ALBERT

Description: Five late Pleistocene lava domes with a combined eruptive volume of ~40 km 3 distributed over an area of ~2000 km 2 represent the waning stages of the 10–1 Ma ignimbrite flare-up in the Altiplano Puna Volcanic Complex (APVC) of the Central Andes. Zircon crystal face (on unsectioned rims) and interior (on sectioned crystals) ages (U-Th and U-Pb, respectively) for a total of 252 crystals indicate remarkably consistent zircon crystallization histories: the youngest zircon surface ages (ca. 104–83 ka) are near 40 Ar/ 39 Ar eruption ages from sanidine and biotite (ca. 120–87 ka), but a significant population of surface ages predates eruption, ranging to secular equilibrium (with U-Pb interior ages to 3.5 Ma). The essentially continuous zircon crystallization history implies protracted magma presence, which agrees with temporally invariant Ti-in-zircon model temperatures, backed by the homogeneity of indirectly temperature-dependent compositional parameters. Zircon age spectra modeled using a finite-difference thermal and mass-balance model for open-system magma evolution indicate protracted zircon production in the magma reservoirs that require time-integrated recharge rates of ~1 x 10 –3 km 3 /yr, corresponding to high intrusive to extrusive ratios of 75: 1. This rate is below the ~5 x 10 –3 km 3 /yr threshold proposed in the literature for incubating the supereruptions defining the flare-up. When accounting for the shorter durations of high versus low recharge episodes over the ~10 m.y. lifetime of the APVC flare-up, the contributions to composite batholith formation in the shallow crust of the APVC remained broadly constant during peaks and lulls in eruptive activity. This connotes that eruptive fluxes are a poor measure for intrusive fluxes. A corollary of this interpretation is that commonly applied intrusive to extrusive ratios will severely underestimate pluton formation rates during periods of low eruptive flux.

Description: The Mu2e Transport Solenoid (TS) is an S-shaped magnet formed by two separate but similar magnets, TS-u and TS-d. Each magnet is quarter-toroid shaped with a centerline radius of approximately 3 m utilizing a helium cooling loop consisting of 25 to 27 horizontal-axis rings connected in series. This cooling loop configuration has been deemed adequate for cooling via forced single phase liquid helium; however it presents major challenges to forced two-phase flow such as “garden hose” pressure drop, concerns of flow separation from tube walls, difficulty of calculation, etc. Even with these disadvantages, forced two-phase flow has certain inherent advantages which make it a more attractive option than forced single phase flow. It is for this reason that the use of forced two-phase flow was studied for the TS magnets. This paper will describe the analysis using helium-specific pressure drop correlations, conservative engineering approach, helium properties calculated and updated at o...

Description: ABSTRACT Optimizing the productivity of nonconventional, low-permeability “shale” reservoirs requires detailed knowledge of the mechanical properties of such materials. These rocks' elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information. Here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional Duvernay reservoir of Alberta, Canada. The complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 MPa. Wave speed anisotropies of up to 35% are observed at even the highest confining pressures. Furthermore, the stress sensitivity of the wave speeds, and hence moduli, is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure, whereas those along the bedding plane show, unexpectedly, nearly no pressure dependence. These observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images. These results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions, for the concentration of stress within such formations, and for estimation of static engineering moduli from sonic log wave speeds.

Description: ABSTRACT Hotspot: The Snake River Geothermal Drilling Project was undertaken to better understand geothermal systems across the Snake River Plain volcanic province. A series of surface and borehole seismic profiles were obtained to provide insights into volcanic stratigraphy and test the capabilities of engineering-scale seismic imaging in such terranes. The Kimberly site drilled through 1.9 km of mostly rhyolite, with thin sedimentary interbeds in the upper part of the section. The Kimama site drilled through 1.9 km of mostly basalt with sedimentary interbeds at ∼200 m depth and 1700 m depth. The Mountain Home site contained numerous sediment and volcanic rock layers. Downhole and surface vibroseis seismic results suggest sedimentary interbeds at depth correspond with low-velocity, high-temperature zones that relate to reflections on seismic profiles. Our results suggest that eruption flow volumes can be estimated and flow boundaries can be imaged with surface seismic methods using relatively high-fold and wide-angle coverage. High-frequency attenuation is observed at all sites, and this deficit may be countered by acquisition design and a focus on signal processing steps. Separation of surface and body waves was obtained by muting, and the potential for large static effects was identified and addressed in processing. An accurate velocity model and lithology contacts derived from borehole information improved the confidence of our seismic interpretations.

