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Shale Gas
- 1. SHALE GAS Marcellus Shale By: Swati Abrol University of Ottawa Nov 2015 © Swati Abrol
- 2. What is SHALE and where do you normally find it? • A fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, (i.e quartz). • Shale has low permeability Permeability: determines how easy or how hard it will be to extract the hydrocarbons located in the reservoir rock --- the ability to flow through a rock • Shale has high porosity (makes an excellent reservoir rock) Porosity: determines how much oil and gas can be held in pore spaces Shale gas is found in shale "plays," which are shale formations containing significant accumulations of natural gas and which share similar geologic and geographic properties. • For example, a decade of production has come from the Barnett Shale formation play in Texas • Also, the Marcellus Shale Formation has proven to be a very significant play in NE USA
- 3. WHAT IS A HYDROCARBON? ● Organic wastes are composed of C, H, N, and O usually resulting from the death of living creatures. ● Carboniferous period: (359-299 mya) unique set of circumstances lead to the creation of fossil fuels, which depended on anaerobic decomposition (protecting them from bacterial action). ➔ Mixes with other sediments, compacts and sinks down on its own weight ➔ Increase in pressure and temperature: O & N are eliminated, leaving behind H & C. (liquids & gaseous hydrocarbon, i.e. natural gas methane)
- 4. HOW DOES IT FORM? RESERVOIR ROCK FORMATION:
- 6. CASE STUDY: MARCELLUS FORMATION
- 7. MARCELLUS SHALE FORMATION Situated in New York, Pennsylvania, W. Virginia (northern Appalachian basin), Maryland, and Ohio Black fissile shale is the dominant lithological unit deposited 400Ma (Devonian) Some limestone interbedding, iron pyrite and siderite Trapped between two layers of limestone 2,500 - 8,000 ft deep below the surface
- 8. ● low density, fissile black shale ● Carbonaceous (organic rich) ● displays vertical fractures ● low permeability ● Contains natural gas ○ requires ‘unconventional’ means of extraction (i.e. horizontal drilling + hydrofrac) due to tighter pore space because of it being a shale. MARCELLUS SHALE FORMATION
- 9. HORIZONTAL DRILLING & HYDRAULIC FRACTURING The process that is undergone to release the gas that is trapped deep within the shale is known as hydraulic fracturing. The process has been used for years to maximize yields for various shale drilling. it is a technique used for extracting natural gas from “tight” rock structures deep below the surface - it involves: ● drilling a well down below the earth ● turning drill to horizontal ● injecting millions of gallons of high pressure fluid to fracture the shale ● the fluid is 99% water + sand + chemicals ● extract natural gas
- 10. HORIZONTAL DRILLING & HYDRAULIC FRACTURING ● fracking increases the permeability of the shale (as it already is not very permeable) ● increases the rate at which gas can be produced and recovered from the reservoir formation ● when the fluid (primarily water) successfully fractures the shale, sand is usually added to the water to keep the fractures open after the injection stops ● the purpose of the sand is that when it’s all compacted, it has interconnected pore spaces which increases porosity and permeability
- 11. Structural Traps: Anticline ● an area of the subsurface where the strata has been pushed into forming a dome shape. ● if there is a layer of impermeable rock present in this dome shape, then the hydrocarbon can accumulate at the crest until the anticline is filled ● most significant type of trap in the hydrocarbon industry
- 12. ● Formed by the movement of permeable and impermeable layers of rock along a fault line ● The permeable reservoir rock faults such that it is now adjacent to an impermeable rock, preventing hydrocarbons from further migration. Structural Traps: Fault
- 13. Controversy of Shale Gas Contamination of groundwater / gas leaks in 2014 there was a methane leakage from both the Barnett and Marcellus shale gas formations this was a result of fracking from defective wellbores lead to methane natural gas to leak into the public water supply source: http://www.theguardian.com/environment/2014/sep/15/drinking-water- contaminated-by-shale-gas-boom-in-texas-and-pennslyvania-study
Notas del editor
- •Shale is a is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, (i.e quartz). This fine grained mudstone with low permeability. It has a high porosity which contributes to the fact that it makes an excellent reservoir rock. Porosity is important because it determines how much oil and gas can be contained. If it has a low porosity, it may not necessarily not worth extracting. Permeability is important in this topic because it determines how easy or how hard it will be to extract the hydrocarbons located in the reservoir rock through, for example, hydraulic fracturing. Shale gas is found in shale "plays," which are shale formations containing significant accumulations of natural gas and which share similar geologic and geographic properties. For example, a decade of production has come from the Barnett Shale formation play in Texas Also, the Marcellus Shale Formation has proven to be a very significant play in NE USA , xenia will be talking about this particular formation later in our presentation
- Organic wastes are composed of C, H, N, and O usually resulting from the death of living creatures. Most of these depositions came from the carboniferous period, where a unique set of circumstances lead to the creation of fossil fuels, which depended on anaerobic decomposition (protecting them from bacterial action). Mixes with other sediments and gets compacted and sinks down on its own weight. As it sinks it undergoes more increase in pressure and temperature, eliminating the oxygen and nitrogen, leaving just carbon and hydrogen (liquids & gaseous hydrocarbon)
- The hydrocarbons (HCs) are formed in the source rock. move around below ground because they’re lighter than water and make their way to the surface and if there’s no cap rock it will ooze out onto the the surface if during the hydrocarbons meet an- impermeable layer (i.e. cap rock) they will be trapped in the microscopic spaces/ pores and cracks of a rock known as the reservoir rock. The succession from bottom to top is the source rock then the reservoir rock which contains water, oil and gas layered in order of density and then the impermeable cap rock is layered above.
