Polarized micro-Raman studies of femtosecond laser written stress-induced optical waveguides in diamond

Understanding the physical mechanisms of the refractive index modulation induced by femtosecond laser writing is crucial for tailoring the properties of the resulting optical waveguides. In this work we apply polarized Raman spectroscopy to study the origin of stress-induced waveguides in diamond, produced by femtosecond laser writing. The change in the refractive index induced by the femtosecond laser in the crystal is derived from the measured stress in the waveguides. The results help to explain the waveguide polarization sensitive guiding mechanism, as well as providing a technique for their optimization.Comment: 5 pages, 4 figure

Integral cross sections for electron scattering by ground state Ba atoms

We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the 5d^2 ^1S, 6s6p^1P_1, 6s7p^1P_1, 6s8p^1P_1, 6s5d^1D_2, 5d^2^1D_2, 6s6d^1D_2, 6p5d^1F_3, 6s4f^1F_3, 6p5d^1D_2, 6s6p^3P_{0,1,2}, 6s5d^3D_{1,2,3}, and 6p5d^3D_2 states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections.Comment: 47 pages, 8 tables, 25 figure

Solid-state laser system for laser cooling of Sodium

We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with up to 800 mW output power. The laser relies on sum-frequency generation from two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a doubly-resonant cavity. We obtain conversion efficiency as high as 2 W/W^2 after optimization of the cavity parameters. The output wavelength is tunable over 60 GHz, which is sufficient to lock on the Sodium D2 line. The robustness, beam quality, spectral narrowness and tunability of our source make it an alternative to dye lasers for atomic physics experiments with Sodium atoms

Calibrating predictions of fault seal reactivation in the Timor Sea

Predictions of the likelihood of fault reactivation for five fault-bound prospects in the Timor Sea are made using the FAST (Fault Analysis Seal Technology) technique. Fault reactivation is believed to be the dominant cause of seal breach in the area. Calculations are made using a stress tensor appropriate for the area, a conservative fault–rock failure envelope and the structural geometries of each prospect. A depth–stress power relationship defines the vertical stress magnitude based on vertical stress profiles for 17 Timor Sea wells. Empirical evidence of hydrocarbon leakage at each trap is used to investigate the accuracy of the fault reactivation–based predictions of seal integrity. There is a good correlation between evidence of leakage and the risk of reactivation predicted using the FAST technique. Risk of reactivation is expressed as the pore pressure increase (ΔP) that would be required to induce failure. This study allows the fault reactivation predictions to be calibrated in terms of risk of seal breach. Low integrity traps are associated with ΔP values less than 10 MPa, moderate integrity traps correspond with values between 10 and 15 MPa and high integrity traps correspond with values greater than 15 MPa. Faults with dip magnitudes greater than 60° in the Timor Sea area are likely to have a high risk of reactivation and shear failure is the most likely mode of reactivation.http://www.profdocs.com/abstract.asp?pid=398

Stress partitioning and wellbore failure in the West Tuna area, Gippsland Basin

Copyright © 2006 Australian Society of Exploration GeophysicistsAbstract Image logs from the deep intra-Latrobe and Golden Beach Subgroups of the West Tuna area in the Gippsland Basin reveal that wellbore failure is restricted to fast, cemented sandstone units and does not occur in interbedded shales. Triaxial testing and analysis of empirically derived, wireline-log based strength equations reveals uniaxial compressive strengths of 60 MPa in sandstones and 30 MPa in shales in the West Tuna area. Conventional analysis of wellbore failure assumes constant stresses in the shales and adjacent sandstones and that breakout is focused in the weaker units. We propose that the flat lying, strong, cemented sandstone units in the West Tuna area act as a stress-bearing framework within the present-day stress regime that is characterised by very high horizontal stresses (SHmax > Shmin = Sv). Stress focusing in strong sandstone units can result in high stress concentrations at the wellbore wall and account for the restriction of wellbore failure to the strong sandstone units. Finite element methods were used to investigate the stress distribution in horizontal, interbedded ?strong? sands and ?weak? shales subject to a high present-day stress state such as exists in the West Tuna area (SHmax > Sv ~ Shmin). Modelling using the present-day stress tensor and estimated elastic properties for the sandstones and shales indicates that the present-day stress is ?partitioned? between ?strong? inter-bedded sandstones and ?weaker? shales, with high stress being focussed into the strong sandstones. The stress focusing causes borehole breakout in the sands despite their higher strength. Conversely, stresses are too low to generate wellbore failure in the weaker shales

