A Proposed Solution to Resolve the Total and Effective Porosity Approaches to Water Saturation

Summary The merits of Total and Effective porosity approaches have always been a source of discussion within the Petrophysical community globally. In general, an operating company adopts a single approach (Total or Effective) in their modelling workflows and ignores the alternative method. This is normally to have a consistent approach across the company so that the end users know what they are receiving into their subsequent workflows. In the proposed method, both Total and Effective Porosity Methods have been applied. The differences are then used to minimise and improve the resulting porosity and saturation calculations such that the results are mutually comparable. Total Porosity based water saturation equations are dependent on the ‘shale/clay’ volume and porosity to compensate for the ‘shale/clay’ bound water resistivity. Effective Porosity is based on water saturation equations on the shale volume and resistivity. The difference is that the Effective Porosity Water Saturation approach is not directly dependent on the ‘shale/clay’ porosity and can be used as a fitting parameter via the dry clay density (that doesn’t exist in-situ) in addition to compensating for the invaded fluid volume. Examples will be presented in a wider range of geological environments will be discussed.