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The Appalachian basin is an oblong sedimentary basin in the eastern United States with an area of approximately 185,500 square miles and a length of around 1,075 miles. The basin covers many eastern states which includes New York, Pennsylvania, Ohio, and parts of Maryland, Tennessee, Kentucky, West Virginia, Alabama, and some of Georgia. The main focus for drilling today is in Tri-State Area which consists of Ohio, West Virginia, and Pennsylvania. The Tri-State Area is home to the Utica, Marcellus, and Upper Devonian Shale, which is where the majority of production comes from in the Appalachian Basin.
The geology of the Appalachian Basin dates back to more than 480 million years ago, with mining for bituminous coal beginning almost three centuries ago. To this day, Virginia and West Virginia have continued mining for coal and it is still used to provide many Eastern states with electrical power generation. About two centuries following the start of the mining era in the Basin, drilling began in 1859 in Venango County, PA when oil was first discovered by the Drake Well. This was the beginning of O&G production in the Basin and by the late 1800s and early 1900s a few more oil plays were discovered. The discovery of gas came soon after, when it was discovered in 1924 near Ohio. Although it is said drilling began in the late 1800’s in a small patch of shale found in the basin, production of large quantities did not take place until more recent years with the discovery of the three powerhouse shale locations. Drilling in the Utica Shale, one of the three powerhouses, first began in 2009 by a Canadian company called GThe first well was in New York and was located in Otsego County. Two years later, more drilling in the Utica Shale began in Ohio, and by 2012 the US Energy Information Administration estimated that the Utica Shale held 15.7 trillion cubic feet of unproved, recoverable gas. They also estimated that the average well was to produce 1.13 billion cubic feet of gas. The first hints of large production in the Marcellus shale began in 2003 when Range Resources – LLC drilled a well that showed a promising quantity of natural gas in Pennsylvania. The first gas production from the Marcellus happened two years later in 2005, and by 2007 almost 400 permits for gas producing wells were issued in the state. In 2012, the Energy Information Administration stated that the Marcellus Shale contained approximately 141 trillion cubic feet of recoverable natural gas. And in 2015, the Marcellus was producing roughly 14.4 billion cubic feet of natural gas per day. The third powerhouse shale, the Upper Devonian, was first drilled in 2009, also by Range Resources – LLC. The “Yeager Well” was the first of many, and still today the number of permits for O&G drilling within the Upper Devonian Shale continues to climb. Primarily due to the Marcellus, Utica, and Upper Devonian shale plays, Appalachia now produces more than 32 percent of U.S. natural gas and 600 thousand barrels per day (BPD) of natural gas liquids (NGLs). In fact, Appalachian shale gas is the principal driver for growth in U.S. natural gas production. The stratigraphy plays a large factor in the basin's abundant production, as the basin contains a multitude of rich petroleum units throughout the stratigraphic column.
The Appalachian basin is defined as a foreland basin that consists of Paleozoic sedimentary rocks. The rocks date back to the early Cambrian through the early Permian ages. The basin covers many eastern states which includes New York, Pennsylvania, Ohio, and parts of Maryland, Tennessee, Kentucky, West Virginia, Alabama, and some of Georgia. It covers an area of 185,500 square miles and is 1,075 miles long. As for its geologic structure, the northwestern flank of the basin is a broad homoclinic that dips towards the southeast. Towards the end of the Paleozoic, a complex thrust fault and folded terrane was formed by the Alleghenian orogeny, a mountain formed in the Appalachians. Also, metamorphic and igneous rocks of the Blue Ridge Thrust Belt were thrust west over the Paleozoic sedimentary rock. As for oil, it was first discovered in 1859 at the Drake Well in Venango County, PA. This started the oil and gas industry in the Appalachian Basin. Oil was produced from Upper Devonian, Pennsylvanian, and Mississippian sandstone reservoirs, which goes through several states. A second and third major oil movements occurred in 1885 and then again in the early 1900s. This is because more oil was discovered In different areas/reservoirs across the Appalachian Basin. Then in 1924, gas was discovered in Lower Devonian sandstone near Ohio, which pushed another movement of mining and producing gas. This lead to gas being produced in many states by 1936 within the Appalachian Basin.
The Appalachian is full of folding, thrusting, and faulting, so they're many different opportunities for traps to be made. One example is the Eastern Overthrust Belt, which is very important to the overall Basin because of its structural traps and associated fractural porosity. Another type of faulty found is in the gas fields of the Oriskany Belt. Here the belt is made up of anticlinal fault traps, which fractures are the most dominant type of porosity. These are examples of a few of the many traps included in the Appalachian Basin.
The Utica and Marcellus Shales of the Appalachian Basin act as seals. These shales contain certain sequences of organic matter that make them unique, as in the shale not only being a hydrocarbon but acting as a seal as well. Shale has low permeability and porosity which make it perfect to act as a seal. These two reservoirs are unconventional-reservoirs where the shale formation becomes the seal, so it's known as self-sealing.
As stated above, the Appalachian Basin has two sequences of source rock which include gray, brown, and black marine shale, and all are rich in organic matter. These sources have been major producers of oil and gas for the Basin over the years. Between New York and Alabama, also known as the Appalachian Plateaus the source rock is derived from the younger sequence of rock; forming between the Middle Devonian and into the Early Mississippian. This source rock is darker shale. Although in states such as West Virginia and Pennsylvania the shale is slightly lighter, but formed around the same time. The older source rock was formed around Middle to Late Ordovician and is mostly brownish with some black and grey shale. All these marine shales are the basis of all oil and gas produced in the Appalachian Basin.
A majority of the oil and gas fields form because zones of fracture porosity form the reservoirs in the Appalachian Basin. The reservoirs are formed by the shale acting as the trap and becoming self-sealing. So therefore, for most cases the reservoirs are formed by the shale in which we mine. The two main reservoirs in the Appalachian that hydrocarbons accumulate is once again the Marcellus and Utica Shales.
Primary Geologic Risks/Uncertainties:
One of the primary risks is the amount of unconventional wells spread out over the Basin. Due to the overwhelming amount of unconventional wells, there has been a rise in awareness if human and environmental health. One of the main concerns that arises is water quality. With the unconventional wells, they're afraid the water reservoirs will become compromised and water quality will diminish. This could lead the EPA to implement more strict policies around mining the Appalachian which leaves the future in uncertainty. Also, there's only a limited supply of coal and there's some guesses on how much longer the Basin can produce, but eventually it will run out.
Future Petroleum Potential:
As of now 2019 some US companies such as Shell believe that the Appalachian Basin could become the next energy hub of the world. They plan to do this by selling polyethylene, a product of shale drilling, and selling it. It also helps that 70% of poly users live near or close to the basin. Scientists and geologists have also estimated that there's still nearly 214 trillion cubic feet of natural yet to be discovered in the Basin. Also is predicted to contain 1.8 billion barrels of oil and 985 million barrels of natural gas liquids yet to be mined. Therefore, the future of the Appalachian Basins looking bright in terms of production and making profit.
Petroleum and Facility Engineering:
One thing Shell has planned to try and accomplish by the end of 2020, is a more unified drilling of the Appalachian Basin. Currently, it's mined by several independent groups, and infrastructure is a weakness as a whole for the Basin. In terms of engineering, Shell is leaning towards selling more polyethylene to customers near the region, and developing ethane storage and distribution facilities. They're preparing for the "new wave of energy" by believing in the poly-technology and heading more towards that path. Other than that the more common drilling facilities are unconventional wells, which produce more pollution and are older and seemingly more out-to-date everyday.
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