Loading
Notes
Study Reminders
Support
Text Version

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Video 1: Gas Hydrates and Methane Gas
We have directly or indirectly taking about the introduction of the course; the scopeof environmental geo mechanics and in the previous lecture, I gave you an idea aboutwhat are the current trends in environmental geomechanics or the subject as such and afterlisting several yesterday of the hard topics, I picked up energy geo technics which is theneed of our, everywhere in the world the big crisis is how to hardness sustainable energy,go to the Western world 6 months of the year, the entire country remains no bound.And imagine the amount of energy they required for refrigeration, heating up of their housesand infrastructure and so on, come to the countries like India where we have temperateclimate, again the energy geo techniques plays a very important role, we have to talk aboutsustainable energy by which we can cool our infrastructure and the buildings, alright.So, imagine the parts of Rajasthan and Northern India which remain under severe heat conditions,you know for almost 4 to 5 months.Now, this is where we have talked about what are the resources which can be exploited togenerate more energy and I talked about a discussion on nuclear energy versus thermalenergy and then we discussed about the volume versus concentration concept and then lateron, I look that concept to quantify like how to solve this type of problems or the philosophiesby using the concept of THMC that is thermo hydro mechanical chemical coupling.And then this is where I also talked about THMCB; thermo hydro mechanical chemical biologicalcoupling and how these types of couplings can help you in solving the issues which arerelated to production of energy and particularly, the nuclear waste disposal and post disposalyou know, monitoring.I will go ahead with this concept of energy geotechnics in today’s lecture and to justgive you an idea what was happening in the contemporary world and some of you who havealready heard about the gas hydrates, I will discuss a bit about what these gas hydratesare, so I have provided link over here, if you click over the gas hydrates, you willget lot of information about what is happening in the contemporary world.So, this is a clipping which shows in a first natural gas hydrates discovered in the IndianOcean, I mean like this is the source of energy in the days to come and people speculate whenthe fossil fuel is over, this is the source of energy or this is the type energy whichcan be exploited for sustenance of the society, since it is an interesting report which youshould go through, most of the time, these hydrates are available in the offshore regionsor in the world body's.And I will discuss in details about these type of structures in today’s lecture indetails and what these structures have to do with the geomechanics, now as for as theIndian scenario is concerned, if you go through the current affairs, this is what is happening.So, India might hold world's second largest gas hydrate reservoirs and this is a verygood news, you know the region which have been identified are the KG Basin, Andamanarea and north-east, so KG Basin is a very rich area in which the hydrates are deposited.If you talk about the South Asia, gas hydrates are the resources and this is a very interestingdocument which is available on the net, this comes from SAARC energy centre, Islamabad,Pakistan, gas hydrate resource potential of the South Asia.Well, whenever you get time, you should go through this, this is how the hydrates lookslike.So, if I expose it to the atmosphere, it catches fire because of the methane getting emittedin the environment.So, basically what hydrates are; these are basically Ice like clathrates, this is howthey look like, so what you will notice is that this is the molecule of methane, thoseof you who left chemistry, these are carbon attached with 4 hydrogen atoms, so these aremethane molecule which gets trapped into water and because of the pressure and temperaturecondition, it gets trapped over there due to action of very high pressure and low temperatures.We call them as ice like clathrates and truly speaking, this is a state of a material ora geomaterial which also is considered as a multi-phase, Americans would call it asmulti-phase, alright, so many people are doing research nowadays on multi-phase geomaterials,multi-phase geomechanics.In conventional geomechanics if you remember, we have talked about only mostly started with3 phases.But then very cleverly, you brought it down to the 2 stages by saturating all the samples,so most of the test which you get in the laboratory were under so many condition, whether it isCBR, whether it is hydraulic conductivity, whether it is shear strength, triaxial consolidation,you saturate the sample first for enough time, so that the air phase gets lost So, trulyspeaking, the conventional geomechanics does not capture the real life response of thegeomaterials.And keeping this in view, people have started working on unsaturated state of the material,they