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Dear Sir,In petrophysical studies for porosity measurement why we use lime stone calibration for density and neutron log.why we can not use sand stone and dolomite for calibration?Please explain with some example.

Dear Tariq,

Thanks for sending me your question.

A little bit of background about calibration; all logging tools are calibrated against a fixed and known value either its radioactivety, Neutron or density to record logs with precision.

Limestone  is the standard rock unit as designated by American Petroleum Institute (API) and stored in a calibration pit in University of Houston In USA. This pit is 6 ft in diameter and 24 ft ft deep with three 6 ft thick limestone zones of different known porosities and kept filled with water. These limestones are Austin Limestone with 26% porosity, Indiana limestone with 19% porosity and the top zone is Carthage marble with 1.9% porosity. Indiana Limestone was used to establish the API Neutron unit and is used for calibrating logging tools in these units.

I understand that in similar manner sandstone and dolomites may also be used for tool calibration but it was not a industry standard practice. However, it's essential to correct limestone porosity to sandstone porosity while interpreting sandstone through porosity charts.

My sincere apology for late response.


Tariq Hasany  


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Syed Tariq Hasany


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