Niobrara formation

The Late Cretaceous Niobrara Formation of the southern Powder River Basin (PRB) is known as a prominent source rock and oil and gas reservoir. The Formation contains intervals of chalks, marls and calcareous shales. The Niobrara can be defined as a deep-water hemipelagic carbonate mudrock. During the Late Cretaceous, the Western Interior Seaway covered the Powder River Basin depositing calcium ...

The underlying organic-rich Graneros Shale provides further hydrocarbon charging (Higley et al., 1995). The Niobrara Formation in the DJ Basin consists of ...The entire formation could produce up to 1 million barrels a day. ... Niobrara boosts interest in local oil development. Oct 9, 2010 Oct 9, 2010; Comments; Facebook; Twitter;Go back in time at the largest Niobrara Chalk formation in Kansas. This mile-long stretch of 100-foot-tall spires and cliffs opened to the public as Little Jerusalem Badlands State Park in October 2019. ... Niobrara Chalk Formations The iconic Niobrara chalk formations in Little Jerusalem Badlands State Park were formed 85 million years ago ...The Niobrara Formation is one of the most extensive rock units in the Great Plains, and was deposited between 87 and 82 million years ago during the Late Cretaceous Period. [57] Michael J. Everhart, "Revisions to the Biostratigraphy of the Mosasauridae (Squamata) in the Smoky Hill Chalk Member of the Niobrara Chalk (Late Cretaceous) of Kansas ...Seismic reservoir characterization of the Najmah Formation, Raudhatain Field, North Kuwait: Alfataierge: Ahmed: MS: 2017: Benson, Robert D. 3D modeling and characterization of hydraulic fracture efficiency integrated with 4D/9C time-lapse seismic interpretations in the Niobrara Formation, Wattenberg Field, Denver Basin: Andrade de Almeida ...The Niobrara Formation produces commercial quantities of oil from fractures in several places in the Denver basin. The Niobrara in this basin is an oil-prone, mature source rock having as much as 3.4% TOC, and has been in the generating window since early Eocene. This implies that hydrocarbon generation from the Niobrara is partly ...

A recent U.S. Geological Survey (USGS) oil and gas assessment of the Powder River Basin , Wyoming and Montana, identified the Upper Cretaceous Mowry Shale and Niobrara Formation as the primary hydrocarbon sources for Cretaceous conventional and unconventional reservoirs.A recent U.S. Geological Survey (USGS) oil and gas assessment of the Powder River Basin , Wyoming and Montana, identified the Upper Cretaceous Mowry Shale and Niobrara Formation as the primary hydrocarbon sources for Cretaceous conventional and unconventional reservoirs.The Upper Cretaceous Niobrara Formation and its stratigraphic equivalents contain good to excellent source rocks capable of generating significant volumes of hydrocarbons where the formation has ...The Cretaceous Niobrara Formation is a productive, unconventional petroleum exploration target in the Denver Basin, Colorado. It is a self-sourced oil and gas play composed of alternating chalk and marl units. Ductile marls can serve as major source rocks with TOC values ranging 2-8 wt. %.Wattenberg Field is the Niobrara Formation. Production in the Niobrara began with vertical wells in 1986, and horizontal drilling began in 2009. Since 2009, there has been extensive horizontal drilling throughout the Wattenberg Field. With such an increase in horizontal drilling in the Niobrara Formation, it is important to address the complex ...The formation overlies the Upper Cretaceous Niobrara Formation and is unconformably overlain by the Paleocene and Eocene Coalmont Formation. The Pierre Shale, which consists of an upper sandy member and a lower shaly member, is primarily marine in origin; however, the sandy member includes minor amounts of coal.

The Cretaceous Niobrara Formation is a prolific organic-rich hydrocarbon reservoir throughout the greater U.S. Rocky Mountain region. Resistivity mapping is a common tool used for maturity mapping ...The Niobrara Formation was deposited in deep, open-marine environments of the Cretaceous Interior Seaway. This broad depocenter enabled the accumulation of a regionally correlative sequence of alternating limestones and calcareous shales covering much of the Rocky Mountain area. In southeastern Wyoming, the limestones were deposited as very ...The Niobrara Formation is emerging as an attractive target for horizontal drilling in the southern Powder River Basin. Although production has previously been established in the Niobrara Formation in this area, advancements in drilling and completion technology have made it a more economically attractive target throughout a greater part of the ...Here wide Q-range total neutron scattering was used to evaluate perdeuterated methane (CD 4) behavior at reservoir pressures (200–750 bar) and temperature (60 °C) in a sample at the late oil/wet gas thermal maturity stage from the Late Cretaceous Niobrara Formation, an active petroleum producing formation within the Denver-Julesburg Basin, U.S.

