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Archie Equation Petrophysics

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INTRODUCTION

Archie Unleashed is an attempt to put the basic log analysis methodology for computing water saturation into a readable reference document. The beginning log analyst or petrophysicist should have little difficulty with the terms and concepts utilized in this paper, however, most terms are redefined in appendix A.

The basic outline of this document closely follows a previous work written for the casual interpeter in log analysis. Archie Unleashed is meant to carry that work one step further. Basic concepts are explained along with more detailed examples and explanations.

The personal computer has revolutionized the way we work and play. The kind and amount of data we work with in petrophysics can be easily handled in …show more content…

Mark intervals selected for quantitative analysis on this log. Depth. correlate the other surveys to this reference log or the Gamma ray curve from this log.
4. Select intervals with at least four feet of constant response whenever possible. Use a single representative value from the center of the zone for each porosity and resistivity measurement. This procedure minimizes thin bed and bed boundary effects on the logs.
5. Consider how to keep the interpretation simple. Analyse the most clear-cut cases first. Look for: The obvious mineral markers (salt, anhydrite). The cleanest, most porous, intervals. The cleanest, water-bearing, intervals. The cleanest, hydrocarbon-bearing, intervals. The fluid contacts: gas/oil, oil/water. The transition zones.

6. Tackle one unknown at a time. For example, when deriving an Rw value from logs, choose a water-bearing zone as nearly identical as possible to the hydrocarbon zone of interest. This means the two zones have the same lithology, have the same or very similar porosity values, have the same type of pore structure (do not compare a zone with moldic porosity to one with granular or fracture porosity for instance), have the same formation water chemistry, etc. Ideally, the two zones are identical except for hydrocarbon content.

Bear in mind what G. E. Archie said about his equations. "It should be remembered that the equations given are not precise and represent only approximate relationships.

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