Properly executed drilling mud tracer programs can provide “gold standard” answers to several important petrophysical and reservoir engineering questions.When tracers are used in water-based muds (WBM) in conjunction with conventional coring, in-situ water saturation (Sw), formation water resistivity (Rw) and clay bound water (CBW) can be accurately determined. Successful tracer studies require tight controls on 1) mud design, 2) mud monitoring and mud sampling during drilling and coring operations, 3) low-invasion coring procedures, 4) wellsite core handling and 5) laboratory measurements.

The best drilling mud tracers have the following characteristics: 1) they do not naturally occur in the formation, 2) they are fully soluble in the mud filtrate, 3) they are biologically stable (i.e., they are not a food source for bacteria), 4) they are chemically stable and non-volatile, and 5) they can be accurately detected at very low concentrations.

Tritiated water (HTO) meets all these criteria. Because it is not naturally occurring, background (signal to noise) issues are eliminated. Simply put, the amount of HTO found in the core is directly proportional to the quantity of filtrate water that entered the rock during coring operations. HTO is safe to use and can be detected at extremely low concentrations. Very small quantities of HTO are required because of the excellent detection levels.

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