Effects Of Control And Revitalization Variables To Improve The Performance Of A Polymer Flooding Strategy

Abstract

Decisions related to production strategy selection are complex tasks involving large investments and high risk. Even applying in-depth probabilistic procedures to define the number and location of wells, the strategy is likely to be sub-optimal when field information is collected and the geologic model becomes better known. The objective of this work is to improve the performance of sub-optimal strategies through analyzing the effects of control and revitalization variables. The simulation models used to optimize the strategies showed variable levels to be different to those predicted, and so modifications to the strategy are necessary. Control variables relate to field management, and can be altered daily, without fore-planning and without requiring further investment (e.g., well rates). Revitalization variables represent possible future alternatives, which are not usually accounted for in the initial production strategy, and involve additional investment (such as infill drilling). The proposed methodology changes both control and revitalization variables throughout the lifetime of the field, using numerical simulation and economic analysis, to improve performance as measured by Net Present Value (NPV). We apply the procedure to two simulation models representative of an offshore heavy oil field using polymer flooding as the recovery mechanism. These are low flexibility cases (the platform already has the maximum number of wells), thus it is necessary to shut down some wells before opening others (well replacement). These new wells generate extra expenditures that were not accounted for in the original project. The results showed that the economic performance was greatly increased by actions that (1) do not generate extra expenditures (adjustment of well rates and specificities of the recovery mechanism) and (2) by actions that require extra investments (for instance, allocation of wells to substitute the ones that present low performance). In the studied case, the economic performance was increased up to 39%, even with the extra costs caused by the substitution of wells. This great increase in NPV was caused mainly by two reasons: the higher amount of oil produced due to the wells replacement (up to 17%) and the reduction in the amount and cost of the polymer injection (up to 89%). We also showed that higher oil recovery not necessary means better economic performance, since large investments may be required to produce more oil, and this increased production must pay the extra expenditures.