Failure of wireline logging (CBL/VDL) for 13"3/8 surface casing at a depth of 272 meters

Logging on CBL/VDL has been conducted since 11th day from spud in, 5 days were spending on this subject. Risks for hole stability (caving and sloughing) is becoming a serious concern as time passing by. 2 sets of logging unit and 2 logging companies have conducted the same job , 4 sets of logging tools were tested with same failure: no clear reading from the tools, though a clear calibration was done before running, and signals may resume by certain depth, where hydrostatic pressure increased. 

As CBL/VDL logging is the mandatory requirement for handing over to production, to figure out failure reason and find solutions are necessary. Malfunction to readings on sonic tools, especially for CBL/VDL tools, was encountered in South- west China Fuling Oilfield. 

The experience to solve it was to change the contaminated drilling fluid with water. Immediately, the clear readings was achieved by such simple change for same VDL/CBL logging. Unfortunately, this approach proved ineffective, and we are still facing the same issue: no readings. Any assistance or suggestions would be greatly appreciated.

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