Abstract
Certain heavy oils that foam under severe depressurization give rise to increased recovery factor and an increased rate of production under solution gas drive. Alongwith stabilizing foam, at lower volume ratios, these oils have the ability of stabilizing dispersion of gas bubbles. Chemistry of oil and its viscosity are the reasons for this. In comparison to conventional oils, response of foamy oils to drawdown of pressure is more favorable; primary recovery factor, rate of production, volume ratio of oil to gas that is recovered and the length of time that a given pressure gradient or rate of production can be maintained, all increase substantially. It is a complex phenomenon with intrinsic properties, thus it requires a robust understanding of each factor in this recovery process. In this study, the significance of factors that influence foamy oil recovery in horizontal wells is investigated and outlined.
A robust commercial optimization and uncertainty software is coupled with a full-physics commercial simulator that models the phenomenon with bubbly oil approach in order to investigate the significance of major parameters, on performance of horizontal wells in a foamy oil reservoir in the North Sea. Fluid properties of Maini et al. are employed. Foamy oil is modeled as small bubbles in oil along with small mobile droplets of gas in oil, larger trapped droplets of gas phase and flowing discontinuous gas foam where bubbles can affect viscosity and compressibility along with foam mobility reduction in relative permeability effects, which are region dependent is incorporated.
Sensitivity and optimization has been done on major reservoir parameters, such as, fluid and rock properties and well operational parameters. Tornado diagrams have been used to portray the significance of each parameter. It is observed that a robust approach on handling of uncertainties in reservoir are as important as management of well operational parameters in the scope of reservoir management.
Reasons for the favorable response of foamy oils in solution gas drive are not well understood and tentative explanations that have been put forward are controversial, where utilization of horizontal wells adds another degree of complexity. This study provides an in depth optimization and uncertainty analysis to outline the significance of each major parameter involved in production performance and ultimately the recovery efficiency in foamy oil reservoirs produced with horizontal wells.
