Network modelling analysis of a depressurization experiment on a North Sea reservoir core sample

Abstract

Solution gas drive following depressurization of oil reservoirs below the bubble point is the oldest and perhaps one of the most challenging oil recovery mechanisms to quantify. Part of the challenge lies in designing repeatable experiments and then translating experimental observations into practical solutions in the field – laboratory depressurization rates are typically orders of magnitude higher than practical field rates. Using a case study we show how pore network modelling can help make sense of the underlying physical mechanisms governing gas flow behaviour in porous media during solution gas drive whilst also serving as a forward modelling tool for developing relative permeability functions for use in field scale simulators. Core scale simulations performed on a pore network anchored to measured petrophysical properties of a 0.23mD chalk core from a North Sea reservoir show a very weak correlation between depletion rate and critical gas saturation, contrary to observations in higher permeability clastic media. In addition, solution gas drive oil recovery was found to increase with higher initial water saturation.