Geotomography for Exploration of Heavy Oil Deposits
Titel:
Geotomography for Exploration of Heavy Oil Deposits
Auteur:
Singh, R. P. Nyland, E.
Verschenen in:
Energy sources. Part A, Recovery utilization and environmental effects
Paginering:
Jaargang 9 (1987) nr. 4 pagina's 229-238
Jaar:
1987
Inhoud:
Seismic and electromagnetic geotomography are useful exploration techniques in heavy oil deposits. They will serve to both delineate reserves and measure the progress of in-situ recovery schemes. The propagation characteristics for various Athabasca sands can be deduced from laboratory and limited field results. Such results are essential to the proper design and interpretation of exploration projects. For instance, the choice of transmission frequency in EM tomography and the choice of source design in seismic tomography are controlled by the kind of propagation expected in the project. Heavy oil deposits are “lossy” media. The range of a transmitter signal is also crucial and can be estimated from such results. Investigations of electromagnetic preheating of heavy oil (Chute et al. 1978) have provided data on electromagnetic properties from 1 to 100 MHz. Dielectric properties are temperature- and frequency-dependent, and this dependence dictates optimum choices of transmitter frequencies for EM geotomography. Other work (Das et al. 1979) provides details of dielectric properties as a function of temperature at 10 MHz and 16 MHz. From these data we can compute attenuation and phase responses that can be measured in field experiments. Laboratory seismic properties (Mraz et al. 1982 and several others) are inevitably measured at frequencies that differ from the useful frequencies in the field. In addition, the acoustic propagation regime can be affected by tube waves, scattering from small-scale inhomogeneities, and seismic anisotropy not easily measured at laboratory scales. Once these properties are converted to propagation characteristics it remains to invert the geotomographic data set to obtain structure. We suggest the use of an inversion method well-known in seismology but not widely used in industrial geotomography. The Lanczos inverse of the observation equations allows investigation of missing data, resolution of conflicting data, and a clear statement of the significance of the results. It is also known under the name of singular value decomposition. The results from this method can be easily compared with more usual reconstruction techniques such as SIRT and ART.
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