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which was also recovered from the Niobrara Formation. The new species consists of an extended anterior spike-like rhachis and a greatly enlarged ventrally open posterior conus. Niobrarateuthis walkeri n. sp. inhabited the Niobrara Sea during late Coniacian to early Santonian time and was recovered from the basal Smoky Hill Chalk. INTRODUCTIONThe bottom of the formational seal rocks of the Niobrara Formation in the oil window occurs at a transformation ratio of 0.99, meaning SWWP occurred during Late Cretaceous time (88-84 Ma). there is essentially no kerogen left to convert to oil. This was followed by deposition of several thousand feet The level of thermal maturity at which oil ...Hydrocarbon source rocks in Wattenberg are the Skull Creek Shale, Graneros Shale, Greenhorn Limestone, Carlile Formation, Niobrara Formation, and Sharon Springs Member of the Pierre Shale. Total source rock thickness in Wattenberg is 200 to 250 ft (>2 wt.% TOC). The source beds are dominantly Type II with some Type III kerogen present.The formation also is easily identified on electric logs. Thickness--Thickness of the Niobrara Formation in Kansas ranges from 0 to 750 feet (Fig. 19). Figure 19--Isopachus map of Niobrara Formation in Kansas. Contour interval 50 feet. A larger version of this figure is available.The purpose of the study was to evaluate the effectiveness of a machine learning workflow to improve resolution within the reservoir intervals of the Niobrara and Codell formations, the primary targets for development in this portion of the basin. The seismic data are from Phase 5 of the GPI/Fairfield Niobrara program in northern Colorado.

Formation, Dakota Group, Benton Group, and Niobrara Formation. The northern alternative is approximately 7.5 miles long, and crosses the same bedrock geologic units. 2.1 Definition and Significance of Paleontological Resources Paleontology is a multidisciplinary science that combines elements of geology, biology,The wireline tool is used with a motor that features a bent sub to control the direction of the bit. A recent five-well drilling program in the Niobrara formation along the Colorado-Kansas border has demonstrated a new bottomhole assembly (BHA) for coiled-tubing drilling (CTD) that is suitable for drilling directional, S-curve and horizontal ...Carlson, C. G., 1964, The Niobrara Formation of eastern North Dakota; its possibilities for use as a cement rock: North Dakota Geological Survey, Report of Investigations 41, 56 p. [ PDF available online ]The organic-rich carbonates are similar to the unconventional fluid oil and biogenic gas-producing Niobrara Formation in North America.The Niobrara formation in the central Rocky Mountain region has been written about at length by several authors, most recently concerning Silo field near Cheyenne, Wyo. The Niobrara has proven an enigma to many explorationists, because while the promise is great (individual wells with cumulative production in excess of 1 million bbl), many ...The NUMERICAL AGE of multiple beds within the Niobrara formation and Pierre Shale is known based on. Beds of volcanic ash, which accumulated when wind carried ash from eruptions to the west. Students also viewed. Ch 8. 10 terms. drp87. Geo Class Midterm 2. 40 terms. hprice16. final- earth and life though time ...The Niobrara and Benton are not now [ca. 1938] treated as groups, the broader term Colorado group, which includes them both, being considered the more useful group name. ... Skull Creek shale, Newcastle sandstone, Mowry shale, Belle Fourche shale, Greenhorn formation, Carlile shale, and Niobrara formation. Greenhorn formation is largely a light ...The vertebrate fauna of the Selma Formation of Alabama. Part 8: The fishes. — Fieldiana: Geology Memoirs3: 383–433. Google Scholar ... Fossil vertebrates of the Niobrara Formation in South Dakota. — Dakoterra5: 39–54. Google Scholar Meyer, R.L. 1974. Late Cretaceous elasmobranchs from the Mississippi and East Texas embayments of the ...Inoceramids are an extinct group of bivalves (clams) that grew to enormous sizes (several feet across) during the Cretaceous. They were well-adapted to many different marine environments from shallow to deep waters. In Nebraska, they are very common in the Greenhorn Limestone and the Niobrara Formation.The Niobrara Formation is formally sub-divided into two members: the Fort Hays Limestone and the Smoky Hill Chalk. The basal Fort Hays Limestone is relatively organic-carbon poor and consists of ledge-forming limestone beds separated by thin shales (Scott and Cobban, 1964).

