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Landman R.L.,University of Colorado at Boulder | Flowers R.M.,University of Colorado at Boulder | Rosenau N.A.,Dolan Integration Group | Powell J.,University of OttawaOntario
Earth and Planetary Science Letters | Year: 2016

Acquisition of thermochronologic data in carbonates and shales has traditionally been elusive owing to the paucity of dateable minerals in these lithologies. Conodont apatite (U–Th)/He (CAHe) thermochronology has the potential to fill this need. We acquired 50 (U–Th)/He dates for conodonts with CAI values ≤1.5 from seven Pennsylvanian shale and limestone samples from two drillcores in the Illinois Basin. We also obtained X-Ray microcomputed tomography (MicroCT) results for 8 conodonts to evaluate the accuracy of alpha-ejection corrections. The simplified geometric corrections yield corrected dates within 5% of those derived from 3D characterization using MicroCT. Nearly all of the conodont CAHe dates are substantially younger than their depositional age, indicating that maximum post-depositional temperatures of ≤90 °C caused He loss over geologic timescales. The youngest and most reproducible dates consist of whole platform elements from shales, and may record a regional Late Cretaceous–early Tertiary cooling and erosion event. The remainder of the data exhibit strong negative date-U and date-Th correlations, characterized by higher and more variable Th/U than the conodonts with reproducible dates. These patterns are best explained by U loss, with more limited Th loss. The results suggest that whole platform elements and higher U–Th conodont materials are the most promising targets for CAHe analysis. © 2016 Elsevier B.V.

Cai M.Y.,University of New South Wales | Wang L.,Indiana University – Purdue University Indianapolis | Parkes S.D.,King Abdullah University of Science and Technology | Strauss J.,Dolan Integration Group | And 3 more authors.
Journal of Hydrology | Year: 2015

The stable isotopes of water are useful tracers of water sources and hydrological processes. Stable water isotope-enabled land surface modeling is a relatively new approach for characterizing the hydrological cycle, providing spatial and temporal variability for a number of hydrological processes. At the land surface, the integration of stable water isotopes with other meteorological measurements can assist in constraining surface heat flux estimates and discriminate between evaporation (E) and transpiration (T). However, research in this area has traditionally been limited by a lack of continuous in-situ isotopic observations. Here, the National Centre for Atmospheric Research stable isotope-enabled Land Surface Model (ISOLSM) is used to simulate the water and energy fluxes and stable water isotope variations. The model was run for a period of one month with meteorological data collected from a coastal sub-tropical site near Sydney, Australia. The modeled energy fluxes (latent heat and sensible heat) agreed reasonably well with eddy covariance observations, indicating that ISOLSM has the capacity to reproduce observed flux behavior. Comparison of modeled isotopic compositions of evapotranspiration (ET) against in-situ Fourier Transform Infrared spectroscopy (FTIR) measured bulk water vapor isotopic data (10. m above the ground), however, showed differences in magnitude and temporal patterns. The disparity is due to a small contribution from local ET fluxes to atmospheric boundary layer water vapor (~1% based on calculations using ideal gas law) relative to that advected from the ocean for this particular site. Using ISOLSM simulation, the ET was partitioned into E and T with 70% being T. We also identified that soil water from different soil layers affected T and E differently based on the simulated soil isotopic patterns, which reflects the internal working of ISOLSM. These results highlighted the capacity of using the isotope-enabled models to discriminate between different hydrological components and add insight into expected hydrological behavior. © 2015 Elsevier B.V.

Strauss J.,Dolan Integration Group | Travers P.,Dolan Integration Group | Dolan M.,Dolan Integration Group | Rosenau N.,Pioneer Resources
Society of Petroleum Engineers - Unconventional Resources Technology Conference, URTeC 2015 | Year: 2015

