance. The warmer the rock, the deeper the cavern must lie to reach the necessary level of groundwater pressure around the cavern.

Refrigerated cavern storage of LPG requires compressors and condensing equipment to maintain low temperature and low pressure in the cavern. The rock around the cavern is below freezing point for water, which means that the ground water is frozen in the fissures, thus forming a tight mantle of frozen rock around the entire cavern. Because of the low pressure in the cavern, the depth of the cavern can be reduced. The roof of such a cavern therefore only needs to be 20 to 30 metres beneath the surface.

TABLE 1

underground storage facilities for lpg and lng (source : geostock, france)

Salt is an ideal material for the creation of storage space. The world's largest underground oil storage system has emerged in Germany in a salt dome near Willhelmshaven. It has 50 caverns with a total capacity of about 14 million tonnes. In Germany's Ruestringen salt dome, a consortium of companies including ESSO and B.P. affiliates have used a leaching process to hollow out the cavities. The storages are created by drilling into the salt dome and pumping in fresh or sea water. Gradually the cavity emerges as water dissolves the salt, which is removed and the resulting brine is pumped away. The interest of German companies in salt caverns was a response to the al Government’s stockpiling regulations which required the companies to build sufficient storage to meet 65 days' demand at the previous year’s level of consumption.

The Ruestringen salt cavities hold about 9 million tonnes of oil in 52 caverns for six oil companies. The caverns are about 390 m high and about 30 m in diameter. The construction cost has been about half that for aboveground tank storage. Similar underground storage has been created by the Shell group to meet the stockpiling obligations of the refinery at Hamburg on Scotdorf salt dome. Near Bremen two caverns with a total capacity of 0.27 million tonnes were flushed out of a salt dome to meet the commitments of Mobil refinerias at Bremen, Werth and Neustadt.

In France about 80 km from Marseilles, Geostock used the leaching process in a project to create a storage capacity for 9 million tonnes of crude oil and diesel fuel These giant caverns range in height from 75 m to 480 m and in diameter from 19.5 m to 75 m.

At Fort Saskatchewan, Canada, the deepest hydrocarbon storage on the continent has been flushed out of a layer of salt which is more than one mile below the surface.

There are no strata with salt near any of the Indian refineries and hence this method is not applicable in India.

An abandoned coal mine has successfullly been used for storing crude oil in South Africa by Fenix Scissions Inc. of Tulsa (USA). The total cost of purchasing the coal mine, testing, and converting the mine for storage of crude was reported to be less than 15% of that for conventional crude tanks.

The Imperial Chemical Industries, U.K., are converting their disused anhydrite mine in Bikingham, Teaside for storage of oil from the North Sea.

At May Sur Orne in Northern France, Geostock has converted a disused ironstone mine to contain about 4 million tonnes of diesel fuel.

The use of reinforced cement concrete in constructing large reservoirs for crude oil storage was tried out in California, USA, during the years of the First World War, due to non-availability of steel. Such a use demonstrated not only its practicability but also its potential as a rival to conventional steel tanks. The adoption of concrete tanks is also considered feasible in the former USSR, and hence recommended as a worthwhile practice for crude oil/product storage. Large concrete reservoirs, resting on the seabed, have come into use for storing crude oil from the Norwegian Ekofisk oilfield in the North Sea. The use of concrete tanks for oil storage is now widespread in the North Sea offshore platforms where the concrete legs are routinely used for oil storage.

The Australian Oil & Gas Review reported that Firestone’s "Fabritank", a nylon-impregnated neoprene fabric which is very strong, can be used for bulk storage of fuels, oils and water upto about 5000 tonnes or even more and that it can be inserted as a pillow in underground excavations. The cost is said to be very low.

In view of the somewhat small capacity mentioned, this method may not meet the requirements of storage of crude oil for stockpiling purposes near our refineries processing imported crude.

Storage of LNG in inground tanks is quite popular in Japan. LNG inground storage tank is intrinsically safe for cryogenic, flammable LNG, since the liquid level stays below ground level and so the liquid never spills out on to the ground surface in any unexpected situations. The tank features a cylindrical configuration because of the structural advantage for inground structure. Its diameter is determined on the basis of cost and effective land use. Side and bottom slab are of reinforced concrete with which the tank is retained against earth pressure and ground water pressure. Inside insulation is installed which preserves the cryogenic condition of the tank interior. Membrane of thin stainless steel is also installed inside for liquid/gas tightness. Steel concrete composite dome roof is laced on the side wall for cutting off the air and keeping inner gas pressure. In the tank surrounding of its side and bottom, heating system is provided so as to control ground freezing.

LNG inground storage tank has been developed in Japan. One with 10,000 kl capacity was first constructed in 1970 in the Tokyo Gas’s Negishi Terminal. Many such tanks have been constructed with increased capacity since then.

The following factors affect the cost of underground construction:

(i) Rock Mass Behaviour

(ii) Size of Opening

(iii) Support requirements including lining, etc.

(iv) Ground water condition

(v) Cost of land

In the western countries the oil and gas had been stored in deep acquifers. Salt leached cavities, unlined mined caverns, inground and mounded tanks and above ground tanks are in vogue. Deep acquifers and the salt leached cavities were found to be most economical. The mined caverns compare well with the above ground tanks. Table 2 gives the cost comparison under French condition (1995). It may be seen that the mounded storages are the costliest of all.

We do not have any underground storage facility so far. The ONGC with the help of Engineers India Limited (EIL) investigated sites near Uran in Mumbai. These sites were prima-facie found suitable, subject to detailed investigations. As per the estimates of the year 1987-88 the underground storages were comparable to the surface storages for 500,000 cu.m of crude and 30,000 cu. m of LPG. Table 3 gives an idea of cost comparison of surface and underground facilities.

TABLE 2

compared costs for storage facilities (under french conditions)

TABLE 3

cost comparison of surface and underground storage facility as per 1987-88

Due to inflation @ 10% per year for 8 years the present cost may be more as given in brackets. This is an over simplification.

The above figures are based upon the data collected from the hydro-electric and other tunnelling projects excavated in India.

The following conclusions are drawn: