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 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 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. polysaccharide polymers for field application. Reservoir condition corefloods should be conducted In non-ferrous metal based rigs to exclude severe face plugging by Fe(III) gels, which can form when Fe(III) 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 characterize 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 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 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). 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. Introduction Conformance control in waterflood operations can be improved by the use of polymer solutions. Addition of polymer to the aqueous phase results in a higher viscosity and it is possible to match the phase results in a higher viscosity and it is possible to match the viscosity of a more viscous oil phase. in this mobility control application, the viscosity matching decreases the tendency of the aqueous phase to finger through and bypass the oil phase within the porous matrix. Polymers can also be used for profile control in layered reservoirs with high permeability streaks. The polymer solution preferentially enters the high permeability layers. Subsequent water injection will be diverted around the slow moving polymer slug, into the lower permeability layers, resulting in a polymer slug, into the lower permeability layers, resulting in a greater sweep efficiency. Corefloods are conducted with polymers to gather data for input into reservoir simulation models. It is essential that the data gathered is both precise and accurate as these parameters will govern the application and economics of the proposed polymer EOR process. Numerous studies have been conducted on polymers in porous media ranging from the fundamental scientific polymers in porous media ranging from the fundamental scientific investigations to realistic field application studies. Fundamental studies investigating the behaviour of idealised (highly filtered polymer solutions removing microgels) have been conducted by Chauvateau et al at IFP. From this work arose the basic concept that polymer in-situ rheology can differ significantly from bulk rheology in a fundamental manner [4]. The in-situ rheology is less than the bulk rheology in both the Newtonian (slip effect) and non-Newtonian regions. We were stimulated to investigate the performance of field applicable systems (those systems without microgel removal) under reservoir conditions to see if similar effects occurred in general in various media. Firstly we wanted to confirm the basic premise of the Chauvateau work: that microgel removal takes place in the near wellbore region, and hence results obtained on microgel free solutions are identical to the in-situ rheology of the polymer deep within the reservoir. Secondly, we wanted to investigate the effects of wettability and oil saturation on in-situ polymer rheology. Critical examination of coreflood procedures showed that several parameters could govern the differential pressure and retention of parameters could govern the differential pressure and retention of polymers in cores and these effects had to be quantified to give polymers in cores and these effects had to be quantified to give unambiguous data relating to polymers in porous media. P. 175