Modelling the impact of geochemical reactions on oil recovery and scale management in chemical Enhanced Oil Recovery (cEOR) flooding processes

Abstract

This research is an investigation of the impact of in situ chemical and geochemical interactions on oil recovery efficiency and inorganic scale management during chemical Enhanced Oil Recovery (cEOR) flooding processes. These reactions are studied for polymer, surfactant and Surfactant-Polymer (SP), Alkaline-Surfactant (AS) and Alkaline-Surfactant-Polymer (ASP) flooding processes. In such flooding scenarios, geochemical reactions occur during the transport of the EOR chemicals in the reservoir, and involve components in the aqueous, oleic and rock phases. These reactions are studied by means of fully coupled reservoir and geochemical calculations, and using data available from the literature, to aid understanding of impacts on oil recovery efficiency, and scale precipitation and management, and to support decision making in the design of such flooding processes. The work shows that reactive transport modelling can be used as a predictive tool to generate production data and trends that are useful for both reservoir engineers and production chemists. Reservoir engineers, who work to maximise oil recovery and minimise the cost expended on EOR chemicals, can benefit from simulating the in situ geochemical reactions to better predict their impact on oil recovery (e.g. pH buffering by rock and aqueous reactions and the impact on in situ soap generation, hence, the expected oil recovery). On the other hand, production chemists, who work to maximise scale management efficiency, can benefit from modelling the impact of the in situ geochemical reactions. This may be done not only for better prediction of the produced brine chemistry and water volumes, but also for better accounting of the impact of the injected EOR chemicals on scale management (e.g. the effect of alkali on scale precipitation, and the impact of buffering due to geochemical reactions on the performance of scale inhibition programmes). Results of these chemical and geochemical interactions on both aspects are presented in this work using generic 2D reservoir models. Optimization of the cEOR flooding scenario is addressed, considering the impact of the in situ geochemical reactions on both oil recovery and scale management perspectives. Moreover, the application of such flooding scenarios in 3D models of actual fields is also presented. Findings include that not only do the various cEOR strategies impact the mobilisation of oil and the relative flow of oleic and aqueous phases, they also impact the degree of mixing of components in the aqueous phase, which is important in assessing the scaling risk in the production system. Furthermore, there is little evidence of the geochemical reactions affecting the flow capacity of the rock deep within the reservoir, but they do have a significant impact on the performance of the injected chemicals as these chemicals are displaced through the reservoir. Strategies to improve the performance of EOR chemicals, such as control on composition of make-up brines, can also strongly influence the scaling risk, and the cost implications in certain case examples are calculated to aid the comparison.