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43-456: The Eagle Ford was one of the most actively drilled targets for unconventional oil and gas in the United States in 2010, but its output had dropped sharply by 2015. By the summer of 2016, Eagle Ford spending had dropped by two-thirds from $ 30 billion in 2014 to $ 10 billion, according to an analysis from the research firm Wood Mackenzie . This strike has been the hardest hit of any oil fields in

86-471: A sediment , sedimentary rock , or soil type which is formed from, or contains a high proportion of, calcium carbonate in the form of calcite or aragonite . Calcareous sediments are typically deposited in shallow water closer to land, as marine organisms that precipitate calcium carbonate primarily reside within shallow water ecosystems due to an inability to precipitate calcium carbonate at depth (see carbonate compensation depth ). Generally speaking,

129-450: A high pH . They are characterized by the presence of calcium carbonate in the parent material; the carbonate-ion is a base. Additionally, these soils may have a calcic horizon, a layer of secondary accumulation of carbonates (usually calciumcarbonate or magnesiumcarbonate) in excess of 15% calcium carbonate equivalent and at least 5% more carbonate than an underlying layer. Calcareous deposits can form in water pipes. An example of this

172-431: A path for oil and gas to reach the surface. When pressure differences are relatively high, oil and gas rise to the well bore naturally through buoyancy. Where the pressures are low, flow can be assisted with pumps (e.g. nodding donkeys ). In the early days of the oil industry , there was no need for stimulation to improve recovery efficiency, because supply vastly outstripped demand and leaving "difficult" oil in

215-766: A sharp downturn swept through Eagle Ford play. In January 2015, there were 840 active drilling rigs in Texas as a whole; by the end of the year, 321. Within the Eagle Ford play, the decline during these twelve months was from 200 to 76 rigs. The oil price decline rendered it uneconomical to drill sub-optimal wells. Particularly hard hit in the decline were the oil-field workers in South Texas. Unconventional (oil %26 gas) reservoir Unconventional (oil and gas) reservoirs , or unconventional resources (resource plays) are accumulations where oil and gas phases are tightly bound to

258-661: Is a form of calcium carbonate sediment that consists of >30% biogenous material predominantly consisting of organisms such as coccolithophores and foraminifera . These oozes form slowly under low-energy environments, and necessitate higher seawater saturation states or a deeper CCD (see supersaturation and precipitation vs. undersaturation and dissolution ). Therefore, in shallow CCD conditions ( i.e. , undersaturation of calcium carbonate at depth), stable, non-calcareous sediments such as siliceous ooze or pelagic red clay will prevail in marine sediment records. Calcareous soils are relatively alkaline , in other words they have

301-415: Is estimated to average 5%. Technically recoverable hydrocarbons are estimated to be 343 trillion cubic feet of shale gas and 6.3 billion barrels of tight oil . The national oil company Pemex first began exploring in 2010. Pemex had an exploration program in progress until 2015. In April 2013, Pemex started producing the nation's first shale gas well, just south of the U.S. border. The well was completed in

344-457: Is generally higher than conventional reservoirs owing to the lack of predictability of the trap extent and of the reservoir quality, which requires extensive well placement and testing to determine the economic reserves /well limit defined by well delivery . As with all forms of fossil fuel , there are established issues with greenhouse gas emissions through export (distribution) as well as consumption (combustion), which are identical whether

387-594: Is known as the Langtry Member of the Boquillas Formation . It contains very little organic matter, and abundant sea urchin fossils . The Kamp Ranch Limestone is found above the unconformity in the Dallas area. It is similar to the older Six Flags and Bluebonnet Limestones, as it is predominantly composed of disaggregated prisms of Inoceramus clams and has ripple marks indicative of shallow-water deposition. As

430-540: Is significant, measurable and predictable. Calcareous Calcareous ( / k æ l ˈ k ɛər i ə s / ) is an adjective meaning "mostly or partly composed of calcium carbonate ", in other words, containing lime or being chalky . The term is used in a wide variety of scientific disciplines. Calcareous is used as an adjectival term applied to anatomical structures which are made primarily of calcium carbonate, in animals such as gastropods , i.e.,  snails , specifically in relation to such structures as

473-489: Is the reverse of organic matter trends seen in the global ocean. An unconformity occurs throughout East Texas at this level, possibly due to a lack of sediments reaching the basin during the sea-level maximum. The sea-level began to drop after the Early Turonian sea-level maximum; this is most obvious at outcrops near Langtry, Texas , where water depths became shallower than 100 ft (30 m). This limestone-rich unit

