Study of the fluid-fluid and rock-fluid interactions: impact of dissolved CO2 on interfacial tenson and wettability for the brazilian pre-salt scenario

Abstract

Pre-Salt carbonate fields are among the most important discoveries of the last decades representing economy game-changing assets in Brazil. Nevertheless, these reservoirs present unique challenges for their development. Literature data for fluids and rocks analogous to Pre-Salt conditions is limited, and the rock-fluid and fluid-fluid interactions remain to be understood. In this context, this work aims to contribute with reliable experimental results and discussions to improve the Pre-Salt reservoir models. The scope of this research is to evaluate initial wettability and interfacial tension as pillars of these interactions with focus on the impact of CO2. Customizing experimental methodologies for material characterization, initial wettability and interfacial tension evaluation at reservoir conditions, it was possible to reach the following conclusions: Aged Pre-Salt rocks were oil-wet., and rock aging is required to achieve the initial wettability. Crude’s acid/base and SARA compositions play an important role during the aging process; CO2 dissolution rendered initial wettability towards water-wet. Thus, PreSalt reservoirs with elevated CO2 concentration are likely to be intermediate to water-wet at initial conditions; finally, the presence surface-active compounds in the oils resulted in a low interfacial tension with brine, so the presence of CO2 did not contribute to increase the Capillary Number.