24 research outputs found
A semi-empirical model for interpreting rock strain sensitivity in 4D seismic data
No full textSeveral models have been recently proposed to connect observations of velocity change with strain deformation in and around reservoirs undergoing production and recovery. In this work we show that a simple compliance-based model combined with the original conceptual understanding of Hatchell and Bourne (2005) can adequately explain the magnitude of R factor values currently observed from calibrated field data in a variety of settings. The model is also used to determine an expression for the gradient of overburden time-shift variation with incidence angle. This gradient is predicted to be low but may vary according to the ratio of tangential to normal compliance at the intergranular contacts. This factor could perhaps be used as an additional parameter to assess the post-production state of the overburden
Star Formation in the Gould Belt: A Submillimetre Perspective
No full textThis thesis presents my work characterising star formation in Gould Belt molecular clouds using submillimetre observations from SCUBA-2 on the James Clerk Maxwell Telescope (JCMT). I use these observations alongside data from previously published surveys using instruments including the Spitzer Space Telescope. I investigate the effect of including submillimetre data on the numbers, classifications and lifetimes of Young Stellar Objects (YSOs) in Gould Belt molecular clouds, particularly protostars.
Following a literature review, I use SCUBA-2 450 and 850 μm observations to characterise star formation in the Lupus I molecular cloud. A total of eleven previously identified YSOs are detected with SCUBA-2, as well as eleven starless cores. Two cores have masses greater than the Jeans mass, and one has a virial parameter of 1.1 0.4, meaning these cores could be unstable against collapse. I use submillimetre emission to calculate disk masses, and find that one YSO has a disk mass greater than the minimum mass solar nebula. I find that Lupus I has a high percentage of both protostars and Very Low Luminosity Objects (VeLLOs). I also fit YSO Spectral Energy Distributions (SEDs) with models, allowing protostellar envelope masses and temperatures to be calculated, and interstellar extinction to be constrained for some YSOs. The signs of recent and future star formation support the hypothesis that a shock has triggered a star forming event in Lupus I.
I also use SCUBA-2 data in conjunction with archival Spitzer and Herschel data to produce SEDs for five new candidate First Hydrostatic Cores (FHSCs) in Serpens South. These observations were then fit with models by the first author of this work, Alison Young. This work was able to identify two of the FHSC candidates as probable FHSCs, and constrain the rotation rate and inclination of one of them.
I use JCMT Gould Belt Survey (GBS) observations of ten molecular clouds to produce an updated catalogue of protostars in these clouds. I use the FellWalker algorithm to find individual sources in the SCUBA-2 maps, and match them to the Spitzer YSO catalogue of Dunham et al. (2015). I use bolometric temperature to classify 362 out of 592 candidates as
Class 0 or Class I protostars - a factor of two increase compared to the Spitzer catalogue due to improved submillimetre coverage. I find that protostellar lifetimes of 0.59 – 0.89 Myr - approximately 25 % longer than previously estimated. I also calculate protostellar luminosities, envelope masses, and envelope temperatures, and examine the distributions. Finally, I newly identify 19 protostars as VeLLOs, and increase the number of known VeLLOs in these clouds by a factor of two.STF
Rapid Autonomous Marine 4D (RAM4D) – an unmanned, time-lapse offshore seismic acquisition system
No full textInstantaneous 4D Seismic (i4D) - An Innovative Concept to Monitor Offshore Water Injector Wells
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