Significance of the Kinetics of Minerals in Reactive-Transport Problems

Abstract The effect of geochemical reactions and the kinetics of minerals are not completely understood in reactive-transport problems such as low-salinity waterflooding (LSF) or alkaline/surfactant/polymer (ASP) injection method. These processes do not only act as an inert displacement and geochemistry also plays a major role in the fluid behavior and oil recovery. In this paper, first, the importance of the kinetics of minerals with fast and slow rate kinetic reactions (e.g., calcite and quartz, respectively) in different conditions during reactive-transport floods is investigated using PHREEQC geochemical package. Then, two-phase Buckley-Leverett (BL) flow is coupled with IPhreeqc which is open-source module of the PHREEQC geochemical package in order to study the effect of the geochemical reactions and the kinetics of minerals on the oil recovery in two different displacement distances. This coupling provides a simple tool for modeling the geochemical reactions to understand the effect of the geochemistry on the two-phase and 1D flow, and consequently the oil recovery. Finally, as an example, the significance of the kinetics of minerals in LSF and in oil recovery is studied at two different scales. The results show that temperature, in-situ water composition and buffering capacity have a great impact on the kinetics of mineral. It has been shown that minerals with slow rate kinetic reaction (e.g., quartz) might be excluded in reactive-transport phenomena at core-scales. However, minerals with fast rate kinetic reactions (e.g., calcite) must be included when modeling lab results. On the other hand, the residence time at field-scales is large enough for the mineral dissolution and precipitation to affect the local equilibrium constants. Therefore, in modeling field-scale applications, local equilibrium assumption (LEA) can be applied for fast rate kinetic minerals, whereas kinetics should be used for slow rate kinetic minerals (e.g., quartz).