The VOLAN computation, whose name is derived from the words "volumetric analysis," is a new log interpretation technique that uses advanced computer analysis for the evaluation of complex formations. This technique has had successful application in the Bone Spring formation (Leonard series) of southeastern New Mexico.

In complex carbonate deposits where the porosity types include vugs and fractures, conventional log analysis generally has been questionable if only the Sonic log was used. The Sonic measurement tends to overlook the variable degree of secondary porosity inclusive of natural vugs and fractures. The neutron-density tools, on the other hand, measure the total porosity. Thus, to accurately determine values of effective porosity, water saturation, and lithology, the VOLAN program uses the unrefined data from three porosity tools (CNL* compensated neutron, Litho-Density* (LDT), and Sonic) and the resistivity measurements from the Dual Laterolog (DLL*) and Microspherically Focused (MSFL) tools. Positive results with this type of computer analysis have been obtained in the Bone Spring formation where the lithology is complex.

Applications derived from this type of computer analysis are:

  1. Identification of potential pay zones by determining the volume of dolomite and degree of secondary porosity.

  2. An in-situ formation description using the LDT three-mineral model enhanced by the Sonic measurement.

  3. Calculation of an effective water saturation value which has been corrected for the influence of bound water.

  4. Correlation with existing logs for mapping.

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