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The Cretaceous Niobrara Formation is one of the latest unconventional exploration targets in North America. In this paper, an overall Type-II marine organofacies with some variability is present within a core which consists of alternating marls and chalks, covering a maturity range of 0.8-1.0 %Rc (calculated vitrinite reflectance).Location Region Stratigraphic Name; Smoky Hill River : Logan Co., Kansas, USA: Colorado - Niobrara - Smoky Hill Chalk: Castle Rock-Hackberry : Gove Co., Kansas, USANamed as top formation of Lower Cretaceous series, top of Lower Cretaceous. Formerly called "formation No. 3" (Meek and Hayden, 1857). Type not designated. Named for Niobrara River, Knox Co, NE in Salina basin, where formation forms 90-100 ft cliffs near mouth along Missouri River.The Niobrara Formation / ˌnaɪ.əˈbrærə /, also called the Niobrara Chalk, is a geologic formation in North America that was deposited between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian stages of the Late Cretaceous. 5. Testimony was heard by the Hearing Officer that indicates that a common source of oil, gas and associated hydrocarbons Niobrara Formation underlies, in addition to the area set forth in Order No. 407‑1 and subsequent orders, the following described lands in Adams, Boulder and Weld Counties, Colorado, to‑wit:Effects of climate, tectonics, and sea-level changes on rhythmic bedding patterns in the Niobrara Formation (Upper Cretaceous), U.S. Western Interior Geology. Regional isotopic variations in the Fort Hays Member of the Niobrara Formation, United States Western Interior: Primary signals and diagenetic overprinting in a Cretaceous pelagic ...The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western Interior Seaway. The usage of the name Dakota for this particular Albian-Cenomanian strata is exceptionally widespread; from British Columbia and Alberta ...

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In April 2010, EOG Resources announced its "Jake" oil well in Weld County, Colo. produced 50,000 barrels over a 90-day period. That news ignited interest in the Niobrara Formation of the Denver-Julesberg Basin, setting off a rush of oil and gas exploration that swept like wildfire across the state line into southeast Wyoming.MUDTOC CONSORTIUM: INCEPTION: JAN 1ST, 2016 (ONGOING) {INCLUDES RESEARCH FROM: BAKKEN: 2009-2016, NIOBRARA: 2010-2017, VACA MUERTA: 2013-2016} NIOBRARA CONSORTIUM - COMPLETED RESEARCH (2013) 23. Tom Arthur: Petroleum Geology of the Greater West Puerto Chiquito Field Area in Rio Arriba County, San Juan Basin, New Mexico (MS, Geology) 24. Armagan Kaykun: Sequence Stratigraphy of Lower Pierre ...The Niobrara Formation of north‐east Colorado, USA, has anomalously negative δ18O values compared to all other Cretaceous chalks. These unique δ18O values have been attributed to elevated heat ...The NUMERICAL AGE of multiple beds within the Niobrara formation and Pierre Shale is known based on. Beds of volcanic ash, which accumulated when wind carried ash from eruptions to the west. Students also viewed. Ch 8. 10 terms. drp87. Geo Class Midterm 2. 40 terms. hprice16. final- earth and life though time ...The Niobrara shale formation is situated in northeastern Colorado and parts of adjacent Wyoming, Nebraska, and Kansas. Primarily an oil play, it is in the Denver-Julesburg Basin, which has long been a major oil and gas province. Technological advances in horizontal drilling and hydraulic fracturing in the last decade has helped create new ...The formation also is easily identified on electric logs. Thickness--Thickness of the Niobrara Formation in Kansas ranges from 0 to 750 feet (Fig. 19). Figure 19--Isopachus map of Niobrara Formation in Kansas. Contour interval 50 feet. A larger version of this figure is available.Locality map for TMP 95.87.01 from the Lower Cretaceous Wabiskaw Member of the Clearwater Formation, northeastern Alberta, Canada. The location of well AA 03-12-93-12W4, illustrated in Fig. 2 is ...Name applied as the basal member of the Niobrara Formation to a 40 ft thick gray hard limestone above the Carlile Shale and beneath the Smoky Hill Shale Member of the Niobrara. Occurs in the Pueblo area, Pueblo Co, CO in the Denver basin as 40 layers of limestone, 1-26 inches thick, separated by gray calcareous shale.Using a geology-based assessment methodology, the U.S. Geological Survey estimated means of 534 million barrels of oil and 939 billion cubic feet of gas in the Niobrara interval of the Cody Shale in the Bighorn Basin Province, Wyoming and Montana.Is the upper member of Niobrara Formation above Fort Hays Limestone Member of Niobrara and beneath Pierre Shale. Divided in the Pueblo area, Pueblo Co, CO in Denver basin, into 7 units described in ascending order: 1) shale and limestone unit is a 20 ft thick gray calcareous shale separated into 18 layers by gray shaly limestone, has INOCERAMUS DEFORMIS, is of early and middle Coniacian age; 2 ... ….

