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Advance Analysis of Old LogsQuantitative analysis of well logs is a critical part of reservoir characterization for initialization of simulation models and provides important information for development of regional exploration plays. Unfortunately many older wells were not logged with modern suites of tools. Often, only single detector neutron, Geiger-Muller detector gamma ray and electric log data exists for these wells. Several non-trivial problems must be overcome to utilize these old logs for quantitative reservoir characterization:
Raw log data cannot be used quantitatively in field or trend studies without considerable editing. Editing involves: 1) correction for rugose borehole, mud weight and temperature effects, 2) reconstruction of invalid tool responses over rugose hole and 3) normalization. Geosystems performs environmental corrections using available algorithms. Reconstruction of invalid borehole is performed using Neural Network technology to construct synthetic curve data for substitution where invalid responses are recorded. Corrected and calibrated log responses are subsequently normalized. Multi-well log normalization and data editing are essential parts of petrophysical studies. Normalization is a procedure to ensure that logging tools respond correctly and uniformly in all wells and accurately reflect rock properties. Field-wide, multi-well normalization is necessary to reduce well-to-well inconsistencies in field to calibration or tool responses. Normalization is an interactive process involving the use of histograms and crossplots of log responses. Histograms and crossplots of individual wells are compared with field wide data distributions and where necessary, normalized to the “standard” field average data set. Log ComputationEdited, environmentally corrected, recalibrated and normalized porosity and resistivity data can be used to calculate porosity and fluid saturations. GeoSystems calibrates log porosity to core porosity data. Corrected gamma ray and neutron data can be used to calculated shale volumes. GeoSystems calibrates log data to shale volumes measured in thin section and X-ray diffraction analyses. GeoSystems calculates Sw from log porosity and resistivity data using conventional or shaly sand techniques modified to incorporate available core-derived electrical properties data. GeoSystems computes permeability, ft-by-ft as K effective to fluid at reservoir conditions based on algorithms derived from core data. Contact GeoSystems
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