A study was initiated with the objective to provide a better estimate of petrophysical parameters in a producing fractured basement reservoir. Emphasis was put on fracture and matrix porosity determination and its vertical and areal distribution. This uas essential in order to accurately define STOIIP as well as to improve the reservoir description and provide a data base for modelling studies. This paper gives an insight into the techniques applied to classify different rock types and the approach taken to compute the mineralogical model as basis for the porosity evaluation with minimum available core data to calibrate the results.

With the help of a program to identify electro-facies a minaralogical model was assigned to each facies and the petrophysical constants were then computed. Whenever possible test and production logging data and Formation Micro Scanner data were utilized to confirm the study results.

Based on the analysis it was possible to subdivide the fractured basement body into segments. Problems in determining porosity as well as water saturation in this type of reservoir are highlighted and the need to initiate a world-wide data base for granitic rocks is stressed.

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