Numerical analysis of effects of low-resistivity-annulus due to invasion on dual-induction logging responses in deviated hole

On account of the comprehensive effects of formation lithology, porosity, permeability, formation heterogeneity, mud filtrate and the other factors, the different invasion profiles with the different depth and shape around borehole arise in the various formations and borehole condition. In fresh mud borehole, the responses of induction logging vary with the different mud invasion annulus in the oil reservoirs. In this paper we obtained the geometrical factors of induction log in the deviated hole by a simple derivation. Based on such geometrical factors, the induction logging responses on the annulus of mud filtration invasion with various angles of inclination and depths of invasion in deviated hole have been analyzed by the numerical calculation. The numerical results show that there are two sensitive angle zones in the deviated angles from 0 to 90 degree for the response of dual induction log. The apparent resistivity is almost close to the real formation resistivity in the sensitive angle zone1, but the apparent resistivity is far from the real formation in the sensitive angle zone2. There is the angle difference, which increases as λ (the ratio of invasion resistivity to formation resistivity) decreases, between deep induction log and medium induction log in the sensitive angle zone2. The responses of deep and medium induction log in various deviated angles changing with invasion depth are almost the same as that at 0 degree deviated angle(the normal borehole). All of these results can be helpful for correcting effects of low-resistivity-annulus when induction logging is used for the recognition and evaluation of oil reservoirs.