talk about the 3 phases and here we are talking about the multi phases, so the differenceis we have solids, we have liquids and in liquids we have let us say water, we havegases, fluids, alright, a composition of the 2 and when you are lowering the temperatureand playing with the pressure, the state of fluid may also get changed.Very high pressures would cause dissolution of the gas, which is present in the poresof the soil into the liquid phase, alright.Similarly, a very high temperature; low temperature might change a certain fraction of the liquidinto a solid phase, say water getting frozen in the pores partially.So, imagine a state of the material where you have soil skeleton, where you have littlebit frozen water, you have completely frozen water, where you have no frozen water.And then you have different type of gases, this could be fumes, this could be chemicals,this could be anything, alright, it could be methane gas, so this is the state of thegeomechanics in the 21st century which people are trying to work on and these are goingto be more realistic.So, whether it is an atomic waste disposal, which we are discussing the other day or whetherit is hydrates; gas hydrates.These are the good examples of how geomaterials when they come in contact with different environmentalsituations conditions they behave, in other words, the response of the material when itis exposed to different environmental conditions.“Professor – student conversation starts” Yes, please; Sir, is this methane trappedin ice like a crystal or like a crystal, solid crystal in an ice, no, gases cannot be crystallised,so methane molecules gets strapped into the crystal water, alright, okay, any other question?So, I hope you have understood what is the state of the heart of the subject, yes, please,the geo mechanics as such, so somebody if I ask you to find out the compressibilityof this type of sediment which is the multi-phase sediment or what is the hydraulic conductivityof a fluid which is passing through these sediments or what is the shear strength ofthese type of sediments, clear, this becomes very, very complicated.The simple thing would be you go out for the reconnaissance, so the way you, the way thatgeo-physicist were finding out the minerals location on the earth, same way you have togo reconnaissance in a ship and find out where these type of reservoirs are or sometimesif you check on the net, mid ocean fires, clear that is an indication that somewheredown below you have a reservoir of hydrates, so the methane gas is leaking and this catchesfire.And in the middle of the sea, you will find there is a big fire, alright.“Professor – student conversation ends”.So, these are the good indications, there are lot of people who are working on resources,so geo-physicist they were talking about location of water table, location of minerals, clearand now the shift is on finding out hydrates.So, where is the habitat of such type of elements?These are marine environment, this could be lakes, this could be water bodies and youknow wherever you have sediments so, each molecule of hydrate would be having 180 metercube of methane gas; methane that means what is happening is as you are asking the moreand more pressure which you apply on the system, the lower the temperatures, so many moleculesof methane gas can be packed inside the matrix that once you take out the system and putit to the STP; standard temperature pressure condition, you can produce 180 meter cubeof the methane gas.Imagine that would be a most wonderful thing, so when you fill your car, you know dieseltank or petroleum tank, what is the capacity of the car diesel tank; it is nearly 27, 28,30 litres, 50 litres, trucks would be about 200 litres, 500l litres and so on, for anaircraft it would be in 1000’s of litres, clear.So, imagine one molecule of the hydrate crystal is capable of producing 180 metre cube ofmethane gas.So, this is what is going to solve the energy crisis of the society, the cotemporary world,this is how they look like, like a cauliflower or a cabbage you may say, I will show youa lot of forecast today.So, what are the different sources of the methane gas; the first thing is; this is thequestion as you are asking.The second thing is the types of methane gas are 2; one is thermogenic, alright.Thermogenic corresponds to the situation which is due to the chemical reactions which areoccurring in the earth crust, alright.Thermal processes; because of the temperature gradient of the sediments inside the sea,so what you are observing here is I have done an animation that the bubbles are coming outand this gas you know gets trapped into the sediments.And under normal; sorry, not normal, under varied conditions of pressure and temperature,they will get trapped over there and they form hydrates.Normally, thermogenic gases are methane, C2H6, any idea, what it is; ethane, you are right,so C2H6 is ethane and C3H8, propane, perfect.So, all these thermogenic gases are methane, propane, ethane; it is a combination know,our interest is mostly in the methane gas.So, I can produce the methane gas, I can