Predicting the rock wettability changes using solutions with different pH, through streaming potential measurement

Abstract

The high reactivity of the carbonate rocks at various pH makes it difficult to evaluate the wettability, hence to find the recovery mechanisms behind modified waterflood in carbonate reservoirs. More recently, the streaming potential measurement is introduced as a method of electrokinetic phenomena more relevant to the subsurface systems. Regarding few experimental studies and in order to improve our understanding on streaming potential measurement, the electrokinetic studies on quartz and calcite surface were conducted as a function of pH in the range of 1.5–11.5 using an in-house novel setup of streaming potential measurement. High sensitivity of streaming potential coupling coefficient to pH variation in domain of pH lower than 4 for quartz and higher than 8 for calcite samples, underscores the fact that pH has to be well monitored during water based EOR tests to have more clear and predictable results. In the experiments reported here, measurements of streaming potential were compared with the adhesion test results to use streaming potential measurement as a promising tool to characterize wetting state and quantify wettability of a porous media. The results showed a clear correlation between streaming potential coupling coefficient/zeta potential change, wetting state and calcium concentration expressed as pCa2+, irrespective of how the pH is changed. Moreover, the equilibrium solutions analyses suggest that streaming potential measurement results are more reliable and applicable compared to electrophoresis method to extend to the subsurface setting during a dynamic injection process.