Since the creation of Chechnya's oil industry at the start of the last century, a virtual lake of black gold has formed beneath the city, seeping into the region's sub-strata from its three Soviet-built refineries.
Little remains of the original refineries, bombed to pieces during the two Chechen wars (1994-96 and post-1999), or looted for scrap by local people.
But the oil that they have leaked into the ground is today proving a boon to Grozny residents who, working day and night in primitive conditions often risking their lives, have formed a cottage oil-extraction industry.
Digging for this oil, a refined product - which locals call "concentrate" – began in the mid-1990s in Grozny's industrial suburbs and in the area near the main railway station.
Pioneers said that to begin with, even a three-metre-deep pit was sufficient to yield several tonnes of the precious oil concentrate daily.
With its high level of refinement, the concentrate could fetch twice as much as a regular oil product. Now however diggers have to delve much deeper to obtain similar results.
"We dig 20 or 30 metres down, sometimes more. The last time we dug a hole 43 metres deep," Salman said.
"It's hard work, but we earn a good living. Over the past four months I've made $1,300. We have to keep going round the clock as our salary depends on how much we extract," said Salman, the father of three small children.
The pit is one of several owned by Salman's boss, who reckons on producing a total of 1.5 tonnes of oil product per day.
A major Russian oil pipeline runs
through the rebellious state
Though the industry is totally unregulated, experts are needed to ensure that the pit functions properly. Errors could allow water to seep in, rendering the pit useless.
"We sleep, eat and rest at the site. Our task is to keep the well functioning. We repair it when necessary and pump out the concentrate whenever it accumulates," said Adlan, a 30-year-old veteran of the industry.
"The work isn't hard but it's dangerous and eats up your health. But you have to earn a living somehow," he sighed.
The riskiest part is pumping the oil to the surface. A worker descends into the pit fitted with a gas mask connected to a long hose allowing him to breathe fresh air from above.
There are no security guarantees and there have been several cases of gas poisoning. Earlier this month, a 28-year-old father of three died of gas poisoning in a 27-metre pit, with his comrades at the surface powerless to come to his aid.
Once pumped to the surface, the concentrate is stocked in special containers and transported to small refineries for sale outside the republic's borders.
According to unofficial figures, up to 500 tonnes of condensed oil products are extracted in this way every day.
Oil and war
Chechnya has always played a significant role in Russia's oil industry. A major pipeline runs through the Caucasus republic and, in the early 20th century, it accounted for nearly 20 percent of Russia's oil output.
Before it unilaterally declared independence in 1991, triggering two Russian military interventions, Chechnya, along with neighbouring Ingushetia, turned out up to four million tonnes of oil a day, although production had fallen by half by the mid-1990s.
In addition to unofficial oil extraction, the war has given rise to a flourishing clandestine refinery industry, with a network of micro-refineries scattered around the republic.
The trafficking in locally refined oil brings huge profits to the Russian military and police who extort protection money from those involved.
Some observers have argued that the illicit oil production is helping to keep the Chechen conflict going as for Russian officers on the take a military pullout would mean the loss of a lucrative sideline.