4D Analysis

Problem
Changes in subsurface conditions as a result of production (e.g. reservoir compaction) needed to be quantified for further field development.

Solution
A 4D AVO and rock physics inversion was conducted to investigate the effects of fluid depletion.

Workflow

  1. A rock physics model was derived for the upper (Figure 1) and lower (Figure 2) reservoir to investigate the relationship between elastic and petrophysical parameters. The difference in the rock physics trends are the result of effects such as differing lithology and fluid content and differential compaction.
  2. A simultaneous 4D AVO inversion was performed to estimate the baseline acoustic impedance, Vp/Vs and density (Figure 3) and associated changes (Figures 4 and 5). The changes in elastic properties highlight the spatial extent of production effects.
  3. A 4D rock physics inversion was performed to investigate the changes in petrophysical parameters as a result of production. The map illustrating the change in water saturation (Figure 7) highlights the spatial extent of the water flood.
Figure 1: Porosity crossplot with the derived rock physics model for the upper reservoir.
Figure 1: Porosity crossplot with the derived rock physics model for the upper reservoir.
Figure 2: Porosity crossplot with the derived rock physics model for the lower reservoir.
Figure 2: Porosity crossplot with the derived rock physics model for the lower reservoir.
Figure 3: Inverted baseline elastic properties.
Figure 4: Changes in elastic properties as a result of production.
Figure 4: Changes in elastic properties as a result of production.
Figure 5: Map view of changes in elastic properties as a result of production at the reservoir interval.
Figure 5: Map view of changes in elastic properties as a result of production at the reservoir interval.
Figure 7: Map illustrating the change in water saturation as a result of production.
Figure 6: Baseline rock physics inversion.