Saturation Modelling in a Geological Complex Clastic Reservoir Using Log Derived Saturation Height Function: A Case Study of the E2 Reservoir, Era Eko Field in the Niger Delta

摘要

The conventional and globally accepted method of saturation modelling is using capillary pressure curve (cap-curve) data from special core analysis (SCAL). The functions describe the drainage process during hydrocarbon migration and are expressed as a relationship between saturation, the height above the Free-Water-Level (established from a wireline pressure analysis) and a model property (commonly porosity and permeability). The functions are established by first fitting some mathematical function to the cap-curve data (smoothing) and then establishing trends between the function parameters ( capillary entry, saturation end point and some shape factor) and the model property, resulting in an averaging of the capillary pressure curves (which have been converted from pressure to height) or log derived saturations. Common curve-fitting or smoothing techniques are the Brooks-Corey, Thomeer, Lambda and Heseldin techniques. This method allows better understanding of the saturation distribution in a reservoir, given that water saturation is distributed in geologic models using a saturation height function (SHF) that relates rock properties (porosity and permeability) and height above free water level (HAFWL). SHF based on cap-curves are used by reservoir engineers to initialise water saturation in dynamic models and depending on the heterogeneity of the reservoir, different SHF are generated to accommodate different rock property classes. However, where there is no core data or no SCAL measurements, SHF can also be derived from available log data.