Orlando Gomez Rivero
Petroleos Mexicanos
Mexico City
Mexico
ABSTRACT
An equation relating porosity exponents, m, of the Archie and the Humble-type formulas was derived; this affords the computation of equivalent porosity exponents. The only one well logging correlation parameter necessary is porosity. A critical comparative analysis is made of both classical equations; as a result, some of their apparent advantages and deficiencies are pointed out and partially clarified.
A computer oriented approach is proposed for determining the porosity exponent of the Archie equation; it can also be used as interpretation parameter, for detecting other secondary porosity conditions, additionally to natural fracture detection, in a similar way as proposed for the porosity exponent of the Humble-type equations. Nevertheless, the interpretations made on this basis must be complemented with other also well log derived data; the formation resistivity factor seems to provide the necessary key information. In complex rocks with dual porosity, it is possible to compute both the resistivity factor for the total porosity system and the resistivity factor for the part of the rock with only primary porosity, as well as its corresponding particular porosity exponents. This new well log derived information when displayed as computed logs greatly facilitates the location of the more permeable probable hydrocarbon bearing zones.
The application of this method is illustrated with actual field examples.