Shale gas, shale oil, tight gas and coal-bed methane are unconventional forms of gas and oil found in shale reservoirs and coal-beds. The extraction process often requires high-volume hydraulic fracturing, also known as 'fracking'. Fracking involves the injection of millions of litres of water, silica sand and chemicals – known as 'fracking fluid' – into a shale reservoir or coal-bed, at high pressure, to fracture the rock and release the gas or the oil. This leads to ground-water contamination, serious health impacts, and significantly higher carbon emissions than other fossil fuels, posing a serious threat to the climate, the environment and local communities.
---------------------------------------
Fracturing Fluid – The primarily water-based fluid used to fracture shale. It is basically composed of 99 percent water, with the remainder consisting of sand and various chemical additives. Fracturing fluid is pumped into wells at very high pressure to break up and hold open underground rock formations, which in turn releases natural gas.
----------------------
Horizontal Drilling – The process of drilling the deeper portion of a well horizontally to enable access to more of the target formation. Horizontal drilling can be oriented in a direction that maximizes the number of natural fractures present in the shale, which provide pathways for natural gas to escape once the hydraulic fracturing operation takes place. The more generic term, “directional drilling,” refers to any non-vertical well.
-------------------------------
Hydraulic Fracturing – The use of water, sand and chemical additives pumped under high pressure to fracture subsurface non-porous rock formations such as shale to improve the flow of natural gas into the well. Hydraulic fracturing is a mature technology that has been used for 60 years and today accounts for 95 percent of all new wells drilled.
-----------------------
Natural gas – A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases beneath the surface, the principal component of which (50-to-90 percent) is methane.
----------------
Permeability – The measure of the ability of a material, such as rock, to allow fluids to pass through it.
--------------
Proppant – A granular substance, often sand, that is mixed with and carried by fracturing fluid pumped into a shale well. Its purpose is to keep cracks and fractures that occur during the hydraulic fracturing process open so trapped natural gas can escape.
-------------------------
Shale – A fine-grained sedimentary rock composed mostly of consolidated clay or mud. Some large shale gas formations were formed more than 300 million years ago during the Devonian period of Earth’s history, where conditions were particularly favorable for the preservation of organic material within the sediment. Methane that remained locked in the shale layers is the source of today’s shale gas. Shale Gas – Natural gas produced from shale formations. Shale gas is widely distributed in the United States and is currently being produced in 16 states. Although data are being constantly revised, the Energy Information Administration currently estimates the recoverable U.S. shale gas resource is 482 trillion cubic feet; domestic shale gas production has increased 12-fold over the past decade and led to a new abundance of natural gas supply in the United States.
---------------
Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.[2] It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.[3]
---------
------------
What is shale gas?
Basically, it is natural gas – primarily methane – found in shale formations, some of which were formed 300-million-to-400-million years ago during the Devonian period of Earth’s history. The shales were deposited as fine silt and clay particles at the bottom of relatively enclosed bodies of water. At roughly the same time, primitive plants were forming forests on land and the first amphibians were making an appearance
Some of the methane that formed from the organic matter buried with the sediments escaped into sandy rock layers adjacent to the shales, forming conventional accumulations of natural gas which are relatively easy to extract. But some of it remained locked in the tight, low permeability shale layers, becoming shale gas.
---------
Innovative advances – especially in horizontal drilling, hydraulic fracturing and other well stimulation technologies – did much to make hundreds of trillions of cubic feet of shale gas technically recoverable where it once was not.
--------
Shale gas formations are “unconventional” reservoirs – i.e., reservoirs of low “permeability.” Permeability refers to the capacity of a porous, sediment, soil – or rock in this case – to transmit a fluid. This contrasts with a “conventional” gas reservoir produced from sands and carbonates (such as limestone). The bottom line is that in a conventional reservoir, the gas is in interconnected pore spaces, much like a kitchen sponge, that allow easier flow to a well; but in an unconventional reservoir, like shale, the reservoir must be mechanically “stimulated” to create additional permeability and free the gas for collection. In addition to shale gas, other types of unconventional reservoirs include tight gas (low-porosity sandstones and carbonate reservoirs) and coal bed methane (CBM – gas produced from coal seams)
---------------
Tight gas differs from shale gas in that it is trapped in sandstone or limestone, rather than shale formations.
