C. V. Moore and R. L. Kaufman
ABSTRACT
The general practice of using a single temperature resistivity measurement may lead to significant errors in log analyses. Errors are present in the measurements of the resistivity itself and in the extrapolation of resistivities from a relatively cool surface temperature to a much hotter subsurface temperature.
Resistivity measurements made by several laboratories at three or more temperatures on the same fluid samples are presented. These measurements indicate that the resistivity - temperature relationship of a relatively fresh water generally deviates from the standard sodium chloride (NaCl) Resistivity-Temperature relationship. Resistivities of some high salinity waters also deviate from the standard relationship. Differences between these multi-temperature resistivity measurements and the standard relationships are attributed to faulty measurement procedures and the presence of ions other than sodium chloride. Differences were also observed in fluid resistivity measurements among wireline service companies and commercial laboratories at normal surface temperatures and in water analysis by different laboratories. These differences on the same samples are caused by poor measurement procedures, and to a lesser extent by poor sample handling.
Failure to correctly measure and extrapolate Rm, Rmf and Rw to formation temperature can cause significant errors in log analysis. To demonstrate the significance of these errors, sensitivities of computed hydrocarbon saturations to Rw errors are presented.