bring it to the refinery and I can filter out allthose things normally, this type of process occurs in the deep seas, so I have drawn aline over here which shows the depth of the water column, alright.So, under deep sea conditions normally, thermogenic processes occur.The second situation which is known as biogenic methane gas, so biogenic methane gas is apure form of the methane.We will be more interested in biogenic methane because thermogenic methane would requiresome sort of a refinery and microbial decomposition of the organic matter which is present inthe sediments is the main cause of biogenic methane production and I hope now you canrealise that why most of geotechnical engineers like us are venturing into the you know, bio-geointerface.Now, what really happens when the sediments are attacked by the biotic activity; microbialactivity?So, this is a very interesting idea where people are trying to master becoming crossdisciplinary, or inter disciplinary subject, where we have to learn a lot from biotechnologists,microbiology’s and so on and to master the whole thing.So, idea is to trap these type of gases alright, now the whole realm of new or neo geomechanicsstarts clear, so some time back I said that I would very eager to know how much is themigration of these type of gases in the sediments.So, until now you have been doing only constant head test, falling head test to find out whatis the permeability of the water which is sitting to the sediments or the soils.Now, the situation is different, we are talking about gas migration through the sediments,alright and when gas migrates through a sediments, pressure temperature conditions are peculiar,microbial activities peculiar, so this is what has to be study.Look at the wok which is done by my research scholar Dr. Jeevan, he is the faculty memberat NIT Trichy right now and he is the one who has established the entire set of himselfand he has done wonderful work on deriving the gas permeability through saturated soil,unsaturated soils under different environmental conditions, refer to his papers alright.So, this is the big challenge how gas flow occurs rather than only the fluid flow, youare talking about the water migrating through it.Normally, the biogenic methane gas or the sediments are in the continental reefs, veryclose to the onshore, you know adjacent to the coastal area, so this is the differentiationbetween the types of gases which you get.Now, coming back to your question, I can always take a sample and I can do different typesof analysis including carbon dating to find out what type of carbon is present in whattype of sediments.So, this subject now becomes absolutely interdisciplinary and this is the future of the geotechnicalengineering, alright, any other question?“Professor – student conversation starts” although sir, biogenic methane is in the purestform but I think its quantity will be far, far less than thermogenic form because ofthat we do not have that much organic matter in the sea bed, even near coastal bed.No, no, no, never say this because you have ignored the organic matter, see, the marineclays typically have like I can have anything up to 90% of the organic matter and thus thereason no wonder why the liquid limit is so high clear, so I think you have mistaken,if you really want to understand a typical organic matter distribution in the clays,please read it on net and particularly, we have come across some clays, where we havemore than 80, 90%.No, quantity of methane is something like as long as the bacterial activity is there,it has to happen, because simple thing is when you ferment something, you know mostof the pickles the way they have been formed, this is fermentation process and thus howthey give a very different taste or you know ting in your tongue, when you put them.So, volumes are not an issue because reservoirs of these different side is enormous, imaginewe were talking about the marine conditions, okay.Any other question; “Professor – student conversation ends” you have to create whenyou do these type of test, different types of pressure and temperature conditions inthe laboratory.So, I am happy to say that my laboratory is the only one right now in the country or maybe in Southeast Asia also, we do not have many such facility you have, you can simulateand you can do testing of hydrates.So, this is how we are very unique and very recently, we have acquired this environmentaltraction set up, we got it done ourselves and where you can simulate the conditionsof pressure and temperature; varied temperature pressure condition and you can see how thesediments are going to behave and then later on, we like to find out their shear strengthparameters and compressibility and the fluid flow and all these engineering properties.So, Bhini is working on creation or synthesis of the hydrates in the lab condition and Lijithis working on the geomechanical stability of the sediments which I will discuss subsequently,so you follow the papers, which have been written by Bhini Rani and Lijith Nambiar fromthe literature we have published several papers, 2-3 papers.