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516-661: The Llano Uplift known as the San Marcos Arch. Primary basins active during Eagle Ford deposition were the East Texas and Brazos Basins in East Texas and the Maverick Basin in South Texas. The bottom waters of the Eagle Ford sea were starved of oxygen when most of the Eagle Ford material dropped to the sea floor, and this is related to the global Oceanic Anoxic Event 2 (OAE2), or Cenomanian-Turonian boundary event , although

559-520: The operculum , the clausilium , and the love dart . The term also applies to the calcium carbonate tests of, often, more-or-less microscopic Foraminifera . Not all tests are calcareous; diatoms and radiolaria have siliceous tests. The molluscs are calcareous organisms, as are the calcareous sponges ( Calcarea ), that have spicules which are made of calcium carbonate. Additionally, reef-building corals, or Scleractinia , are calcareous organisms that form their rigid skeletal structure through

602-709: The redox proxies molybdenum and vanadium . After the significant drop in sea level ( marine regression ) associated with deposition of the Woodbine during the Early Cenomanian, the sea level began to rise ( marine transgression ), allowing for the deposition of Lower Eagle Ford organic-rich marls in South Texas and limestones of the Terrell Member of the Boquillas Formation in West Texas starting at about 96 million years ago. The rise in sea level eventually drowned

645-500: The Eagle Ford Shale Play were estimated in 2011 at 3 billion barrels. The U.S. Energy Information Administration (EIA) estimated that the Eagle Ford held 50.2 trillion cubic feet (TCF) of unproved, technically recoverable gas. The average well was estimated to recover 2.36 billion cubic feet (BCF) of gas. In 2011, the Eagle Ford produced an average of 1.14 BCF/day of gas and 211,000 barrels/day of oil and condensate . In 2012,

688-478: The Eagle Ford is one of factors that led to the oil price drop of late 2014. Total production peaked in March 2015 at 2.62 MMBOE/day (1.625 MMBO/day and 5.75 BCF /day). Eagle Ford production has occurred in 27 counties in Texas. The large area of oil and gas operations of the Eagle Ford are visible on nighttime satellite photos of the United States, appearing as a diffuse bright patch about two hundred miles long, between

731-480: The Eagle Ford produced an average of 2.43 BCF/day of gas and 566,000 barrels/day of oil and condensate. By the end of 2013, production had skyrocketed to well over 1,000,000 BOE /day (1 MMBOE/day). In 2013, the Eagle Ford produced an average of 3.73 BCF/day of gas and 975,000 barrels/day of oil and condensate. In 2014, the Eagle Ford produced an average of 4.85 BCF/day of gas and 1,376,000 barrels/day of oil and condensate. The large increase in tight oil production from

774-636: The East Texas Woodbine river deltas , initiating Eagle Ford deposition in East Texas. The initial deposits , known as the Six Flags Limestone in Dallas and the Bluebonnet Limestone in Waco, are calcarenites predominantly composed of disaggregated prisms of " Inoceramus " clams and planktonic foraminifera tests. Following deposition of the calcarenites, a river delta began to prograde from

817-658: The Harris Delta complex. Clay from this delta reached as far south as DeWitt County, Texas . Towards the end of the Late Cenomanian, the bottom waters of the Texas shelf and the Western Interior Seaway became oxygenated, which may be related to the sea-level maximum associated with the Cenomanian-Turonian boundary event. Evidence for this oxygenation event, known as the "Benthonic Zone," include an increase in

860-785: The Ouachita Uplift to the northern East Texas Basin. Although the sandstones and siltstones from this delta, known as the Templeton Member, were originally placed within the Woodbine Formation, the ammonites found within them indicate that they are better associated with the Eagle Ford. In areas unaffected by the Templeton Delta, depositional rates were low, producing a condensed section composed of organic-rich, calcareous marls , limestones, and volcanic ash beds in both South Texas and West Texas. The microfossils found within

903-646: The Sabine Uplift is in the subsurface, and the middle Cretaceous unconformity is not seen because it is buried below a massive wedge of clastic sediments from the Late Cretaceous to the present. Paul Basinski, the geologist who helped discover the Eagle Ford basin, has been called "one of the fathers of fracking". Petrohawk drilled the first well to unconventionally produce gas from the Eagle Ford in 2008, in LaSalle County, Texas . Oil companies quickly extended

