Saturation Height Modelling in a Partially Appraised Gas Field using analogue Field Core Data: An optimisation case study of ZAN Field in the Niger Delta

Abstract

Saturation height modelling is a critical input into 3-D based resource volume estimates. Calibrating saturation height models with in-field core data, particularly from the reservoir of interest, helps to reduce the uncertainties in reservoir saturation estimates. Due to paucity of Core data in most fields; Saturation height modelling is usually done with wireline logs only, using analytical equations. These equations sometimes do not have unique solutions with the same set of log data. The accuracy of the derived solutions is further reduced when these fits are derived without calibration to core data. Some of the log-only model-fits may also not have physical meaning even when there are good visual match with saturation profile at well points; thus failing when exported into a reservoir simulator. It is therefore pertinent to find a way of constraining the results from log-derived capillary models with fitting parameters obtained using core data from analogue fields in the absence of in-situ core data in subject field.The paper demonstrates the value in the use of analogue field core data for calibration of log-derived saturation model. ZAN field is a partially appraised field that has been identified for gas development with two well penetration that have complete suite of logs required for reliable saturation estimates and no core data. Log-based Capillary Pressure models were initially built, without any form of core calibration, with very limited success. To improve the quality of the model, capillary pressure measurements from analogue fields were used as building block for an improved capillary pressure model that was subsequently calibrated with logs from the field of interest. This resulted in an improved saturation match at well positions and also improved dynamic model initialisation.