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Abstract

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, 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 porosity, water saturation, and lithology, the VOLAN program uses the unrefined data from three porosity tools (CNL* compensated neutron, 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 LOT 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.

Introduction

The theoretical principles and premises behind the VOLAN program have been thoroughly discussed in previous publications. Therefore, only a previous publications. Therefore, only a brief review of the basic principles and models will be covered here. The intent of this paper is to present the VOLAN package and explain its interpretation using examples from the Bone Spring formation (Leonard series) in southeastern New Mexico.

Log interpretation using this type of logging program has proven useful in evaluating the complex program has proven useful in evaluating the complex lithologies of the Bone Spring formation found in the Scharb field of Lea County, New Mexico. Fig. shows the major geological features in southeast New Mexico and the location of the Scharb field. In the area of study, the Bone Spring formation is described as a stratigraphic-type reservoir formed from an accumulation of detritus which was transported from the shelf area to the north and deposited on the northern rim of the Delaware basin, lower Leonard (Permian) time (Fig. Lithologically, this formation consists of sediments described as being light to dark brown, very fine- to medium-crystalline fossiliferous detrital dolomite, with fractured, intercrystalline, and vuggy porosity. Gross thickness of the Bone Spring formation is approximately 3000 ft, with the beds of interest generally found from 7000 to 10,300 ft. Production in the Scharb field has been from two Bone Spring zones, the lower Scharb pay (10,100 ft), and an upper pay (9450 ft) shown in Fig. 3. The best hydrocarbon accumulation occurs in dolomitized detrital carbonate overlain by siltstone and silty dolomite. The cores in these zones show the pay contains vugs and fractures. Porosities in the productive areas range from 3% to 15% at variable pay thicknesses of 5 to 60 ft.

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