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946-405: The Texas shelf became that way nearly two million years prior to OAE2. The low-oxygen conditions helped preserve the organic matter that ultimately generated the hydrocarbons associated with the Eagle Ford in the subsurface. Evidence for anoxia include the high amounts of organic matter, the lack of fossils or trace fossils of the kind of creatures that live on the sea floor, and enrichment in

989-558: The abundance of benthic organism fossils and bioturbation , a decrease in redox proxies uranium , molybdenum, and vanadium, and a reduction in organic matter. This oxygenation event marks the boundary between the Lower and Upper Eagle Ford in West Texas and the subsurface of South Texas. In general, Upper Eagle Ford rocks deposited during the Cenomanian-Turonian boundary event (OAE2) contain much less organic matter than Lower Eagle Ford rocks, which

1032-615: The equivalent of the Eagle Ford Formation. Gas drilling in the Burgos Basin, close to the U.S. border, has been hampered by drug gangs. One Mexican industry expert said that Mexico was unlikely to develop the Eagle Ford because of lack of pipeline infrastructure and lack of expertise and because the Mexican company Pemex was investing in oil deposits that yield a higher rate of return. With the worldwide decline in crude oil prices in 2015,

1075-461: The farther from land sediments fall, the less calcareous they are, and deviations from this expectation arise if (a) the ocean floor is shallower than the CCD or (b) storms/ocean currents transport calcareous sediments away from their origin point, leading to the interbedding of calcareous sediments in alternative locations. An additional form of calcareous marine sediment consists of calcareous ooze, which

1118-427: The ground was economically expedient. Two world wars , followed by huge economic growth resulted in surging demand for cheap portable energy, while the availability of new conventional oil and gas resources declined. The industry initially sought to enhance recovery of trapped oil and gas, using techniques like restricted , or low volume hydraulic fracturing to stimulate the reservoir further, thereby reducing

1161-623: The limestones of the overlying Austin Chalk , although an unconformity is found between the Eagle Ford and the Austin Chalk in both South Texas and East Texas. In the Cretaceous after the Woodbine and Eagle Ford formations were deposited, the Sabine Uplift started to become elevated again due to its reactivation ~88 mya. A decrease in the effective elastic plate thicknesses caused the basin to subside as

1204-463: The marls are predominantly coccoliths and planktonic foraminifera , whereas the limestones contain abundant radiolaria and calcispheres (calcareous cysts produced by some dinoflagellates ). Inoceramus fragments and fish bones are also found in these deposits. During the Late Cenomanian the Sabine Uplift along the modern-day Texas/ Louisiana border became active, causing erosion of Eagle Ford and Woodbine sediments and deposition within

1247-475: The more concentrated lights of San Antonio , Austin , Houston , Victoria , Corpus Christi , Laredo , and neighboring cities. *EIA estimate includes reserves in the basin in other overlying and underlying strata including the Austin Chalk, Olmos/San Miguel, etc. The Eagle Ford Formation extends into northern Mexico's Burgos Basin, where it is known as the Boquillas Formation and has an average thickness of 200 metres (660 ft). Total organic content (TOC)

1290-476: The oil or gas are derived from conventional or unconventional reservoirs. Their carbon footprints , however, are radically different: conventional reservoirs use the natural energy in the environment to flow oil and gas to the surface unaided; unconventional reservoirs require putting energy into the ground for extraction, either as heat ( e.g. tar sands and oil shales) or as pressure ( e.g. shale gas and CBM ). The artificial transfer of heat and pressure require

1333-463: The precipitation of aragonite ( i.e. , a polymorph of calcium carbonate). Calcareous grassland is a form of grassland characteristic of soils containing much calcium carbonate from underlying chalk or limestone rock. The term is used in pathology, for example in calcareous conjunctivitis , and when referring to calcareous metastasis or calcareous deposits , which may both be removed surgically. The term calcareous can be applied to

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1376-519: The productive area, which stretches from the Texas- Mexico border in Webb and Maverick counties and extend 400 miles toward East Texas . The play is 50 miles wide and an average of 250 feet thick at a depth between 4000 and 12,000 feet. The shale contains a high amount of carbonate , which makes it brittle, and it is thus easier to use hydraulic fracturing to produce the oil or gas. The oil reserves in