The relative abundances and stable isotope compositions (δ13C and 5H) of low molecular weight (C1-C5) hydrocarbons are key parameters for determining the origin of natural gases and interpreting thermal maturity in unconventional petroleum systems. Gases released from drill cuttings may provide insight into matrix-bound components of the petroleum system. Cuttings gases commonly exhibit greater compositional and stable isotopic variability relative to mud gases sampled from the same intervals. This variability can be induced by in situ methanogenesis occurring after collection in poorly preserved samples. In such cases, previous work (Rosenau et al. 2014) has shown the thermogenic isotopic signatures of methane to progressively shift to more negative δ13C values, with decreasing gas wetness due to microbial generation of methane. Here we report results from continued monitoring of carbon isotopes in headspace gases of the Piceance Basin cuttings samples from the Rosenau et al. study. New measurements, performed from September to March of 2014, showed continued variation of C1 δ13C values. Surprisingly, the δ13C of methane shifted to less negative values in the samples where microbial activity was evident after approximately 11 months of storage. In all but one of the samples, these values began approach the initially measured values, consistent with a thermogenic source. In the remaining sample, the rebounded δ13C is higher than the initial measurement. More promising, all samples show very little variation of C2-C5 δ13C values throughout the entire course of the study. Time series results from additional samples from the Fort Worth Basin shows both microbial influence as well as C1-C3 δ13C increasing over time. Time series of Appalachian Basin samples show virtually no C1-C3 carbon isotope variation over one year of storage. Overall, these data show cuttings samples can retain the carbon isotopic signature of C1-C5 hydrocarbons for spans greater than 1 year. While methane carbon isotope values are often obscured by microbial processes, that influence may subside over time. While methane δ13C values can be critical data for petroleum system evaluations, the δ13C of ethane and propane, if available, are often more useful for predicting system maturity and evaluating vertical trends. Thus, our results indicate cuttings samples can be of value, even in cases where samples are not well preserved. Copyright 2015, Unconventional Resources Technology Conference.

Clauer N.,CNRS Hydrology and Geochemistry Laboratory of Strasbourg | Lewan M.D.,U.S. Geological Survey | Dolan M.P.,Dolan Integration Group | Chaudhuri S.,Kansas State University | Curtis J.B.,Colorado School of Mines
Geochimica et Cosmochimica Acta | Year: 2014

Progressive maturation of the Eocene Kreyenhagen Shale from the San Joaquin Basin of California was studied by combining mineralogical and chemical analyses with K-Ar dating of whole rocks and <2μm clay fractions from naturally buried samples and laboratory induced maturation by hydrous pyrolysis of an immature outcrop sample. The K-Ar age decreases from 89.9±3.9 and 72.4±4.2Ma for the outcrop whole rock and its <2μm fraction, respectively, to 29.7±1.5 and 21.0±0.7Ma for the equivalent materials buried to 5167m. The natural maturation does not produce K-Ar ages in the historical sense, but rather K/Ar ratios of relative K and radiogenic 40Ar amounts resulting from a combined crystallization of authigenic and alteration of initial detrital K-bearing minerals of the rocks. The Al/K ratio of the naturally matured rocks is essentially constant for the entire depth sequence, indicating that there is no detectable variation in the crystallo-chemical organization of the K-bearing alumino-silicates with depth. No supply of K from outside of the rock volumes occurred, which indicates a closed-system behavior for it. Conversely, the content of the total organic carbon (TOC) content decreases significantly with burial, based on the progressive increasing Al/TOC ratio of the whole rocks. The initial varied mineralogy and chemistry of the rocks and their <2μm fractions resulting from differences in detrital sources and depositional settings give scattered results that homogenize progressively during burial due to increased authigenesis, and concomitant increased alteration of the detrital material. Hydrous pyrolysis was intended to alleviate the problem of mineral and chemical variations in initially deposited rocks of naturally matured sequences. However, experiments on aliquots from thermally immature Kreyenhagen Shale outcrop sample did not mimic the results from naturally buried samples. Experiments conducted for 72h at temperatures from 270 to 365°C did not induce significant changes at temperatures above 310°C in the mineralogical composition and K-Ar ages of the rock and <2μm fraction. The K-Ar ages of the <2μm fraction range from 72.4±4.2Ma in the outcrop sample to 62.4±3.4Ma in the sample heated the most at 365°C for 216h. This slight decrease in age outlines some loss of radiogenic 40Ar, together with losses of organic matter as oil, gas, and aqueous organic species.Large amounts of smectite layers in the illite-smectite mixed layers of the pyrolyzed outcrop <2μm fraction remain during thermal experiments, especially above 310°C. With no illitization detected above 310°C, smectite appears to have inhibited rather than promoted generation of expelled oil from decomposition of bitumen. This hindrance is interpreted to result from bitumen impregnating the smectite interlayer sites and rock matrix. Bitumen remains in the <2μm fraction despite leaching with H2O2. Its presence in the smectite interlayers is apparent by the inability of the clay fraction to fully expand or collapse once bitumen generation from the thermal decomposition of the kerogen is completed, and by almost invariable K-Ar ages confirming for the lack of any K supply and/or radiogenic 40Ar removal. This suggests that once bitumen impregnates the porosity of a progressively maturing source rock, the pore system is no longer wetted by water and smectite to illite conversion ceases. Experimental attempts to evaluate the smectite conversion to illite should preferentially use low-TOC rocks to avoid inhibition of the reaction by bitumen impregnation. © 2014 Elsevier Ltd.

