On the Importance of Reservoir Rock Mineralogy on Design and Performance of Surfactant-Based EOR Processes

Abstract

Chemical EOR processes based on surfactants are highly constrained by chemicals losses due to retention in porous media. Surfactant adsorption is usually considered as the main retention mechanism. It can lead to a decrease in process efficiency and to an increase in costs. Among the factors impacting surfactant adsorption – namely reservoir rock mineralogy, brine composition and chemicals types — mineralogy is known to be prominent with an impact that is hard to predict and should be dealt with. This paper presents a comprehensive review on the importance of reservoir rock mineralogy on laboratory design and performance evaluation of surfactant-based EOR processes, using several field cases as illustrations. First, the main effects of the various factors quoted above on surfactant adsorption will be presented. Then a summary of the mitigation strategies that can be applied on field, based on either brines treatments, chemical selection or specific injections processes, will be presented. Four representative cases studies of Surfactant-Polymer process design and evaluation at the lab scale on different mineralogies and conditions will be discussed. Each of them exhibits specific hurdles and requires solutions to mitigate mineralogy impact on designed process. Oil recovery corefloods on reservoir rock were conducted with surfactant in effluent and oil production measurements. Mineralogy analysis were also conducted using XRD, SEM and NMR experiments. The first case focuses on a low clay – low temperature sandstone, an apparently simple case which nonetheless shows a very high and unexpected surfactant adsorption due to a very particular clay repartition. The second case focuses on a high clay — high temperature sandstone: this expectedly difficult case was mitigated by the use of adsorption inhibitors, leading to a good oil recovery and a low adsorption. The third case focuses on an unconsolidated – low clay sandstone containing heavy oil which shows a pronounced sensitivity to fine mobilization by surfactant-polymer process. The selected solution was an adapted brine treatment. The last case focuses on a high temperature carbonate which classically shows high adsorptions. A combined process using brine treatment and adsorption inhibitor resulted in particularly low surfactant adsorption of 60 μg/g. Mineralogy is shown to be a key factor that controls surfactant adsorption in chemical EOR processes. Using representative mineralogy in the lab feasibility studies is therefore mandatory to design relevant Surfactant-Polymer processes. This review demonstrates that efficient strategies can be developed to mitigate the impact of mineralogy on SP chemical EOR processes in a wide range of challenging conditions.