When a new oilfield starts producing oil, the oil is driven up the well by the internal pressure of the oil deposit. Unfortunately, only about 10% of the oil in place can be recovered this way (primary production). With supporting technical methods, such as pumping water into the oilfield to push the crude oil out of the porous stone or sand layer towards the production well, oil production can be increased to 20 – 40% of the oil in place (secondary production). Due to the viscosity difference between water and oil, sooner or later so-called fingering will occur, where the water injected will break through the oil instead of pushing the oil towards the production well. To push the total recovery up to 30 – 60%, enhanced oil recovery (EOR) techniques are used (tertiary production). One of these techniques is polymer flooding. Here polymers are used to increase the viscosity of the injection fluid to suppress the fingering. Unfortunately, the standard oilfield does not exist. Every oil deposit has its individual characteristics depending on a large number of parameters, for example temperature, pressure, crude oil viscosity, crude oil composition, salinity, and pore size distribution. Consequently, the polymers used for flooding have to be selected or even tailored to perform effectively under the conditions of the individual oil deposit. For example, issues such as shear thickening due to extensional effects can cause polymer solutions to show an increase in viscosity above a characteristic flow rate, influencing the effectiveness of polymer solutions in EOR. There is an increasing demand for analytical techniques capable of characterizing the extensional properties of low viscous polymer solutions used in polymer flooding. Classical studies have mostly been done via flooding real rock material retrieved from the well or synthetic porous media made of sand or similar materials. These porous media are difficult to make, difficult to characterize, and difficult to maintain due to absorption of the polymers. For a systematic characterization it is much easier to expose polymer solutions to an extensional field directly. Extensional rheometers for low viscous fluids are able to test the elongational behavior of even low viscous liquids like polymer flooding solutions. Since the elongational viscosity of liquids is not accessible using a rotational viscometer or rheometer, an elongational rheometer is the perfect complement to get the full information needed to understand applications which are clearly influenced or even dominated by elongational flow effects. This technology works by pulling a small volume of a liquid apart to form a liquid filament. It measures the thickness of this filament, or more precisely, how quickly this filament collapses. The thickness of the collapsing filament is measured at the mid-point between the two plates and plotted as a function of time. Our next article will go over the test results evaluating two different polymer samples using an extensional rheometer instrument.
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