Shale volume determination using sonic, density and neutron data
Walid M. Mabrouk 1 2 Mostafa H. Kamel 11 Geophysics Department, Faculty of Science, Cairo University, Giza, Egypt.
2 Coresponding author. Email: walid_mabrouk@yahoo.com
Exploration Geophysics 42(2) 155-158 https://doi.org/10.1071/EG10014
Submitted: 7 May 2010 Accepted: 11 March 2011 Published: 28 June 2011
Abstract
The volume of shale calculation based on naturally occurring gamma rays frequently overestimates shale volume when radioactive material other than shale is present, for example where sand appears to be shale. In this situation, shale volume calculations from other methods are highly recommended in order to avoid overestimation or underestimation of shale volume. This paper introduces an equation relating shale volume to porosity logs (neutron, density and acoustic logs), which takes into account the effect of matrix, fluid and shale parameters. This equation, which is based on the effective porosity definition and the Dresser Atlas (1982) equation, has been successfully applied to many shaly formations, regardless of the type and distribution of shale. Solved examples are used to test and compare this equation and the results come close to what actually exists, with the amount of error ranging from –5 to +5%.
The advantages of the proposed equation can be summarised as: (1) it is a function of several parameters that affect the determination of shale volume in one formula; (2) it collects the three porosity tools for a more accurate calculation; and (3) it works best where radioactive material other than shale is present.
Key words: shale volume, sonic density and neutron logs, shale volume from porosity.
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