Video 2: Extraction of Methane
Now, it so happens that it is a very tricky interesting subject, so morphology of thehydrates would depend upon you know, the different types of freezing processes, so this is asubject which also deals with the interfaces with the frozen geomechanics.So, what I have shown over here is the morphology of the hydrates which governs the geomechanicalproperties can be understood like this.This is the skeleton of the particles, sediments and if you look at the animation carefully,you will find that this is the pore filling you know, the crystallisation of water takesplace in the pores and this is where the methane gets trapped.Now, these type of sediments are not going to very good load bearing sediments, I hopeyou can understand because the bridging between the particles is not so good.And the permeability are going to extremely high as compared to the other situation whichwe call as load bearing, so what has happen?I think you missed this animation, some of you, so please do not write and see on theslides that is going to help you.So, you say, start from the pore filling, the further growth of the crystals is goingto now be like this that means, the particles are getting cemented and hence the systemwill becoming load bearing.So, this system would have higher bearing as compared to the previous one and furtherwhat is going to happen is; if I say cementing process, all the particles get cemented andthey become like cemented sands.So, these are the 3 mechanisms which people are trying to study and these are the conceptualmodels, you know remember in conventional geomechanics, you talked about a rhombic structureand cubic structure, if you remember, is it not.This is how you visualise the entire granular material now, the same thing is being doneover here with different mechanisms of the material and finding out of the response atdifferent environmental conditions, hope this point is clear.So, a big challenge is how to differentiate between pore filling, load bearing and cementingprocesses and the way you talked in conventional geomechanics the moisture content.Here, people talk about what is the gas content in the sediments, once the hydrates are formed,alright, so we call it as gas hydrate concentration and the shear strain properties are goingto be a function of gas hydrate concentration and the type of morphology with the systemis exhibiting, it remain same as what you have studied in conventional geomechanicsas card house structure, flocculant, dispersed and so on, okay, is easy said than done youknow, it is very difficult to simulate these type of situations .And particularly, I would like to see inside what is happening inside the cells, you knowhow the system is getting altered from one state to another state and you can realisewhen you are working at such high pressures of let us say 30, 35 MPa traction pressures,you cannot look into the system because this is made up of a opaque still, alright butstill people are trying to see inside and where you have to learn lot of biopsy.Now, look at this animation slightly carefully and this is where I have talked about theextraction process because after locating the places where the reservoirs are ultimately,you want to harness this energy, you want to tap this energy, you want to extract itfrom the ground is it not, from the sea bed, the way the petroleum is extracted.So, when you extract the methane gas, there are lot of challenges, you know the gas isgoing to get dissociated from the crystals which you are talking about, Lovinder.So, the moment you bring it back to the normal standard temperature pressure conditions,the methane gas will liberate, this is what is known as dissociation, there is lot ofscience and mechanics behind this which you should study or you should attend the seminarsby these guys.Ultimately, what I want is; I want to produce energy, so this is the hydrate and the momentyou expose it to the environment, it will catch fire and it produces heat and this isthe whole purpose.So, most of the time, these expeditions are created by government of India, alright veryexpensive expeditions, the way there was a time and people used to go for you know Antarcticexpedition, you must have heard about the scientist used to go there and they used todo lot research.Nowadays, mars, moon expeditions are going on, they are call it as a mission; I do notknow what is the difference between mission and expedition.Climbing up on the mountains is expedition is it not, so this is how it happens, so youknow the place where the hydrate reservoirs are, you go in a ship and then lower downa casing, this is what is known as extraction well.How to design the extraction well itself is a big challenge, so what the Lijith is tryingto do is; he is trying to simulate the whole process, I will tell you how.Now, once you start extracting