Lewan M.D.,U.S. Geological Survey | Dolan M.P.,Dolan Integration Group | Curtis J.B.,Colorado School of Mines
AAPG Bulletin | Year: 2014

The amount of oil that maturing source rocks expel is expressed as their expulsion efficiency, which is usually stated in milligrams of expelled oil per gram of original total organic carbon (TOC0). Oil-expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water (i.e., hydrous pyrolysis) at temperatures between 350°C and 365°C for 72 hr. This pyrolysis method generates oil that is composition-ally similar to natural crude oil and expels it by processes operative in the subsurface. Consequently, hydrous pyrolysis provides a means to determine oil-expulsion efficiencies and the rock properties that influence them. Smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous-pyrolysis study involving a representative sample of smectite-rich source rock from the Eocene Kreyenhagen Shale in the San Joaquin Basin of California. Smectite is the major clay mineral (31 wt. %) in this thermally immature sample, which contains 9.4 wt. % total organic carbon (TOC) comprised of type II kerogen. Compared to other immature source rocks that lack smectite as their major clay mineral, the expulsion efficiency of the Kreyenhagen Shale was significantly lower. The expulsion efficiency of the Kreyenhagen whole rock was reduced 88% compared to that of its isolated kerogen. This significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix. Within the interlayers, much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking. As a result, smectite does not promote oil generation but inhibits it. Bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet. This change prevents potassium ion (K+) transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite. As a result, illitization only reaches 35% to 40% at 310°C for 72 hr and remains unchanged to 365°C for 72 hr. Bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite-rich source rock to determine its expulsion efficiency. Complete illitization prior to bitumen generation is common for Paleozoic source rocks (e.g., Woodford Shale and Retort Phosphatic Shale Member of the Phosphoria Formation), and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis. Conversely, smectite is more common in Cenozoic source rocks like the Kreyenhagen Shale, and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface. Copyright © 2014. The American Association of Petroleum Geologists. All rights reserved.

Travers P.,Dolan Integration Group | Cumella S.,Endeavour International Corporation | Dolan M.,Dolan Integration Group
Society of Petroleum Engineers - SPE Western North American and Rocky Mountain Joint Meeting | Year: 2014

Stable carbon (δ13C) and hydrogen (δ2H) isotopes have been used to characterize hydrocarbons for exploration, development and production since the 1960s, and have re-emerged as predictive tools with the development of unconventional "tight" oil and gas plays. Here we report on publicly available Colorado Oil and Gas Conservation Commission (COGCC) and U.S. Geological Survey (USGS) datasets of production gases collected from the Greater Wattenberg Area (GWA) of Colorado. The δ13C and δ2H of natural gas can be used to interpret gas origin (i.e., bacterial versus thermal), hydrocarbon maturity, migration and reservoir compartmentalization, and production allocation. Maturities derived from carbon and hydrogen isotopes can serve as controls in regional maturity maps, which are used to help define areas of oil, wet gas and dry gas production. Stable isotope analysis can be executed pre-completion on samples obtained from mud gas and/or gas desorbing from cuttings and core. These data can help predict fluid type, API gravity, and gas-oil ratio (GOR), all of which can help guide land acquisition and development decisions. Production gases from the lower to upper Cretaceous Muddy "J" Sand, Codell, Niobrara and Sussex formations are characterized isotopically as early-mature to post-mature oil-associated gases. Progressing from shallow to deeper formations, δ13C of methane, ethane, propane and δ2H of methane components all increase, reflecting increasing maturity with depth, and the presence of multiple, discrete petroleum systems (Sherwood et al., 2013). Stable carbon and hydrogen isotope values show a strong correlation to both initial and cumulative GOR for the unconventional Niobrara and Codell intervals of Wattenberg Field. While this relationship does not hold for wells actively producing from the Muddy "J", this could be a result of geologic compartmentalization in this interval due to faulting, natural migration and other factors. Validation of the correlation between Niobrara and Codell production GOR and stable isotope composition was provided by an independent geochemistry dataset from the USGS. The predicted GOR values were then used to accurately distinguish reservoir fluid classification. These results demonstrate the potential of natural gas stable isotope signatures as a useful and reliable fluid quality prediction tool. Copyright 2014, Society of Petroleum Engineers.

