Intrinsic geological formation carbon to oxygen ratio measurements

A method of forming casing perforations in a casing of a wellbore, the method comprising:

• measuring an intrinsic carbon to oxygen (CO) ratio in a geological formation by:
• disposing a petrophysical tool downhole proximate the geological formation, the petrophysical tool including at least one gamma-ray detector;
• using the petrophysical tool, reading a carbon gamma-ray peak for the geological formation and an oxygen gamma-ray peak for the geological formation;
• determining a measured CO ratio of the geological formation from the carbon gamma-ray peak and the oxygen gamma-ray peak;
• correcting the measured CO ratio by applying a corrective algorithm specific for the petrophysical tool or the type of petrophysical tool to obtain an intrinsic CO ratio of the geological formation,
• wherein the intrinsic CO ratio of the geological formation is the ratio between atomic number density values of carbon and oxygen, and the corrective algorithm is derived by a mathematical analysis of measured CO ratios of a sample with a known intrinsic CO ratio using the same petrophysical tool or a petrophysical tool representative of a same type of petrophysical tool;
• assigning carbon in the intrinsic CO ratio as representative of hydrocarbon in the geological formation and oxygen in the intrinsic CO ratio as representative of water in the geological formation and calculating the hydrocarbon to water ratio for the geological formation based on the intrinsic CO ratio;
• and
• when the hydrocarbon to water ratio is greater than a set amount, forming at least one casing perforation in a casing of a wellbore adjacent the geological formation.

A drilling, evaluation, and exploration system used in a wellbore drilled through geological formations, the system comprising:

• a petrophysical tool disposed downhole, the petrophysical tool including at least one gamma-ray detector and one neutron source;
• and
• a processor, which may be included in the petrophysical tool or located in a surface processing unit, that
• using the petrophysical tool, reads a carbon gamma-ray peak for the geological formation and an oxygen gamma-ray peak for the geological formation;
• determines a measured carbon to oxygen (CO) ratio of the geological formation from the carbon gamma-ray peak and the oxygen gamma-ray peak;
• and
• corrects the measured CO ratio by applying a corrective algorithm specific for the petrophysical tool or the type of petrophysical tool to obtain an intrinsic CO ratio of the geological formation,
• wherein the intrinsic CO ratio of the geological formation is the ratio between atomic number density values of carbon and oxygen, and the corrective algorithm is derived by a mathematical analysis of measured CO ratios of a sample with a known intrinsic CO ratio using the same petrophysical tool or a petrophysical tool representative of a same type of petrophysical tool.