After nearly thirty years of research and development, it is now commonly agreed that Low Salinity Waterflood (LSW) is an attractive enhanced oil recovery (EOR) method because of its incremental oil recovery performance, reasonable operating cost and low environmental impact compared to conventional waterflood and other EOR processes. From the past studies, LSW is known as a process that comprises many mechanisms, i.e. multiple ion exchanges, wettability alteration, complex geochemical reactions, and fines migration and deposition. However, most studies in the literature have only focused on a single recovery mechanism, with varying, sometimes contradictory conclusions. This paper presents: (1) a comprehensive model that takes into account all the different important physics in LSW, i.e. fines transport, geochemistry and wettability alteration; (2) validation with a core-flood experiment; and (3) field-scale optimization of LSW.
A model for fines transport has been developed and incorporated in an Equation-of-State compositional reservoir simulator with geochemistry and wettability alteration modeling. The proposed model is capable of accounting for complex transport phenomena of fines (clay) particles in porous media including fines deposition, entrainment, and plugging. The simulator also considers physical phenomena in the oil/rock/brine system such as aqueous chemical equilibrium, rate dependent mineral reactions, multiple ion exchanges, and relative permeability alteration due to wettability changes. Validations with a LSW core-flood experiment were carried out, which provide insights into the important mechanisms for the incremental oil recovery by LSW.
The proposed model shows good agreement in terms of oil recovery and pressure drop with a benchmark LSW core-flood experiment which was conducted with a non-polar oil and in which migration of clay particles and their plugging of pores were considered as the main recovery mechanism. It is shown that the proposed model can efficiently capture the important physics in LSW processes related to fines transport. The impact of formation damage during LSW can be efficiently evaluated using this model. Finally, an optimization workflow helps maximize the recovery factor of the LSW process.
To our knowledge, this paper describes one of the first LSW mechanistic models to capture the three principal mechanisms of LSW, i.e. fines transport, geochemistry, and wettability alteration. Excellent match with laboratory experiments and field-scale optimization reinforce validity of the model. The proposed workflow can be extended to other recovery methods such as Low-Salinity Polymer or Low-Salinity Alkali-Surfactant-Polymer.