India’s Deep Drill Mission | 16 Jul 2024

Source: TH

Why in News?

Recently, the Ministry of Earth Science has started the task of scientific deep drilling of the earth’s crust to a depth of 6 km with the help of a specialised institute named Borehole Geophysics Research Laboratory (BGRL) in Karad, Maharashtra.

• It has already completed the drilling to a depth of 3 km.

What is Scientific Deep Drilling?

• About: 
  • Scientific deep drilling involves drilling deep into the Earth's crust to study its composition, structure, and processes. 
  • This research can provide insights into geological formations, natural resources, and Earth's history. 
  • Deep drilling projects often aim to advance our understanding of tectonics, earthquake mechanisms, and geothermal energy potential.
• Techniques and Methods:
  • Rotary Drilling: This method uses a rotating drill bit to cut through rock formations. The drill bit is attached to a drill string, which is rotated by a rig. Drilling mud is circulated to cool the bit and carry rock cuttings to the surface.
  • Percussion Drilling (Air Hammering): It uses high-pressure air to power a hammer that rapidly impacts a drill bit, efficiently breaking rock and flushing out cuttings. It's fast, cost-effective, and versatile for hard rock applications like mineral exploration, water wells, and geothermal energy, though it can be noisy and is best suited for shallower depths.
    • The Koyna drilling technique combines mud rotary drilling and percussion drilling (air hammering).
  • Hydraulic Fracturing (Fracking): Sometimes used to create fractures in rock formations, enhancing the flow of fluids for sampling or stimulating production in resource extraction.
  • Geophysical Surveys: Employ seismic, magnetic, and gravitational methods to map subsurface structures and identify drilling targets before and during drilling operations.

What are the Other Ways to Study the Interior of the Earth?

• The interior of the Earth is studied through direct methods like drilling and sampling rock from deep boreholes, and indirect methods such as seismic wave analysis, gravity measurements, and studying Earth's magnetic field.
  
  • Seismic Waves: The study of seismic waves generated by earthquakes provides valuable information about the Earth's interior structure. 
    • Seismic waves travel through the Earth's interior and their behaviour, such as refraction and reflection, helps scientists infer the composition and properties of the different layers.
  • Gravitational and Magnetic Field Measurements: Variations in the Earth's gravitational and magnetic fields can indicate changes in the density and composition of the interior. These measurements help identify the boundaries between the Earth's core, mantle, and crust.
  • Heat Flow Measurements: The heat flowing out of the Earth's interior provides clues about the temperature and thermal properties of the different layers. This information is crucial for understanding the Earth's internal processes and dynamics.
  • Meteorite Composition: The study of meteorites, which are believed to be remnants of the early solar system, can provide insights into the composition and formation of the Earth's interior.

What are the Key Findings from the Deep Drilling Mission in Koyna?

• Region's Critical Stress: The Koyna region is highly stressed, making it susceptible to small stress perturbations that could trigger frequent, small-magnitude earthquakes.
• Water Presence to 3 km: Water found down to 3 km is meteoric or rain-fed, indicating deep percolation and circulation.
• Insights into Reservoir-triggered Earthquakes: The mission revealed 1.2 km of 65 million-year-old Deccan trap lava flows overlying 2,500-2,700 million-year-old granitic basement rocks.
• Rock Information: Core samples from 3 km depth provided new information on the physical and mechanical properties of rocks, the chemical and isotopic composition of formation fluids and gases, temperature and stress regimes, and fracture orientations.
• Data Validation: High-resolution images of the borehole wall using acoustic and micro-resistivity techniques allow global scientists to validate data from other cores.
• Hydraulic Fracturing and Fault Detection: The team conducted hydraulic fracturing experiments to measure the in-situ stress regime of the rocks. By integrating various datasets and advanced analysis, they detected and studied buried fault zones.

What is the Significance of Deep Drilling Mission?

• Enhanced Earthquake Understanding and Geohazard Management: It can be achieved by installing sensors in deep boreholes to monitor fault lines, leading to better predictive models and risk mitigation. 
  • Additionally, deep drilling provides precise data on the Earth's crust, essential for managing geohazards and exploring geo-resources like minerals and hydrocarbons.
• Verification of Geological Models: Drilling allows for direct observation and sampling, confirming or refuting geological models and enhancing our understanding of tectonic processes and crustal dynamics.
• Technological Innovation and Self-Reliance: Investing in deep drilling drives advancements in seismology, drilling techniques, sensor development, and data analysis, promoting technological self-reliance in India.
• Global Scientific Contribution: Findings from deep drilling projects in India contribute to global geoscience knowledge, fostering international collaboration and enhancing overall understanding of Earth's systems.

What are the Challenges with Deep Drilling Missions?

• Rig Capacity: The drilling rig's hook load capacity becomes a critical limitation at greater depths, requiring a significantly more powerful rig for 6 km compared to the 100-tonne rig used for the 3 km pilot.
• Drilling Complexity: Drilling through fractured and seismically active rock formations becomes increasingly complex at greater depths, with higher risks of equipment getting stuck and complications in troubleshooting due to limited access.
• Core Handling: Extracting and lifting the long, heavy rock cores from over 3 km depth poses significant technical challenges.
• Borehole Stability: Deeper boreholes are more prone to encountering fault lines and fracture zones, which can compromise borehole stability and require specialised equipment for steering the drill.
• Human Resources: The extended duration of deep drilling operations, lasting 6-8 months for 3 km and 12-14 months for 6 km, places a significant burden on the highly skilled technical personnel required to work on-site 24/7 in harsh conditions.

Conclusion

The 3 km pilot drilling data will guide future 6 km plans, including equipment and sensor design for temperatures of 110-130°C. Koyna's findings enable diverse research, from fault zones to deep subsurface microbes, with industrial potential. International interest includes projects on carbon capture in deep Deccan traps. This effort strengthens India's scientific drilling capacity and broadens interdisciplinary knowledge.