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In this thesis, I assess the impact of data quality on the use of P-wave seabed seismic recordings for fracture characterisation. A noise removal technique for removing refracted noise from dual-sensor OBC records was developed and tested on 2D data. A practical correlation based approach to dual-sensor summation was devised, tested on real and synthetic data, and compared with existing approaches. A North Sea seafloor seismic dataset was processed into azimuth sector stacks which were used to map amplitude differences between azimuths, highlighting regions of anisotropic variation. Subsequent azimuthal amplitude analysis (AVAz) used the concept of the effective angle of incidence of a stacked reflection to implement surface fitting. The AVOA fits and subsequent fracture interpretation were constrained by modelling a range of fluid-fill and crack properties using information from a nearby well. Maps of fits to the orientation and magnitude of anisotropy produced at each CMP, proved to be biased due to poor signal-tonoise ratios (SIN). To improve the fits analysis was performed over groups of CMPs where the AVOA parameters were expected to be stable, improving the SIN ratio. Testing these AVAz fits against no variation with azimuth showed them to be insignificant, due to the low SIN (3.5) of this data. The impact of different levels of noise on AVAz fitting was determined for the rock properties of this North Sea data, highlighting a requirement for a SIN greater than 10 for meaningful fracture orientation estimates. This was extended to the general case of AVO classes I and III, for a range of azimuth sampling, showing the level of SIN required to reliably fit an AVAz signature. Variations in fold associated with creating restricted azimuth stacks were assessed, as were variations in the effective angle of incidence. Maps of timing errors between azimuth stacks associated with centring on the peak everit were also created. These maps aid interpretation of the AVAz showing regions of low fold, unreliable picks and changes in the vent position with azimuth.

As a consequence of the aims of this project, this thesis is divided into two distinct sections. Initially, the computationally efficient phase-screen forward modelling technique is extended to allow investigation of non-normal ray paths. The code is developed to accommodate all diffracted and converted phases up to critical angle, building on a geometrical construction method previously developed with a narrow-angle approximation. The new approach relies upon pre-scanning the model space to assess the complexity of each screen. The propagating wavefields are then divided as a function of horizontal wavenumber, and each subset is transformed to the spatial domain separately, carrying with it angular information. This allows both locally accurate 3D phase corrections and Zoeppritz reflection and transmission coefficients to be applied. The phase-screen code is further developed to handle simple anisotropic media. During phase-screen modelling, propagation is undertaken in the wavenumber domain where exact expressions for anisotropic phase velocities are incorporated. Extensive testing of the enhanced phase-screen technique includes simple analytical models to justify the inclusion of multiple energy alongside synthetic examples from models commonly used to test numerical modelling techniques. Additionally the code is tested with real models from a producing field in a marine sedimentary location where an exhaustive range of geophysical techniques were used to constrain the VTI parameters. Secondly within this thesis, the narrow angle version of the phase-screen method is used to generate a comprehensive pre-stack seismic reflection dataset for our industrial partners. Current exploration within the European oil and gas community is heavily focused on regions where the targets for production are positioned beneath plateau basalts oh the north west European margin. These environments produce a complex seismic response due to the scattering generated by the internal composition of the basalt flows. This study generates a large subsurface volume, derived from geological mapping projects in the Hold-with-Hope region of north east Greenland, and synthetically acquires a realistic 3-D reflection study across it. The basalt is uniquely generated as a single random volume with distinct correlation lengths in each orthogonal direction and a novel approach to determine seismic attenuation through basalts is developed. Initial results from this data set are presented after careful optimisation of the modelling code and parameters.

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