M1L8: Conventional and unconventional gases-II

In the previous lecture, we uncovered the benefits of gaseous fuels compared to liquid and solid fuels. In the light of what we studied till now, can we replace metallurgical coke/coking coal with natural gas in iron and steel industry? Google the name of that method and figure out if it carries more or less amount of embedded carbon.

In this lecture, we move one step forward towards Methanol. Try to recall, from our past lectures that bioethanol and biodiesel can be used as an alternate to fossil fuels. So, if that helps to reduce pollution, is there any scope of using bio methanol?

Based on this question, the government had formed two committees back to back. The former committee name came out with a report, known as ‘Saumitra Chaudhary committee report’. Later on, a new committee was formed under Dr. V K Saraswat committee, and it too came out with a report on the same.

Either ways, the crux is methanol is beneficial and therefore it should be used in India. The problem is developing an infrastructure for the same. This is due to the fact, that methanol is transparent and toxic. Hence any leakage or spillover, may lead to a disaster as it can spread through air and is highly inflammable.

But, before we step any further, we will first understand if biogas and bio methanation are same or different?

Biogas is basically methane and is produced during decomposition of organic matter. In landfill sites, that are exposed to air, this gas would be called as biogas. However, in villages where this methane is used as a cooking fuel, they tightly cover the pit containing organic waste with a lid, so as to prevent foul odour coming out of it. In this case, since the pit is tightly enclosed, the respiration happening inside the chamber is essentially anaerobic. In this case, when the process of respiration happening inside the chamber is anaerobic, it would be known as bio methanation plant. If the process is aerobic, i.e. organic waste is exposed to air, it would be called as bio gasifier.

Now we shall jump to two non-conventional gases viz. CBM and Shale gas

Recall the fact, that in case of Underground coal gasification, the coal in underground coal seams is partially oxidized and heated to release syn gas. This syn gas contains Hydrogen, Methane and many other gases, some of which may be environmentally polluting and toxic (for e.g. Sulphur is present as an impurity in coal. It also gets oxidized to form SOx)

In case of Coal Bed Methane (CBM), the situation is other way around. Here coal in underground coal seams is neither oxidized nor heated. In the case of CBM, first of all, all the water that is mixed in underground coal seam is removed using a pump. The water present in underground coal seams exerts an external pressure on lumps of coal, thereby not allowing methane to escape out of it.

As soon as this water is removed, the external pressure on the lumps of coal gets relieved. The methane trapped inside starts degassing out of it. The methane is known as coal bed methane (CBM) or coal seam gas (CSG)

This gas is held in fractures of underground coal seams and therefore requires drilling through a process known as fraccing or “fracking”. (short form of Fracture Stimulation) This process is used to fracture underground coal seams in order to increase the flow of gas & water. 

A fluid called “fraccing fluid” or “frac fluid” is pumped down well bores at high pressure to fracture the coal seam. The fractures create a pathway for the gas & water from underground to be extracted through the gas well.

So, when we compare CBM with UCG, we find a difference.

[1] Coal Seam Gas / Coal Bed Methane (CBM) recovers gas from coal seams without utilizing the energy within the coal itself whereas Underground Coal Gasification (UCG) is used to convert underground coal into gas using a series of boreholes operated remotely from the surface. Air or a combination of oxygen and steam are injected into the coal seam that does partial heating of coal. As a result, UCG delivers 20 times more energy from the same coal resource than what’s possible from CSG.

[2] UCG does not involve pumping groundwater out of the coal mine nor involves practices that reduce the natural groundwater pressure on the lumps of coal. In case of CBM, the groundwater pressure is artificially reduced in order to promote gas flow.

[3] UCG does not involve “fraccing” while CBM/CSG involves fraccing.

So, while the Coal Bed Methane contains methane, what do we find in shale gas?

In case of shale gas, its mostly Natural gas liquids (NGL) with methane + propane with some amounts of and butane.

Shale is basically a sedimentary rock. Think about it. From which kind of rocks, do we find maximum amount of oil and gas? Igneous, sedimentary or metamorphic? An obvious answer to this would be sedimentary. Why? Because its made up of organic matter.

So, assuming that the sedimentary rock is allowed to pass through its cycle for say, 30,000 years, what do we get? We find that the sedimentary rock has got completely converted to either coal, oil or gas.

In the light of this, may I ask now, if we allow shale rock to decompose and undergo its cycle of passing through intense heat and pressure inside the crust of the earth, will it also get converted to oil and gas? Answer is 100% yes. Shale rock is a sedimentary rock. This means, that if it were subjected to intense heat and pressure for say 30,000 year, it will also get converted to a matured form of oil and gas. But for that, we need to wait for the cycle to get over. May be 30,000 years, if we are patient enough and are able to survive.

Incase of shale technology, what we do is that, we pull whatever oil and gas that has accumulated inside this rock even before it has completed its cycle. This process involves fraccing, as we discussed earlier.

Hydraulic fracturing requires pumping of fracturing fluid into the well. This fluid is a mixture of water, sand and chemicals. Around 200 trucks of water are required for each well which is mixed with 300,000 to 400,000 pounds of proppants (sand and ceramic beads) per well. The chemicals make up 0.5% to 2% (around 330 tons) of total volume of fracturing fluid.

The pressure exerted by this fracturing fluid causes the rock surrounding the pipe to crack. The proppants open these cracks further to allow the trapped natural gas to escape. This gas flows up the well to be collected.

Challenges of Shale gas technology

(1) Water use: Around 70 to 140 billion gallons of water is used to fracture 35,000 wells in the US every year. This equals approximately the water consumption of 40 to 80 cities with a population of 50,000

(2) Groundwater contamination: Industry reports show that 6% of gas wells leak immediately and 50% of all gas wells leak within 15 years. Shale gas exploration requires many wells to be drilled. These wells can never be removed or recycled, the steel and concrete structures plunged deep into the geology decay slowly over time. All gas wells will leak eventually leading to pollution of aquifers and surface water by methane migration into it.

(3) Air Pollution: A wide variety of dangerous pollutants, including ozone, aromatic hydrocarbons & silica dust are produced by the drilling and fracking process. There is a growing catalogue of human and animal health impacts associated with this invasive industrial activity.

Thus, there is a growing body of literature on the dangers of shale oil and gas technology. There is growing opposition in USA against fracking and already Scotland, Ireland, Germany, France and Bulgaria have banned fracking. Should India go ahead with it?