Abstract
The injected brine composition has been observed to have intense effect on efficiency of waterflooding in carbonate reservoirs. This process is known as smart waterflooding and has proved to be an effective process in improving oil recovery. Different approaches have been tested in carbonate reservoirs due to the complexity of the process. Based on these approaches, different mechanisms have been proposed with some level of uncertainties. This has led to several arguments on the chemical mechanisms responsible for such feat achieved. One of the approaches is discussed in this paper, however with much interpretation considering all factors influencing the oil-brine-rock interactions. Therefore, this paper presents the influence of multi-ion interactions during smart water flood on carbonates. Sequential flooding of formation brine and smart brines and the effluent ion analysis were conducted to confirm the multi-ion interactions leading to improved recovery. In addition, zeta potential measurement was conducted to examine the alteration process and correlated with the core flood results. The results from zeta potential measurement showed that multi-ion interaction alters the rock surface charge, which led to more water-wetness. Significant improvement in oil displacement efficiency was observed beyond the secondary waterflood and effluent ionic analysis demonstrated that these multi-ionic interactions led to the observed alteration.
Highlights
Waterflooding has been an effective and relatively inexpensive process of improving recovery beyond the primary natural drive
The results showed positive surface charges at the rock/brine interface at all range of salinity and they are discussed below; Surface charge with salinity dilution: The baseline condition (SO42- : NaCl = 1: 2129.4), gave a positive zeta potential value of 4.49 mV at a solution pH of 7.33; SW (SO42- : NaCl = 1: 11.6), gave a positive value of 2.2 mV at a solution pH of 8.08
The multi-ion interaction leading to improved recovery by smart waterflooding was thoroughly investigated through series of experiment on candidate carbonate reservoirs
Summary
Waterflooding has been an effective and relatively inexpensive process of improving recovery beyond the primary natural drive. The brine-rock interaction has been observed to be prompted by the reactivity of the ions in the injected water, which is crucial in creating a surface charge alteration [5]. The result indicates that brine salinity/ionic strength reduction due to brine dilution results in increasing the rock surface charges which is influenced by decreased in solution pH.
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