The Determination of a Volumetric Mixing Law for Use with the Neutron Porosity Logging Tool

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Mixing laws are an instrumental aspect of the interpretation of wireline logs of potential oil and gas wells. Through the use of volumetric mixing laws it is possible to estimate the porosity of a formation from a measure of its density or interval transit time. Estimation of porosity from the neutron logging tool measurements, however, is not based upon a mixing law. Determination of porosity from a measurement made by a neutron logging tool is currently based on experimental data of similar measurements made in matrices of pure sandstone, pure limestone, or pure dolomite only. The porosities estimated are thus accurate under conditions of pure matrices only; when the matrix consists of a mixture of these three matrix types, slight errors arise. More significant, however, are the errors that arise when shaly sands are encountered. Although the neutron tools actually measure a property of the formation known as the slowing down length, this property has not been used to estimate porosity because no mixing law for it has previously been determined. This report presents a new mixing law for slowing down length. In addition to its applications in pure matrices, it can be used in matrices containing mixtures of the three principal matrices and anhydrite and also in shaly sands. This is especially useful in shaly sands because of the errors which currently exist when shaly sands are encountered and because of additional applications if the porosity and volume of shale are known from other independent measurements.


Type of resource text
Date created June 1986


Author Sinner, Joseph R.
Primary advisor Ellis, Darwin
Degree granting institution Stanford University, Department of Petroleum Engineering


Subject School of Earth Energy & Environmental Sciences
Genre Thesis

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Sinner, Joseph R. (1986). The Determination of a Volumetric Mixing Law for Use with the Neutron Porosity Logging Tool. Stanford Digital Repository. Available at:


Master's Theses, Doerr School of Sustainability

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