ABSTRACT

Cased hole pulsed neutron logs are conventionally run for time-lapse saturation monitoring logging. The technology has recently evolved, with the introduction of new hardware sondes with longer spaced and higher resolution detectors. The improvements in the measurements encouraged the extension of the original time-lapse logging objectives in a particular well to include high resolution spectroscopy passes. The elemental spectroscopy data provides mineral spectroscopy information that can be integrated with core data and other well logs to better define the mineralogical and petrophysical models. The results are discussed and compared to the current three mineral model which mainly uses conventional open hole log data; Gamma Ray, Density and Neutron open hole logs.

The spectroscopy log interpretation results were incorporated into a study including core description, grain density, and other core measurements to enhance the lithology interpretation. A review of the consistency between these independent lithology measurements is given. Additionally, any differences are reviewed and possible causes are suggested. Some of the logged interval is confidently known to be very largely dolomite while other parts of the interval are known to be very largely calcite. Thus a comparison is provided that covers the full range of dolomite content.

This study provides one of the first field comparisons of the mineralogy provided by the latest generation of PNL spectroscopy logs with core data - thus allowing insights of the compatibly of the measurements. An accurate estimate of dolomite content will allow the enhancement of the mineralogical model with consequential improvement in both porosity and saturation estimates which will assist in predicting well performance throughout its life.

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