Most historic wells in the Marcellus produced gas at a very slow rate because of the low permeability mentioned above. This is typical for a shale. However, some of the most successful historic wells in the Marcellus share a common characteristic: they intersect numerous fractures.
These fractures allow the gas to flow through the rock unit and into the well bore. The fractures intersecting the well also intersect other fractures, and those fractures intersect still more fractures. Thus, an extensive fracture network allows one well to drain gas from a very large volume of shale. A single well can recover gas from many acres of surrounding land. Horizontal well: The most promising wells drilled into the Marcellus employ two technologies that are relatively new to Appalachian Basin gas shale production.
One is horizontal drilling, in which a vertical well is deviated to horizontal so that it will penetrate a maximum number of vertical rock fractures and penetrate a maximum distance of gas-bearing rock. The second is "hydrofracing" or hydraulic fracturing. With this technique, a portion of the well is sealed off and water is pumped in to produce a pressure that is high enough to fracture the surrounding rock.
The result is a highly fractured reservoir penetrated by a long length of well bore. The fractures also known as "joints" in the Marcellus Shale are vertical. So, a vertical borehole would be expected to intersect very few of them. However, a horizontal well, drilled perpendicular to the most common fracture orientation, should intersect a maximum number of fractures.
The accompanying diagram illustrates the concept of a horizontal well. High-yield wells in the Marcellus Shale have been built using the horizontal drilling technique. Some horizontal wells in the Marcellus Shale have initial flows which suggest that they are capable of yielding millions of cubic feet of gas per day, making them some of the most productive gas wells in the eastern United States. Although some experts are very optimistic on the long-term production rates of these wells, it is too early to determine their productive life or long-term yield.
Shale fractures: Natural fractures or "joints" in Devonian-age shale. This is a highly fractured shale. A second method is used to increase the productivity of a well. That is to increase the number of fractures in a well using a technique known as "hydraulic fracturing" or "hydrofracing. Hydrofracing is done by sealing off a portion of the well and injecting water or gel under very high pressure into the isolated portion of the hole.
The high pressure fractures the rock and pushes the fractures open. To prevent the fractures from closing when the pressure is reduced, several tons of frac sand or other " proppant " is pumped down the well and into the pressurized portion of the hole.
When the fracturing occurs, millions of sand grains are forced into the fractures. If enough sand grains are trapped in the fracture, it will be propped partially open when the pressure is reduced.
This provides an improved permeability for the flow of gas to the well. The presence of an enormous volume of potentially recoverable gas in the eastern United States has a great economic significance. This transportation advantage will give Marcellus gas a distinct advantage in the marketplace. Gas produced from the shallower, western portion of the Marcellus extent see map above might be transported to cities in the central part of the United States.
It should have a positive impact on the stability of natural gas supply of the surrounding region for at least several years if the resource estimate quoted above proves accurate. Gas well site: Aerial photo of a gas well site. Many landowners who own the mineral rights to their property are being approached with offers to lease their land. The size of the signing bonuses that have been paid in transactions between informed buyers and informed sellers is directly related to two factors: 1 the level of uncertainty in the mind of the buyer, and 2 the number of other buyers competing to make the purchase.
These factors have changed significantly in a very short time. As recently as , there was very little interest in leasing properties for Marcellus Shale gas production. The Marcellus was not considered to be an important gas resource, and a technology for tapping it had not been demonstrated.
At that time the level of uncertainty in the minds of the buyers was very high, and the signing bonuses were a few dollars per acre. In late signing bonuses of a few hundred dollars per acre were common. Then, as the technology was demonstrated and publicized, signing bonuses began to rise rapidly. If the results of current and future drilling activity do not match the expectations of companies paying for leases, the amounts that they are willing to pay could drop rapidly.
