ENERGY FROM GASHYDRATESGuided by:Pro: Gigi SebastianSubmitted by:AFSAL AMEEN C
INTRODUCTION Gas hydrates are cage-like structures of watermolecules, surrounding molecules of gas, primarilymethane. Methane is the principal component of natural gas. They form when water and natural gas combine atsufficiently low temperatures and high pressures. They seen in the regions of permafrost and insubseafloor sediments. Theoretically estimated that maximum of 270 milliontrillion cubic feet of natural gas exist in hydrate deposits.
HISTORY Russian scientists in the late 1960s were the first topropose that gas hydrate might occur naturally in marineand onshore locations (Makogon and Medovskiy,1969) In the early 1970s, scientists found that gas hydrateexisted below the permafrost and in marine sediments(Stollet al., 1971; Bily and Dick, 1974). Deep sea drilling expeditions confirmed that gas hydrateoccurred naturally in deepwater sediments along outercontinental margins (Paull et al., 1996; Tréhu et al.,2003;Riedel et al., Proceedings of the ODP, 2006).
OCCURANCE Natural gas hydrates are solid, crystalline, ice-likesubstances composed of water, methane, and usually asmall amount of other gases, With the gases being trapped in the interstices of awater-ice lattice. They form under moderately high pressure and attemperatures near the freezing point of water. In the United States, very large methane hydratedeposits are located both on- and offshore northernAlaska.
OCCURANCEFig:3 Location of known and inferred gas hydrateoccurrencesKvenvolden and Rogers, 2005)Reproduced with permission from Keith Kvenvolden and Bruce Rogers.
HYDRATE STABILITY stability of the gas hydrate mostly depends on pressureand temperature. the mechanical properties of gas hydrate are similar tothose of ice because gas hydrate contains about 85 %water by mass. It may look like ice, it does not behave like ice — forexample, it burns when lit with a match. colder temperatures and/or higher pressures — the gashydrate is stable.
HYDRATE STABILITY Cont…Gas Hydrate Occurrence Zone and Stability Zone
NATURAL GAS HYDRATES Gas hydrates form when water and natural gas combineat low temperatures and high pressures. Gas hydrates are cage-like structures of watermolecules. surrounding molecules of gas, primarily methane.Methane is the principal component of natural gas. They are members of a highly varied class of substancescalled clathrates.
NATURAL GAS HYDRATES cont.. Natural gas hydrate is a potentially vast source ofhydrocarbon energy that is currently unexploited. They are seen in the regions of permafrost and in marinesubseafloor sediments. They substances composed of water, methane, andusually a small amount of other gases. It has been estimated that a maximum of 270 milliontrillion cubic feet of natural gas could theoretically exist inhydrate deposits
NATURAL GAS HYDRATES cont..It is highly inflammable and are called "Fiery ice"or ―Ice that burns‖
PRODUCTION METHODS There are three mainly used production methods are1. DEPRUSSURIZATION.2. THERMAL STIMULATION3. CHEMICAL INHIBITION
PRODUCTION METHODS Cotd..1. DEPRUSSURIZATION. Its objective is to lower the pressure in the free-gaszone immediately beneath the hydrate stability zone,causing the hydrate at the base of the hydrate stabilityzone to decompose and the freed gas to move towarda wellbore..
PRODUCTION METHODS Cotd..2. THERMAL STIMULATION. which a source of heat provided directly in the form ofinjected steam or hot water or another heated liquid, orindirectly via electric or sonic means. It is applied to the hydrate stability zone to raise itstemperature, causing the hydrate to decompose. The direct approach could be accomplished in either oftwo modes: a frontal sweep similar to the steam floodsthat are routinely used to produce heavy oil, or bypumping hot liquid through a vertical fracture betweenan injection well and a production well.
PRODUCTION METHODS Cotd..3. CHEMICAL INHIBITION. It is similar in concept to the chemical means presentlyused to inhibit the formation of water ice. This method seeks to displace the natural gas hydrateequilibrium condition beyond the hydrate stabilityzone’s thermodynamic conditions through injection of aliquid inhibitor chemical adjacent to the hydrate.
PRODUCTION METHODS Cotd..Fig:3 Schematic of proposed gas hydrate productionmethods: (a) thermal injection (b) depressurization, and (c)inhibitor or other additive.
TRANSPORTATIONThere are at least three ways to transport the gasashore; by conventional pipeline; by converting the gas hydrates to liquid middle distillatesvia the newly-improved Fischer-Tropsch process andloading it onto a conventional tanker or barge; or by reconverting the gas into solid hydrate and shipping itashore in a close-to-conventional ship or barge
SAFETY &ENVIRONMENTALCONCERNS Normal drilling can generate enough downhole heat todecompose surrounding hydrates, possibly resulting inloss of the well. While large volumes of oceanic natural gas hydratedeposits are known to have decomposed in the pastabsent human influence. It is clear that the release of large quantities of methaneinto the atmosphere, can cause increase its greenhousecapability since methane is 21 times more potent agreenhouse gas than is CO2.
APPLICATIONSused in power generation.urea fertilizer production.room heating& cooking .
CHALLENGES During drilling wells as part of the development of gashydrate will produce significant amount of cuttingscontaining methane gas. CO2 produced when methane is burned as a fuel. methane itself is a greenhouse gas with 21 times than ofcarbon dioxide. High cost for long pipe lines across unstable continentalslops.
COMPARISONS The natural gas is found is gaseous state, while gashydrate is a solid . When natural gas is burned, it emits CO2, leads toglobal warming. But the amount released is less thanthat of coal or oil is burned. Oil and coal, emit air pollutants like SO2 & nitrogenoxides. But in natural gas no such emissions. Methane gas is the cleanest fuel, because it emitsminimum residue in the environment.
CONCLUSION exploration and quantification of gas- hydrates are verymuch required for evaluating the resource potential andhazard assessment. Proper exploitation of methane at one hand can meetthe ever-increasing demand of energy and on the otherhand will reduce the environmental and submarine geo-hazard. There are several technical problems in extracting andproducing gas from gas-hydrates at this moment. The recoverability of gas from gas hydrate may beevaluated if the hydrate occurs in unfrozen sandysediments
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