恒定电流测井中的电荷分布和电流流动特征研究

CHARGE DISTRIBUTION AND CURRENT FLOW FEATURES IN THE DC ELECTRICAL LOGGING

研究电荷分布和电流流动特征对基于恒定电流原理的测井仪器设计和解释具有重要的理论和实际意义。以三侧向测井为例,计算不同层厚、不同侵入深度、不同侵入和地层电导率时的恒定电流场,分析电荷分布、电流线和等位线特征。结果表明:电荷仅分布在电极表面和不同电阻率交界面,正负由两侧电阻率差确定;电流流动受交界面不同电荷及其分布作用会发生复杂的变化,在不同电阻率交界面产生折射。流动正方向为正电荷时,电流线到达交界面前向内弯曲,负电荷时向外弯曲,穿过界面后沿均匀地层时的路径流动。流动侧面为正电荷时,电流受到排斥,向外弯曲,负电荷时电流受到吸引,向内弯曲。

The study on the charge distribution and current flow features has an important theoretical and practical significance for the tool design and data interpretation of the DC electrical logging. Taking three lateral logging as an example, the static current fields with different thickness, invading depth and formation resistivity are calculated. Features of the charge, current line and equipotential line are analyzed. The results show that the charges distribute only on the electrode surface and the interface with different conductivities, which polarity is determined by the conductivity differential at two sides. The current flow will generate a complicated change due to the effect of different charge and distribution. Reflection occurs on the interface. If the forward direction is the positive charge, the current line will bend inward before it reaches. If it is the negative charge, the current line will bend outward. After the current line come cross the interface, it will flow along the routine in the homogeneous formation. If the side is the positive charge, the current will be repelled, and bends outward. Otherwise, it is attracted, and bends inward.