Sandwich (three-layer) model

The simplest configuration for a pseudo-well is a three-layer sandwich where a finite-thickness reservoir is bounded by two non-reservoir layers, for example, sand embedded in shale. The properties of shale and sand have to be selected to reflect the relevant geological conditions at the site of investigation. The same holds for the conditions that include the pore and differential pressure and fluid properties.

For the examples shown in this section, we select the fluid properties and conditions listed in Table 5.1. Also, in order to translate the rock properties and conditions into the elastic properties, we use the soft-sand model where the differential pressure is 25 MPa, critical porosity is 0.40, coordination number is 6, and the shear modulus correction factor, f, (Eq. (2.26)) is 1. The density and elastic properties of the fluid phases are computed using the Batzle–Wang (1992) equations. Finally, the effective bulk modulus of mixtures of brine and oil and brine and gas are computed using the harmonic average of the bulk moduli of the respective fluid phases (Eq. (2.11)). An example of the shale and sand elastic properties according to the soft-sand model in the impedance–porosity and impedance–Poisson’s ratio planes is shown in Figure 5.1.