Petrophysics review

In this chapter, basic topics of petrophysics are reviewed and some concepts such as “shale”, “effective porosity” and “total porosity” are defined. It is shown how the shale parameters are taken from Neutron/Density plots and the simple theory of evaluation of shaly sands using the Neutron and Density logs is presented. The theory for the evaluation of gas-bearing shaly sands is presented as well. The estimation of the gas density and hydrogen index at reservoir conditions (fundamental in the evaluation of gas-bearing sands) is discussed in the Appendix of this chapter. This chapter reviews basic topics of petrophysics, and defines some concepts such as “shale”, “effective porosity” and “total porosity”. It shows how the shale parameters are taken from Neutron/Density plots, and presents the simple theory of evaluation of shaly sands using the Neutron and Density logs. The chapter also presents the theory for the evaluation of gas-bearing shaly sands, and discusses the estimation of the gas density and hydrogen index at reservoir conditions (fundamental in the evaluation of gas-bearing sands). Although “shale” still refers to a collection of very fine particles with a high proportion of clay minerals and quartz, it is considered to be a single (hypothetical) mineral, with the properties of the mixture of its constituents. This mineral has its own porosity, which is a measure of the pore volume between the fine particles constituting the “shale” and by water adsorbed by the clay minerals.