Response Of 2-Mhz Lwd Resistivity And Wireline Induction Tools In Dipping Beds And Laminated Formations

The responses of wireline induction and 2-MHz resistivity tools for logging while drilling (LWD) are compared in dipping formations. The differences in measurement physics, depths of investigation and vertical resolutions between induction and 2-MHz tools lead to different responses in steeply dipped beds. Some new and interesting effects are presented that are characteristic of all 2-MHz LWD tools. These effects have been observed on field logs and have also been reproduced with computer modeling. In particular:- In thin (2 ft-10 ft) beds, dip and shoulder effects can cause separations between phase shift and attenuation resistivity curves and affect the readings for all 2-MHz tools. The amount of separation is a function of dip angle, resistivity level and resistivity contrast. - At dipping bed boundaries, 2-MHz logs can show horns caused by electric polarization of the interface. The horns are more prominent on phase shift resistivity logs. - Resistivity anisotropy causes a separation of 2-MHz phase shift and attenuation resistivity curves in laminated or shaly formations logged at an angle. A thorough understanding of the effect of dip improves interpretation of 2-MHz tools.