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Geology/Well Logging


Assalam-O-Aliqum Sir,
Hope you are fine. Kindly sir brief me how to identify Normal & Reverse Faults through these logs (Resistivity, induction, Sp, Micro log, & through gamma ray logs).

Dear Nohman Khan,

Thank you very much for sending me this question.

All the names of open hole logs you have mentioned in your question are for determining the rock properties of the wellbore to find the zones of oil and gas bearing.

These logs do not alone help to determine zones of faults but may contribute in the wells correlation with other wells within the same field or with nearby wells or a correlation scheme combining both type of wells. In the same field wells it is expected that thickness of the each geological horizon either decrease or increase to certain direction unless there is a fault which may reduce the thickness abruptly due to a missing section in case of normal faults or there may be an unexpectedly higher thicknesses in case of Reverse faults as multiple zones will give abnormally thicker sections. Though, every area is already known for the type of faults present in the area where you are studying due to the basin's tectonic history. Normal faults represent Rifting tectonics whereas Reverse or thrust faults represent Compressional tectonics. One is always aware about the tectonics of the area.

Gamma Ray and SP logs are the best tools for correlations purposes and to determine the difference of thickness while comparing with other wells same suite of logs. Other logs  may also be used if you are interest to add but only GR and SP are suffice for this task.

The best tool which helps to  determine the faults in the well  bore is Formation Micro Imager (FMI)or multi finger electrical resistivity tool. FMI has covered up to 80% pf the hole and read the lithological variation with greater details.

Fault is basically a major shift of lithological behaviour and juxtaposition of two different type of rocks due to vertical or lateral movement, FMI can read such stratigraphic and structural attributes (dip and strikes), fault cuts and unconformity surfaces may be identified in the well bore.

Hope, this answer is helpful. Do Not forget to RATE this answer if you are happy and satisfy.



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Syed Tariq Hasany


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