Note that the Utica Shale is about feet below the Marcellus under western New York but about feet below the Marcellus in south-central Pennsylvania. Also note that the Marcellus Shale potential source rock does not extend as far into New York as the Utica.
The thickness of the Utica Shale is variable. Throughout most of its extent, it ranges in thickness from less than feet to over feet. Thickest areas are on the eastern side of its extent, and it generally thins to the northwest.
A thickness map of the Utica Shale is shown as Figure 6. Although thickness of a rock unit is important in determining its oil and gas potential, the organic content, thermal maturity and other characteristics must all be favorable. The Utica Shale is an organic-rich rock unit. The organics are what give it a dark gray to black color - and hydrocarbon potential.
The amount of organic material in the shale varies throughout its extent and also varies vertically within the rock unit. A map of the regional variation in total organic carbon is shown as Figure 7. The organic carbon content is generally highest in the center of the rock unit's extent and decreases towards its margins. High total organic carbon values are often correlated with a high potential of oil and natural gas generation.
CAI correlates with the thermal maturity of the rocks. CAI values between 1 and 2 are normally associated with the presence of crude oil, while CAI between 2 and 5 are normally associated with the presence of natural gas.
Figure 8: Examples of color alteration in conodont fossils. Image by USGS. Conodonts are microfossils of eel-like animals that lived in marine environments from the Cambrian through Triassic Periods. They are composed of calcium phosphate and range in size from about 0. See Figure 8. They are useful in determining the age of a rock unit and correlating rock units from one location to another. When heated, conodonts change color through the sequence shown in Figure 9, according to the temperature of the surrounding rocks.
This progressive color change has been linked to rock temperatures by the "conodont alteration index" or "CAI". The color progression is not reversible and records the maximum temperature to which the rocks have been heated.
As the rocks are heated, organic materials in the rocks are modified by rising temperature. At a CAI of 1, organic materials in the rocks yield crude oil. At a CAI of 2, oil is starting to convert into natural gas.
Where the CAI is greater than 2, natural gas is likely to be the dominant hydrocarbon. The area in green is where wells are likely to encounter crude oil. The area in pink is where natural gas is likely to be the dominant hydrocarbon. They identified two assessment units in the Utica Shale. The geographic areas covered by these units are shown on the map in Figure Their Utica Shale Gas Assessment Unit Gas AU is defined where the thermal maturity of the organic matter is greater than a CAI of 2, and where the total organic carbon is greater than 1 weight percent.
See Figure 7 for TOC map. Under certain circumstances the layer can eventually produce oil and gas. Therefore, geologists look for specific rock types and geologic formations in areas that were once covered by large bodies of water such as ancient seas or lagoons. Sedimentary rocks are formed when many layers of sediments are compacted together; most sedimentary rocks form under large bodies of water. Since Earth's continents are continually moving and areas that were once covered by water may no longer be covered by water, geologists look for sedimentary rocks with high organic matter content.
Shale is a tightly packed sedimentary rock. The shale is very porous, but it is not very permeable. Recent technologies have made it possible to extract the oil and natural gas trapped in deep shale formations. Hydraulic fracturing increases the permeability of the shale by forcing open the natural cracks in the shale.
Water or other fluids, such as propane, are pumped into wells, cracking open the natural fissures in the rock. The fractures are kept open by use of proppants, such as sand. Also called fracking. To save students' data for grading online, register your class for free at the High-Adventure Science portal page.
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The Rights Holder for media is the person or group credited. Elaine Larson, National Geographic Society. Jeannie Evers, Emdash Editing. Natural Gas Gross Withdrawals and Production. Energy Information Administration. Generalized cross section of Catskill delta magnafacies across western Pennsylvania and Ohio adapted from Harper, The remainder of the section is Upper Devonian.
United States Geological Survey. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.
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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. The customary royalty rate is Higher royalty rates are sometimes paid by aggressive buyers for highly desirable properties. The royalties paid to eligible property owners from a well yielding over one million cubic feet of natural gas per day can be hundreds of thousands of dollars per year.
Unfortunately, production levels in most wells fall rapidly, yielding much lower amounts year after year. If the Marcellus Shale holds up to the optimistic expectations of some natural gas experts, Pennsylvania, Ohio, New York, and West Virginia could temporarily have an enormous boost in income that might be sustained for a few decades.
Number of Marcellus wells: This graph shows the number of unconventional wells drilled in Pennsylvania between and Between and , unconventional wells were only targeting the Marcellus Shale. Starting in , some wells began targeting the Utica Shale in western Pennsylvania.
Data in this chart was obtained from the Pennsylvania Department of Environmental Protection. Several companies are actively drilling or leasing Marcellus Shale properties. The Pennsylvania Department of Environmental Protection reports that the number of drilled wells in the Marcellus Shale has been increasing rapidly. In general, hydraulic fracturing fluid is composed of water, proppant typically sand , and chemicals.
A public website known as FracFocus has been established by industry that lists specific materials used in many, but not all, hydraulically fractured wells. Individual companies select a few chemicals to be used from hundreds that are available What is the USGS role related to hydraulic fracturing?
The USGS is a science research agency with no regulatory, land management, or enforcement powers. The USGS role includes: research and assessments on the location, quantity, and quality of unconventional oil and gas resources whose production could involve hydraulic fracturing.
Resource assessments estimate the quantity of oil and gas that is yet What environmental issues are associated with hydraulic fracturing?
Environmental issues that are specifically related to hydraulic fracturing include: water availability spills of chemicals at the surface impacts of sand mining for use in the hydraulic How does hydraulic fracturing affect the surface or landscape of an area?
An area undergoing production of oil or gas using hydraulic fracturing technology shares many features with areas where conventional oil or gas is being developed, including: Roads Pipelines Compressor stations Processing facilities. Features that are unique to areas in which hydraulic fracturing is used include: Fewer but larger drilling pads, How does hydraulic fracturing differ from traditional petroleum development methods?
In a conventional oil or gas field, where the oil or gas is in relatively porous and permeable rock i. Nonetheless, a variety of techniques are often used to improve the flow of oil or gas, including hydraulic fracturing.
Rock formations Can hydraulic fracturing impact the quality of groundwater or surface water? Properly constructed wells prevent drilling fluids, hydraulic fracturing fluids, deep saline formation waters, or oil and gas from entering aquifers. Carefully constructed and operated well sites have the ability to contain potential How and where do drillers dispose of waste hydraulic fracturing fluid? After a well is brought on Are other countries using hydraulic fracturing for oil and gas extraction?
Yes, hydraulic fracturing is being used extensively in Canada and is increasingly being used in countries in Asia, Europe, and South America. Learn more: Hydraulic Fracturing Induced Earthquakes.
Filter Total Items: 5. Year Published: Conceptual model to assess water use associated with the life cycle of unconventional oil and gas development As the demand for energy increases in the United States, so does the demand for water used to produce many forms of that energy. Valder, Joshua F. View Citation. Valder, J. Geological Survey Scientific Investigations Report —, 22 p.
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