Question

Explain the concepts behind the three types of resistivity logs

Answer 1

Resistivity log - The three types of resistivity logs are follows Induction log , lateral log and micro resistivity log.

Induction log : This log used for to measure formation resistivity inside the bore hole containing oil base mud.

- This log has high depth of penetration in rock layer.

- Induction log best works in non coductivity mud inside the borehole.

- In this log current supply into transmitter through coil . This coil produce secondary eddy current then this eddy current goes into rock layer , then this current measure by reciever inside bore hole.

- This log good vertical and horizontal resolution.

Lateral log : This type of log measure resistivity of rock formation beyond the invaded zone.

-Lateral log measure true resistivity of rockformation in invaded zone .

- this log best works in high salinity mud and does not work in cased bore hole or air filled borehole.

- According to spacing of electrode lateral log has different penetration power in rock formation. Higher spacing of electrode , current passs more depth in rock formation.

- low , middle and high depth of penetration inside the rock formation.

- different type of lateral logs are LL3 , LL7 and LL8 according to depth of penetration.

Micro- resistivity log : This log used for to measure the resistivity of flush zone.

- This log has more bed resolution in flush zone than induction and lateral log.

- This log used for to detect the mudcake thickness with its resistivity.

- this log has low depth penetration and high resolution .

- This resistivity log is best interpretation about flush zone resistivity and mud cake resistivity.