A NEW DRY CLAY TOTAL POROSITY MODEL FOR INTERPRETING PULSED NEUTRON CAPTURE LOGS IN SHALY SANDS

摘要

Interpretation of Pulsed Neutron Capture (PNC) logs in shaly sands has always been tricky using the basic volumetric interpretation model. This industry-wide volumetric model is premised upon having homogeneous formations. Increases in formation shale volume tend to drive the water saturation to low values and can result in serious interpretation errors. Historically, several different models have been devised to compensate for the effects of formation shaliness in interpreting PNC logs. These models include the Stieber non-linear volume of shale approach, the Neuman variable sigma matrix approach and the Schlumberger cased hole dual water model. Conversely, methods for interpreting open hole log data in shaly sands such as the Waxman-Smits, Dual water and Juhasz methods have been centered around the clay properties and uses a total porosity approach. This paper presents a method that integrates the volumes of dry clay and total porosity in the interpretation model. We will review the previous models and show examples of the computation of this new model to the older methods.