Pulsed neutron capture (PNC) logging in steamfloods-a hostile environment

Steamfloods in heavy oil and tar sand reservoirs have been monitored successfully with various cased hole logs. Particularly, high quantitative data have been provided by the pulsed neutron capture (PNC) log. The results have been useful in reservoir characterization and flood management. Special data acquisition techniques involving vacuum-flasked tools were used to accommodate temperatures as high as 223 degrees C (450 degrees F) with success despite limited operating time. Deviation of tool response in air-filled boreholes has been compensated by either an outboard sleeve or empirical normalization. Neither precision nor vertical resolution were adversely affected. The high temperatures in the formation affects log response due to thermal expansion of rock and fluids. An equation was modified to account for these effects in the interpretation of the PNC log, and its use was validated from field data. Specifically, expansion of the liquid phases is the dominant factor affecting log-response, and its inclusion improves on the accuracy of steam saturation calculations.<>