16-July-2024-Editorial

DEEP DRILLING MISSION 

The Ministry of Earth Science in India has embarked on a significant mission to conduct scientific deep drilling of the Earth’s crust, aiming to reach a depth of 6 km.  

This project is being executed with the assistance of the Borehole Geophysics Research Laboratory (BGRL) in Karad, Maharashtra.  

The mission has already achieved a drilling depth of 3 km. This deep drilling initiative is crucial for understanding the Earth’s composition, geological processes, and seismic activities, particularly in the Koyna region, which is uniquely suited for this mission due to its geological and seismic characteristics. 

Why Koyna for Deep Drilling Mission? 

Triggered Seismicity 

• Reservoir-Induced Seismicity (RIS): Koyna experienced a series of tremors after the construction of the Koyna Dam in 1962. This phenomenon, where human activities like reservoir filling trigger earthquakes, is called RIS. 

• Study Focus: Scientists aim to study the Earth’s composition and stresses directly at the source of these triggered earthquakes through deep drilling. 

Active Fault Zone 

• Geological Fault Line: The Koyna-Warna region is located on a geological fault line, making it prone to earthquakes. 

• Differing Events: The triggered seismic events here differ from those occurring along tectonic plate boundaries. 

Isolated Activity 

• Seismic Isolation: There are no other significant sources of seismic activity within a 50 km radius of the Koyna Dam, making it an ideal location for focused research. 

What is Scientific Deep Drilling? 

About 

• Objective: Scientific deep drilling involves boring into the Earth’s crust to examine its composition, structure, and processes. 

• Research Insights: It provides insights into geological formations, natural resources, and Earth’s history, advancing our understanding of tectonics, earthquake mechanisms, and geothermal energy potential. 

Techniques and Methods 

• Rotary Drilling: Uses a rotating drill bit to cut through rock formations. Drilling mud cools the bit and carries rock cuttings to the surface. 

• Percussion Drilling (Air Hammering): Uses high-pressure air to power a hammer that impacts the drill bit, breaking rock and flushing out cuttings. 

• Hydraulic Fracturing (Fracking): Creates fractures in rock formations to enhance fluid flow for sampling or resource extraction. 

• Geophysical Surveys: Utilize seismic, magnetic, and gravitational methods to map subsurface structures and identify drilling targets. 

Methods for Studying the Earth’s Interior 

Seismic Waves 

• Seismic Wave Analysis: The study of seismic waves generated by earthquakes provides information about the Earth’s interior structure through their behavior such as refraction and reflection. 

Gravitational and Magnetic Field Measurements 

• Field Measurements: Variations in Earth’s gravitational and magnetic fields indicate changes in density and composition, helping identify boundaries between the core, mantle, and crust. 

Heat Flow Measurements 

• Heat Flow: Measuring the heat flow out of the Earth’s interior provides clues about the temperature and thermal properties of different layers. 

Meteorite Composition 

• Meteorite Study: Analyzing meteorites, remnants of the early solar system, provides insights into the Earth’s interior composition and formation. 

Other Deep Drilling Projects in the World 

Project Mohole (US) 

• 1960s Effort: Attempted to drill to the boundary between Earth’s crust and mantle. Disbanded in 1966, it demonstrated deep-ocean drilling potential for geological insights. 

Kola Superdeep Borehole (Russia) 

• World’s Deepest Hole: Reached a depth of 12,262 meters. Revealed unexpected findings such as liquid water at great depths and microscopic fossils. 

China’s Deep Hole Project 

• Xinjiang Region: Aiming to drill 10,000 meters to explore above and below Earth’s surface, penetrating over 10 continental strata and the cretaceous system. 

Deep Sea Drilling Project (DSDP) 

• Ocean Drilling: Began in 1966, involved drilling and coring in various oceans, leading to significant discoveries, including salt domes. 

Integrated Ocean Drilling Project (IODP) 

• International Initiative: Uses ocean research platforms to study Earth’s history and processes via seafloor samples, contributing to understanding Earth’s systems. 

Key Findings from the Deep Drilling Mission in Koyna 

Region’s Critical Stress 

• Susceptibility: The Koyna region is highly stressed, making it susceptible to small stress perturbations triggering frequent, small-magnitude earthquakes. 

Water Presence to 3 km 

• Deep Percolation: Water found down to 3 km is meteoric or rain-fed, indicating deep percolation and circulation. 

Insights into Reservoir-triggered Earthquakes 

• Geological Layers: 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: Provided new information on the physical and mechanical properties of rocks, chemical and isotopic composition of formation fluids and gases, temperature and stress regimes, and fracture orientations. 

Data Validation 

• High-Resolution Images: Borehole wall images using acoustic and micro-resistivity techniques allow global scientists to validate data from other cores. 

Hydraulic Fracturing and Fault Detection 

• In-situ Stress Measurement: Conducted experiments to measure the in-situ stress regime of rocks, detecting and studying buried fault zones. 

Significance of Deep Drilling Mission 

Enhanced Earthquake Understanding and Geohazard Management 

• Fault Monitoring: Installing sensors in deep boreholes to monitor fault lines, leading to better predictive models and risk mitigation. 

• Geohazard Management: Provides precise data on Earth’s crust, essential for managing geohazards and exploring geo-resources like minerals and hydrocarbons. 

Verification of Geological Models 

• Direct Observation: Allows direct observation and sampling, confirming or refuting geological models and enhancing understanding of tectonic processes and crustal dynamics. 

Technological Innovation and Self-Reliance 

• Technological Advancements: Drives advancements in seismology, drilling techniques, sensor development, and data analysis, promoting technological self-reliance in India. 

Global Scientific Contribution 

• International Collaboration: Findings contribute to global geoscience knowledge, fostering international collaboration and enhancing understanding of Earth’s systems. 

Challenges with Deep Drilling Missions 

Rig Capacity 

• Hook Load Capacity: Greater depths require a significantly more powerful rig, posing a critical limitation with the 100-tonne rig used for 3 km pilot drilling. 

Drilling Complexity 

• Fractured Rock Formations: Drilling through fractured and seismically active rock formations becomes complex at greater depths, with higher risks of equipment getting stuck. 

Core Handling 

• Technical Challenges: Extracting and lifting long, heavy rock cores from over 3 km depth poses significant technical challenges. 

Borehole Stability 

• Fault Lines and Fractures: Deeper boreholes are prone to encountering fault lines and fracture zones, compromising stability and requiring specialized equipment. 

Human Resources 

• Operational Duration: Extended duration of deep drilling operations places a significant burden on 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 higher temperatures. The findings from Koyna enable diverse research, from fault zones to deep subsurface microbes, with industrial potential. This effort strengthens India’s scientific drilling capacity and broadens interdisciplinary knowledge.