1419-462: The qualities of the reservoir and/or the physical properties of the oil and gas ( i.e. permeability and/or viscosity ). These characteristics significantly impact predictability (risk to find, appraise and develop) and in turn the methods of extraction from those reservoirs such as fracking . Conventional oil & gas accumulations are concentrated by buoyancy driven aquifer pathways into discrete geological traps, which are detectable from

1462-817: The remains of sea life that dropped to the floor of an inland sea (or epeiric sea) that covered much of modern-day Texas . The Texas shelf during the Cenomanian - Turonian was bounded by the Ouachita Uplift to the north, the Sabine Uplift to the East, relict reef margins of the Stuart City Formation and the Sligo Formation to the southeast, and the Western Interior Seaway to the west. The East Texas and South Texas regions were divided by an extension of

1505-485: The rock by strong capillary forces incapable of flowing naturally through buoyancy. The limits of an unconventional field are therefore usually defined by relatively expensive well testing for delivery. Extraction from unconventional reservoirs requires changing the physical properties of the reservoir, or the flow characteristics of the fluid, using techniques such as fracking or steam injection . The technical and commercial risk associated with unconventional reservoirs

1548-424: The rock fabric by strong capillary forces , requiring specialized measures for evaluation and extraction . Oil and gas are generated naturally at depths of around 4 or 5 kms below Earth’s surface . Being lighter than the water saturating rocks below the water table , the oil and gas are driven by buoyancy up through aquifer pathways towards Earth's surface over time. Some of the oil and gas percolate all

1591-631: The sea level continued to fall during the Late Turonian, deltaic sediments originating from the Ouachita Uplift prograded into the northern East Texas region. These sandstones are known as the Sub-Clarksville Delta in the subsurface and the Bells Sandstone in outcrop . In the South Texas subsurface, the age equivalent unit to the Langtry Member is more calcareous than the underlying Upper Eagle Ford rocks, making them difficult to distinguish from

1634-830: The surface. These traps constitute relatively small but high resource density fields . Most conventional oil or gas fields initially flow naturally by buoyancy alone into the well bore, with their limits defined by fluid mechanics measurable from the well bore ( e.g. fluid pressure, OWC/GWC etc. ). In general, the technical and commercial risk associated with discrete conventional reservoirs can be reduced using relatively inexpensive remote techniques such as reflection seismology and extracted with relatively few appraisal and development wells. Unconventional reservoirs, in contrast, are regionally dispersed over large areas with no indicative trap geometry that can be used for predictive purposes. The oil and gas in unconventional reservoirs are generally low density resources, frequently trapped in

1677-487: The uplift became increasingly elevated. As a result, an estimated 150 m of uplift over the Sabine region caused the eastern parts of the Woodbine and Eagle Ford formations to have a subaerial exposure, which eventually resulted in their easterly erosion. Deposition of the Austin Chalk after this erosional occurrence caused a sealing of the East Texas petroleum reservoir and the creation of a middle Cretaceous unconformity. Currently,

1720-425: The use of large volumes of fresh water creating supply and disposal issues . The distribution of the resource over large areas creates land use issues, with implications for local communities on infrastructure, freight traffic and local economies. Impact on the environment is an unavoidable consequence of all human activity but the difference between the impact of conventional reservoirs compared with unconventional

1763-740: The volume of oil and gas left in the ground to an economic minimum. By the turn of the millennium , a new kind of energy resource was required, particularly by the USA, who were driven to achieve energy independence . The USA turned to unconventional reservoirs to achieve their goals, which had been known about for decades but had previously been too costly to be economically attractive. Today, unconventional reservoirs include basin-centered gas , shale gas , coalbed methane (CBM), gas hydrates , tar sands , light tight oil and oil shale , mostly from North America. The distinction between conventional and unconventional resources reflects differences in

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1806-413: The way to the surface as natural seepages , either on land or on the sea floor. The rest remains trapped underground by geological barriers in a variety of trap geometries . In this way, underground pockets of oil and gas accumulate by displacing water in porous rock . If the pockets are permeable , they are referred to as conventional reservoirs . Wells are drilled into these reservoirs to create

1849-432: The world. As of 2016, the spending was, however, expected to increase to $ 11.6 billion in 2017. A full recovery was not expected any time soon. Fossils are relatively common in Eagle Ford rocks. Fossilized Plesiosaurs , mosasaurs , Fish, shark teeth, crustaceans , sea urchins , feather stars , ammonites , oysters , clams, and other gastropod shells have all been found there. The Eagle Ford rocks were created by

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