Methane Hydrate:A Burning Ice

By Priyaranjan

2nd Year Petroleum Engineering

What is a Gas Hydrate?

• Gas Hydrates are solid mixture of natural gas and water

• Gas molecules are encaged between ice lattices. (85 : 15 :: water : gas molecules)

• Contains 160-180 times the natural gas by volume atstandard conditions.

Hydrate samples

Gas hydrates in sea-floor mounds Here methane gas is actively dissociating from a hydrate mound.

Gas hydrate can occur as nodules, laminae, or veins within sediment

Ice That Doesn’t Melt !

• Formed at low temperatures and high pressure.

• Known to occur at temp. below 295K and pressure greater than 3000KPa.

• Water molecules attach themselves through hydrogenbonding and form cavities which are occupied by asingle gas or volatile liquid molecule.

• Gas or volatile liquid inside the water cage stabilizes thestructure through physical bonding via weak van derWaals forces.

Gas Hydrate Potential

Worldwide Estimate of Gas Hydrates

• 700,000 Tcf (20,000 trillion cubic meters)

• Conventionally recoverable methane 8,800 Tcf ( 250 trillion cubic meters)

• Two times the total energy in coal oil and conventional gas.

If 1% of gas –in-place in gas hydrate is recoverable : 2000 Tcf

Stability Zone In Sea

Found inside sea at depths greater than 500m and attemperatures even higher than those for ice stability.Stable in association with permafrost in the polarregions, both in offshore and onshore sediments.

Why is it urgent to be studied ?

• A future energy source

• Climate change

• It can affect sediment strength, which can initiate landslides on the slope and rise.

• When hydrate fills the pore space of sediment, it can reduce permeability and create a gas trap, The gas can continually migrate upwards to fill any open pore spaces.

• This process, in turn, causes the trap to become more

effective, producing highly concentrated methane and methane hydrate reservoirs.

A Future Energy Source

• Hydrate is a gas concentrator; the breakdown of a unit volume of methane hydrate at a pressure of one atmosphere produces about 160 unit volumes of gas.(The worldwide amount of methane

in gas hydrates is considered to contain at least

1x104 gigatons of carbon in a very conservative estimate).

• This is about twice the amount of carbon held inall fossil fuels on earth.

A Future Energy Source … Continued

• Methane from the hydrate reservoir might significantly modify the global greenhouse, because methane is ~20 times as effective a greenhouse gas as carbon dioxide, and gas hydrate may contain three orders of magnitude more methane than exists in the present-day

atmosphere.

• Because hydrate breakdown, causing release of methane to the atmosphere, can be related to pressure changes caused by glacial sea-level fluctuations, gas hydrate may play a role in controlling long-term global climate change.

Climate Change

• Methane is an environmentally cleaner fuel than oil, coal, or oil shale which all have an immense environmental impact during production and combustion.

• We can find a way to trap carbon dioxide at the seafloor where it would eventually be buried by sediment.

Climate Change … continued

• Gas hydrate apparently cements sediment, and, therefore, it can have a significant effect on sediment strength; its formation and breakdown may influence the occurrence and location of submarine landslides.

• Such landslides may release methane into the atmosphere, which may affect global climate.

Affects sediment strength

• Changes in water pressure due to sea level changes may generate landslides by converting the hydrate to gas plus water, causing significant weakening of the sediment, and generating a rise of pore pressure. Conversely, sea-floor landslides can cause breakdown of hydrate by reducing the pressure in sediments.

• These interacting processes may cause cascading slides, which would result in breakdown of hydrate and release of methane to the atmosphere.

Affects sediment strength … continued

Present Day Techniques

1. THERMAL INJECTION

2. INHIBHITORS

3. DEPRESSURISATION

Courtesy :slb

Production of Gas Hydrates

Problems with present day techniques

Thermal injection – Unavoidable heat losses due to host rock, economical infeasibility.

Depressurization – Endothermic nature causing decrease in reservoir temperature.

Inhibitors – methanol and ethylene glycol are expensive chemicals.

Production well

Antenna(micro waves)

Gas hydrate reservoir

New conceptdiagram of reservoir.

Injection well

Steps involved Release of microwaves (@2450Mhz).

Melting of gas hydrate or ice .(Temp. > 273 k )

Injection of Fluorine.

Reaction between methyl radical and injected fluorine gas (halogenation).

CH.3 + F2 = CH3F( -431KJ/mole)

(Solubility of methyl fluoride(166cc in 100ml of water))

Recovery of liquefied gas hydrate solution.

Step 1: Wurtz Reaction 2 CH3F + Na ----- 2 NaF + CH3-CH3

Step 2 :Electrolysis NaF ----- Na + 1/2 F2 ↑

Step 3 :Cracking CH3-CH3 ------ 2 CH4 ↑

Advantages with respect to normal techniques

• Cost effective ,instantaneous and selective heating,catalyze chemical reaction.

• Methyl fluoride is not an class 1 or 2 ozone depleting chemical and stable compound.

• Huge reduction in disaster on rig floor or drill floorrelated issues.

• Increase in the permeability and porosity of rock.

Challenges

• Fluorine is highly electronegative and reactive in nature e.g. injection problems.

• Transportation of methyl fluoride solution.

Conclusion

• Huge amount of natural gas trapped in hydrates : too enormous to ignore.

• It’s a threat to climate as well so there is an urgent need that we use it for positive purpose.

• Technology and scientific understanding for exploitation of gas hydrate is to be developed .

• Much to be learned before gas hydrates can be considered a resource.

• The integration of various sciences and using the fluorine in this technique will definitely play a vital role in the methane extraction.

References

• www.spe.org

• http://en.wikipedia.org

• http://www.cbc.ca

Thank You !

QUESTIONS…??