Measurements of Polysaccharide Polymer Properties in Porous Media

Abstract

Abstract Accurate determination of polymer properties in porous media is an important input requirement of the reservoir simulation of polymer EOR. Data pertaining to in-situ viscosity and polymer retention are essential parameters which will govern the performance and economics of the application. At reservoir conditions, the acquisition of relevant and precise data is not a straight forward process, but one where extremely careful and reproducible coreflooding experiments are required. We address the question of coreflood procedures best suited to evaluate polysaccharide polymers for field application. Reservoir condition corefloods should be conducted in non-ferrous metal based rigs to exclude severe face plugging by Fe(lll) gels, which can form when Fe(lll) is present at concentrations greater than 3 ppm. Other sources of face plugging including microgels and incomplete dissolution of polymer must be quantified rigorously. Evidence of face blocking can be assessed rapidly from residual resistance factor (RRF) behaviour, and a measurement of the RRF over the complete flow rate range is essential to characterise polymer behaviour. Quantification of these effects can only be made in experiments with multiple pressure ports, or with two cores in series. From experiments conducted on a variety of polysaccharide and porous media, using the above procedures, several important findings are reported. All polymers investigated, after fully quantifying face plugging pressure effects, showed a Newtonian plateau at low shear rates. The observed porous media viscosity was lower than that of the bulk, both with and without presence of oil, and can be attributed to slip phenomena. The presence of a residual oil phase results in a lower viscosity for aqueous polymer than that calculated from simple relative permeability arguments. It is shown that polymer viscosity is a function of pore scale tortuosity and wettability, with greatest viscosity loss in highly water wet systems. Polymer retention is a function of polymer type and molecular association. When face plugging effects are quantified, the polymer retention in the remainder of the core is shown in some cases to be very low (less than 10 μg g-1). Polymer retention is dependent on rock type and preparation procedures. In all cases a significant inaccessible pore volume (IPV) of 0.15 – 0.22 was measured.