Developing a reliable height function from the J-Leverett parameters to populate water saturation: a case study

Abstract

Populating water saturation is a critical step in dynamic modelling. This work introduces a different height function that equates directly with the Leverett-J formula. In doing so, the model initialises under quiescent conditions without the need for end-point scaling. The resulting water saturation is a function of permeability, porosity, clay volume and height above the free water level. The Vcl—or clay content—is an important feature in this formulation because it compensates between extreme values of permeability and porosity. This peer-reviewed paper describes how a single height function was sufficient to match the log-derived water saturation for all wells in the Coracle sand of the Surprise Field in the North Sea. The process involved fitting a simple height formula, with the least possible parameters, to the J-function calculated from all the special core analysis (SCAL) data. These parameters were then tuned to match the log-derived water saturation. This technique was subsequently used in other fields where a single height function, which honoured the measured capillary pressures, accurately matched water saturation in all of the wells.