Description: ABSTRACT Assuming Vertical Transverse Isotropy (VTI) symmetry the elastic anisotropy as a function of confining pressure of four carbonates and one evaporite from the Williston sedimentary basin in Saskatchewan, Canada is investigated using the ultrasonic pulse transmission method. Ultrasonic P- and S- wave velocities are obtained from cylindrical plugs cut from a main sample along horizontal, vertical and 45° orientations with respect to the sample's presumed vertical axis of symmetry. The elastic constants were then calculated from the measured velocities and densities. Anisotropy was quantified by estimating Thomsen parameters (Thomsen 1986) from elastic constants. The results show that the samples are at the best weakly anisotropic. The presence of microcracks and pores as well as the heterogeneity of the samples play an important role in defining the P- and S- wave velocities. The weak anisotropy found in these samples suggests that ‘intrinsic’ properties of these rocks negligibly contribute to the anisotropy observed at the seismic scale.

Description: ABSTRACT Wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the Cu‐Au New Afton porphyry deposit, Canada, with the objectives of imaging lithological contacts, fault zones that may have acted as conduits that channeled the mineralization, and alteration zones. Log data provide physical rock properties for the main lithologies and alteration zones. Caliper logs reveal many faults and caved‐in zones generally indicating rocks with low integrity at the borehole wall. The preponderance of these zones, as indicated by the logs, suggests that their response may dominate the seismic reflection wavefield. Outside fault zones, compressional and shear‐wave velocities exhibit significant variability due to porosity, the heterogeneity of volcanic fragmental rocks, and alteration. Distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs. Straight and helically‐wound fibre‐optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator. Standard and engineered optical fibres placed in the two boreholes were daisy‐chained together to form two 5 km long continuous fibres that were interrogated at once with two interrogators. A new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal‐to‐noise ratio. This data with higher signal‐to‐noise ratio from straight fibre‐optic cable were processed and used for depth imaging. Depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre‐optic cable and limit the extent of migration artefacts. Migration results show several reflectors with shallow dips to the northwest, some explained by faults intersecting the surveyed boreholes. The main sub‐vertical lithological and alteration contacts at New Afton generated downgoing reflections that were not considered in the migration. This article is protected by copyright. All rights reserved

Description: SUMMARY Seismic velocity anisotropy measurements are made of a fractured metamorphic formation from the 2.5-km-deep International Continental Scientific Drilling Programme (ICDP) borehole in Outokumpu, Finland. Three component walk-away vertical seismic profile (VSP) measurements are made along two source-line azimuths at three receiver depths (1000, 1750 and 2500 m) and incidence angle-dependent qP - and qS -wave velocities are extracted with a τ– p method. The highest qP -wave anisotropy, 13.6 per cent ( v fast = 6160 m s −1 , v slow = 5370 m s −1 ), is measured between 1000- and 1750-m depth, with anisotropy of up to 9.4 per cent ( v fast = 6090 m s −1 , v slow = 5540 m s −1 ) measured between 1750 and 2500 m depth. The top ∼1300 m of the region is composed of a homogeneous, strongly intrinsically anisotropic biotite-rich schist, and is sampled by the shallowest walk-away profile. Anisotropy of up to 11.1 per cent ( v fast = 5950 m s −1 , v slow = 5320 m s −1 ) is measured by the walk-away VSP between 50 and 1000 m depth, along with shear wave splitting averaging 5 per cent (180 m s −1 ). Laboratory-derived intrinsic anisotropy of the schist cannot by itself explain the degree or orientation of the anisotropy measured in the walk-away VSPs, however, a model which modifies the intrinsic stiffnesses by the inclusion of a single set of dipping, aligned cracks allows the observed in situ velocities to be reproduced. Forward modelling of the qP -wave walk-away VSP measurements from 50 to 1000 m depth is undertaken using an effective medium model to develop a 3-D velocity model of this region. An orthorhombic medium is used to represent the intrinsic anisotropy of the biotite-rich schist, and a single set of aligned cracks is added to give a bulk elastic stiffness. The resulting model predicts the schist to have an overall anisotropy of 16.8 per cent, with qP -wave velocities of up to 6315 m s −1 . The accuracy of the model is assessed through its fit to the walk-away VSP measurements as well as a comparison to known geology of the region.