Abstract
Inflow performance in some heavy oil reservoirs is not well understood as the fluid properties differ from conventional behavior. In this work, we develop an expression for inflow performance as a function of properties of foamy oils such as density, viscosity, solution gas-oil ratio and formation volume factor. We define two parameters, the end point entrained gas fraction and the apparent bubble point, adapted from previous studies, to account for the extent of entrained gas fraction in the liquid. The fluid properties are modified to account for the entrained gas and then incorporated in the equations describing flow from a reservoir at pseudo-steady state.
The results of our study show that the entrained gas and the apparent bubble point impacts the fluid properties and therefore the inflow performance at the bottom-hole conditions. In the presence of entrained gas, the density of the fluid decreases and the formation volume factor increases. Both these parameters show an inflection below the bubble point pressure and the solution gas oil ratio shows a constant value until the apparent bubble point is reached. The inflow performance curve, therefore, displays an inflection as opposed to the monotonically changing curve normally seen with conventional oils. The outflow performance curve is lowered when the effect of entrained gas is included and hence, the nodal systems analysis predicts a greater production rate for a foamy oil reservoir compared to a conventional reservoir.