These tributaries flow over the Rosebud Formation. Some waterfalls drop into the Niobrara, while others are found in spring-fed streams. The Ogallala Aquifer, a fragile, vast underground reservoir, is partially recharged by rainwater and snowmelt. Through springs, seeps, and waterfalls it provides most of the water to the Niobrara. Biological ...Summary The gas producing section of the Niobrara formation is a low pressure, low permeability chalk. To evaluate the potential of this tight gas reserve, reservoir data were obtained in a systematic program. These data demonstrate that many Niobrara wells can be produced profitably when stimulated by hydraulic fracturing and that an economically optimal fracture treatment can be designed.More than 160 mapped paleontology sites are present within the Niobrara National Scenic River's reach. The Niobrara River is exceptionally rich in documented fossil sites, averaging ten times the number of sites per unit area when compared to the State of Nebraska as a whole. Please leave fossils where they are and contact either a park ranger ...Jul 7, 2023 · Named for Niobrara River, Knox Co, NE in Salina basin, where formation forms 90-100 ft cliffs near mouth along Missouri River. Consists of lead-gray, calcareous marl that weathers to light buff or whitish color resembling true chalk; lower part grades into more compact beds of soft, bluish-gray limestone; locally weathers to hard, whitish ... Niobrara First White Specks Medicine Hat Verger Carlile Second White Specks Pseudoclavulina sp. 1 y cles Niobrara Cycle Transgression Greenhorn Cycle Transgression Regression a) 87 89 tage Santonian Coniacian Turonian Late Cretaceous iod Modi˛ed from Nielsen et al., 2008 Carlile Formation - Anoxic bottom water conditions in early Carlile ...Underlain by Niobrara formation; overlain by Shannon member. Shows isopach map and correlation of sandstone beds in the upper part of the member in electric-log correlation diagrams. Varies in thickness from 850 to 1,200 ft in the central Powder River basin. It contains the "Fishtooth" sandstone in southwest part of the basin, and the lower ...Benton formation. Recognized in subsurface of Williston basin, northwestern and central South Dakota. Conformably underlies Dakota sandstone and conformably overlies Niobrara formation. Correlates with (ascending) Graneros, Greenhorn, and Carlile formations of Ward County, north-central North Dakota.Niobrara Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area. White to dark-gray argillaceous chalk, marl, and shale. Weathers yellow to orange. Contains thin, laterally continuous bentonite beds, chalky carbonaceous shale, minor sand, and small concretions. Thickness up to 150 ft (46 m). Niobrara formation, A recent U.S. Geological Survey (USGS) oil and gas assessment of the Powder River Basin , Wyoming and Montana, identified the Upper Cretaceous Mowry Shale and Niobrara Formation as the primary hydrocarbon sources for Cretaceous conventional and unconventional reservoirs., Corrected on September 17, 2014: Earlier version incorrectly referenced well completion in the Ft. Hays member of the Niobrara The Niobrara formation, deposited between 87 and 82 million years ago during the Late Cretaceous is composed of two structural units, the Smoky Hill Chalk Member and the Fort Hays Limestone Member which is overlain by the Smoky Hill Chalk Member. To date, the main focus of, MUDTOC CONSORTIUM: INCEPTION: JAN 1ST, 2016 (ONGOING) {INCLUDES RESEARCH FROM: BAKKEN: 2009-2016, NIOBRARA: 2010-2017, VACA MUERTA: 2013-2016} NIOBRARA CONSORTIUM - COMPLETED RESEARCH (2013) 23. Tom Arthur: Petroleum Geology of the Greater West Puerto Chiquito Field Area in Rio Arriba County, San Juan Basin, New Mexico (MS, Geology) 24. Armagan Kaykun: Sequence Stratigraphy of Lower Pierre ..., The Niobrara Formation in the Southern Powder River Basin, Wyoming: An Emerging Giant Continuous Petroleum Accumulation. Steve Sonnenberg Colorado School of Mines Halo Reservoir Tight Shale==Chalk Systems Very low matrix K Low matrix k Analogous to shale gas Thin bed, bioturbated Source = reservoir Source ≠ reservoir Migrated HC's Examples: Niobrara, Clastics or Carbonates Austin Chalk ..., The Niobrara