==============
For shale gas, hydraulic fracturing of a reservoir is the preferred stimulation method (see graphic below). This typically involves injecting pressurized fluids to stimulate or fracture shale formations and release the natural gas. Sand pumped in with the fluids (often water) helps to keep the fractures open. The type, composition and volume of fluids used depend largely on the geologic structure, formation pressure and the specific geologic formation and target for a well. If water is used as the pressurized fluid, as much as 20 percent can return to the surface via the well (known as flowback). This water can be treated and reused – in fact, reuse of flowback fluids for subsequent hydraulic fracture treatments can significantly reduce the volume of wastewater generated by hydraulic fracturing. Producible portions of shale gas formations are located many thous
------------------
typical shale reservoir from surface= 5000 to 10000 feet
--------
Another major technology often employed in producing natural gas from shale is horizontal drilling (see graphic on previous page). The shallow section of shale wells are drilled vertically (much like a traditional conventional gas well). Just above the target depth – the place where the shale gas formation exists – the well deviates and becomes horizontal. At this location, horizontal wells can be oriented in a direction that maximizes the number of natural fractures intersected in the shale. These fractures can provide additional pathways for the gas that is locked away in the shale, once the hydraulic fracturing operation takes place.
---------------
Developing any energy resource – whether conventional or non-conventional like shale – carries with it the possibility and risk of environmental, public health, and safety issues. Some of the challenges related to shale gas production and hydraulic fracturing include: • Increased consumption of fresh water (volume and sources); • Induced seismicity (earthquakes) from shale flowback water disposal;Chemical disclosure of fracture fluid additives; • Potential ground and surface water contamination; • Air quality impacts; • Local impacts, such as the volume of truck traffic, noise, dust and land disturbance.
----
fracturing fluid composition: 99.2% is water (fresh water) and others 0.8%
-------
---------------------------------------
Fracturing Fluid – The primarily water-based fluid used to fracture shale. It is basically composed of 99 percent water, with the remainder consisting of sand and various chemical additives. Fracturing fluid is pumped into wells at very high pressure to break up and hold open underground rock formations, which in turn releases natural gas.
----------------------
Horizontal Drilling – The process of drilling the deeper portion of a well horizontally to enable access to more of the target formation. Horizontal drilling can be oriented in a direction that maximizes the number of natural fractures present in the shale, which provide pathways for natural gas to escape once the hydraulic fracturing operation takes place. The more generic term, “directional drilling,” refers to any non-vertical well.
-------------------------------
Hydraulic Fracturing – The use of water, sand and chemical additives pumped under high pressure to fracture subsurface non-porous rock formations such as shale to improve the flow of natural gas into the well. Hydraulic fracturing is a mature technology that has been used for 60 years and today accounts for 95 percent of all new wells drilled.
-----------------------
Natural gas – A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases beneath the surface, the principal component of which (50-to-90 percent) is methane.
----------------
Permeability – The measure of the ability of a material, such as rock, to allow fluids to pass through it.
--------------
Proppant – A granular substance, often sand, that is mixed with and carried by fracturing fluid pumped into a shale well. Its purpose is to keep cracks and fractures that occur during the hydraulic fracturing process open so trapped natural gas can escape.
-------------------------
Shale – A fine-grained sedimentary rock composed mostly of consolidated clay or mud. Some large shale gas formations were formed more than 300 million years ago during the Devonian period of Earth’s history, where conditions were particularly favorable for the preservation of organic material within the sediment. Methane that remained locked in the shale layers is the source of today’s shale gas. Shale Gas – Natural gas produced from shale formations. Shale gas is widely distributed in the United States and is currently being produced in 16 states. Although data are being constantly revised, the Energy Information Administration currently estimates the recoverable U.S. shale gas resource is 482 trillion cubic feet; domestic shale gas production has increased 12-fold over the past decade and led to a new abundance of natural gas supply in the United States.