Tischer M.,Dolan Integration Group | Zimbrick G.,Dolan Integration Group | Dolan M.,Dolan Integration Group
Society of Petroleum Engineers - SPE/AAPG/SEG Unconventional Resources Technology Conference | Year: 2016

In basins with unconventional plays, the importance of structural and tectonic inheritance on explorability and producability is oftentimes neglected. While a structural evaluation of the area of interest is routinely achieved locally (e.g., to predict natural fractures in the target zone), integration of this information into a regional framework is hampered by several factors - these can include a lack of appropriate company expertise, time and acreage constraints and the prevailing notion that structural information is less important for a particular unconventional play. The importance of an adequate regional structural evaluation is particularly relevant for the basin modeler, as basin models are used to predict maturity and fluid type by determining burial and thermal histories. In many basins, however, burial history alone does not adequately describe the observed maturity-controlling temperature gradient (e.g., Williston Basin). In these cases, an integration of structural and tectonic basin histories will commonly improve the accuracy and predictability of the basin model and basin maturity, respectively. This can be achieved in most cases by integration of available well information with regional datasets such as gravity and magnetics. In this study, we detail the integration of publicly available basin-wide structure data into a basin model for the Powder River Basin. Located in northeast Wyoming and southeast Montana, the Powder River Basin represents a foreland basin that formed during the Laramide orogenic event (Late Cretaceous - Early Cenozoic) when basement rock was thrust eastward loading the underlying crust and creating the Bighorn Mountains. As a result, sediment thickness and depth to basement typically increase towards the west and reach a maximum close to the major basin bounding fault system at the western edge of the basin. One would assume that any temperature distribution will follow that trend. However, analysis of available maturity and temperature data shows two major southwest-tonortheast trending thermal anomalies crossing the basin - a trend that is clearly at odds with the existing sediment thickness pattern. Hence, the temperature trend cannot be explained solely by burial history. We propose that temperature and temperature gradient in the basin is controlled at least partially by the makeup of the underlying basement. Comparison with magnetic anomaly data shows that the temperature trends can be correlated with magnetic highs that have been interpreted to represent major tectonic boundaries between several basement domains. We speculate that these domain boundaries represent pathways for heat to migrate upward through the basement into the sediment section. The resulting basin maturity distribution can significantly alter exploration and production strategies. The control of basement structures on heat flow and basin temperature distribution has been investigated previously. However, we argue that it has been underutilized when it comes to characterizing the impact of these datasets on unconventional play assessment. The method discussed herein represents an economic time-saving tool to improve the accuracy of play maturity and predictability of hydrocarbon commodities. This is especially important in unconventional settings where source presence is not a major controlling factor, but rather the goal is to delineate oil versus gas recovery. In these settings, mapping local or sub-regional maturity patterns are imperative for a successful exploration strategy. Copyright 2014, Unconventional Resources Technology Conference (URTeC).

Gibson C.M.,The National Ecological Observatory Network | Kao R.H.,The National Ecological Observatory Network | Blevins K.K.,The National Ecological Observatory Network | Travers P.D.,The National Ecological Observatory Network | Travers P.D.,Dolan Integration Group
PLoS ONE | Year: 2012

Although 21st century ecology uses unprecedented technology at the largest spatio-temporal scales in history, the data remain reliant on sound taxonomic practices that derive from 18th century science. The importance of accurate species identifications has been assessed repeatedly and in instances where inappropriate assignments have been made there have been costly consequences. The National Ecological Observatory Network (NEON) will use a standardized system based upon an integrative taxonomic foundation to conduct observations of the focal terrestrial insect taxa, ground beetles and mosquitoes, at the continental scale for a 30 year monitoring program. The use of molecular data for continental-scale, multi-decadal research conducted by a geographically widely distributed set of researchers has not been evaluated until this point. The current paper addresses the development of a reference library for verifying species identifications at NEON and the key ways in which this resource will enhance a variety of user communities. © 2012 Gibson et al.