formation spans much of underground Wyoming and Colorado. Until recently, it wasn't a viable oil target in southeast Wyoming. One exception was the Silo field north of Cheyenne, where ..., A recent U.S. Geological Survey (USGS) oil and gas assessment of the Powder River Basin , Wyoming and Montana, identified the Upper Cretaceous Mowry Shale and Niobrara Formation as the primary hydrocarbon sources for Cretaceous conventional and unconventional reservoirs., The Niobrara Formation in the studied cores appears to be hiatus-free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development. The relationship between carbonate content and sedimentation rate throughout the Niobrara Formation indicates that the decameter-scale oscillations of chalk and marl are ..., Sea and Sky: Set 85 million years ago in the Niobrara Formation and follows a group of Geosternbergia trying to hunt during a thunderstorm, but there are dangerous creatures in these Cretaceous seas., The Smoky Hill Chalk Member of the Niobrara Chalk was deposited in the Western Interior Sea during a span of about five million years extending from the upper Coniacian through the lower Campanian. Coincidentally, this period also encompasses much of the early evolution and radiation of the family Mosasauridae. Thousands of mosasaur specimens …, Full reference: R. G. Green. 1977. Niobrarateuthis walker, a new species of teuthid from the Upper Cretaceous Niobrara Formation of Kansas. Journal of Paleontology 51(5):992-995. Belongs to Niobrarateuthis according to R. G. Green 1977. Sister taxon: Niobrarateuthis bonneri Type specimen: Its type locality is Hays, Ellis County [Smoky …, The Niobrara Shale formation is a geological formation located in the central United States that contains vast amounts of oil and natural gas. The formation extends from Wyoming, through Colorado and Nebraska, and into Kansas. The Niobrara Shale is known for its high-quality oil and gas reserves, and has become a major focus for energy ..., Its fossils specimens were found in the Niobrara Formation and Pierre Shale Formation in Kansas, Alabama, Nebraska, Wyoming, and South Dakota. What was a Pteranodon's habitat? The Pteranodon lived near the ocean or sea. The area where their fossils were found was covered by a large inland sea. Considering their diet they nested …, In recent years it has become clear that many shallow‐marine heterolithic and mudstone‐dominated successions are deposited as mud belts forming part of subaqueous deltas that are related to major fluvial sources either upstream or along shore. Here the Havert Formation is presented as an ancient example of this kind of system. The Havert …, The Niobrara Formation provides a robust and continuous astronomical signal 9,10 that is constrained with numerous coherent high-precision 40 Ar/ 39 Ar and …, These tributaries flow over the Rosebud Formation. Some waterfalls drop into the Niobrara, while others are found in spring-fed streams. The Ogallala Aquifer, a fragile, vast underground reservoir, is partially recharged by rainwater and snowmelt. Through springs, seeps, and waterfalls it provides most of the water to the Niobrara. Biological ..., Introduction The recent increase in North American unconventional oil and gas production has spurred exploration efforts into organic rich formations throughout the …, NTSC is a video format developed by the National Television System Committee. It is a standard that was used for broadcasting over-the-air signals as well as displaying DVD video. While the broadcasting has been replaced by the ATSC format,..., NPS Photo Valentine Formation Beneath the Ash Hollow is the Valentine Formation. This loosely-consolidated sandstone crumbles easily, but holds the primary source of the Niobrara River in this area: the Ogallala, or High Plains, aquifer. About 70% of the water in the river comes directly from groundwater., Figure 2: (a) Core plug containing partially cemented fracture in limestone of the Niobrara Formation, Lyons, C olorado. Core plug is 1 inch (2.5 cm) in diameter . (b) T omographic image slice, 1 ..., When it comes to applying for a job, having a well-crafted resume is essential. Your resume is your first impression and can