CO\u3csub\u3e2\u3c/sub\u3e Sequestration in Basalt: Carbonate Mineralization and Fluid Substitution

Geologicalsequestration of carbon dioxide in deep reservoirs may provide alarge-scale option for reducing the emissions of this gas intothe atmosphere. The effectiveness of sequestration depends on the storagecapacity and stability of the reservoir and risk of leakageinto the overburden. Reservoir rocks can react with a CO2-watermixture, potentially resulting in the precipitation of minerals in theavailable matrix pore space and within pre-existing fractures. This inducedmineralization may form internal seals that could help mitigate theleakage of CO2 into the overburden. For basaltic host rocks,carbonic acid partially dissolves minerals in the host rock, suchas the calcium plagioclase mineral, freeing various cations (e.g., Ca2+and Mg2+) for later precipitation as carbonate cements (Gislason etal., 2010)

Multiple scattering of surface waves

Multiple scattering of elastic waves in disordered media offers a complexity of the wave field that is challenging to unravel. The subsurface is an example of a medium with disordered inhomogeneity at all scales. However, because waves that bounce around for a long time and/or distance sample the Earth well, they potentially offer great insight into the structure of the subsurface. A surface wave scattering model is presented to aid the understanding of multiple scattering. Advantages of this model include accessibility of the wave field within the scattering medium, tunable scattering strength, availability of phase and amplitude information, and the relative longevity of surface waves. Accompanied by a state-ofthe-art non-contacting data acquisition scheme, this system proved ideal for unveiling the effects of multiple scattering. When a pulse is launched in a strongly scattering medium, it travels ballistically at first, but turns diffusive as multiply scattered waves interfere with the incident pulse. Radiative transfer has proven to describe both the transmission of the coheren

Data Continuation for Data Regularization and Internal Multiples

Seismic data collected in the field are often not ideal for processing. The process known as data continuation computes data not recorded from those that are recorded so that data requirements for processing techniques can be met. Although there are many techniques of data continuation currently used in seismic processing, the majority of these assume that the seismic wave velocity is either constant or varying only with depth. A notable exception is the downward continuation of data, often referred to as survey sinking, for which techniques applicable in most velocity models exist. We extend data continuation techniques used to fill in missing data to velocity models in which caustics are generated in the wavefield. To do this, we use a method based on the composition of Fourier integral operators. To demonstrate that this method doesn’t introduce false reflections, we show that the composite operator is also a Fourier integral operator. We illustrate the utility of this theory with a synthetic example, with caustics, in which we fill in missing traces in a shot record. This method is computationally more expensive than similar methods that assume simple velocity models. First order internal multiples are a source of errors seismic imaging. Artifacts caused by internal multiples are often similar to true reflectors and thus can be difficult to attenuate. Typically multiples are estimated in the data and then subtracted from the data before an image is created. We propose a method by which artifacts in the image are estimated as part of the imaging process; an integral part of this method is the downward continution of data. i i