Pyrite is electrical conductive and can interferfer on SW calculation because the classical methods (Archie and Simandoux) use the resistivity log (RT) as an input parameter. Does anybody knows an alternative method to calculate SW, avoiding pyrite effect com pyrite-rich sandstones reservoirs?
Determine the empirical SW from sample core plugs. From the obtained core SW values, you can use machine learning techniques to predict the remaining SW from the available well logs.
Thank you Solomon, but I do not have core plugs. SW calculation needs to become from logs.
I have faced the pyrite-rich typical reservoir for several projects in Indonesia. Based on my little experiences, The Waxman-Smith and Modified Indonesia are the most optimistic methods and valid with core laboratory data analysis but must be validated to Pc data
No, we do not use the formulas of these authors. To predict we build our own empirical expressions for specific data. The theoretical-empirical methodics of prediction of oil-gas-water-saturation of rocks in boreholes of wells is realized as a system of theoretical and empirical relations and the resulting functional. It is based on acoustic logging (АL) and the core research (CR) data.
There exists an old paper by C. Clavier, A. Heim, and C. Scala titled EFFECT OF PYRITE ON RESISTIVITY AND OTHER LOGGING MEASUREMENTS (SPWLA, 17th Annual Logging Symposium, June 9-12, 1976) where it is shown that pyrite effect on resistivity logs is a function of tool frequency (the higher the frequency the higher the correction factor). According to this paper, in zones with pyrite you should privilege Dual Laterolog-type tools (LLD 35 Hz, LLS 280 Hz) over induction-type tools (ILD 20 kHz)).
Pyrite affects all tools and a multi-mineral analysis-type interpretation is recommended.
Dear Michel Krief, thank you very much. I will check this paper.
Dear Ongki Ari Prayoga, do you have any reference about the Waxman-Smith and Modified Indonesia methods?
Dear L. V. Skakalska, I think your own empirical expressions are cofidential, but do you have any published data to share?
See Clavier et al. (1976), Effect of pyrite on resistivity and other logging measurements: SPWLA Seventeenth Annual Logging Symposium, June 9-12, 1976. They have figures showing corrections for various logging tools to compensate for the pyrite content in the rocks. The abstract is posted on Research Gate, and you can request a copy for the authors: Article Effect of pyrite on resistivity and other logging measurements
Another more recent reference would be Holmes et al. (2013), "A Petrophysical Model to Quantify Pyrite Volumes and to Adjust Resistivity Response to Account for Pyrite Conductivity, Presented at the 2013 AAPG ACE, Pittsburgh PA," that can be downloaded from http://www.digitalformation.com/publications.php
These should get you started. Once you can correct the logs for the pyrite content, the problem is reduced to applying the Archie equation to your log data.
Dear J. Richard Bowersox ,
Nice contribution. I will check both papers. Yes, that is the main point. I think that lots of oil/gas accumulations are "forgotten" under bad well-logs avaliation, because pyrite effect. Pressure tests show these "forgetfulness".
Dear Fernando.
We are working with Sw from Archie equation in organic rich shales (Vaca Muerta Formation in the Neuquen Basin). The pyrite content in Vaca muerta is around 2-5% and the calibration with core data is good. However and as you know, the Sw in shales is an issue with long technical discussions. SW from Archie should be considered a pesimistic case. We calculated the Sw with total inorganic porosity without the effect of the organic matter (TOC).
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Waves