Rosenau N.,Dolan Integration Group | Strauss J.,Dolan Integration Group | Travers P.,Dolan Integration Group | Schaiberger A.,Dolan Integration Group | Dolan M.,Dolan Integration Group
Society of Petroleum Engineers - SPE/AAPG/SEG Unconventional Resources Technology Conference | Year: 2016

The molecular and stable isotope composition (13C and H) of low molecular weight (C1-C6) hydrocarbons (HC) are key parameters used to deduce the origin (i.e., thermogenic vs. bacterial) of natural gases. Two common sample types collected during drilling include (1) drill cuttings collected in sealed jars and (2) mud gas extracted from the drilling fluid and collected in gas cylinders. Gases desorbing from cuttings (headspace gas; HG) commonly exhibit greater molecular and stable isotopic variability compared to mud gas samples from the same interval. The widespread use of these sampling vessels and critical interpretations that are made based upon these data necessitate an investigation of the degree, and manner in which, the molecular and isotopic composition of HG varies over time. Herein we document the evolution of the 13C values (C1-C5) and molecular composition of 12 HG samples desorbing from Niobrara Formation drill cuttings over a period of five months. All of the HG samples show a rise in total HC (C1-C6+) concentration, as well as progressive increase in CH4 and attendant decrease in gas wetness (C2+/C1+) over time. Four of the five samples that initially had a thermogenic signature shift progressively towards more negative 13CCH4 values over the course of the study (up to a -34 change). This behavior is consistent with secondary bacterial CH4 production in the jars and suggests that the biocide (e.g., benzyalkonium chloride) that is normally added to these samples in the field may have been omitted. The 13CCH4 values and molecular composition of four of the seven samples that initially preserved a mixed microbial/thermogenic gas signature become progressively more negative and drier (>C1/(C2+C3), respectively, over the first 3-4 weeks. For the remainder of the study, the same samples shift towards more positive 13CCH4 values (up to a +32 change over the last four months of the study). The other three samples that initially exhibited a mixed microbial/thermogenic gas signature become progressively drier and show more positive 13CCH4 values over the course of the entire study. This behavior is attributed to the combination of a secondary bacterial methane source in the jars and continued desorption of thermogenic/bacterial gas from the cuttings. Accurate stable isotope and molecular composition data of HG are critical to the successful interpretation of the origin, maturity, and potential migration history of natural gases and associated liquids. This work demonstrates the importance of implementing standardized collection methods and timeframes for laboratory analyses, urges consistent use of a biocide, and provides a suite of parameters that can be used to assess the origin of secondary HC production in HG samples. Copyright 2014, Unconventional Resources Technology Conference (URTeC).

Strauss J.,Duke University | Strauss J.,Florida Atlantic University | Strauss J.,Dolan Integration Group | Oleinik A.,Florida Atlantic University | Swart P.,University of Miami
Marine Biology | Year: 2014

Oxygen and carbon stable isotope profiles were constructed for two species of large subtropical gastropods of the family Fasciolariidae-Triplofusus giganteus and Fasciolaria tulipa-from the Florida Keys and the Bahamas, to evaluate their life history and to assess their potential as paleoenvironmental proxies. Oxygen isotope profiles revealed T. giganteus and F. tulipa grew their shells for 6 and 3 years, respectively. Both mollusks show faster growth rates during the first half of their lifespan. Mean annual temperatures (MAT) derived from oxygen isotopes for T. giganteus were 26.5 °C and for F. tulipa were 26.7 °C, both matching instrumental MATs of 26.7 and 26.5 °C for the Florida Keys. Both shells, however, failed to record entire mean annual temperature ranges (MART). Fasciolaria tulipa yielded a calculated MART of 5.6 °C compared with a measured MART of 9.3 °C, and T. giganteus showed a calculated MART of 6.9 °C compared with a measured MART of 9.4 °C. Carbon isotopes of T. giganteus were ambiguous and reveal no significant relationships with trends in nutrient concentrations (N and P), dissolved oxygen, and dissolved organic carbon, although they did exhibit more negative values concomitant with landfall of Hurricane Irene and trended to increasing values with ontogeny that could reflect migration. Carbon isotopes in F. tulipa were lower during winters, possibly reflecting seasonal upwelling or seagrass-mediated carbon cycling. © 2014 Springer-Verlag Berlin Heidelberg.

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