Accounting for Changing Rock & Fluid Properties in the Oil URM

The classical unconventional reservoir model (URM) analysis for oil is performed under the assumption that the variation of oil properties (compressibility, viscosity, formation volume factor) with pressure is negligible; therefore this variation is not taken into account.

To account for the variation of oil properties with pressure (on square-root-time plots and on the FMB plot), select the Changing Properties (Pseudo-Pressure) option. Calculations performed when this option is selected are based on using oil pseudo-pressure and are described in Accounting for Variation in Rock and Fluid Properties in the Oil URM (theory). Calculations use the oil properties that are set in the Properties Editor.

If you chose to account for the variation in properties using pseudo-pressure, you can access these additional options: GeoMechanical, Use Corrected Pseudo-Time, and Changing Oil Saturation.

• GeoMechanical — accounts for the variation in rock properties (permeability and formation compressibility) with pressure. Calculations use the rock properties that are set in the Geomechanical section of the Properties Editor.
• Use Corrected Pseudo-Time — this is an advanced option that is not displayed by default. You can display this option by clicking the Display Pseudo-Time Option checkbox in the Options dialog box under the Analysis, URM node. Using pseudo-time introduces an additional correction that accounts for the variation of oil properties (mainly oil compressibility) with pressure. For more information on the pseudo-time correction for URM, see Using Pseudo-Time. Since pseudo-time transformation is inexact, it should be used with caution. When using the corrected pseudo-time option, it is important to adjust the analysis line on the FMB plot, such that it represents the "best guess" total fluid in place (not contacted fluid in place, or fluid in place within the stimulated reservoir volume).
• Changing Oil Saturation — enables you to model behaviour when pressure in the reservoir drops below the bubble point, and the gas saturation starts building up. This option is only available if flowing pressures are below the oil bubble point pressure for a portion of the production data. For more information, see Accounting for Changing Oil Saturation.