ENVIRONMENTAL GEOMECHANICS CE-641 Lecture No. 6 Prof. D N Singh Department of Civil Engineering
Energy Geotechnics: Multi-phase Geomaterials Gas Hydrates (Ice-like clathrates) Indian Scenario South Asia Habitat: Marine Environment, Each molecule of hydrate.. 180 m 3 of CH 4 ) Geomechanical properties Morphology 1. Different sources of CH 4 1. Thermogenic (CH 4 +C 2 H 6 +C 3 H 8 ) Laboratory Simulation: A big challenge • 2. Biogenic (CH 4 ) Pore-filling Load bearing Cementing 2. Gas flows in saturated/unsaturated sediments 3. Gas hydrate formation under favourable P - T conditions Microbial decomposition 3 2 of organic matter Thermogenic Biogenic Due to Chemical 3 2 reactions in Earth’s crust
Extraction of Methane (Dissociation of Gas Hydrates) Methane Gas Hydrates • Wellbore instability Challenges: • Seabed subsidence - - - - - - - - 1. Water outflow • Foundation instability (of Rigs) 2. Migration of fines • Uncontrolled Methane release Green house effect 3. Loss of strength • Possible trigger of Tsunami Extraction by: • Depressurization • Thermal stimulation Extraction well Ministry of Petroleum and Natural Gas, GOI Related Geomechanical mechanisms Directorate General of Hydrocarbons (DGH) • Heat migration through multiphase porous NATIONAL GAS HYDRATE PROGRAMME media NGHP1, NGHP2 and NGHP 3 • Multiphase (Methane and water) flow KG, Mahanadi and Andaman basins 3 (Sands and Clays bearing Hydrates) 3
SOIL: A LIVING ENTITY Hence quite susceptible & Sensitive to the Environment in which it stays just like Human (living) beings Heritage Parentage …….. Rock cycle Linkage Genetics Memory Emotions Response to external stimulus
Panc anch T h Tatvas tvas (Elements (Elements) of of J Jee eevan (Lif van (Life) e) Kshitij (Horiz Kshitij (Horizon) on) Infinity Ga Gagan (Sk gan (Sky) y) Formation of Pavak (Fir vak (Fire) e) soil Jal (W al (Water) ter) Deposition & Sameer (Air) Sameer (Air) Transportation of soil
A Boulder >12” C Cobble >6” T S Experience Gravel >4.75mm I O V Sand >0.075mm I I Silt >0.075mm L T Clay >0.002mm Y Organic matter
Soil: particulate, much more complex than steel & its Behavior is influenced by: • Soil type (grain size, shape, minerals etc.) • Water, Air, content • Electro-chemical effects • Climate (humidity, temperature, pressure, permafrost) • Stress history (of loading and unloading, N.C., O.C. behavior) • Still much more (& better) predictable & workable than the living beings (who originate from it)
SYMPTOMS COMMON TO HUMANS & SOILS Obesity Expansive soil Aneroxia Shrinkage High B.P. Excess pore water pressure Giddiness Instability Epilepsy Liquefaction Fractures Failures/collapse of foundations retaining walls, piles etc. Cyclic loading Fatigue Drainage Urinary problems
Challenges and Concerns?? Geotechnical Engineering Professionals are involved with: Diagnostics [of Symptoms & Abnormalities] + Prescription [adequate corrections] + Prolonged Monitoring (Effectiveness of Prescription)
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