Study of the Effects of Various Waters on Reservoir Rocks During Waterflooding, Using Scanning Electron Microscope

Injection of plain or modified water is one of the methods used to enhance the recovery of oil. A prior knowledge of the effects of injection fluids on the reservoir rock minerals and interstitial fluids is essential for designing a proper enhanced recovery program. A Scanning Electron Microscope (SEM) can be used to evaluate qualitatively the physicochemical changes that are taking place during waterflooding. Studies have been carried out by the writers on cores from an oil field situated in Gujarat State, India. This sandstone reservoir has medium-viscosity crude oil, with favorable acid number, low concentration of Ca⊃++ ⊃ and Mg⊃++ ⊃ cations in formation water, small quantity of water-sensitive clays, and relatively poorly cemented fines. Plain water (economy considerations), polymer solutions (for mobility control), and dilute caustic solutions (for improving displacement efficiency and for mobility control) were used as injection fluids in a large number of laboratory experiments in order to select the optimum parameters, such as concentration and slug size.The results were studied by examining micrographs of rock samples flooded for different time intervals, at low and high magnifications. Movement of fines during waterflooding, emulsification of oil on using caustic soda, and sticking of polymer and fines (partially removable)during polymer flooding has been observed. The SEM technique has helped in visualizing the actual phenomena taking place inside the reservoir cores during various stages of flooding, and supplements the results of flow studies for selecting and designing an enhanced recovery program.