---------------
Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.[2] It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.[3]
---------
originates by the same geological thermal cracking process that converts kerogen to petroleum. As a consequence, oil and natural gas are often found together. In common usage, deposits rich in oil are known as oil fields, and deposits rich in natural gas are called natural gas fields.
In general, organic sediments buried in depths of 1,000 m to 6,000 m (at temperatures of 60 °C to 150 °C) generate oil, while sediments buried deeper and at higher temperatures generate natural gas. The deeper the source, the "drier" the gas (that is, the smaller the proportion of condensates in the gas). Because both oil and natural gas are lighter than water, they tend to rise from their sources until they either seep to the surface or are trapped by a non-permeable stratigraphic trap. They can be extracted from the trap by drilling.------------
What is shale gas?
Basically, it is natural gas – primarily methane – found in shale formations, some of which were formed 300-million-to-400-million years ago during the Devonian period of Earth’s history. The shales were deposited as fine silt and clay particles at the bottom of relatively enclosed bodies of water. At roughly the same time, primitive plants were forming forests on land and the first amphibians were making an appearance
Some of the methane that formed from the organic matter buried with the sediments escaped into sandy rock layers adjacent to the shales, forming conventional accumulations of natural gas which are relatively easy to extract. But some of it remained locked in the tight, low permeability shale layers, becoming shale gas.
---------
Innovative advances – especially in horizontal drilling, hydraulic fracturing and other well stimulation technologies – did much to make hundreds of trillions of cubic feet of shale gas technically recoverable where it once was not.
--------
Shale gas formations are “unconventional” reservoirs – i.e., reservoirs of low “permeability.” Permeability refers to the capacity of a porous, sediment, soil – or rock in this case – to transmit a fluid. This contrasts with a “conventional” gas reservoir produced from sands and carbonates (such as limestone). The bottom line is that in a conventional reservoir, the gas is in interconnected pore spaces, much like a kitchen sponge, that allow easier flow to a well; but in an unconventional reservoir, like shale, the reservoir must be mechanically “stimulated” to create additional permeability and free the gas for collection. In addition to shale gas, other types of unconventional reservoirs include tight gas (low-porosity sandstones and carbonate reservoirs) and coal bed methane (CBM – gas produced from coal seams)
---------------
Tight gas differs from shale gas in that it is trapped in sandstone or limestone, rather than shale formations.
==============
For shale gas, hydraulic fracturing of a reservoir is the preferred stimulation method (see graphic below). This typically involves injecting pressurized fluids to stimulate or fracture shale formations and release the natural gas. Sand pumped in with the fluids (often water) helps to keep the fractures open. The type, composition and volume of fluids used depend largely on the geologic structure, formation pressure and the specific geologic formation and target for a well. If water is used as the pressurized fluid, as much as 20 percent can return to the surface via the well (known as flowback). This water can be treated and reused – in fact, reuse of flowback fluids for subsequent hydraulic fracture treatments can significantly reduce the volume of wastewater generated by hydraulic fracturing. Producible portions of shale gas formations are located many thous
------------------
typical shale reservoir from surface= 5000 to 10000 feet
--------
Another major technology often employed in producing natural gas from shale is horizontal drilling (see graphic on previous page). The shallow section of shale wells are drilled vertically (much like a traditional conventional gas well). Just above the target depth – the place where the shale gas formation exists – the well deviates and becomes horizontal. At this location, horizontal wells can be oriented in a direction that maximizes the number of natural fractures intersected in the shale. These fractures can provide additional pathways for the gas that is locked away in the shale, once the hydraulic fracturing operation takes place.
---------------
Developing any energy resource – whether conventional or non-conventional like shale – carries with it the possibility and risk of environmental, public health, and safety issues. Some of the challenges related to shale gas production and hydraulic fracturing include: • Increased consumption of fresh water (volume and sources); • Induced seismicity (earthquakes) from shale flowback water disposal;Chemical disclosure of fracture fluid additives; • Potential ground and surface water contamination; • Air quality impacts; • Local impacts, such as the volume of truck traffic, noise, dust and land disturbance.
----
fracturing fluid composition: 99.2% is water (fresh water) and others 0.8%
-------
கருத்துகள் இல்லை:
கருத்துரையிடுக