Estudo experimental, modelagem e simulação da injeção de salmouras e CO2 em reservatórios carbonáticos

Abstract

The development and improvement of enhanced oil recovery methods (EOR) to increase the oil recovery rate represents one of the major challenges of reservoir engineering. Water and gas injection are widely used methods. Therefore, in the Brazilian pre-salt context, seawater and CO2 are important candidates to be used as EOR methods, due to the high availability of these fluids. CO2 injection has received special attention because it favors recovery providing a miscible or near-miscible condition in the reservoir; and for being an option of destination for this greenhouse gas, since the gas associated from the pre-salt has a huge amount of CO2. In addition to seawater injection, the use of diluted seawater (low salinity water), which is a relatively new EOR process, has also been reported by several authors as a method that increases the oil recovery factor. Another approach that has been evaluated is the association of the particular advantages of continuous injections of these fluids, through alternating injection (WAG). However, understanding the effects of each one of these methods is a challenge due to the complexity of interactions between the rock, oil and aqueous phase. Therefore, the need for an adequate understanding of the mechanisms involved in oil recovery when these methods are used in carbonate reservoirs, characteristic of the pre-salt, motivates the performance of experimental, modeling and simulation studies that were developed in this thesis. Regarding the results of the simulation studies, carried out with data from the literature, corroborate the understanding of the synergistic effect between CO2 and brines injections, providing an overview of the dynamic process of oil recovery and flow, in which different factors influence simultaneously. Concerning the analysis of the results, emphasis is given to: the interaction of the fluids with the rock, which can result in mineral dissolution and wettability alteration; the CO2 solubility in oil and in the aqueous phase, which leads to changes in phase properties that have a direct effect on oil recovery, such as density and viscosity; and the influence of system characterization on recovery estimates, considering the petrophysical properties distribution and relative permeability curves. In turn, the results obtained in the laboratory present unprecedented experimental data for the characterization of an oil sample from the Lula field located in the Brazilian pre-salt with limited publication in the literature. In addition, core flooding tests and measurements of interfacial tension and contact angle were carried out in this work, highlighting: i) the additional oil recovery when applying continuous injection of seawater and low salinity water in secondary mode and also during CO2 low salinity water-alternating-gas or CO2 seawater-alternating-gas in tertiary mode in the evaluated system; ii) that the compositional effects of the CO2 interaction with the oil and the aqueous phase and the mobility control of the WAG process were most relevant mechanisms to the observed production increase; iii) and that the geochemical interactions of the investigated brine presented less influence on the recovery since the dolomite core used presented an initial behavior slightly water-wet.