Experiment design for time domain surface-to-borehole electromagnetic applications.

摘要

Surface-to-borehole electromagnetic (EM) measurements have been used extensively for many applications. Successful application of these techniques requires an extensive presurvey design--the design of the field experiment. Such experiment design should use the most powerful interpretation concepts and software available. The purpose of this dissertation is to illustrate the application of the latest concepts and software on surface-to-borehole experiment design, with particular attention to hydrocarbon applications.; The dissertation begins by discussing petrophysical models relating conductivity to primary formation parameters and synthetic noise models for time-domain data. With a reliable noise model and petrophysical information the resolution of the surface-to-borehole technique is illustrated on three typical hydrocarbon applications. The three examples include a three-dimensional (3-D) oil lens at depth, an anisotropic reservoir, and a lateral oil-water contact (OWC) for shallow heavy sands. The 3-D oil lens model study suggests using receivers close to the boundary to resolve the lateral extent of the target, whereas receivers in the center of the body better resolve the resistivity of the reservoir. The second example demonstrates how a joint interpretation of both horizontal magnetic field components can yield superior resolution of the anisotropic conductivity structure compared to an interpretation of individual components. The third case illustrates that the resolution of an OWC is best when the contact is maximally illuminated by the transmitter, and the best receiver locations are at the same depth or deeper than the contact. The vertical magnetic field component offers superior resolution of the OWC location compared to that offered by the horizontal magnetic field component parallel to strike. The physical basis of the resolution for the oil-water contact is illustrated using visualization of the propagating fields.; One method of enhancing resolution is to design the transmitter waveform to optimize the image resolution for a particular application. Optimal transmitter waveform design is illustrated for the anisotropic layer model using both local and global optimization algorithms. Improvement of the signal to noise ratio using "designer" waveforms can be dramatic, arising from either an increase in the target's response or from a decrease in the geological "noise." Such techniques can be applied adaptively at both the data acquisition and the data processing stages. It is conceivable that different source waveforms could be applied at different time windows.; The dissertation concludes by noting the wide range of methods and potential applications of experiment design facilitated by recent advances in computer software and hardware.