- Shale gas is found in shale "plays," which are shale formations containing significant accumulations of natural gas and which share similar geologic and geographic properties. the barnett formation located in Texas is also a very significant shale gas play where horizontal and hydro fracking are used, But Xenia Xenia will be talking about our case study which is situated in the Northeastern United States.
- About 380 million years ago during the Middle Devonian period the African continent shoved against the North American continent and created an anticline or fold that is today known as the Appalachian Mountains. Under intense pressure rotting vegetation became trapped in the sediment that became Marcellus Shale, a rock so dense that the gas was trapped within it. The Marcellus Shale basin extends from western New York to West Virginia and eastern Ohio to eastern Pennsylvania
- The Marcellus Shale was formed approximately 390 million years ago during the Devonian ages. During this time, much of the earth was covered by water. Having gone through a major transformation, the Marcellus Shale formed as sediment was deposited on the bottom of the ocean. It is located in between two impermeable layers of limestone which have naturally trapped a great quantity of natural gas inside the shale. Limestone can be both permeable and impermeable but typically what makes a limestone permeable is if it contains joints or fractures, in this case because it’s trapping the gas inside the shale, it most likely does not possess fractures or joints.
- Facies descriptions: from a publication on the Marcellus shale, there were some facies descriptions. One of them being described as “silt-rich, clay-poor, not much organic material. Very friable and breaking into pencil fractures. Possible joints.” Another facies description was: “calcareous and fissile black shale”
- For those who don’t know, hydraulic fracturing or “hydrofracking” is the process of injecting millions of gallons of water at an extremely high pressure into dried up oil and gas wells. Some of these wells can be as deep as 10,000 feet. These highly pressurized mixtures of water and chemicals breaks up the rock formations that contain high quantities of natural gas. Technique used for extracting natural gas from “tight” rock structures deep below the surface- it involves: drilling a well down below the earth turning drill to horizontal injecting millions of gallons of high pressure fluid to fracture the shale the fluid is 99% water + sand + chemicals extract natural gas
- the reason sand is put in it is because sand when it’s all compacted has interconnected pore spaces which increases porosity and permeability they pump the sand into fluid mixture which fractures the rock along already existing bedding planes where there is least resistance and most porosity. and what happens is the fracking fluid forces the rock apart, it goes into the cracks along with the sand. then only the fluid gets pumped back out where the gas comes out. the sand is still in there and allows the porosity and permeability to the oil and gas to come out into the wellbore the deal with horizontal drilling is that it exposes a lot more oil/gas and covers a lot more surface areas of the shale… and when they frack in that, then you’ll get a large quantity of oil and gas into the wellbore at once
- These traps hold oil and gas because the earth has been bent and deformed in some way. The trap may be a simple dome (or big bump), just a “crease” in the rocks, or it may be a more complex fault, such as a fault trap. All pore space is filled with water, oil and/or gas.
- The next type of structural trap that we will discuss is the fault trap. These are formed by the movement of rock along a fault line. These fault lines allow oil to flow in. Clay material between the walls traps the oil, prohibiting it from further migration.
- References: •http://archives.datapages.com/data/sepm/journals/079/079012/848_gsjsedres790848.htm •http://archives.datapages.com/data/bulletns/2007/04apr/BLTN06068/BLTN06068.htm?doi=10.1306%2F12190606068 •http://archives.datapages.com/data/bulletns/2005/02feb/0155/0155.HTM •http://archives.datapages.com/data/bulletns/2007/04apr/BLTN06018/BLTN06018.HTM •http://www.searchanddiscovery.com/documents/pollastro/index.htm?q=#06e http://www.priweb.org/files/marcellus/Marcellus_issue5.pdf http://www.srbc.net/whatsnew/docs/marcellusshale61208ppt.pdf http://www.bfenvironmental.com/pdfs/Marcellus_Shale_Study_Guide_Parts_1-5.pdf http://dnr.louisiana.gov/assets/TAD/reports/about_shale_gas.pdf