Waterflooding for improved oil recovery (IOR) could lead to the deposition of mineral scale in the near-wellbore area, wells, and production facilities, due to the mixing of incompatible injection water (IW) and formation water (FW). Scaling may hamper critical elements such as the safety valves (Baraka-Lokmane et al. 2014) and may reduce the permeability, causing oil productivity decline. Near-wellbore and downhole scale deposits are often prevented by scale squeeze treatment, where scale inhibitor (SI) is pumped into the reservoir via producer wells. In this paper we report uncertainty quantification of scale squeeze designs, based on field return data from a producer well in the Gulf of Mexico.
Field data was used to derive history matched adsorption isotherms, required to simulate the SI retention on the formation rock, and consequently to accurately predict the lifetime of SI squeeze treatments. Such treatments are usually defined by the injected SI concentration, main slug volume and, overflush volume. When the well is back in production, the SI slowly releases into the production brine. Scale will be inhibited if the concentration is above a certain concentration threshold, known as the MIC (minimum inhibitor concentration). Optimization of the results was carried out to maximize treatment lifetime.
SI adsorption isotherm models were derived by history matching the SI concentration return profile from a production well that has been on stream for several years. The derived models were improved, based on two subsequent treatments in the same well, and then used to find optimum treatment designs for the next squeeze design. The results indicated that effective overflush volume, for maximizing treatment lifetime, was significantly higher than the main slug inhibitor injection volume. Several isotherms reasonably matching the field SI return concentration profile were identified, which resulted in a significant impact on treatment lifetime. Isotherm history matching uncertainty was quantified by calculating the confidence interval, for identifying optimal scale squeeze designs.
The results indicate that scale squeeze design should include multiple scenarios to find the optimum treatment strategy, including confidence range due to uncertainty in isotherm history matching. Prior to scale squeeze design, it is recommended to accurately assess the SI adsorption to the reservoir rock as it significantly affects the results.