Although signing bonuses generate an enormous amount of interest because they are guaranteed income, royalties can be significantly higher. A royalty is a share of a well's income. Undiscovered resources are those that are estimated to exist based on geologic knowledge and theory, while technically recoverable resources are those that can be produced using currently available technology and industry practices. Whether or not it is profitable to produce these resources has not been evaluated.
Using a geology-based assessment methodology, the U. Geological Survey estimated undiscovered, technically recoverable continuous mean resources of The distribution of lithium concentrations in different mineral groups was The Middle Devonian Marcellus Shale in the Appalachian basin extends from central Ohio on the west to eastern New York on the east, and from north-central New York on the north to northern Tennessee on the south.
Its thickness ranges from 0 feet ft where it pinches out to the west to as much as ft in its eastern extent. Within the Broadtop The U. The Marcellus Shale was assessed as a continuous gas accumulation using a methodology identical to that used in the assessment of shale and other continuous-type assessment units throughout Geological Survey USGS estimated a mean undiscovered natural gas resource of 84, billion cubic feet and a mean undiscovered natural gas liquids resource of 3, million barrels in the Devonian Marcellus Shale within the Appalachian Basin Province.
All this resource occurs in continuous The Marcellus Shale is a sedimentary rock formation deposited over million years ago in a shallow inland sea located in the eastern United States where the present-day Appalachian Mountains now stand de Witt and others, This shale contains significant quantities of natural gas. New developments in drilling technology, along with higher The Marcellus Shale and Point Pleasant-Utica Shale formations of the Appalachian Basin contain an estimated mean of trillion cubic feet of undiscovered, technically recoverable continuous resources of natural gas, according to new USGS assessments.
Geological Survey. Using a geology-based assessment method, the U. Geological Survey estimated a mean undiscovered natural gas resource of 3. The Marcellus Shale contains about 84 trillion cubic feet of undiscovered, technically recoverable natural gas and 3. Updated: September 14, am. July 13, AM. Updated: March 13, pm. March 2, AM. December 24, AM. Pennsylvania, Ohio and West Virginia accounted for one third of the country's shale gas production in December 20, AM. Tom Wolf Tom Corbett Pa.
Anne Danahy. High yield wells in the Marcellus Shale have been built using the horizontal drilling technique. Some horizontal wells in the Marcellus Shale have initial flows that suggest that they are capable of yielding millions of cubic feet of gas per day, making them some of the most productive gas wells in the eastern United States. Although some experts are very optimistic on the long-term production rates of these wells, it is too early to determine their productive life or long-term yield.
A second method is used to increase the productivity of a well. That is to increase the number of fractures in a well using a technique known as "hydraulic fracturing" or "hydrofracing". This method uses high-pressure water or a gel to induce fractures in the rock surrounding the well bore.
Hydrofracing is done by sealing off a portion of the well and injecting water or gel under very high pressure into the isolated portion of the hole. The high pressure fractures the rock and pushes the fractures open.
To prevent the fractures from closing when the pressure is reduced several tons of sand or other "propant" is pumped down the well and into the pressurized portion of the hole. When the fracturing occurs millions of sand grains are forced into the fractures. If enough sand grains are trapped in the fracture it will be propped partially open when the pressure is reduced.
This provides an improved permeability for the flow of gas to the well. The events described above are not unique to the northeastern United States or the Marcellus Shale.
The horizontal drilling and hydrofracing technologies were perfected for shale reservoirs a few years ago in the Barnett Shale of Texas. The technology was then applied in other areas such as the Fayetteville Shale of northcentral Arkansas, the Haynesville Shale of northwestern Louisiana, and the Marcellus Shale in the Appalachians. These are just a few of several unconventional gas plays now happening in the United States and Canada. Similar organic shale deposits in other parts of the world might also produce gas as use of the new technologies spread.
Filter Collections. Starting the play Fractured in Devonian-age shale. The need for horizontal wells Horizontal wells with hydraulic fractures are needed in order to establish productivity in shale gas reservoirs.
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