something, first of all extraction cannot be done aslong as the system remains in the frozen state.So, what you have to do is either you have to dissociate it and for dissociation, youhave to do different types of techniques, so extraction is by depressurisation; releasethe pressure which the system as got; if the system has because of the natural conditionsand the natural conditions are because you have so much of water column, the depth ofthe sediments is big this much so, total height would be gamma water multiplied by this totalstress not height.Total stresses would be gamma water multiplied by the water column plus gamma saturated multipliedby this much depth of the sediments, so this much pressure are acting on the hydrate systemwhich has to be depressurised by allowing vacuum, so that the gas may come out.The second could be by thermal stimulation, remember the hydrates are at lower temperature,so what you have to do is you have to go drill the well, put heater wires and heat up theentire soil mass.Imagine, so just now you are asking about the volumes, now I am giving an idea thatentire sea bed is to be heated up and once you heat it up, you are playing with the temperatures,so either you play with the pressure or you play with the temperature, you can liberatethe sediments.Now, what is happening is once we are extracting something, I am sure you must have heard aboutthe you know subsidence process in geotechnical engineering.So, the more and more water you extract from the wells or the aquifers, what happens; theentire system subside, it settles, so most of the cities are setting you know, Thailandis a good example, the more and more mining you do the area is subsiding, alright so,these are the challenges people are trying to handle these days.So, coming back to the point when I do this depressurisation or thermal stimulation, thechances are that you know what is going to happen?There will be a heat migration through multi-phase system and this is how the entire thing getsliberated, so the methane is catching fire and the water is coming out during the extractionprocess, so there are coupled mechanisms which are associated with this.First is the heat migration into the system, once you are heating the sediments, you haveto study what happens to the sediments when they get heated up.So, later on in the course, we will be talking about you know, thermal properties of geomaterials,it is a big section which I will be discussing, I will be talking about electrical propertiesof the geomaterials and that is the reason you know why we are discussing these typeof topics in geomechanics because live example is here, you have to heat the sediments toliberate the methane gas and then only you can utilise it for your purpose.Remember one more interesting thing; now, we are talking about multi-phase porous media,alright so, we are not; the porous media is not divide of microbial activities, in conventionalgeomechanics, you never bothered about, we thought about only 3 phases; solids, liquid,gases, microbial activity also comes, organic matter also comes in the play and whateverfluid force is taking place is a coupled phenomenon.That means water and gases are travelling together through the porous system at environmentalor subenvironmental temperatures and pressures, so this becomes a complicated scheme.So, what is going to happen when you are extracting things, water will come out and I am sureyou must have heard in your conventional geomechanics, whenever discharge takes place through thebody of the dam, because of the critical gradient was going to happen, quick sand conditionor piping action will occur, clear.So, the more and more water comes out, what it does; it take out all the fines along withit so, this is what is known as washing out of the fines from the sediments.If the fines gets washed out from a sediment, what is going to happen; the voids of thecavities will get created and the chances are that the bearing capacity of the systemis going to decrease, hydraulic conductivity is going to increase, gas permeability isgoing to increase and so on.So, look at the whole geomechanics is now changing, in the conventional geo mechanics,you thought that everything is constant volume, inflow is equal to outflow, all the time youderive this, your control volume never deform here, we have all challenges so, migrationof fines causes loss of strength, so all these problems are time and space dependent.Shear strain is a function of x, y, z and t; time, cohesion is a function of x, y, zand t, friction angle is a function of x, y, z and t.Hydraulic conductivity itself is a function of x, y, z and t depending upon the fluid,whether the gas phase you are talking about or whether the fluid phase sorry, water phaseyou are talking about.So, this problem becomes very complicated which people are trying to solve right now,so