Determination of Wettability and Its Effect on Waterflood Performance in Limestone Medium

Abstract

Wettability measurement methods, the effect of wettability on fluid distribution, and fluid flow in porous media were discussed, and the influence of rock wettability on the relative permeability and recovery of oil by waterflooding were investigated. Experimental studies were conducted on a total of 23 core plugs from two different limestone formations. Synthetic brine (NaCl solution) and mineral oil, which has a viscosity ratio of ∼10, were used as the test fluids. Core samples, saturated with synthetic brine, were flushed with mineral oil to establish the initial conditions, and the wettability of the samples was measured by the Amott−Harvey method. Test results showed that the wettability of the samples ranged from strongly water-wet to intermediately wet. Wettability measurements were repeated and showed that the Amott−Harvey wettability indices were reproducible. The effects of aging time, brine salinity, and saturation procedure on wettability were examined. Long-time aging in mineral oil altered the wettability of a water-wet core sample to intermediately wet. Unfortunately, there was only one water-wet sample, and correlation of the alteration of wettability, with respect to aging time, was not possible. Increasing the brine salinity also reduced the water wetness. However, the saturation procedure had almost no effect on the wettability of the core samples. Aging could not alter the wettability of the intermediately wet samples, by varying brine salinity and by changing saturation procedure; therefore, it was concluded that intermediate wettability was more stable than water wetness. Relative permeability and waterflood studies were conducted on core samples that had different wettability levels. In a water-wet medium, water breakthrough occurred relatively late and a considerable amount of oil was produced before the breakthrough. After the breakthrough, the rate of oil production was decreased very sharply. Decreasing the water wetness resulted in decreasing the breakthrough recovery. In the intermediately wet system, breakthrough occurred very early and most of the oil was produced after the breakthrough. Water breakthrough had almost no effect on the rate of oil production. Waterflood in the water-wet system seemed more economical, because a lesser volume of water was required to produce the same amount of oil.

Two-Phase Flow in Porous Media with Slip Boundary Condition

“…In most of the documented cases the endpoint relative permeabilities 1.4 < k r < 2.4 (McPhee 1994;McPhee and Arthur 1994). These cases have in common that the (near) endpoint relative permeabilities k r > 1 in particular, when the non-wetting phase is the majority phase (McPhee 1994;McPhee and Arthur 1994;Karabakal and Bagci 2004) and the wetting phase is present only as thin wetting films covering the rock surface. In oil-wet systems (wetting-index −1) the k r,w (S o,r ) > 1 and in water-wet systems k r,o (S w,c ) > 1.…”

“…It is usually assumed that the relative permeabilities 0 ≤ k r ≤ 1. However, there are several reports in the literature that explicitly show endpoint relative permeabilities k r > 1 (Odeh 1959;Dullien 1992;Anderson 1987;McPhee 1994;McPhee and Arthur 1994;Karabakal and Bagci 2004;Honarpour et al 2000;Arps and Roberts 1995;Ehrlich 1993;Mikkelsen and Scheie 1991). The term "endpoint" refers to the relative permeability at the saturation endpoints, S w,c and S o,r .…”

“…The observation of k r > 1 is sometimes termed "lubricating effect" (McPhee and Arthur 1994; Karabakal and Bagci 2004;Dong et al 2006). In most cases, no further explanation about a microscopic physical mechanism is given.…”

An Overview of Wettability Measurements in Fractured Carbonated Reservoir and Investigate the Effects of Wettability Changes in the Optimization of Enhanced Oil Recovery Techniques

“…Literally, from the view of neutral wettability. In addition, there are another wettability along neutral and extremely wettability which is called partial wettability [9,10,11]. …”

Review of studies on pore-network modeling of wettability effects on waterflood oil recovery

“…It determines the microscopic distribution of fluids in the pore-space which, in turn, determine important multiphase properties such as capillary pressure, relative permeability, residual saturation and resistivity index (Karabakal and Bagci, 2004;Ju and Fan, 2012). Crude oil/water/rock interactions leading to wettability variations can result to large variations in the displacement efficiency of waterfloods.…”