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.