盐水泥浆钻井对感应测井的影响

THE INFLUENCE OF SALT MUD SURVEY ON INDUCTION LOG

中山大学

盐水泥浆钻井侵入带的电阻率ρ一般低于地层真电阻率ρt_o然而,对无限厚层所作的计算结果表明,当侵入较浅时(大约在直径为0.25～0.55米的范围内)感应所测机电阻率高于真电阻率;而在侵入较深时(不同的条件下有不同的界限),感应视电阻率则大大低于真电阻率。这充分体现出盐水泥浆、低侵影响的特点。泥浆电阻率越低,上述影响就越严重,以至使求准地层真电阻率有困难。在某油田盐水泥浆井的感应测井实测资料上可以观察到这些特点。

The resistivity ρi of zone invaded by salt solution is usually lower than the true resistivity ρt of geological formations. However, the results of calculation for infinite thick layers show that when the invaded zone is shallow (approximately in the runge of 0.25-0.55m in diametes) the apparent resistivity obtained by induction method is higher than the true ones. In the case of deep invasion, the inverse phenomenon can be observed. It is characterized by the inherent nature of the salt mud. The lower the resistivity of salt mud is, the severeer its influence will be. Consequently, it creates problem in the precise determination of true resistivity. The field data obtained from oil well logging confirm the theoretial calculation.