Experimental Investigation of Polymer Flow through Water- and Oil-Wet Berea Sandstone Core Samples

Abstract

Polymer behavior under different wettability conditions is investigated through coreflood experiments conducted on cores with different wettabilities, but of the same pore structure. Berea core samples are used in the experiments with the wettability of one core altered to oil-wet conditions. A series of polymer and water floodings are performed with the polymer properties in porous media calculated and the formation wettability evaluated based on the measured laboratory data.The effect of wettability on polymer behavior in porous media is the main focus of this work. In the first part of this study, the bulk rheology of a hydrolyzed polyacrylamide (HPAM) dissolved in two synthetic brines of different salinities is studied. A Carreau-type model is fitted on the experimentally measured data and the effect of salinity on the rheological properties of the HPAM polymer is investigated. A power-law model is also developed for the same experimental data.For the core flooding experiments, a new setup is implemented in which, instead of measuring manually the core effluent concentrations during the polymer flooding, a capillary tube is connected to the core outlet. Using the notion of the intrinsic viscosity, a formula is derived to estimate the polymer concentration from the pressure drop recorded across a capillary tube mounted at the core effluent. In addition, basic properties related to polymer flow in porous media, such as polymer adsorption, inaccessible pore volume, and apparent viscosity are evaluated for the cores and both wetting conditions.From the bulk and coreflood experiments conducted in this work, several important findings are reported. The examined polymer solutions display both upper Newtonian and shear thinning flow regimes in our bulk rheology investigation, with the effect of brine salinity on polymer viscosities to be significant. From the core flooding experiments, both polymer shear thickening and degradation flow regimes are observed on the water-wet core sample. The oil recovery factors and oil recovery vs. time profiles for the Berea oil-and water-wet core samples vary significantly and in accordance to the expected wetting conditions of the cores. The Berea water-wet core has the highest value of polymer retention, inaccessible pore volume (IPV) and permeability reduction factor (RRF) compared to the oil-wet core sample. The results displayed in this work confirm that the formation wettability has a significant effect on the polymer behavior in porous media.

Less-Concentrated HPAM Solutions as a Polymer Retention Reduction Method in CEOR

“…In these cases, 0.25 and 0.23 PV were calculated as IPV. These results are consistent with previous developed studies, which report values are between 0.1 and 0.3 pore volumes (Dawson and Lantz, 1972;Szabo, 1975;Gupta, 1978;Lotsch et al, 1985;Huh et al, 1990;Hughes et al, 1990;Mezzomo et al, 2002;Pancharoen et al, 2010;Hatzignatiou et al, 2013;Ferreira and Moreno;. It probably means that the inaccessible pore volume for the high-permeability samples presented a reasonable value according to the literature and the HPAM 3630S is well-selected for this high-permeability range.…”

“…Brine-SF was used in experiments 1 and 2 performed with 3230S HPAM solutions. The brine-SW represented the seawater used in offshore polymer applications (Hatzignatiou et al, 2013), its total dissolved solids content was 35.301 ppm and its density was 1.026 g/cm 3 . Brine-SW was used in experiments 3 and 4, which involved 3630S HPAM solutions.…”

“…The enhanced oil recovery by polymer flooding appears to remedy problems presented in water injection, increasing the water viscosity and reducing the permeability to the aqueous phase (Hatzignatiou et al, 2013;Aya et al, 2018). Polymer solutions are designed to develop a favorable mobility ratio between the ºinjected polymer solution and the oil displaced ahead of the polymer.…”

Polymer Flow in Porous Media: Relevance to Enhanced Oil Recovery

“…Within the extensional flow regime, the apparent viscosity generally reaches a maximum value, subsequently followed by a decreasing viscosity interval. This phenomenon may be interpreted as high viscoelastic stresses causing polymer rupture and chain halving, and it has been reported as being more severe in low-permeability porous media [46]. As molecular rupture occurs, new molecular weight distributions emerge (larger molecular weight fractions are distorted) and viscosity behavior of the polymer may be governed by a new molecular weight distribution.…”

Polymer Flow in Porous Media

“…During extensional flow regime, apparent viscosity generally reaches a maximum value, subsequently followed by a decreasing viscosity interval. This phenomenon may be interpreted as high viscoelastic stresses causing polymer rupture and chain halving, and has been reported as more severe in low permeable porous media [43]. As molecular rupture occurs, new molecular weight distributions emerge (larger molecular weight fractions is distorted) and viscosity behavior of the polymer may be governed by a new molecular weight distribution.…”