Study of ionically modified water performance in carbonate reservoir system by multivariate data analysis

Adjustment of the ionic composition and strength of injected or imbibed brine for enhanced oil recovery (EOR) in carbonate reservoirs has been an area of active research for the past two decades. Despite many successful laboratory and field applications, the method has been reported ineffective in other cases. Most of the published results attributed EOR to improved water wetness in initially oil-wet carbonates. Nevertheless, in a few studies EOR was observed without apparent wettability alteration. We undertake the analysis of a large set of published recovery experiments to try to identify the critical mechanisms at the pore scale. Better pore scale physico-chemical understanding will guide to formulate accurate reservoir-scale models.
This paper presents a comprehensive meta-analysis of the proposed mechanisms using multivariate data analysis. Detailed review of the subject, including mechanisms with supporting and contradictory evidence has been presented by Sohal et al. (2016). In this study, the significance of each contributing factor to EOR was quantified and subjected to rigorous multivariate statistical analysis. The analysis was limited because there is no uniform methodology or sampling protocol. We confined our analyses to experiments with sufficient data so as many potential contributing factors as possible could be evaluated.. We were able to identify the most important factors that control increased recovery in chalk and limestone experiments. We also found the most critical measurements to provide the best basis for interpretation of the experiments that guide future recovery experiments and provide better results.