Electrokinetics in Low Salinity Waterflooding

Abstract

Low salinity waterflooding (LSF) is a promising improved oil recovery (IOR) technique. The enhanced composition of injected water in LSF can change the wettability of the formation from oil-wet/ mixed-wet towards a more water-wet state. This leads to improved relative oil permeability (kro). The zeta potential, which is the electric potential at the shear plane, generally a couple of nanometers away from the rock/clay surface, can give an indication on rock wettability. Streaming potential measurements and electrophoretic (zetasizer) measurements give information on the zeta potential. Electrophoretic measurements can only be performed with crushed rock – brine or crushed rock – oil combinations. Streaming potential measurements are performed with sandstone cores. This allows for measurements with a full crude oil-brine-rock (COBR) system, which takes into account the proper ratio between rock/clay surface and bulk rock. In this thesis, we assess whether streaming potential measurements can give more information on rock wettability and wettability alteration for LSF. Therefore, we first compare the obtained experimental single-phase streaming potential data with bundle-of-tubes (BOT) models that use the zeta potential from electrophoretic measurements and the pore geometry from micro CT data as an input. Secondly, single-phase streaming potentialmeasurements are compared with two-phase streaming potential measurements. These two-phase measurements are then compared to specifically designed water-wet and oil-wet BOT models. The two-phase measurements are performed at residual oil saturation (Sor). The last objective is to see the qualitative streaming potential response of an aged COBR system, consisting of Dagang brine, Berea 700 sandstone and crude oil H. This thesis describes the streaming potential capabilities for single- and two-phase measurements that have been established at Delft University of Technology. Also, the results as obtained from streaming potential measurements and electrophoretic measurements are described in detail. Furthermore, a model (single- and two-phase (water-wet and oil-wet)) has been developed that contains both the overlapping of double layers and Stern layer conduction. The models use input from micro CT data (pore throat radius) and zetasizer measurements. This has not been done in literature before. A comparison of modeling data to experimental data shows that the models that include the overlapping of double layers and Stern layer conduction represent the laboratory data best. The Stern layer conduction can be used as a fitting parameter. The two-phase water-wet models show similar trends compared to the lab data. The three effects that have the largest influence on the coupling coefficient are Stern layer conduction, the overlapping of double layers and the effective flow (velocity) through the pores. At a higher salinity (10^-3 – 1 M), which coincides with the LSF region of interest (1500 – 5000 ppm), the coupling coefficients are geometry independent, not influenced by Stern layer conduction and more difficult to obtain, due to a high bulk conductivity of the liquid. It is hard to distinguish between measurements in this region; they all lie on the same line. Charge inversion in presence of Dagang brine in Berea 700 at 70 °C, indicates a flipped sign of the zeta potential. This might indicate that the positively charged system would like to bind negative oil components to it. This might influence the wettability of the rock. In final conclusion, streaming potential measurements should become standard practice in core flooding experiments. As this thesis shows, SP measurements give insight on surface processes occurring inside the core plug and therefore are a valuable addition to pressure drop measurements. This thesis provides valuable insights for continued research on IOR and EOR (enhanced oil recovery) topics. However, the continuation of streaming potential research for LSF should be assessed.