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Russian Geology and Geophysics

2004 year, number 8


M.I. Epov, I.N. Yeltsov, A.A. Kashevarov*, A.Yu. Sobolev, and V.N. Ul'yanov
Institute of Geophysics, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Lavrentiev Institute of Hydrodynamics, Siberian Branch of the RAS,
15 prosp. Akad. Lavrentieva, Novosibirsk, 630090, Russia
Keywords: Electromagnetic soundings, hydrodynamic modeling, reservoirs
Pages: 985-995


The geoelectrical and hydrodynamic parameters of the near-hole space bear much useful information on the physical properties of hydrocarbon reservoirs. Time-dependent changes in the zone where wellbore fluids leak off into permeable formation make it difficult to estimate the electrical resistivity of the undisturbed portion of the reservoir. However, the invaded zone itself can be a target of studies.
The available advanced multiprobe logging tools yield high-resolution images of resistivity near a well. These data, integrated with the available advanced theoretical background and computing facilities for hydrodynamic modeling of porous media with a two-component fluid fill, provide a clue to reliable interpretation of electromagnetic logs.
The suggested 2D models of drilling mud circulation near the bore face take into account the real size of drill, growth and erosion of mud cake, filtration of water and oil (two immiscible fluids), salt transport, rock compressibility, and fluid viscosity.
Results of 2D simulation of the process in which drilling mud displaces oil and formation water from the invaded zone are reported for different drilling conditions and hydrophysical parameters of reservoirs. The parameters of the invaded zone show different distributions classified on the basis of numerical experiments and porosity and water content dependences of resistivity.
Problems related to inversion of EM logs in vertical and horizontal wells are discussed for specific field examples.