Transport of polymer particles in a oil-water flow in porous media: enhancing oil recovery

We study a heuristic, core-scale model for the transport of polymer particles in a two phase (oil and water) porous medium. We are motivated by recent experimental observations which report increased oil recovery when polymers are injected after the initial waterflood. The recovery mechanism is believed to be microscopic diversion of the flow, where injected particles can accumulate in narrow pore throats and clog it, in a process known as a log-jamming effect. The blockage of the narrow pore channels lead to a microscopic diversion of the water flow, causing a redistribution of the local pressure, which again can lead to the mobilization of trapped oil, enhancing its recovery. Our objective herein is to develop a core-scale model that is consistent with the observed production profiles. We show that previously obtained experimental results can be qualitatively explained by a simple two-phase flow model with an additional transport equation for the polymer particles. A key aspect of the formulation is that the microscopic heterogeneity of the rock and a dynamic altering of the permeability must be taken into account in the rate equations.Comment: 20 pages, 9 Figures Submitted to Transport in Porous Medi

EFFECT OF WETTABILITY ON OIL RECOVERY FROM CARBONATE MATERIAL REPRESENTING DIFFERENT PORE CLASSES

ABSTRACT This paper discusses experimental studies of waterflooding native state cores and also waterflooding results for the same cores after aging in crude oil. The topics discussed are related to the effect of wettability change on relative permeability and oil recovery for different carbonate core materials. The unsteady state method was used as experimental procedure for measuring relative permeability and obtaining oil recovery data. The wettability was measured after aging, using the combined Amott / USBM method. The core material used in this study represents different pore classes within carbonate reservoirs. The cores used represent outcrop and gas well cores and had an initial waterwet state. Different carbonate pore classes showed large variation in properties with regard to two-phase flow properties. The waterflood experiments showed that low permeable carbonate (K << 1 mD) may still display a high oil recovery efficiency. The wettability of the cores after aging was intermediate towards oil wet, and nearly all the material displayed a mixed-wet small behaviour. The initial water saturation (S wi ) was very similar for the water-wet cores and the same cores after aging, which is essential for comparing the different wetting states. A strong increase in oil recovery after aging was observed in most cases, except for the cores that showed no spontaneous imbibition after aging. These cores had a lower oil recovery for aged cores compared to waterflood at initial water-wet conditions

A strategy for low cost, effective surfactant injection

Ideally, in a chemical flooding process, one would like to inject a surfactant solution that has good solubility at the relevant conditions, ultralow interfacial tension (efficient oil mobilisation) and low loss of surfactant (better economics) in the porous medium. The key question is – can you have low loss of surfactant, i.e. low retention, at ultralow interfacial tension? To answer this question, we have undertaken a systematic study of surfactant solubility, phase behaviour, interfacial tension and retention as a function of salinity for a given surfactant formulation. The idea is to explore the interrelationship between these properties and find the best condition(s) for combined low interfacial tension and low retention in a surfactant flooding process. For the investigated surfactant formulation, ultra-low interfacial tensions (<0.01 mN/m) can be found in the Winsor III region at optimal salinity. The aqueous solution at optimal salinity is, however, turbid, and retention values are high. On the other hand, for light oils, there are regions in the Winsor I area where (i) interfacial tensions are low (0.01 mN/m<IFT<0.1 mN/m), but not ultralow, (ii) aqueous solutions are clear and (iii) retention is 10 times lower than at optimal salinity. The search for an optimum surfactant formulation has to consider solution properties and retention in addition to the low interfacial tension. Based on our result, we therefore propose that Winsor I phase behaviour is the best option for a compromise between the properties in question

Transport of polymer particles in oil–water flow in porous media: Enhancing oil recovery

We study a heuristic, core-scale model for the transport of polymer particles in a two-phase (oil and water) porous medium. We are motivated by recent experimental observations which report increased oil recovery when polymers are injected after the initial waterflood. We propose the recovery mechanism to be microscopic diversion of the flow, where injected particles can accumulate in narrow pore throats and clog it, in a process known as a log-jamming effect. The blockage of the narrow pore channels leads to a microscopic diversion of the water flow, causing a redistribution of the local pressure, which again can lead to the mobilization of trapped oil, enhancing its recovery. Our objective herein is to develop a core-scale model that is consistent with the observed production profiles. We show that previously obtained experimental results can be qualitatively explained by a simple two-phase flow model with an additional transport equation for the polymer particles. A key aspect of the formulation is that the microscopic heterogeneity of the rock and a dynamic altering of the permeability must be taken into account in the rate equations