G. R. Coates, R. P.Schulze, and W. H. Throop
Schlumberger Well Services
ABSTRACT
The dual water principle was introduced in 1977 to explain the influence of clay minerals on resistivity measurements. Since the time it was introduced, evidence has supported the principle, and its premises are now being used in advanced log processing.
The new VOLAN program uses a model based on the dual water principle to produce a volumetric analysis of the formation. Shaly sands are the initial target of this new processing technique; subsequent developments will include applications for carbonates and mixed lithologies.
This new program was developed to:
1. Use the concepts of the dual water model to full advantage
2. Functionally incorporate new log measurements
3. Utilize automatic parameter selection
4. Use statistical calibration for secondary calculations of the bound water fraction
Until the VOLAN program was developed, the dual water model was used only in the Schlumberger Cyberlook wellsite interpretation and TDT analysis. In the new program, the model provides sound values of porosity and brings a new degree of accuracy to the basic analysis of water saturation. The program also permits the theoretical principles of the model to be used, including the idealized bound water conductivities.
The dual water model overcomes the principal limitations of the basic shaly sand models which relied on neutron-density behavior and clay volume analysis measurements. The VOLAN program also integrates measurements from the new Litho-Density, EPT, and NGS logs to provide an accurate volumetric calibration.