Crude Oil–Brine–Rock Interactions in Tight Chalk Reservoirs: An Experimental Study

Abstract

We present a systematic study of crude oil–brine–rock interactions in tight chalk cores at reservoir conditions. Flooding experiments are performed on outcrops (Stevns Klint) as well as on reservoir core plugs from Dan field, the Ekofisk and Tor formations. These studies are carried out in core plugs with reduced pore volumes, i.e., short core samples and aged with a dynamic ageing method. The method was evaluated by three different oil compositions. A series of synthetic multicomponent brines and designed fluid injection scenarios are investigated; injection flow rates are optimized to ensure that a capillary-dominant regime is maintained. Changes in brine compositions and fluid distribution in the core plugs are characterized using ion chromatography and X-ray computed tomography, respectively. First, we show that polar components in the oil phase play a major role in wettability alteration during ageing; this controls the oil production behavior. We also show that, compared to seawater, both formation water and ten-times-diluted seawater are better candidates for enhanced oil recovery in the Dan field. Finally, we show that the modified flow zone indicator, a measure of rock quality, is likely the main variable responsible for the higher oil recoveries observed in Tor core samples.

Water/oil emulsion and asphaltene instability in different formations during low-salinity waterflooding: an experimental study

“…Low-salinity waterflooding (LSWF) is a promising method for improving oil recovery in oil reservoirs with low recovery rates. Although a definitive recovery mechanism remains uncertain, empirical evidence suggests that adjusting ion type and concentration in the water phase can enhance oil recovery by altering reservoir and fluid properties such as wettability, permeability, capillary pressure, and interfacial properties between water and oil [1][2][3][4][5][6][7][8].…”

The Simultaneous Effect of Brine Salinity and Dispersed Carbonate Particles on Asphaltene and Emulsion Stability

“…Various laboratory and field studies have demonstrated that manipulating the type and the content of ions in the injection water, known as low-salinity waterflooding (LSWF), can lead to incremental oil recovery. Even though the effect of LSWF has been justified by several measurements such as rock wettability, relative permeability, capillary pressure, and rock-fluid and fluid–fluid interfacial properties, there is no consensus on the dominant governing mechanism. − Unlike the overwhelming number of papers on solid–liquid interactions and underlying mechanisms of enhanced oil recovery by LSWF, studies on the side effects of LSWF, such as asphaltene instability, (viscous) emulsion formation, and organic scaling–eventually impeding flow and leading to formation damage–are scarce. − It is worth mentioning that some experimental results suggest that emulsion production and asphaltene deposition, as the side effects of the LSWF process, could improve the injection performance by increasing the breakthrough time and sweep efficiency. − …”