Hydrodynamic processes during drilling oil well and their influence on geophysical study in boreholes
© I.N. Yeltsov, A.A. Kashevarov, G.V. Nesterova
During drilling an oil well, mud invades permeable formations and therefore spatial distribution of water saturation and salt concentration are changed in vicinity of borehole. Density and electrical resistance distributions are also changed, and geophysical logging data reflect these variations. Influence of filtration and salt transport processes on time-lapse electromagnetic logging data is described in this article. Two-dimensional simulation of two-phase filtration and salt transport is used. Hydrodynamic model and geo-electric one are connected by extension of Archi equation. Joint electro-hydrodynamic model of borehole environment has to satisfy both geotechnical well study and geophysical well logging. Geo-electric properties of borehole environment can be described as the result of redistribution of fluids which arises from two-phase filtration and salt transport. Time-lapse geophysical well logging data enable to construct dynamic model of borehole environment. Geo-electrical model, taking into account evolution of borehole vicinity, makes it possible to estimate formation permeability. Such estimation is not correct based on the static models. Recently relative permeability estimation on borehole logging data becomes very important especially because of difficulty of laboratory core sample investigations for total reservoir depth. Comprehensive hydrodynamic and geophysical inversion of time-lapse observations makes up for incomplete information obtained on core samples. Quantitative petrophysical inversion of logging data, i.e. formation evaluation, becomes possible after creation of the dynamic model of borehole environment.