| The thesis deals with the development of scaling models for acoustic imaging of pore pressure in reservoir. This topic has gained interest in the last decade mainly because of the appealing possibilities given by non invasive methods of imaging, which are very flexible and cost effective. P and S wave velocities and attenuation characteristics are used to retrieve information from the earth through non-destructive techniques. However, there are some problems on how to resolve the discrepancies between, laboratory/core velocity that uses high frequency waves and field velocity that uses low frequency waves. This velocity discrepancy, discussed intensively in scientific literature, is referred to as scaling problem, and has caught the attention of many practitioners. Extensive literature review indicates that, to date, Backus averaging is the only practical method that provides a finely foliated velocity model in an attempt to solve the scaling problems. However, Backus averaging has two major shortcomings and limitations: (i) there is no source of intrinsic energy dissipation such as friction or viscosity (attenuation) catered for in the model, (ii) the model also applicable to layered formation and requires that layer thickness of the media must be larger than the seismic wavelength: how greater is still a question of disagreement among scientist. The author believes that, the way to reconcile the various velocity differences is to develop a numerical model that would scale the velocities depending on the type of waves used at a given frequencies and wavelength.; The research therefore provides the opportunity to examine the dispersion of elastic wave velocity over a wide frequency range. The thesis has three main objectives: (i) To answer the question of what factors contribute to velocity differences in acoustic imaging across the various frequency bands; (ii) to develop practical scaling models and methodology that take into account intrinsic energy dissipation; and (iii) to find ways to image pore pressure at high overburden pressure (deep depth of reservoirs).; The methodology used was based on laboratory experimental methods and numerical modeling. The laboratory experiments coupled elastic, petrophysical and geomechanical measurements under insitu conditions, over a broad frequency band, on texturally well-characterized artificial and natural sandstones. (Abstract shortened by UMI.)... |
