Quantification of α-particle radiation damage in zircon

Analysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the α-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10B + n → 7Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29Si NMR to be 252 ± 24 atoms for the 10B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ~6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as α function of a dose of 0.21 A3/1018 α-events/g, which is significantly less than the increase of 3.55 A3/1018 α-events/g seen in Pu-doped zircon and 2.18 A3/1018 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil

Quantification of α-particle radiation damage in zircon

Analysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the α-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10B + n → 7Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29Si NMR to be 252 ± 24 atoms for the 10B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ~6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as α function of a dose of 0.21 A3/1018 α-events/g, which is significantly less than the increase of 3.55 A3/1018 α-events/g seen in Pu-doped zircon and 2.18 A3/1018 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil

Stratigraphic architecture and petrophysical characterization of formations for deep disposal in the Fort Worth Basin, Texas

Disposal of hydraulic fracturing flowback and produced water into Ordovician and Cambrian formations of the Fort Worth Basin (FWB), coupled with an increase in observed seismicity in the Dallas-Fort Worth area, necessitates an understanding of the geologic character of these disposal targets. More than 2 billion barrels (Bbbls) of wastewater have been disposed into the Ordovician Ellenburger Group of the FWB over the past 35 years. Since the implementation of the TexNet Earthquake Catalog (1 January 2017), more than 20 earthquakes of local magnitude ML2.0 or greater have been detected in the area, with depths ranging from 2 to 10 km (approximately 6500–33,000 ft). The cited mechanism for inducement of these earthquakes is reactivation of basement faults due to pore pressure changes, either directly related to proximal disposal or due to disposal volume buildup over time. Here, we present a stratigraphic and petrophysical analysis of FWB disposal targets and their relation to basement rocks. The Ellenburger consists of alternating layers of limestone and dolomite, with minor siliciclastics above the basement toward the Llano Uplift. Matrix porosity averages &lt;5 porosity units (p.u.), with higher porosity in dolomitic layers than in limestone. Dolomite dominates at the top of the Ellenburger, which was exposed at the end of both the Lower and Upper Ordovician. Where crystalline basement rocks are penetrated, the composition ranges from granitic to chlorite-bearing metamorphosed lithology. The basement-sediment interface is frequently marked by increased porosity. An updated map of structure on top of basement indicates elevations ranging from outcrop at the Llano Uplift to more than [Formula: see text] ([Formula: see text]) subsea toward the northeast. The disposal zone pore volume is estimated from thickness and porosity maps and ranges from [Formula: see text] to [Formula: see text] billion barrels per square mile ([Formula: see text]). </jats:p

Evaluating hydrocarbon-in-place and recovery factor in a hybrid petroleum system: Case of Bakken and three forks in North Dakota

An integrated workflow to estimate the hydrocarbon-in-place and recovery factor is applied in the Bakken-Three Forks petroleum system. Evaluating factors that control the generation and storage of hydrocarbon, such as the total organic carbon, maturity of shale, thickness, porosity, and permeability is a challenge in any shale play study. In addition, the hybrid nature of the Bakken petroleum system, where the source and reservoir rock are present within a short depth interval, adds complexity to the production interpretation and outlook of the play. One complexity is the contribution from Upper and Lower Bakken organic-rich shales to the production of horizontal wells completed in the Middle Bakken low-permeability laminated sandstone/siltstone and Upper Three Forks sandy/silty dolostone. We have performed geologic and petrophysical studies and calculate and map the hydrocarbon pore volume. For fluid characterization, we use three models to accurately cover a range of American Petroleum Institute gravity and gas/oil ratio. We evaluate the contribution of Upper and Lower Bakken to production by constructing simulation models and used that knowledge to estimate the recovery factor of the horizontal wells. Production depletes the Middle Bakken, creating a pressure difference between the Middle Bakken and the Upper/Lower Bakken, which in turn depletes the Upper/Lower Bakken. Vertical permeability controls production from the Upper and Lower Bakken, and higher vertical permeability increases the contribution of the two shale members. An understanding of the maturity and trap mechanism can help to explain the water-saturation distribution, and understanding these factors is crucial to any future development of the play. </jats:p