Indian contractor Hindustan Construction Company is using four Sandvik DT820 underground drill rigs to construct the country's first underground crude oil storage cavern at Vizag, Andhra Pradesh.
Four Sandvik DT820 underground jumbo drill rigs are being used for the construction of India’s first underground crude oil storage cavern, located at Visakhapatnam in Andhra Pradesh. Furthermore, two Sandvik DX700 surface drill rigs are also being used for benching work on the same site. The cavern is being constructed under a Rs 375 crore ($75.5 million) contract by Mumbai-based Hindustan Construction Company (HCC), for Indian Strategic Petroleum Reserves (ISPRL), which is a subsidiary of the Oil Industry Development Board under the Petroleum Ministry.
Located on a hill named Dolphin’s Nose, the cavern is being constructed on land that belongs to the Eastern Naval Command in Visakhapatnam, and will have a storage capacity of 1.33 million tonnes of crude. Vizag, located on the east coast and considered the eastern gateway to India, was selected as the site because it has a large seaport that can support the import of oil. Adjacent to the cavern site is southeast Asia’s first underground LPG storage cavern, which was commissioned early last year and which also used Sandvik jumbos during its construction.
HCC began work on the cavern in January last year and plans to work over a 36 month schedule. The contract covers detailed engineering and design, underground excavation, access tunnels, water curtain galleries, main storage caverns, shafts and associated underground civil works.
The contractor’s Project Manager KV Ramana Rao, says that there are two caverns for the storage of the crude, both 30 m in height and 20 m wide, together with associated tunnelling. High-sulphur crude will be stored in the cavern. The complete length of the underground storage cavern is more than three km, and the amount of rock that is being excavated is about five million tonne.
The floor of the caverns are 60 m below mean sea level, which means that the working fronts are accessible through an inclined access tunnel from ground level. In order to facilitate the pumping in and out of oil, five shafts have been sunk to the floor of the caverns.
Rao says that the rock strata is khondalite, a form of high grade metamorphic rock derived from alumina-rich clay, with a fair amount of iron content. The similar rock sequence together with charnokites can be seen all through the Eastern Ghats of India. HCC is using four Sandvik jumbos simultaneously for much of the time, as the functions of drilling and blasting is being undertaken on several fronts at once.
“Our logistics are designed to supply power and water to four headings simultaneously, and to remove the rock and do the shotcreting,” he says. “The four Sandvik machines are therefore working within this cycle.”
The jumbos are drilling at least 150 holes per blast cycle, at depths of between 2 m and 4 m, depending on the section of the cavern on which they are working. On an average, it takes two minutes to drill one hole, with the holes closely following the tunnel profile.
With a tunnel profile of 11x8 m holes, it needs to be packed with a total of 480 kgs of explosives. A 10x8 m profile requires 473 kg, and an 8x8 m profile needs about 365 kgs of explosives.
The drilling per blast cycle takes around six hours, and rock bolting is simultaneously being undertaken from a basket fixed to the jumbo. Once the drilling is complete, the jumbos are moved out of the tunnel where they are washed down after each drilling shift. With the blasting and rock removal complete, the jumbos are moved back into position for the next cycle. Rao says that with work proceeding 24 hours a day, the production cycle allows three blasts during a two-day period in every phase, and that each blast advances the work by 3.5-3.8 m.
HCC’s Project Mechanical Engineer Kaushal Kumar Sharma, says that the machines are hosed down at the washing area next to the access tunnel, and that routine maintenance is undertaken once a week. “We inspect the hoses, linkages and the drill bits, and oil and lubricate the machines. Our own staff does this job as well, but Sandvik has an onsite presence and works very closely with our maintenance and operating teams.
”The jumbos were supplied to HCC by Sandvik India, whose Senior Engineer on site, Harish Pokharkar, says that spare parts are supplied via the company’s Pune headquarters. The two Sandvik DX700 surface drill rigs are being used in two caverns, where they are undertaking vertical drilling for the benches. Pokharkar says that both machines are fitted with 45 mm R32 drill bits, with an R 38 shank adapter and R 38 and R 32 drifter rods. “The DX700s are drilling down to depths of 21 m,” he says. “We have a grinding facility for the drill bits installed at the jobsite, and we have recorded data that by grinding we are achieve 30 per cent extra life with the bits. “We have also ascertained that machine availability has been slightly over 96 per cent per month.” The crude oil cavern at Vizag is one of three such caverns that have been planned by the Indian government, with a storage capacity of five million. Two other caverns are on the anvil and will be located at Mangalore and Padur, with the crude designed to act as a buffer in the event of emergencies or disruptions in supply. All three projects will be operational by 2012.
• The Sandvik DT820 is a two-boom electro hydraulic jumbo for fast and accurate drilling in tunnelling and cavern excavation of 12-110 m2 cross sections.• It is equipped with an HLX5 rock drill and a TB 90 universal boom, which gives a large optimum shaped coverage and full automatic parallelism.• The booms can also be used for cross-cutting and bolt hole drilling. An optional basket boom for bolting and utility works is available.• The four-wheel-drive centre articulated carrier ensures rapid and safe tramming with good balance.