Fracture Porosity from Conventional Logs with Image Tool Calibration

摘要

Petrophysical evaluation of the Moki Formation in the Toka-1rnexploration well, required rapid quantification of fracturernporosities, enabling likely hydrocarbon volumes to bernestimated. A resistivity imaging tool had been run over thernapproximately 400m of fractured interval. This informationrnwas being processed for fracture apertures by the acquisitionrncontractor, but the rate of quantification was too slow to meetrnthe operators objectives. A technique was developed to rapidlyrnestimate fracture porosities using the difference between therndensity and the compressional sonic porosities and therndifference between the shear and compressional sonicrnporosities. The fracture porosity estimates were cross-checkedrnagainst the image log analysis completed. Owing to washoutsrnacross the most heavily fractured intervals, it was expectedrnthat fracture porosities from the density and compressionalrnsonic logs were maximum values. The most likely fracturernporosities were thought to be those derived using the shear andrncompressional velocities. The fracture porosities estimated byrnhand-picking fractures from the image data were consideredrnthe minimum values, since the identification process wasrnincomplete. The work described represents a new techniquernfor fracture porosity quantification. The comparison withrnimage log interpretation over a short interval gives confidencernin the methodology. The results are significant in that theyrnshow rapid quantification of fracture porosity is possible byrnusing conventionally acquired logs, although it should bernrecognised that the uncertainty in this approach is significant.rnApplication of this technique to other fields with limited imagerndata may prove helpful in reservoir modelling andrnunderstanding of production behaviour.