be the difference between getting an interview or not. With so many different resume formats available, it can be d..., Underlain by Niobrara formation; overlain by Shannon member. Shows isopach map and correlation of sandstone beds in the upper part of the member in electric-log correlation diagrams. Varies in thickness from 850 to 1,200 ft in the central Powder River basin. It contains the "Fishtooth" sandstone in southwest part of the basin, and the lower ..., The Niobrara Formation, one such organic-rich shale, is a particularly hot target here in Colorado. While a large volume of natural gas (>700 billion cubic feet by one estimate) has already been produced, it is now Niobrara oil that is the focus of everyone’s attention. Often mentioned for comparison purposes are the Bakken Formation of North ..., Although the Niobrara National Scenic River is comprised mostly of private land, the Fort Niobrara National Wildlife Refuge and Niobrara Valley Preserve protect much of the area. ... The escarpment on the north side of the valley is a good place to view the lateral exposure of the Ash Hollow Formation (6-11 million years old). Below that is the ..., Niobrara Chalk. One of the most famous formations is the Niobrara Chalk. This formation is exposed in northwest Kansas and southern Nebraska. Formations are sometimes divided into members, subsections of the formation based upon its rock type. The Niobrara Chalk has two members: the lower Fort Hays Limestone and the upper Smoky Hill Chalk., The Niobrara Formation is formally sub-divided into two members: the Fort Hays Limestone and the Smoky Hill Chalk. The basal Fort Hays Limestone is relatively organic-carbon poor and consists of ledge-forming limestone beds separated by thin shales (Scott and Cobban, 1964)., Niobrara Formation. For ash to be the key to organic enrichment (1) a connection must exist between Oceanic Anoxic Events (OAEs) and voluminous ash fall and, (2) altered ash must largely be un-quantified in sedimentary rocks. Ross et al. (2005) observed “the near-ubiquitous, richness is known from the oldest deposits (such as the marine Niobrara Formation), im- plying much information on the evolution and diversification of this group remains un- known., reservoir is the Niobrara Formation. It is a mixed carbonate/chalk and mudrock /marlstone interval, approximately 300 feet (90m) thick (Figure 3). Underneath the Niobrara is the Codell. The Niobrara and Codell reservoir intervals within Wattenberg may contain recoverable reserves of 2 billion barrels oil equivalent. Improving the, The Niobrara Formation limey shale facies have had unusually high mud-gas shows. It has been postulated that this interval may have the potential for high volume of gas reserves from fractured shales, particularly in the Crooks Creek area (Wellborn and Wold, 1993), located to the East of the study area in 27 N-92 W (Fig. 3).Abundant fractures have been encountered in many wells at Antelope Arch., Niobrara Shale Overview. The Niobrara shale formation is situated in northeastern Colorado and parts of adjacent Wyoming, Nebraska, and Kansas. Primarily an oil play, it is in the Denver-Julesburg Basin, which …, The Niobrara shale formation is situated in northeastern Colorado and parts of adjacent Wyoming, Nebraska, and Kansas. Primarily an oil play, it is in the Denver-Julesburg Basin, which has long been a major oil and gas province. Technological advances in horizontal drilling and hydraulic fracturing in the last decade has helped create new ..., The Niobrara Formation of the Denver Basin is an unconventional oil and gas drilling target composed of alternating chalk and marl units. These units act as the source, seal and trap for hydrocarbons generated in the organic rich marl beds of the Niobrara. Organic geochemical data, such as oil-to-source rock correlations, oil biomarkers and gas ..., Dakota Formation of the San Juan basin, which produces gas from very low-permeability sand­ stones of Cretaceous age. The "J" sandstone in the Wattenberg area is similar to the Lower Cre­ taceous Dakota Sandstone reservoir of the San Juan basin (Table 1). Supporting data were provided by an earlier discovery at Roundup field , in T2N R60W,