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Title: Modelling the wide-band laboratory response of rock samples to fluid and pressure changes
Author: Chapman, Mark
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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The Biot-Gassmann theory of poroelasticity forms the basis of most in­vestigations of wave propagation in fluid saturated rock. In recent years the need to incorporate the concept of squirt flow into the theoretical framework has been recognised. Microstructural models which contain squirt flow give inconsistent predictions which contradict rigorous results from poroelastic theory. I derive a microstructural poroelastic model which incorporates the squirt flow mechanism. The model is consistent in its limiting forms with the stan­dard results of poroelasticity and effective medium theory. An important feature of the model is that it is relatively independent of assumptions about the aspect ratio spectrum. I describe how the various parameters which occur in my model may be derived or estimated from experimental data, and proceed to a preliminary calibration of the model using published resonant bar data. Although I show that the data can be fit satisfactorily, significant ambiguity remains in the interpretation of the results. A number of ultrasonic tests of P- and S- velocity, in rock similar to the resonant bar, as a function of both effective stress and pore fluid type show results which are at variance with the predictions of published poroelastic theories. I demonstrate that the anomaly can be explained with reference to physical effects predicted by my model. Moreover, the requirement to explain the ultrasonic results places constraints upon the modelling of the resonant bar data, removing much of the ambiguity from the analysis. I present a calibration which gives a consistent qualitative explanation of both the resonant bar and ultrasonic data. The calibrated model makes a number of predictions concerning the ef­fect of changing pore fluid viscosity, sample permeability and frequency. In principle experiments could be carried out to test these predictions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available