The Spherically Focused Log is a new resistivity log developed to replace the short-normal in the Induction-Electrical sonde (IES). It uses an electrode array and includes a current focusing system. Bucking currents, flowing mainly in the borehole, cause the measuring current to enter the formation and then diverge spherically.

The Spherically Focused Log (SFL, trademark of Schlumberger) has much better bed definition and considerably less borehole effect that the short normal. It has a shallower investigation, hence it gives more accurate invaded-zone resistivity.

The Induction-SFL can be run in combination with a borehole-compensated Sonic, thus providing a simultaneous recording of deep resistivity, shallow resistivity, SP, Sonic transit time (porosity information), a caliper or Gamma Ray, and computed R_wa. This combination makes possible a more immediately available evaluation of zones of interest with less expenditure of rig time.

End_of_Article - Last_Page 1698------------