Neutron-density crossplot

The most frequently applied plot is the neutron-density crossplot. Figure 5.19 shows the principle of a neutron-density crossplot for the three main reservoir rock components sandstone, limestone and dolomite. Plots start in the lower left comer with the matrix-point and go up to the right upper comer with the water-point . The three lines describe pure limestone, dolomite and sandstone. Lines are scaled in porosity units. 

FIGURE 5.19 Calculated neutron-density crossplot x-axis gives the neutron porosity for a limestone-calibrated tool y-axis gives the bulk density. Lines are plotted for sandstone/quartz (matrix density 2.65 g/cm, matrix neutron response —0.03) limestone (matrix density 2.71 g/cm, matrix neutron response 0.00) dolomite (matrix density 2.86 g/cm, matrix neutron response +0.04) freshwater (density 1.00 g/cm, neutron response 1.00). 

FIGURE 5.20 Neutron-density crossplot. Data from three depths of a carbonate section are plotted into the chart. Schlumberger 2000, 2013, Courtesy of Schlumberger. 

Crossplots are two-dimensional graphic presentations of the response equations. Crossplots present the variation of any two porosity-sensitive properties (for example density and neutron, but also slowness/see next chapter). All combinations are possible ... 

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