these challenges lead to what; the first thing is the piping’s and all whatever youhave installed in the system you know, it gets unstable.So, well bore instability becomes a big issue that means, the chances are that the wellbore itself may become unstable, all the methane gas may bypass the extraction well and thenwhat is going to happen; it will get liberated into the environment and if that happens,what is going to happen; greenhouse gas, are you realising, this is a very intricate andsophisticated process, you do not want methane gas to enter into the atmosphere because ofthe extraction process.I am sure you must be getting an idea, these extraction wells are nothing but you knowstraws which we use for drinking the cool drinks from the cans or the bottles, the moreand more you suck alright, what happens, we are applying a negative pressure, inside thepressure was positive, high-pressure and then you depressurise it or you apply a bit ofsuction, then you can suck all the gases.So, this is something which people are trying to simulate in laboratory including us now,when well bores instability occurs, this is one issue, the second issue is sea bed subsidence,I hope you saw this animation or not, you missed it, how many of you saw this; good,that is what I say there is no point in writing things, it should be all written in the mind,you know these are all the mechanics problems.So, look at this again, so when you are taking out the fluids from this type of systems,what is going to happen; concentrate here, seabed subsidence, alright so the collapseof the sea bed takes place.Now, imagine whatever paraphernalia you have created on the seabed because of this collapse,it is going to get destroyed, so this could be a man-made disaster so, this is a subjectwhich also deals with disasters associated with offshore systems.In case, Tsunami comes the chances are; that this you know, there could be a dislocationof the sediments and the methane gas may get liberated into the atmosphere.Earthquakes; what is going to happen; because of the relative movement of the seabed chancesare that if you have reservoirs along the slip line, the gases will enter into the atmosphereand that is what causes mid ocean fires.So, these are the issues like if you have identified that these are the places wherehydrates are, it is a good idea to extract them as soon as possible because now, sorry,nowadays, you have lot of Tsunami’s affecting the system, you have earthquakes affectingthe system, you have lot of human activities affecting the system, you never know tomorrowsomebody might be putting a you know off shore pipe line, cross-country pipe line for datacommunication.Most of a fibre optic cables are running on the sea beds, I do not know whether you areaware or not, alright, so how Andaman’s are connected with India; main land India,read this all story.So, these are the geotechnical engineering jobs which people are into.

Video 3: Modelling of Gas Hydrate Bearing Sediments
Now, if you want to learn more about the sea bed subsidence and what it does; please readthis pdf file, where people are trying to simulate these types of conditions.Santamarina is number 1 in this subject so, read the papers written by him and I wishsome of you should get a chance to work with him in the you know Saudi Arabia, he establisheshis own lab, is what is known as American University of Sharjah.So, mechanical and numerical modelling of gas hydrate bearing sediments, this is whatLijith is working on, very intricate subjects, no doubt but very satisfying and very youknow sure to contemplate a lot, to understand how things happen, yeah, Famy, you would havesomething to ask, no, alright, any questions.So, you read this text whatever is written over here and you may get a feel of what isgoing on right now.So, I hope you realise that again THMC or THCM is coming into picture, these are hydratebearing sediments and worth reading whenever you get time, alright.Lijith has published an interesting literature, review paper on geomechanical aspects of gashydrates, very recently over 3, 4 months back, okay.


Video 4: Government Expeditions
Alright, so, these type of expeditions have been taken up by Ministry of petroleum andnatural gas, government of India, I hope you are aware of what is going on in the worldthese days and this is the special directorate of; directorate general of hydrates or hydrocarbonswhich is known as DGH until now, there have been 3 expeditions; one is NGHP1, NGHP2 andNGHP3 and this is what is known as national gas hydrate program. Those are the tricks to see what is happening inside, so that is the reason we will be talkingabout electrical properties of geomaterials in details, how electrical properties, thermalproperty should be utilised to sense something, to see something, to visualise something,to feel something, to quantify something.