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Context: India’s mission to drill a 6-km deep hole in Koyna, Maharashtra.

 

Details

Scientific deep-drilling

• Scientific deep-drilling is the enterprise of strategically digging boreholes to observe and analyse deeper parts of the earth’s crust.
• It offers opportunities and access to study earthquakes and expands our understanding of the planet’s history, rock types, energy resources, life forms, climate change patterns, the evolution of life, and more.

Deep drilling by countries

• Countries like the U.S., Russia, and Germany conducted such scientific projects in the 1990s. Recently, in 2023, there were reports of China undertaking a deep-drilling mission of its own.

India’s deep drill mission

• The Borehole Geophysics Research Laboratory (BGRL) in Karad, Maharashtra, is a specialised institute under the Ministry of Earth Sciences of the Government of India mandated to execute India’s sole scientific deep-drilling programme.

Aim

• The aim is to drill the earth’s crust to a depth of 6 km and conduct scientific observations and analysis to help expand the understanding of reservoir-triggered earthquakes in the active fault zone in the Koyna-Warna region of Maharashtra.
• This region has been experiencing frequent and recurrent earthquakes since the Shivaji Sagar Lake, or the Koyna Dam, was impounded in 1962. 

Significance of  deep-drilling mission

• Surface-level observations don’t suffice to understand interior completely.
• Scientifically drilled boreholes to great depths can be thought of as downward-looking telescopes, which when instrumented with sensors serve as geological observatories.
• They can be a hub of direct, in-situexperiments and observations and strategically monitor a region’s fault lines and earthquake behaviour (including nucleation, rupture, and arrest).
• Provides exact, fundamental, and globally significant knowledge of the composition of the earth’s crust, structure, and processes and helps in a range of societal problems related to geohazards and geo-resources in India.
• Investing in scientific deep-drilling can also help expand scientific know-how and technological innovation, especially in seismology.
• It can also spur the development of tools and equipment for drilling, observation, data analysis, sensors,, which is another front on which India has the opportunity to be self-reliant.

Other ways to study the interior Seismic wave speed, gravitational and magnetic fields, and electrical conductivity from the near surface. Scientists can also examine xenoliths: fragments of the crust brought from deep underground to the surface along with volcanic magma.

Deep-drilling challenges

• It is also the most challenging method: deep-drilling is labour- and capital-intensive.
• The earth’s interior is also a hot, dark, high-pressure region that hinders long and continuous operations.

Drilling technique at Koyna

• The Koyna pilot borehole is about 0.45 m wide (at the surface) and roughly 3 km deep.

Drilling technique

• A hybrid of two well-established techniques called mud rotary drilling and percussion drilling (a.k.a. air hammering).

Rotary drilling technique

• The rotary drilling technique uses a rotating drilling rod made of steel, attached to a diamond-embedded drill bit at the bottom.
• As it cuts the rocks and penetrates the crust, it generates a lot of heat due to friction, so a cooling liquid or drilling mud is flushed through the drilling rod into the borehole to cool the drill bit.
• In addition to working as a coolant and a lubricant, the drilling mud also helps bring up the debris or rock cuttings from the borehole.
• An annular (ring-shaped) space separates the drilling rod and borehole wall.
• The debris moves out from the annular ring space due to the pressure of the drilling mud pumped from the top through the drilling rod.
• The deeper the borehole, the more pressure is required to bring up the debris from the annular space.

Air hammering

• Pushes highly compressed air (in place of the drilling mud) through the drilling rod to deepen the borehole and flush the cuttings out.

Challenges of drilling to 3 km

• A particularly critical limitation of scientific deep-drilling itself is the hook load capacity of the drilling rig mast.
• The load on the rig’s hook keeps increasing as the borehole gets deeper and with the addition of new drilling rods and steel casing pipes.
• Also with increasing depth, the required compressed air pressure to lift the drill cuttings increases manifold.

Challenges of drilling to 6 km

• When the borehole depth increases beyond 3 km and strikes for 6 km, the entire rig will have to be updated with exponentially enhanced capacity.
• The complexities of drilling through fractured rocks in the Koyna seismic zone, and the possibility of drill rods and sensors getting stuck all become significantly higher.
• Troubleshooting also becomes more complicated because of limited access (to instruments, probes or cables), in turn because the rocks at these depths are softer.

Human resources

• Human resources are also a challenge in scientific deep drilling.
• The process needs highly skilled and trained technical personnel for a 24/7 on-site engagement for about six to eight months at a time in harsh weather conditions.

Key Findings

• It revealed 1.2-km thick and 65 million-year-old Deccan trap lava flows, and below them 2,500-2,700-million-year-old granitic basement rocks.
• Down hole measurements of core samples and conditions from a depth of 3 km have provided the physical and mechanical properties of rocks.
• The chemical and isotopic composition of formation fluids and gases
• Temperature and stress regimes, and fracture orientations at depth.
• Captured high-resolution images of the borehole wall using acoustic and micro-resistivity techniques.
• The team at Koyna also conducted hydraulic fracturing experiments (akin to synthetically induced triggers) to measure the in-situstress regime of the rocks.
• The presence of water down to 3 km, It was found to be meteoric or rain-fed, implying deep percolation and circulation are possible.
• The Koyna region is critically stressed, so even small stress perturbations could cause the rock to fail and potentially trigger frequent, small-magnitude earthquakes in the region.

Implications

• The Koyna data and samples will also facilitate new experiments.
• More than 20 research groups nationwide are already studying the Koyna samples.
• For example- one group is examining the gouge from fault zones — the rock dust generated by friction — to understand the frictional properties of rocks in quake-prone regions.
• Another is characterising the microbes on these rocks to understand life forms that thrive in dark, hot, and nutrient-poor environments.
• Climate change: Members of the international geological research community have also been requesting access to core samples for collaborative projects in emerging fields such as carbon capture and storage in the deep Deccan traps, which could help mitigate climate change.

Conclusion

The Koyna exercise is establishing a firm footing in scientific deep-drilling for India. Its lessons will inform future deep-drilling experiments as well as expand academic knowledge in multiple ways.

Sources:

TheHindu

PRACTICE QUESTION Q. Discuss about the “Deep Drilling Mission” of india and its future implications for both national and international importance. 150 words.