RESERVOIR SIMULATION OF THE GIPPSLAND BASIN

Abstract

A three-dimensional, single-phase reservoir simulation model of the entire Gippsland Basin aquifer system, together with its oil and gas reservoirs, was first developed in 1973. It was replaced by an improved version in 1975. Now, after fifteen years of production, pressure predictions from the model still compare very well with data obtained from current exploration and development wells.

The model, consisting of 4186 grid blocks, incorporates the geological description, and pressure and fluid distribution of the basin. The geological description includes porosity, net-to-gross ratio and permeability with fluid properties representing the aquifer. A well-established initial pressure/depth relationship for the Gippsland Basin is included in the model. Although it is a single-phase model, oil and gas reservoirs are represented by pseudo rock and fluid properties.

The model is regularly updated with historical and forecast production rates in order to predict pressure behaviour and therefore aquifer strength in various areal and stratigraphic locations in the basin. Such information is essential for defining external boundary conditions in individual reservoir simulation models and assists in gas deliverability forecasts. In exploration wells, measured pressures are compared with model predictions to help understand the degree of pressure communication with the basin aquifer and hence the level of pressure support. Detailed predictions of the pressure gradients expected in both exploration and development wells are often of assistance in identifying fluid contacts, overpressure and reservoirs with limited communication with the aquifer.