ENVIRONMENTAL GEOMECHANICS CE-641 Lecture No. 6 Prof. D N Singh - - PowerPoint PPT Presentation

ENVIRONMENTAL GEOMECHANICS

CE-641 Lecture No. 6

• Prof. D N Singh

Department of Civil Engineering

Thermogenic Biogenic 3 3

• 1. Different sources of CH4
• 1. Thermogenic (CH4+C2H6+C3H8)
• 2. Biogenic (CH4)
• 2. Gas flows in saturated/unsaturated sediments
• 3. Gas hydrate formation under favourable P-T conditions

2 2

Energy Geotechnics: Gas Hydrates Indian Scenario South Asia

Due to Chemical reactions in Earth’s crust Microbial decomposition

• f organic

matter

Geomechanical properties Morphology

• Pore-filling

Laboratory Simulation: A big challenge Habitat: Marine Environment, Each molecule of hydrate.. 180 m3 of CH4) Load bearing Cementing Multi-phase Geomaterials (Ice-like clathrates)

Methane Gas Hydrates

Challenges:

• 1. Water outflow
• 2. Migration of fines
• 3. Loss of strength
• Wellbore instability
• Seabed subsidence - - - - - - - -
• Foundation instability (of Rigs)
• Uncontrolled Methane release  Green house effect
• Possible trigger of Tsunami

3 3

Extraction of Methane (Dissociation of Gas Hydrates)

Extraction by:

• Depressurization
• Thermal stimulation

Related Geomechanical mechanisms

• Heat migration through multiphase porous

media

• Multiphase (Methane and water) flow

Extraction well

Ministry of Petroleum and Natural Gas, GOI Directorate General of Hydrocarbons (DGH) NATIONAL GAS HYDRATE PROGRAMME NGHP1, NGHP2 and NGHP 3 KG, Mahanadi and Andaman basins (Sands and Clays bearing Hydrates)

SOIL: A LIVING ENTITY

Hence quite susceptible & Sensitive to the Environment in which it stays

Heritage Parentage Linkage Genetics Memory Emotions Response to external stimulus

just like Human (living) beings …….. Rock cycle

Panc anch T h Tatvas tvas (Elements (Elements)

• f
• f J

Jee eevan (Lif van (Life) e) Kshitij (Horiz Kshitij (Horizon)

• n)

Ga Gagan (Sk gan (Sky) y) Pavak (Fir vak (Fire) e) Jal (W al (Water) ter) Sameer (Air) Sameer (Air)

Infinity Formation of soil Deposition & Transportation

• f soil

A C T I V I T Y

Sand >0.075mm Boulder >12” Cobble >6” Gravel >4.75mm Silt >0.075mm Clay >0.002mm Organic matter

S O I L

Experience

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 Aneroxia High B.P. Giddiness Epilepsy Fractures Fatigue Urinary problems Expansive soil Shrinkage Excess pore water pressure Instability Liquefaction Failures/collapse of foundations retaining walls, piles etc. Cyclic loading Drainage

Challenges and Concerns??

Geotechnical Engineering Professionals are involved with:

Diagnostics [of Symptoms & Abnormalities] + Prescription [adequate corrections] + Prolonged Monitoring (Effectiveness of Prescription)