The in situ stress field of the Cooper Basin and its implications for hot dry rock geothermal energy development

Hot dry rock (HDR) geothermal energy resources are currently being investigated in the Cooper Basin, an area with a high geothermal gradient. The in situ stress field and natural fracture network are critical to the design of the subsurface circulation system in any HDR development. This study uses knowledge of the in situ stress field from petroleum–based data in the Cooper Basin to predict the likely stress conditions in basement granite bodies and thus determine the most probable fluid flow paths. In situ stress data indicate a relatively consistent maximum horizontal stress orientation of 1010 in the Cooper Basin and a transitional strike–slip to reverse faulting stress regime. Exploration for HDR geothermal energy should target areas with a high geothermal gradient and a reverse faulting stress regime. In a reverse faulting stress regime, shallowly dipping fractures have the highest permeability. Fluid flow is predicted to be focussed in the intermediate principal stress direction because this is the direction in which the elements of structural permeability intersect. Hence, in a reverse faulting stress regime in the Cooper Basin, fluid flow would be focussed in the minimum horizontal stress or north–south direction. Vertical conjugate shear fractures striking 073° and 133° have the greatest permeability in a strike–slip faulting stress regime where the intermediate principal stress and thus fluid flow is likely to be focussed vertically. Production and injection wells should be aligned in the direction of maximum fluid flow and configured to intersect the greatest number of permeable fractures

Constraining stress magnitudes using petroleum exploration data in the Cooper-Eromanga Basins, Australia

Copyright © 2006 Elsevier B.V. All rights reserved.The magnitude of the in situ stresses in the Cooper-Eromanga Basins have been determined using an extensive petroleum exploration database from over 40 years of drilling. The magnitude of the vertical stress (Sv) was calculated based on density and velocity checkshot data in 24 wells. Upper and lower bound values of the vertical stress magnitude are approximated by Sv= 14.39 × Z)1.12 and Sv = (11.67 × Z)1.15 functions respectively (where Z is depth in km and Sv is in MPa). Leak-off test data from the two basins constrain the lower bound estimate for the minimum horizontal stress (Shmin) magnitude to 15.5 MPa/km. Closure pressures from a large number of minifrac tests indicate considerable scatter in the minimum horizontal stress magnitude, with values approaching the magnitude of the vertical stress in some areas. The magnitude of the maximum horizontal stress (SHmax) was constrained by the frictional limits to stress beyond which faulting occurs and by the presence of drilling-induced tensile fractures in some wells. The maximum horizontal stress magnitude can only be loosely constrained regionally using frictional limits, due to the variability of both the minimum horizontal stress and vertical stress estimates. However, the maximum horizontal stress and thus the full stress tensor can be better constrained at individual well locations, as demonstrated in Bulyeroo-1 and Dullingari North-8, where the necessary data (i.e. image logs, minifrac tests and density logs) are available. The stress magnitudes determined indicate a predominantly strike-slip fault stress regime (SHmax > Sv > Shmin) at a depth of between 1 and 3 km in the Cooper-Eromanga Basins. However, some areas of the basin are transitional between strike-slip and reverse fault stress regimes (SHmax > Sv ≈ Shmin). Large differential stresses in the Cooper-Eromanga Basins indicate a high upper crustal strength for the region, consistent with other intraplate regions. We propose that the in situ stress field in the Cooper-Eromanga Basins is a direct result of the complex interaction of tectonic stresses from the convergent plate boundaries surrounding the Indo-Australian plate that are transmitted into the center of the plate through a high-strength upper crust. © 2006 Elsevier B.V. All rights reserved.Scott D. Reynolds, Scott D. Mildren, Richard R. Hillis and Jeremy J. Meyerhttp://www.elsevier.com/wps/find/journaldescription.cws_home/503362/description#descriptio

Present-day state-of-stress of southeast Australia

Copyright © 2006 Australian Petroleum Production and Exploration AssociationThere have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area. Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.E. Nelson, R. Hillis, M. Sandiford, S. Reynolds and S. Mildre